Microbiology & Immunology Exam Flashcards
what are the main components of a TCR?
1 antigen binding site • variable regions • constant regions • transmembrane region • α chain • β chain
what is the difference between a BCR and a TCR’s CD molecules?
on a B cell IgM and IgD are associated with CD79 • TCR is associated with CD3
what are the 2 classes of TCR?
α:β • γ:δ
how are gene rearrangements in a TCR similar to gene rearrangements in a BCR?
VDJ segments for beta and gamma chains • VJ segments for alpha and delta chains
unlike a B cell where a B cell carries IgM and IgD as antigen receptors, a T cell carries what?
either alpha beta receptor or gamma-delta receptor
which has more variation, V region of alpha and beta chain or V region of gamma and delta chains
V region of alpha and beta chains
generation of the variable region of TCR is generated the same way like in BCR, except what?
that TCR does not undergo somatic mutation
which enzymes are involved in TCR development?
RAG1 and RAG2 • the same enzymes involved in TCR development
generation of antigen-binding diversity for TCR depends on what?
the same somatic recombination and junctional mechanisms used for BCR diversity
How is diversity created in TCR?
- joining of VDJ segments for beta and gamma chains • 2. joining of VJ segments for alpha and delta chains • 3. RAG-1 and RAG-2 encoded recombinase and TdT are required for somatic recombination • 4. junctional diversity
is there somatic hypermutation in TCR?
NO
T cell progenitors originate from and develop where?
they originate from bone marrow and develop in the thymus
to what is the TCR’s source of diversity in antigen recognition similar?
BCR because of random rearrangements of gene fragments VDJ and VJ
what is the structure of TCR?
has 2 peptides • α and β
how many epitope receptors does a TCR have?
1
how many CD3’s is each TCR associated with?
2
what is the function of ζ peptides in TCR?
signal transduction
what are the co-receptor molecules of CDR’s?
CD4 • CD8
when is Pre-TCR found?
on immature T cells; expressed early in development
when is TCR found?
on mature T cells
what is the major difference between pre-TCR and TCR?
pre-TCR has an incomplete α peptide: • pTα
how do T cell receptors recognize processed epitope?
in association with MHC
TCR require which co-receptors?
CD4 • CD8
which T cell type has co-receptor CD4?
Helper T cell
which T-cell type has the co-receptor CD8?
cytotoxic T cell
what is the MHC restriction of Helper T cells?
MHC II
what is the MHC restriction of cytotoxic T cells?
MHC I
what is the function of helper T cells?
B cells help macrophage activation • help for CD8 T cell cytokine secretion
what is the function of cytotoxic T cells?
killing virus infected cells • killing tumor cells
what are the parts of a CD4 co-receptor?
D1 • D2 • D3 • D4
what are the parts of the CD8 co-receptor?
α • β
what is the immune consequence of DiGeorge Syndrome?
thymic hypoplasia
What CD is expressed on a lymphoid precursor that just entered the thymus?
CD34
in the subcapsular zone of the thymus the cell becomes committed to develop to T cells by expressing what?
CD2
what are the two lines of development of committed CD2+ cells in the subcapsular zone?
beta-alpha expressing TCR • gamma-delta expressing TCR
in the beta-alpha line of development, the genes for beta gene segments are rearranged first and if it is productive, what happens next?
it is transcribe and translated to a beta chain that gets associated with a pTα.
what does a preT cell of the beta-alpha line express?
β • PTα
what happens if the pre T cell expressing β and PTα is functional?
the cell is signaled to rearrange the gene segments for α chain.
what is expressed on double positive T cells and where are they found?
double positive CD4+, CD8+ express TCR (βα) and are found in the cortex
What is positive selection in T cell development of the αβ line?
the TCR is checked if it can interact with MHC alleles of the person. • thymic epithelial cells present self antigen on MHC to the TCR. T cells expressing TCR that can interact with the MHC of the individual survive, if not they die
what is MHC restriction also known as?
positive selection
where and by what cells is negative selection in T cell development carried out?
by dendritic cells in the corticomedullary junction
what happens in negative selection during T cell development?
dendritic cells present self antigens on MHC I and II to the double positive cells. T cells with high affinity die, T cell with weak or intermediate affinity live. T cells that survive either become CD4 or CD8 depending on their affinity to either MHC I or MHC II
what happens in terms of CD during T cell development, to T cells with affinity to MHC I molecules?
CD8 marker retained • CD4 will be lost
what happens in terms of CD during T cell development to T cells with affinity to MHC II molecules?
CD4 will be retained • CD8 will be lost
what are single positive T cells?
CD4+ or CD8+ and self tolerant
which type of T cells leave the thymus after T cell development?
single positive
what is AIRE?
autoimmune regulator gene that plays a role in negative selection to T lymphocytes specific to self antigens not found in the thymus
what is the purpose for AIRE’s existence?
not all self antigens are present in the thymus to cause deletion of self reacting lymphocytes • -AIRE gene induces the expression of such self antigens in the thymus-m so that they can be used in negative selection
what % of the T cell pool is CD4-, CD8-, γδ+?
2-10% of total T cell pool
where are CD4-, CD8-, γδ+ cells found?
in tissue just before the dermis
do CD4-, CD8-, γδ+ T cells undergo selection?
no
how do CD4-, CD8-, γδ+ T cells emigrate?
Emigrate as CD4CD8 to epithelial tissues in skin, intestines and lungs
what is the function of CD4-, CD8-, γδ+ T cells ?
immunosurveillance of transformed, damaged, or stressed epithelial cells
what do CD4-, CD8-, γδ+ T cells recognize?
non-peptides • lipids • not completely identified (microbes or stressed host cells
do CD4-, CD8-, γδ+ T cells require APC?
no
what is the level of diversity of CD4-, CD8-, γδ+ T cells ?
limited diversity
what do naive T CD4 cells do upon exposure to antigens presented by APC?
differentiate into effector T CD4 cells
what are the effector T CD4 cells?
Th1 • Th2 • Th17 • Treg
the development of effector T CD4 cells depends on what?
cytokines in the environment, produced by the APC
what happens in naive T CD4 cells when they are exposed to the cytokines in the surroundings?
different transcription factors are activated
what do the effector T CD4 cells do?
produce a variety of cytokines that mediate different immunological activities
does clonal selection theory apply to T cell post antigen exposure development?
yes
What happens in development of Th1?
naive T CD4, under the influence of IL-12 and IFN-γ, induces T-bet, producing Th1
what are the cytokines produced by Th1?
IL-2 • IFNγ
what is the major effector function of Th1?
Cell mediated immunity, • intracellular pathogens • Activate macrophages • Activate B cells and CD8
what happens in development of The2?
Naive T CD4, under the influence of IL-4, induces GATA-3, producing Th2
what are the cytokines produced by Th2?
IL-4 • IL-5 • IL-13 • IL-10
what are the major effector functions of Th2?
Humoral immunity, • B cell activation • extracellular pathogens • parasites and allergy
what happens in the development of Th17?
Naive T CD4, under the influence of IL-23, IL-6, IL-1 induces RORyt, producing Th17
what cytokines are produced by Th17?
Proinflammatory: • inflamamtion • autoimmunity • response to fungi and extracellular bacteria
what happens in the development of Treg?
Naive T CD4, under the influence of TGF-β, induces FoxP3, producing Treg
what cytokines are produced by Treg?
TGF-β, IL-10
what are the major effector functions of Treg?
Down regulation: • Suppress other T cell subsets- anti-inflammatory activity
cytokines produced by Th1 act on what?
macrophages • NK cells • CD8 cells • B cells to switch to IgG1
cytokines produced by Th2 act on what?
eosinophils • B cells to switch to other class of IgG and IgE
cytokines produced by Th17 act on what?
neutrophils and epithelial cells
Treg acts on what cells?
other lymphocytes to prevent T cell proliferation
how many peptides in BCR?
4
how many peptides in TCR?
2
how many antigen binding regions in BCR?
2
how many antigen binding regions in TCR?
1
do TCR or BCR have variable and constant regions?
both have both
do TCR or BCR have gene segments and gene rearrangement?
both have both
what is the signal transducer molecule on BCR?
CD79
what is the signal transducer molecule on TCR?
CD3
Can BCR recognize free unprocessed antigen without MHC?
YES
can TCR recognize free unprocessed antigen without MHC?
NO
how does TCR recognize antigen?
recognize processed antigen in association with MHC on antigen presenting cells
what are the co-receptor molecules on TCR?
CD4 or CD8
from where does Tcell progenitor cell originate?
bone marrow
once a T cell progenitor migrates to the thymus, what can it develop into?
- γδ (CD4-, CD8-); • 2. αβ cells (CD4+ or CD8+) carrying TCR
how does the source of antigenic diversity of TCR relate to BCR?
source of antigenic diversity of TCR is similar to BCR
what is the difference between αβ and γδ T cell development?
α:β T lymphocytes undergo through positive and negative selection in the thymus while γδ cells do not
AIRE gene has a role in what type of disease?
autoimmune
CD3 and zeta associated with TCR serves as what?
signal transducer
CD4 and CD8 are coreceptors of what?
TCR
TCR recognizes epitopes associated with what?
MHC
Which CD interacts with which MHC in TCR?
CD4 interacts with MHC II and CD8 interacts with MHCI
under the influence of cytokines in the environment, naive CD4 (helper cells differentiate into what?
into Th1 • Th2 • Th17 • Treg
what is the function of Th1, Th2, Th17, and Treg?
these subsets of cells produce different set of cytokines with different roles in the immune system
what are the pre-antigen exposure B cell stages?
Pro B cell–> • Pre B cell –> • Immature B cell–> • mature B cell
what are the post antigen exposure B cell stages?
mature B cells become either Plasma cells or Memory cells
pre antigen b cell development involves what?
generation of antigen specific receptors which are immunoglobulin molecules of IgM and IgD isotypes
what is the specificity of BCR?
is antigen (epitope) specific
what type of immunoglobulin is BCR?
membrane immunoglobulin (mIg)
BCR is associated with which CD?
CD79 (Igα,β)
what is the function of CD79 (Igα,β)?
it’s a signal transducer
BCR belong to which two isotypes?
IgM • IgD
what is the similarity of the IgM and IgD on a single B cell clone?
both belong to the same idiotype (specific to a particular antigen)
the maturation stages of the B cell can be identified by what?
- changes in enzyme activity • 2. CD marker expression • 3. synthesis of BCR (IgM and IgD)
CD10, CD19, and CD20 are markers of what?
B cells
is CD 20 found on plasma cells?
no
what cells is CD 20 found on?
early to late B cell • lymphoma cells
how many B cell clones and repertoires can a person generate?
in any given individual it is possible to generate 10^9-10^10 different B cell clones, each with different epitope binding regions
construction of a unique variable region is possible by the process known as what?
somatic recombination
what factors contribute to somatic recombination?
- existence of multiple copies of gene segments that code for the variable regions • 2. combinatorial diversity generated by random selection and combination of gene segments • 3. junctional diversity generated by addition of deletion of bases • 4. random assortment of light and heavy chains
on which chromosome is the λ light chain locus?
chromosome 22
on which chromosome is the κ light chain locus?
chromosome 2
on which chromosome is the heavy chain locus?
chromosome 14
immunoglobulins are encoded by how many gene complexes?
3 gene complexes located on separate chromosomes
what are the functions of the 3 gene complexes located on separate chromosomes?
one for all heavy chains • one for κ chains • one for λ chains
how continuous are the gene complexes that code for immunoglobulins?
these genes are discontinuous and require translocations to be activated
what are the segments that encode the variable region of the light chain?
V • J
what are the segments that encode the variable region of the heavy chain?
V • D • J
what post-transcriptional processing do the gene complexes that encode immunoglobulin chains require?
DNA rearrangement • RNA splicing
what is the term for the process of gene rearrangement that occurs in generating BCR?
Cut and Paste process
RAG1 and RAG2 are what and what do they code for?
Recombination activating genes code for RAG1 and RAG2
what is an example of alternative splicing in gene selection for BCR?
the rearranged VDJ segment recombines first with Cμ segment creating the heavy chain μ for IgM, followed by Cδ segment creating the heavy chain δ for IgD
what is the reason for the alternative splicing seen in gene selection during synthesis of BCR?
in this way, both the IgM and IgD expressed on a B cell have the same VDJ
what are the 6 sources of BCR diversity?
- multiple copies of germline VDJ • 2. Random recombination of gene segments • 3. imprecision during cut and paste • 4. junctional diversity • 5. random reassortment of any light chain with any heavy chain • 6. somatic hypermutation
what is junctional diversity?
addition of sequence at the splice junction between V_D or D_J gene segments
what is somatic hypermutation?
fine tuning change after mutation
what is the cause of imprecise recombination in BCR formation?
the precise positions at which the genes for the V and J or VDJ segments are joined are not constant
imprecise DNA recombination can lead to what?
changes in the amino acid at the junctions
where does insertion of a new piece of DNA at the junctions take place?
at the junction of new segments
what is TdT?
terminal deoxynucleotidyl transferase
what is affinity maturation?
when somatic hypermutation improves the affinity of the antibody to the epitope
what is somatic hypermutation?
change in nucleotide in the rearranged variable gene segment of the light and heavy chain mainly in the CDR regions
the maturation stages of B cell development can be identified by what?
changes in enzyme activitiy • CD marker expression • synthesis of the BCR
what is allelic exclusion?
in a single B cell only one set of genes is expressed either maternal or paternal
what is Heavy chain rearrangement in the Pro B Cell?
DJ joined in both the chromosomes. Then VDJ is formed in one of the chromosomes
where do B cells develop?
in the fetal liver and adult bone marrow
when does heavy chain rearrangement take place?
in the pro B cell
what happens durring Ig Gene expression in the Pre B Cell?
VDJ get joined to the HCμ. μ chain together with surrogate chain is expressed
what is the μ chain together with the surrogate chain in the pre-Bcell called?
pre-B cell receptor
at the pro B cell level in the bone marrow, gene rearrangement of the H chain start with what?
a union of the D and J genes in both chromosomes (maternal and paternal)
what are the genes need to complete IgM?
VDJCμ
what happens if VDJCμ is productive- capable of being properly transcribed and translated?
further rearrangement of VDJ gene from the other chromosome is shut down, if not, the cell is given a second chance to use the other chromosome. if this fails, the cell dies by apoptosis
what is a surrogate light chain?
a false light chain
do the genes for VpreB and λ5 undergo rearrangement?
no
what do Igα and Igβ do in the pre-B cell?
singal the cell that has successfully rearranged its Ig H chain and has made functional μ chain to shut down further H chain rearragement
what is Bruton’s tyrosine Kinase?
one of the enzymes involved in intracellular signalling by Igα/β
mutation in the Btk gene results in what?
lack of differentiation to proB cell level
what is the condition caused by deficiency or defect in Btk?
X-linked agammaglobinemia
what happens if in the maturation of a B cell the cell is not self reactive?
alternative mRNA splicing of heavy chain gene transcripts then produces the δ and μ expressing both IgD and IgM
what happens once a functional pro-B cell receptor is produced?
rearrangement of the light chain genes start
which light chain genes rearrange first?
κ chain
what is central tolerance?
negative selection of self reacting immature B cells
what is receptor editing?
alteration of speecificity: • further round of light chain (V and J) gene rearrangement
what happens when an immature B cell recognizes a multivalent self molecule?
DELETION: • clonal deletion or receptor editing –> apoptosis
what happens when an immature B cell recognizes soluble self molecules?
ANERGY: • migrates to the periphery
what happens when an immature B cell recognizes low affinity non cross linking self molecule?
IGNORANT: • migrates to periphery • Mature B cell is clonally ignorant
what happens to an immature be cell with no self reaction?
FUNCTIONAL: • it migrates to the periphery and becomes mature
do anergic B cells express IgD?
yes
do clonally ignorant B cells express Ig?
yes, IgM and IgD
what is a clonally ignorant cell?
ligand is present but is not able to activate the cell
what are the cell stages of B cell maturation?
- Stem Cell • 2. Early Pro-B cell • 3. Late pro-B cell • 4. Large Pre-B cell • 5. small pre-B cell • 6. immature B cell • 7. Mature B cell
what is the status of the H-chain genes in a stem cell?
germ line
what is the state of the L chain genes in a stem cell?
germline
what is the state of surface Ig in a stem cell?
Absent
what is the state of H chain genes in an early pro-B cell
D-J rearranging
what is the state of L chain genes in an early pro-B cell?
Germline
what is the state of surface Ig in an early pro-B cell?
absent
what is the state of the H chain genes in a late pro B cell?
V-DJ rearranging
what is the state of the L chain genes in a late pro-B cell?
germline
what is the state of the surface Ig in a late pro-B cell?
absent
what is the state of the H chain genes in a large pre-B cell?
VDJ rearranged
what is the state of the L chain genes in a large pre-B cell?
germline
what is the state of surface Ig in a large pre-B cell?
μ chain transiently at surface as part of pre-B cell receptor. mainly intracellular
when does the μ + surrogate arrive in B cell maturation?
at the large pre-B cell stage
what is the state of the H chain genes in a small pre-B cell?
VDJ rearranged
what is the state of the L-chain genes in a small pre-B cell?
V-J rearranging
what is the state of the surface Ig in a small pre-B cell?
intracellular μ chain
at what stage in B cell maturation is the check to see if they recognize self antigens?
immature B cell stage
what is the state of the H chain genes in an immature B cell?
VDJ rearranged
what is the state of the L chain genes in an immature B cell?
VJ rearranged
what is the state of surface Ig in an immature B cell?
IgM expressed on cell surface
what is the state of the H chain genes in a mature B cell?
VDJ rearranged
what is the state of the L chain genes in a mature B cell?
VJ rearranged
what is the state of surface Ig in a mature B cell?
IgD and IgM made from alternatively spliced H-chain transcripts
what do naive B cells express on their surface?
IgM and IgD
what do plasma cells express on their surface?
plasma cells do not express surface Ig, but secrete Ig
what do memory cells express on their surface?
other Ig: • either IgG, IgA, or IgE
what is the clonal selection theory?
upon exposure to an antigen, a B cell with a BCR specific to that particular antigen proliferates to give rise to a clone of B cells expressing BCR of the same specificity
what happens in Ig class/isotype switch?
change of C domain, but not the VDJ because of alternative mRNA splicing
what does DNA recombination in isotype switch permit a cell to do?
enables the rearranged VDJ to be used with other heavy chain C chains
what is the first Ig produced after a B cell encounters an antigen?
IgM, followed by IgG or IgA with the same VDJ
what is affinity maturation?
mutation that takes place in the rearranged VDJ segment gives rise to antibodies with better affinity to epitopes
do antibodies produced in primary infection have more or less affinity for the epitope than Ab produced in subsequent infections?
less
what is detection of CD10/19/20 used for?
determine the developmental stage of leukemias and lymphomas of B cell origin
what does B cell coreceptor do?
increaes the sensitivity of B cell response to an antigen in the presence of complement activation and deposition of C3d
what is C3d?
a fragment of C3b of complement component
what are the 2 important subsets of B cells?
B2 • B1 (CD5+)
when do B2 cells develop?
after birth
when are B1 cells produced?
in fetal life
which type of B cell has a poorly understood developmental pathway?
B1
which type of B cell comprises the majority of B cells?
B2
What percentage of B cells are B1 cells?
5%
where are B2 cells found?
in secondary lymphoid organs
where are B1 cells found?
in body cavities
which surface Ig do B2 cells express?
both sIgM and sIgD
which surface Ig do B1 cells express?
sIgM but little sIgD
what type of antigens do B2 cells respond to?
protein antigens
which type of antigens do B1 cells respond to?
carbohydrate antigens • T independent antigens
which B cells require T cell help?
B2 cells
which B cells do not require T cell help?
B1 cells
which B cells secrete mainly IgM?
B 1 cells
which B cells give rise to plasma cells that secrete IgM, IgG, and IgA?
B2
which B cells leave memory?
B2 cells
which B cells leave little to no memory?
B1
B cells develop where in the body?
fetal liver • adult bone marrow
stages of B cell differentiation are defined by what?
Ig gene rearrangement ‘status’ and expression of certain CD 10, 19, 20
what is essential to the clonal nature of immunity?
allelic exclusion
how many opportunities do B cells have to rearrange their antigen receptors?
several
what are the possible fates of self reacting immature B cells expressing only IgM?
- allowed for receptor editing • 2. deleted, made anergic or ignorant
why are IgM and IgD expressed simultaneously on mature B cells?
due to differential RNA splicing
what is the function of CD79?
signal transducer
what does a B cell do upon an exposure to an antigen?
proliferates and differentiates into plasma cells and memory cells
what is class switch and what does it refer to?
class switching is isotype switching and refers to changes in CH gene selection but with no change in other genes (V domains or antigen specificity) by alternative RNA splicing
what makes up B cell co-receptor?
CD19 • CD21 • CD81
what are the two subsets of B cell types?
B1 • B2
What are immunoglobulins/antibodies?
glycoprotein molecules produced by plasma cells in response to an immunogen that can recognize the immunogen/antigen
what is myeloma?
a cancer that affects B cells, the immune cells responsible for the production of antibodies
from where do immunoglobulins derive their name?
the finding that when antibody-containing serum is placed in an electrical field the antibodies migrated with the globular proteins
the Ig molecule is made up of how many proteins?
4 peptide chains
what is the composition of the 4 peptide chains in an Ig?
2 heavy identical chains • 2 light identical chains
what are the regions present in Ig molecules?
the chains have variable region and constant region
what are VL and CL?
variable and constant region of the light chain
what are VH and CH?
variable and constant region of the heavy chain
what are responsible for the folding in the domains of an Ig?
sulfide bonds
what makes up an Ig?
- 4 peptide chains with heavy and light chains with variable and constant regions • 2. hinge region • 3. domains folded by sulfide bonds • 4. oligosaccharides
what are Ig classes/isotypes?
5 different classes based on the differences in the amino acid sequences in the constant region of the heavy chain
what are the 5 different heavy chains that determine the Ig classes?
- γ • 2. μ • 3. α • 4. δ • 5. ε
What Ig is associated with the γ chain?
heavy chain of IgG
what Ig is associated with the μ chain?
heavy chain of IgM
what Ig is associated with the α chain?
heavy chain of IgA
what Ig is associated with the δ chain?
heavy chain of IgD
what Ig is associated with the ε chain?
heavy chain of IgE
what is the difference between the IgG subclasses?
differ in amino acid sequence in their constant region of H chain: • 1. IgG1- gamma 1 heavy chains • 2. IgG2- Gamma 2 heavy chains • 3. IgG3- Gamma 3 heavy chains • 4. IgG4- Gamma 4 heavy chains
what is the difference between IgA Subclasses?
differ in aa sequence in their H constant region: • 1. IgA1 • 2. IgA2
what are the 2 types of L chains of Ig?
Kappa- κ • Lambda- λ
what is the difference between κ and λ L chains of Ig?
they differ in amino acid sequences in their constant region
what is the prevalence of κ and λ chains in Ig?
both types occur in all classes of Ig, but any one Ig molecule contains only one of them, either λ or κ
how many subclasses of IgG?
4
how many classes of IgA?
2
What is the organization of H2L2 structures?
2 identical L chains • 2 identical H chains • the H chain defines the class (and subclass) of the Ig produced
what is the functional organization of H2L2 structures?
- variable N terminal regions define the antigen binding site • 2. constant regions of the heavy chains define the functions of the immunoglobulin
in humans, what is the ratio of immunoglobulins containing two kappa vs two lambda chains?
2:01
how can the distinct fragments of the heavy chains be isolated into distinct fragments?
proteolysis
what happens when you reduce and acidify immunoglobulin?
you get isolated chains separated at the sulfide bonds
what happens when you treat an immunoglobulin with papain?
you get papain fragments
what does the Fc region do?
determines the biological function of Ig
what does the Fc region of Ig bind to?
Fc receptors on: • 1. phagocytic cells • 2. NK cells • 3. eosinophils • 4. Mast cells • 5. complement C1q • 6. placental cells
what are the different kinds of Fc receptors on cells?
different Fc receptors on these cells for the different Ig classes: • FcγR- IgG • FcμR- IgM • FcαR- IgA • FcεR- IgE
why is an antibody able to bind a particular antigenic determinant?
because it has a particular combination of VH and VL
specificity of antigen binding is determined by what?
hypervariability regions within the variable region domain
how many hyper-variable regions per variable region?
3
each variable region has 3 hyper-variable regions also called what?
complementary determining regions (CDR)
how many CDR’s per antigen binding site?
an antigen binding site is composed of three light chain CDR’s and 3 heavy chain CDRs
different combinations of a VH and VL result in what?
antibodies that can bind a different epitope
what is the antigen binding region called?
Fab Region
how is variability distributed in V domains?
there are discrete regions of hypervariability in V domains
what are the positions of CDR in the 2-D and 3-D models of the light chain and heavy chain?
-CDRs are separated in the linear 2D model of the peptide chains • - the hypervariable regions of the light chain and heavy chain are brought together in the folded 3D form of the intact antibody molecule
together the CDRs constitute what?
the combining site, which is complementary to the epitope
the variability in CDRs provides what?
the diversity required for the function of antibodies of different specificities
what is affinity in an Ab/Ag interaction?
strength of interaction between one epitope and one epitope binding site (the region between the variable region of heavy chain and light chain)
what is avidity in Ag/Ab interaction?
strength of interaction of multiple epitopes on a multivalent antigen molecule such as a big protein and several epitope binding site
what are hinge options?
the ability of an antibody to bind more than one protein with variable spacing on the surface of a bacterium
what is the structure of IgG?
monomer (7S)
how do the subclasses of IgG differ?
number of disulfide bonds and length of the hinge region
which is the most versatile Ig molecule?
IgG isotype
why is IgG isotype the most versatile immunoglobulin?
because it is capable of carrying out all of the functions of immunoglobulin molecules
what is the major Ig in serum?
IgG
how much of serum Ig is IgG?
75%
which is the major Ig in the extravascular spaces?
IgG
what are the capabilities of IgG?
- neutralization • 2. fixes complement • 3. binding to cells • 4. opsonization
what is neutralization by IgG?
inhibit binding of toxins or pathogens on target cells
do all subclasses of IgG fix complement?
not all subclasses fix complement equally well; IgG4 does not fix complement
which IgG does not fix complement?
IgG4
which cells have Fc receptors for the Fc region of IgG?
- macrophages • 2. monocytes • 3. PMNs • 4. NK cells
do all subclasses of IgG bind to cells?
not all subclasses bind equally well; • IgG2 and IgG4 do not bind Fc receptors
describe opsonization by IgG
IgG is a good opsonin. • a consequence of binding to the Fc receptors on PMN’s, monocytes and macrophages is that the cell can now internalize the antigen better
what is the name for adaptive immune defense mediated by antibodies?
humoral immunity
which is the only Ig that crosses the placental barrier?
IgG
what is transfer of IgG across the placental barrier mediated by?
receptor on placental cells for the Fc region of IgG
do all IgG subclasses cross the placental barrier?
not all subclasses cross equally • IgG2 does not cross well
which IgG does not cross the placental barrier well?
IgG2
what is ADCC?
antibody dependent cell-mediated cytotoxicity
NK cells have Fc receptors for which IgG?
IgG1 and IgG3
binding of NK cells to human cells coated with IgG1 an IgG3 results in what?
killing
ADCC targets what kind of cells?
tumor cells and virally infected human cells
why are tumor cells and virally infected human cells targeted by NK cells in ADCC?
they express antigens that are not found in normal cells
what are the steps of ADCC by NK cells?
- antibody binds antigens on the surface of target cells • 2. Fc receptors on NK cell recognize bound antibody • 3. cross-linking of Fc receptors signals the NK cell to kill the target cell • 4. target cell dies by apoptosis
what are the features of the structure of IgM?
Pentamer (19s) • extra domain (CH4) • J chain
in what 2 configurations can IgM exist?
- IgM normally exists as a pentamer (19S) in serum • 2. can exist as a monomer as antigen receptor on B lymphocytes
which is the third most common Ig in serum?
IgM
what is the valence of an Ig?
it’s epitope binding capacity
what is the similarity between chains in IgM when it is in its pentameric form?
all heavy chains are identical • all light chains are identical
what is the valence of IgM in its pentameric form?
10
what are the extra peptide features of IgM?
- extra domain on the μ chain (CH4) • 2. another protein covalently bound via S-S bond called the J chain
what is the J chain on IgM?
another protein covalently bound to IgM via S-S bonds
which chain functions in polymerization of the IgM molecule into a pentamer?
J chain
what is the first Ig to be synthesized by B cells during infection in adults?
IgM
what is the first Ig produced in fetal life?
IgM
in the newborn, an increased level of IgM is an indication of what?
in utero stimulation of the immune system by pathogens such as rubella virus, CMV, syphilis, toxoplasmosis
what are the pathogens that cause increased IgM in a newborn?
- rubella virus • 2. cytomegalovirus • 3. syphilis • 4. toxoplasmosis
which is the first type of antibody to appear in the primary response, between IgG and IgM?
IgM
what happens to IgG levels in the secondary response (compared to the primary response)?
IgG: • 1. appears earlier • 2. shows a more rapid rise • 3. has higher final concentration
what would happen if at the time of the second exposure to Ag1, a second, non-cross reacting Ag2 was injected?
a primary response to Ag2 would occur while a secondary response to Ag1 was occuring
how can the IgM Fc region affect complement?
the IgM Fc region can bind and activate complement
how many antigen binding sites does IgM pentamer have?
10
how many Fc regions for complement binding does an IgM pentamer have?
10
which Ig has the most efficient complement fixation?
IgM
which Ig is most efficient at agglutinating antigens?
IgM
how is the response of IgM to T cell independent (carbohydrate) antigens?
good
how is the structure of surface IgM different than serum IgM?
- exists as monomer • 2. lacks J chain • 3. extra 20 amino acids at the C terminal end to anchor it to the membrane
what is the function of cell surface IgM?
receptor for antigen on B cells
what is the structure of serum IgA?
monomr
what are the structural features of secreted IgA (sIgA)?
Dimer (11s) • J chain • secretory component
when IgA exists as a dimer, what is associated with it?
J chain
when IgA is found in secretions it also has, in addition to the J chain, what associated with it?
another protein called the secretory piece
what is IgA in secretions called?
sIgA
where is most of IgA made?
in the plasma cell
unlike the remainder of the IgA which is made in the plasma cell, the secretory piece is made where? and when?
in the epithelial cells and is added to the IgA as it passes into the secretions
what is the function of the secretory piece?
the secretory piece helps IgA to be transported across mucosa and also protects it from degradation by enzymes in the mucosal secretions
during which part of secretion of sIgA is the secretory component added?
during trancytosis between the extracellular space and the lumen
for transcytosis and association with the secretory component to take place, the IgA dimer must bind what?
a membrane bound Fc receptor (poly-Ig receptor)
what is the second most common serum Ig?
IgA
IgA is the major class of Ig in what?
secretions: • 1. tears • 2. saliva • 3. colostrum • 4. mucus
how is IgA transferred from mother to child?
breast feeding
what type of immunity transfer is breast feeding?
passive transfer of immunity
since it is found in secretions, sIgA is important in what type of immunity?
local (mucosal) immunity
does IgA fix complement?
normally IgA does not fix complement unless aggregated
how does IgA function in mucosal immunity?
IgA inhibit by neutralizing adhesion of pathogens/toxins to epithelial cell on mucosal surface
what are the structural components of IgD?
monomer • tail piece
how does IgD exist?
IgD exists only as a monomer
is IgD found in serum?
IgD is found in low levels in serum
what is the role of serum IgD?
role in serum is uncertain
where is IgD primarily found?
on B cell surfaces
what is the function of B cell bound IgD?
receptor for antigen
which Ig’s are found on the B cell surface?
IgD • IgM
IgD on the surface of B cells has what for anchoring to the membrane?
extra amino acids at C-terminal end
does IgD bind complement?
no
what are the structural components of IgE?
monomer • extra domain Cε4
which is the least common serum Ig?
IgE
why is IgE the least common serum Ig?
it binds very tightly to FcεR receptors on basophils and mast cells
IgE is primarily involved in what?
allergic reactions
why is IgE involved in allergic reactions?
as a consequence of its binding to basophils and mast cells
does IgE fix complement?
IgE does not fix complement
Binding of IgE to mast cell surface receptors does what?
primes the cell to respond to allergen
introduction of allergen and its subsequent binding to IgE on a mast cell induces what?
crosslinking of IgE and clustering of Fc receptors
clustering of Fc receptors on a mast cell post introduction of allergen does what?
initiates a signal transduction event that stimulates the mast cell to degranulate
besides allergic reactions, what does IgE play a role in?
parasitic helminth infections
what are the functions of IgE?
allergic reactions • parasitic helminth infections
why is measuring IgE levels helpful in diagnosing parasitic infections?
because serum IgE levels rise in parasitic diseases
how does IgE help kill parasites?
eosinophils have Fc receptors for IgE and binding of eosinophils to IgE-coated helminthes results in release of granular contents which kill the parasite
which Ig’s predominate in the blood?
IgM, IgG and monomeric IgA predominate in the blood
which are the major Ig’s in the extracellular fluid?
IgG and monomeric IgA
which Ig predominates in the secretions?
dimeric IgA
where is IgE found?
IgE is associated with mast cells and is therefore found in the connective tissue beneath epithelial surfaces, particularly of the skin, respiratory tract and the GI tract
which Ig’s are in the brain?
THE BRAIN IS DEVOID OF IMMUNOGLOBULIN
isotypes of Ig have variations in what?
the Fc region, constant heavy chain
what are allotypes of Ig?
alleles: • variations in the Fc region found in members of the same species
when is the allotype of Ig important?
tissue typing for transplantation
what are idiotypes of Ig?
variation in the variable region
what does the idiotype of an Ig determine?
antigen specificity
what differentiating class of an Ig is present in all individuals of a species?
isotype
which differentiating class of an Ig is different alleles within a species?
allotypic determinants
which differentiating Ig class determines the antigen binding site?
idiotypic determinants
What is the degree of neutralization functionality of IgM?
+
what is the degree of neutralization function of IgD?
-
what is the degree of neutralization function of IgG1?
+++
what is the degree of neutralization function of IgG2?
+++
what is the degree of neutralization function of IgG3?
+++
what is the degree of neutralization function of IgG4?
+++
what is the degree of neutralization function of IgA?
+++
what is the degree of neutralization function of IgE?
-
which Ig’s have + degree of neutralization function?
IgM
which Ig’s have - degree of neutralization function?
IgD • IgE
which Ig’s have +++ degree of neutralization function?
IgG1 • IgG2 • IgG3 • IgG4 • IgA
what is the degree of opsonization function of IgM?
-
what is the degree of opsonization function of IgD?
-
what is the degree of opsonization function of IgG1?
+++
what is the degree of opsonization function of IgG2?
* req complement
what is the degree of opsonization function of IgG3?
++
what is the degree of opsonization function of IgG4?
+
what is the degree of opsonization function of IgA?
+
what is the degree of opsonization function of IgE?
-
which Ig’s have - degree of opsonization function?
IgM • IgD • IgE
which Ig’s have + degree of opsonization function?
IgG4 • IgA
which Ig’s have ++ degree of opsonization function?
IgG3
which Ig’s have +++ degree of opsonization function?
IgG1
what is the degree of sensitization for killing by NK cells function of IgM?
-
what is the degree of sensitization for killing by NK cells function of IgD?
-
what is the degree of sensitization for killing by NK cells function of IgG1?
++
what is the degree of sensitization for killing by NK cells function of IgG2?
-
what is the degree of sensitization for killing by NK cells function of IgG3?
++
what is the degree of sensitization for killing by NK cells function of IgG4?
-
what is the degree of sensitization for killing by NK cells function of IgA?
-
what is the degree of sensitization for killing by NK cells function of IgE?
-
which Ig’s have - degree of sensitization for killing by NK cells function?
IgM • IgD • IgG2 • IgG4 • IgA • IgE
what is the degree of sensitization of mast cells function of IgM?
-
what is the degree of sensitization of mast cells function of IgD?
-
what is the degree of sensitization of mast cells function of IgG1?
+
what is the degree of sensitization of mast cells function of IgG2?
-
what is the degree of sensitization of mast cells function of IgG3?
+
what is the degree of sensitization of mast cells function of IgG4?
-
what is the degree of sensitization of mast cells function of IgA
-
what is the degree of sensitization of mast cells function of IgE?
+++
which Ig’s have - degree of sensitization of mast cells function?
IgM • IgD • IgG2 • IgG4 • IgA
which Ig’s have + degree of sensitization of mast cells function?
IgG1 • IgG3
which Ig’s have +++ degree of sensitization of mast cells function?
IgE
what is the degree of activation of complement system function of IgM?
+++
what is the degree of activation of complement system function of IgD?
-
what is the degree of activation of complement system function of IgG1?
++
what is the degree of activation of complement system function of IgG2?
+
what is the degree of activation of complement system function of IgG3?
+++
what is the degree of activation of complement system function of IgG4?
-
what is the degree of activation of complement system function of IgA?
+
what is the degree of activation of complement system function of IgE?
-
which Ig’s have - degree of activation of complement system function?
IgD • IgG4 • IgE
which Ig’s have + degree of activation of complement system function?
IgG2 • IgA
which Ig’s have ++ degree of activation of complement system function?
IgG1
which Ig’s have +++ degree of activation of complement system function?
IgM • IgG3
what is the degree of transport across epithelium of IgM?
+
what is the degree of transport across epithelium of IgD?
-
what is the degree of transport across epithelium of IgG1?
-
what is the degree of transport across epithelium of IgG2?
-
what is the degree of transport across epithelium of IgG3?
-
what is the degree of transport across epithelium of IgG4?
-
what is the degree of transport across epithelium of IgA?
NAME?
what is the degree of transport across epithelium of IgE?
-
which Ig’s are not transported across epithelium?
IgD • IgG1 • IgG2 • IgG3 • IgG4 • IgE
which Ig’s are transported across epithelium to some degree?
IgM
which Ig’s are transported across epithelium A LOT?
sIgA
what is the degree of transport across placenta of IgM?
-
what is the degree of transport across placenta of IgD?
-
what is the degree of transport across placenta of IgG1?
+++
what is the degree of transport across placenta of IgG2?
+
what is the degree of transport across placenta of IgG3?
++
what is the degree of transport across placenta of IgG4?
++
what is the degree of transport across placenta of IgA?
-
what is the degree of transport across placenta of IgE?
-
what Ig’s are not transported across placenta?
IgM • IgD • IgA • IgE
which Ig’s are transported across placenta to some degree?
IgG2 (+)
which Ig’s are transported across placenta to a moderate degree?
IgG3 • IgG4 • (++)
which Ig’s are transported across placenta A LOT?
IgG1 (+++)
what is the mean serum level (mg/mL) of IgM?
1.5
what is the mean serum level (mg/mL) of IgD?
0.03
what is the mean serum level (mg/mL) of IgG1?
9
what is the mean serum level (mg/mL) of IgG2?
3
what is the mean serum level (mg/mL) of IgG3?
1
what is the mean serum level (mg/mL) of IgG4?
0.5
what is the mean serum level (mg/mL) of IgA
2.5
what is the mean serum level (mg/mL) of IgE?
5 x 10^-5
what is an immunogen?
substance capable of inducing adaptive immune response
what is an antigen?
substance capable of being recognized by the adaptive immunity.
what is the relationship between antigens and immunogens?
All immunogens are antigens, but not all antigens are immunogens
what is an epitope?
the region(s) of the antigen in direct contact with the antibody, B-Cell Receptor, or T-Cell Receptor
what is a synonym for epitope?
antigenic determinant
how many epitopes are there per antigen?
there may be one or more epitopes per antigen
what is a hapten?
a small molecule which can function as an antigen, but by itself is incapable of inducing an immune response
is a hapten an immunogen?
no
what are the 3 types of antigen/immunogen receptor molecules?
- BCR (b cell receptor) • 2. TCR (t cell receptor) • 3. MHC
of the 3 types of antigen/immunogen receptor molecules, which are surface immunoglobulins?
B-Cell Receptors
how many antigen recognition sites are there on a BCR?
two identical antigen recognition sites
how many antigen recognition sites are there on a TCR?
one antigen recognition site
where are MHC-I molecules expressed?
on all nucleated cells
where are MHC-II molecules expressed?
macrophages • dendritic cells • lymphocytes
which of the 3 types of antigen/immunogen receptor molecules is expressed on antigen presenting molecules?
MHC
which various antigens or sources of antigens are immunogens?
- parasites • 2. foreign proteins • 3. bacteria • 4. viruses • 5. fungi
antigens are big molecules- however, the area that triggers the specific immunity is a small part, known as what?
epitope
how big is an epitope?
an epitope in a protein antigen could be as few as 20 amino acids long
what is the shape of an epitope?
could be linear, conformational
what type of cells recognize a conformational epitope?
BCR only, not TCR
what is the difference between a linear and conformational epitope?
in a conformational epitope, the sequence of amino acids is discontinuous, but they are brought into proximity by the protein’s 3-D structure
what is a synonym for conformational epitope?
discontinuous epitope
when is there cross-reaction between different antigens?
when a different antigen has one identical determinant or a similar determinant
when is there no reaction between different antigens?
when there is no structural similarity
what is the receptor/binding activity of a BCR?
BCR–> Ag
what is the receptor/binding activity of a TCR?
TCR –> Ag/MHC
is MHC required for BCR?
no
is MHC required for TCR?
yes
does a BCR bind soluble antigen?
yes
does a TCR bind soluble antigen?
No
what is the chemical nature of BCR antigens?
protein • polysaccharides • lipids • nucleic acids
what is the chemical nature of TCR antigens?
proteins • some lipids, glycolipids
what type of epitope is recognized by BCR?
accessible, either linear or conformational
what type of epitope is recognized by TCR?
linear peptides (short)
what makes a good antigen/immunogen?
- physical size : > –> better • 2. complexity: chemical composition and structural complexity • 3. solubility or degradability by antigen processing cells, macrophages, dendritic cells and B cells • 4. foreignness to the individual
what size are the best immunogens?
>=100kD
what is the minimum size for active immunogens (proteins)
>30kD
how immunogenic is an immunogen that is <5-10kD?
minimally immunogenic, usually require carrier
what is an example of a <5-50kD immunogen that is minimally active and requires a carrier?
hapten
How do the categories of chemical compounds rank in terms of their immunogenicity based on complexity in descending order?
HIGH IMMUNOGENICITY: • 1. proteins and glycoproteins • 2. Polysaccharides • 3. nucleic acids, phospholipids • 4. haptens • LOW IMMUNOGENICITY:
are proteins and glycoproteins good immunogens?
yes
how complex are proteins and glycoproteins in terms of their immunogenicity?
complex in composition and structure
can proteins and glycoproteins induce immunity?
can induce humoral and cell-mediated immunity
how complex are polysaccharides in terms of their immunogenicity?
repeating structures, generally low affinity
what type of response do polysaccharide immunogens elicit?
IgM response
do polysaccharides stimulate a cell-mediated immune response?
cannot be processed and presented as linear epitopes for T cells, thus do not induce cell-mediated response
how foreign are nucleic acids and phospholipids in terms of their immunogenicity?
evolutionarily conserved; less foreign
how do nucleic acids and phospholipids become better immunogens?
conjugation with proteins or polysaccharides
how immunogenic are haptens?
insufficient in size to be immunogenic. need carrier
what examples of natural haptens?
hormones, lipids, simple sugars
what are examples of synthetic haptens?
chemicals, drugs (penicillin)
what types of drugs can act like haptens and be associated with severe, life threatening anaphylactic reactions?
antibiotics, particularly penicillins
how do penicillins act as haptens?
they form covalent bonds with proteins to produce protein-drug adducts that elicit an immune response (hypersensitivities) in some individuals
what are the 3 types of epitopes in a hapten-conjugate complex?
- the pure hapten • 2. the pure antigen • 3. the hapten-antigen complex
how can a hapten be made immunogenic?
immunizing with a hapten-carrier conjugate
do identical twins recognize each other’s proteins as foreign?
no. • they have the same genetic makeup and their immune systems would recognize eachother as self
what are examples of immunologically privileged anatomical sites (sequestration)?
corneal, spermatic, CNS cell antigens
What are the types of antigens?
- mitogens • 2. superantigens • 3. T cell independent • 4. T cell dependent
mitogens are characterized by what?
the same epitope repeated many times
how many types of B cells can mitogens activate?
more than one B cell type/clone
are mitogens B cell monoclonal or polyclonal activators?
B cell polyclonal activators
what are superantigens?
antigens that can activate more than one type of T cell
are superantigens polyclonal/monoclonal B/T cell activators?
polyclonal T cell activators
what effect do superantigens have on the immune system?
cause hyper activation of the immune system
what is an example of excessive T cell activation having drastic effects?
toxic shock syndrome
what does an antigen being T cell independent vs. T cell dependent depend on?
whether an anigen can stimulate B lymphocytes with or without the help from T lymphocytes
How do superantigens induce activation of multiple types of T cells?
they are polyclonal stimulators of T cells, binding to the MHC-TCRβ (on the outside of the polypeptide of TCR) complex, without regard for antigen specificity
How much of CD4 T cells are activated by super antigens?
up to 20%
what is the result of a superantigen activating up to 20% of circulating CD4 T cells?
massive production of cytokines such as IL1, IL2, and TNFα which causes systemic shock
what are examples of conditions that are caused by superantigens?
food poisoning • toxic shock syndrome
what microbes cause food poisoning and/or toxic shock syndrome?
bacterial exotoxins: • staphylococcal • enterotoxins • staphylococcal toxic shock toxin • staphylococcal exfoliating toxin • streptococcal pyrogenic exotoxins
what forms a bridge between CD4 T cell’s receptor and the MHC II molecule?
superantigens
what do T cells do in response to a superantigen?
divide and differentiate into effector cells
what are T-independent antigens?
antigens which can directly stimulate B cells to produce antibody without the requirement for T cell help
do T independent antigens require to be presented by APC?
no
usually, T independent antigens are what?
mitogen and are resistant to degradation by antigen presenting cell
what are examples of T independent antigens?
pneumococcal polysaccharide • lipopolysaccharide • flagellar antigen
what are T dependent antigens?
antigens that require the help of T lymphocytes to activate be cells to produce antibody
are T dependent antigens degradable by antigen presenting cell?
yes
what type of compounds are T dependent antigens?
protein
in addition to size, molecular complexity and foreignness, immunogenicity of an antigen depends on what?
- physical form • 2. degradability • 3. route • 4. dose • 5. adjuvant
which physical form of an antigen is more immunogenic, particulate or soluble?
particulate > soluble
why are particulate antigens more immunogenic than soluble ones?
particulate form are more easily taken up by antigen presenting cells
which physical form is more immunogenic, denatured or native?
denatured > native
what speed of release is important for immune response?
slow release
what are the relative immunogenicities of routes of administration?
subcutaneous > intraperitoneal > intravenous > intragastric
what is the limitation of the oral route of administration’s immunogenicity?
oral route induces local mucosal immunity but not systemic immunity
what is low zone tolerance?
low doses appear to inhibit the specific antibody production
what is high zone tolerance?
very high doses of antigen inhibit immune responsiveness to a subsequent challenge
what is the effect of an adjuvant on immunogenicity?
substances mixed together with an antigen and enhance an immune response to an antigen
what is the difference between an adjuvant and a carrier molecule?
unlike carrier molecule an adjuvant does not form stable linkage with the antigen
what is an example of an adjuvant?
- complete Freund’s adjuvant • 2. aluminum hydroxide/aluminum phosphate
what is Complete Freund’s Adjuvant?
water in oil emulsion containing killed mycobacteria
how does an adjuvant increase immunogenicity of an antigen?
- insolubilize antigen for better phagocyte uptake • 2. insolubilize antigen for gradual release over time in lipid emulsions called liposomes with delayed time release of antigen • 3. stimulating the influx of phagocytic cells or other immune cells to the site
some adjuvants contain mycobacterial components capable of stimulating what?
the innate immunity- acitvation of macrophages
what can inflammation be thought of as?
a regulatory event aimed at mobilizing various innate immune effectors and trafficking them to the anatomic location where they can be most effective
what is the etymology of inflammation?
latin: inflammare- to set on fire
inflammation is initiated by the presence of what?
infectious agents • tissue damage • self (auto) antigens (autoimmunity)
in inflammation an innate or adaptive immune action?
combined action of several immune responses of both innate and specific immunity
inflammation leads to what?
- vascular dilation/ increased vascular permeability • 2. accumulation of inflammatory cells • 3. destruction of initiating agent • 4. tissue repair • 5. tissue damage/scarring
what are the symptoms of inflammation?
rubor • tumor • calor • dolor • functio laesa
what are the cellular players in acute inflammation?
tissues mast cell • neutrophil • macrophage
what cells, in addition to the cellular players in acute inflammation, may also be found at site of inflammation?
eosinophils • basophils
what are the functions of tissue mast cells in acute inflammation?
release of histamine and other mediators
what are the functions of neutrophils in acute inflammation?
phagocytosis and killing
what are the functions of macrophages in acute inflammation?
phagocytosis and killing • antigen presentation
what are the functions of eosinophils in acute inflammation?
killing of parasites
inflammatory stimuli do what?
- activate the complement system • 2. degranulate mast cells • 3. acitvate macrophages • 4. activate coagulation system
inflammatory stimulia activate the complement system, degranulate mast cells, activate macrophages and coagulation system leading to the production of what?
bradykinin, which increases vasodilation
in response to inflammatory stimuli, platelts are a mojor component of clotting, releasing what?
prostaglandins • hydrolytic enzymes • growth factors • other mediators that stimulate various cell types to contribute to antimicrobial defense, wound healing, and inflammation
microbes and/or their products that enter through a breach in the dermis induce what?
phagocytes to secrete pro-inflammatory cytokines (IL1, TNFα), also activate complement leading to the expression of adhesion molecules by vascular endothelium
the net movement of WBC’s from circulation into tissue is called what?
extravasation
what are the steps of extravasation?
- Rolling Adhesion • 2. Firm Adhesion (tethering and tight binding, margination) • 3. diapedesis (transendothelial migration) • 4. Migration toward the site of infection
Extravasation is driven by what compounds?
TNFα • IL1 • IL8 • C3a • C5a
how does rolling in extravasation work?
- rolling uses selectins • 2. rolling is a low affinity adhesion • 3. E-selectin on endothelium bind to mucin like adhesion molecule on the phagocytic membrane briefly. • 4. force of blood moves rolling on
what are the proteins that bind in rolling during extravasation?
E-selectins on endothelium bind to mucin-like adhesion molecules (selectins/Sialyl Lewis sugars) on the phagocytic membrane briefly
what force causes rolling during extravasation to move on?
blood flow
describe activation by chemoattractants during extravasation
chemokines released during inflammation stimulate conformational change in integrin molecules in phagocytic membrane that incresae their affinity for ICAM adhesion molecules on the endothelium
what are the chemokines released during inflammation that stimulate conformational change in integrin molecules in phagocytic membrane that increase their affinity for ICAM adhesion molecules on the endothelium?
IL-8 • C5a
to what family of compounds does ICAM belong?
immunoglobulin superfamily
what proteins are associated with tethering and tight binding during extravasation?
integrins (LFA)
what is LFA?
lymphocyte function-associated antigen 1
what types of adhesions are formed in tethering and tight binding during extravasation?
firm adhesion to ICAMS
what is diapedesis?
transendothelial migration
diapedesis is mediated by what?
PECAM, now renamed CD31
what is PECAM?
platelet endothelial cellular adhesion molecule
where is CD31 expressed?
on endothelial cells and neutrophils
what happens to endothelial expression of E and P selectins under the influence of inflammatory stimuli?
endothelial expression of E and P selectins increases
to what family of compounds does LFA-1 belong?
part of the integrin family of leukocyte adhesin molecules
What is CD18?
common β chain of the leukocyte integrins
what does absence of CD18 cause?
leukocyte adhesion deficiency disease
what cytokine released by macrophages upregulate the expression of P selectin on endothelial cells?
TNFα
what do P and E selectin do?
together E and P selectin slow the motion of leukocytes through the bloodstream by causing them to roll along the endothelial surface, allowing other molecules to interact with the slowed leukocytes to stop them and promote their movement into the tissues.
what compounds stimulate E and P selectin expression?
IL-1 • LPS • TNFα
what is LPS a component of?
the membranes of many gram negative bacteria
what do LPS binding proteins on macrophages do when they come into contact with their ligand?
stimulate macrophages to release inflammatory cytokines
Both E and P selectins are known to bind with what?
Sialyl-Lewis x like glycans
where are Sialyl-Lewis x-like glycans expressed?
in relatively high numbers by circulating leukocytes
in addition to Sialyl Lewis glycans, what else does P selectin bind?
P-selectin glycoprotein ligand-1 (PSGL-1)
where is PGSL-1 expressed?
modestly expressed on human leukocytes
leukocyte recruitment by E and P selectin is analogous to what?
throwing a tennis ball at a velcro surface
tight adhesion to the rolling leukocyte is performed by what?
ICAM-1
what does ICAM-1 bind to?
integrins LFA-1 and CR3 on the leukocyte surface
what does ICAM-1 do?
binds to the Integrins LFA-1 and CR3 on the leukocyte surface and arrests the motion of the rolling leukocyte.
why does ICAM-1 stop the rolling leukocyte?
stopping the leukocyte allows it to enter the tissues by secreting proteases to breach the endothelial basement membrane
what is the acute phase response?
physiological processes that occur during inflammation or tissue damage, triggered by IL-1, IL-6, TNFα
which cytokines trigger the acute phase response?
IL-1 • IL-6 • TNF-α
on what systems do IL-1, IL-6, and TNFα act during the acute phase response?
hypothalamus • bone marrow • liver
what does the acute phase response cause by acting on the hypothalamus?
fever
what does the acute phase response cause by acting on the bone marrow?
stem cell differentiation and proliferation
what does the acute phase response cause by acting on the liver?
increase production of acute phase proteins
what are the purposes of the acute phase response?
- provides replenishment of cells and acute phase proteins used during an inflammation response • - increase metabolic activity
what are acute phase proteins?
heterogenous group of serum proteins that increase during inflammation
what do acute phase proteins do?
replace exhausted components and reinforce innate defenses against infection
what are the important acute phase proteins?
- C-reactive protein • 2. mannose-binding lectin • 3. complement • 4. fibrinogen
what is CRP?
a protein found in the blood, the levels of which rise in response to inflammation
what does CRP do?
- acts as an opsonin AND • 2. it binds to phosphocholine expressed on the surface of dead or dying cells (and some types of bacteria) in order to activate the complement system via the C1q complex (classical pathway in the absence of antibody)
what are the relative levels of CRP and MBL in the plasma?
the levels of CRP and MBL are low in the plasma, but levels can increase by up to 1000 fold during the peak of the acute phase response
when is the peak of the acute phase response?
about 2 days after its start
CRP and MBL both bind to what?
distinct structures that are common features of pathogens and not features of human cells
what is the clinical application of CRP?
levels of CRP are routinely measured in clinical diagnostic laboratories to indicate an acute inflammation
what does MBL do?
acts as opsonin and triggers complement activation via lectin pathway
