Exam 2 Flashcards
What is the solution that explains antibody diversity?
genes for both chains come from multiple discontinuous genetic segments
How many constant regions does a kappa chain gene have?
1
Describe the differences of the J and C region between kappa and lambda chain genes
- kappa: one C region with J regions grouped separately
- lambda: J and C are grouped together; before every C region there is a J region
What cells express these chain genes and can they express both kappa and lambda at the same time?
- B cells
- express one or the other; once one is expressed, the other will be permanently silenced
- this gives 300 possible variable regions and 5 different isotypes (4 from lambda, 1 from kappa)
Which chromosome are kappa chain genes located?
chromosome 2
Which chromosome are lambda chain genes located?
chromosome 22
Which chromosome are heavy chain genes located?
chromosome 14
How many constant region does a lambda chain gene have?
4-5
How many constant region does a heavy chain gene have?
9
Where can VDJ recombinase be found?
only in B cell and T cell
What does VDJ recombinase do in B cells?
rearrangement of Ig genes
What does VDJ recombinase do in T cells?
rearrangement of T cell receptor
How does VDJ recombinase change the genome?
2 RAG subunits on the linear chain come together to form a loop which gets budded off; I remember RAG as Re Arrange Genome (not sure what it really stands for)
IgM producing cells
produce both IgM and IgD; this happens via how they process RNA transcript viav alternate splicing
Stages of B cell development
- Stem cell
- Early pro-B cell
- Late pro-B cell
- Large pre-B cell
- Small pre-B cell
- Immature B cell
- Mature B cell
What happens in the bone marrow after B cell generation before those B cells are activated?
the B cells that are self-reactive are eliminated
What happens during pro-B cell phase?
heavy chain starts to assemble; light chain is still in the germline
What happens during pre-B cell phase?
heavy chain is rearranged; light chain starts to rearrange but not expressed yet; surrogate light chain serves as quality control to make sure that the heavy chain that has been expressed is not useless
What happens during immature B cell phase?
both heavy and light chain are rearranged; will express lambda or kappa but not both; have mature antibody appear on the surface
What happens during mature B cell phase?
IgD and IgM antibody both appear on the surface
Define antibody
protein produced in response to an immunogen; specifically binds to immunogen that stimulated its formation
composition of immunoglobulin
- two identical heavy chains (H)
- two identical light chains (L)
What are examples of secondary activities of Ig?
- activation of complement
- opsonization
- transport across placental barrier into fetal circulation
- secreted in external secretions of the body
Where are the N-termini and C-termini region on the antibody?
- N-termini are located on the antigen binding region
- C-termini are at the C region of the heavy chain where Fc receptors are
What does gamma globulin refer to?
total collection of immunoglobulin or antibody molecules present
Where is the hypervariable region and what is its purpose?
- near the variable region end
- give each CDR its properties
How is cleft formed and what is its purpose?
- formed by folded Vh and Vl regions
- plays a role in antigen binding
What is the purpose of the intermolecular disulfide bonds that link the heavy and light chains?
stabilize the structure
What is the purpose of the intramolecular disulfide bonds? (in antibody)
stabilize constant and variable region
What are advantages of using pepsin instead of papain?
- crosslinking tumor antigens can trigger apoptosis
- penetrate tissue better
T/F: If you undergo class switch, classes will change but CDR remains the same.
True
How many different heavy chain isotypes are there in humans?
9: four IgG, two IgA, IgM, IgD, IgE
Why is IgE so low in concentration in the serum?
they are not free floating; they are tied up to mast cells; their half life is 2 days
What are the two forms of IgM and how do you get them?
there are two polyadenylation site encoded in the gene and the primary transcript looks the same; depending on the processing steps and which polyadenylation site gets recognized, you can get transmembrane or secreted IgM
Properties of IgM
- 10% of serum
- decavalent pentamer [macroglobulin]
- efficient complement activator
- major receptor on B cells
- natural antibody to A and B blood group antigens
- diffuses poorly
Properties of IgG
- 75% of serum Ig
- longest half life
- complement activator (G3 best, no G4)
- cross placenta (G2 poor)
- opsonizing antibody
Properties of IgG4
- can swap half of its molecule with another IgG4 antibody molecule
- compete with IgE to bind to allergens
- help dampen allergic immune response
- tie up antigen because cannot crosslink
Properties of IgA
- 15% of serum
- high concentration in external secretions
- dimeric IgA via J chain
- tetravlent dimer
- serum IgA is monomer
What is the secretory piece?
- synthesized by epithelial cells
- protein that reacts with IgA
- when IgA binds, it triggers receptor mediated endocytosis
Properties of IgD
- interacts with basophils
- surface receptor with IgM
Properties of IgE
- cytophilic for mast cells and basophils via Fc receptors
- may be involved in immunity against some parasites
Why does allergic response happen so fast?
once IgE on mast cells is attached to its antigen, it triggers degranulation of mast cells and gets dumped out into surrounding tissues; IgE already primed on mast cells
Define allotypes
Genetically-determined differences in the proteins (antigens) between individuals in the same species; usually differ by 1 aa
Effect on immunogenicity in allotype variation.
Variant C regions can be immunogenic in some circumstances
What are the different types of Fc receptors and their function?
- FcγRI – Binds IgG
- FcεRI – Binds IgE
- FcRn – Transports IgG across epithelia
- FcγRIIB1 – Negative feedback mechanism to limit antibody synthesis
What are Fc receptors on NK cells good for?
to detect virally infected cells
Immunity in prenatal stage: 8 weeks
B cells in fetal liver
Immunity in prenatal stage: 10 weeks
Small amounts of immunoglobulin may be detected in this order
IgM > IgD > IgG > IgA
When do you have transport of maternal antibody during pregnancy?
16th week but more than 50% happens after the 34th week
How can you determine if the fetus has been exposed to an infection?
presence of IgM and IgA in cord blood
Immunity in neonatal stage
immuno-competent
How long does maternal IgG antibodies last?
6 months; side note: mother must be immune in order to protect child against a specific pathogen and there is no memory to this passive immunity
Immunity in childhood stage
immune response is mature but child is immunologically inexperienced
Immunity in adult stage
immunologically developed and experienced
What does SIgA-antigen complex do?
- excreted with mucus
- block bacteria from binding to host cell
Which antibody helps with opsonization?
IgG
What is toxin neutralization?
Physical binding of an antibody (IgG is most plentiful) to prevent a protein toxin from binding to its receptor site and thereby inhibit the toxic activity
What are types of antibody-mediated immunity?
- molecular antigens
- extracellular infections
- viremia
- transfusion reactions
What are types of cell-mediated immunity?
- intracellular infections
- cellular antigens
- molecular antigens that causes things such has contact dermatitis
B cell binding with epitopes
bind to epitopes on complete immunogens
T cell binding with epitopes
bind to epitopes from metabolized immunogen; usually associated with MHC; surface of an APC
T cell always attached to the surface of the cell. Why?
if it’s not attached, it can act like an antagonist
T cell recognition characteristics
- requires antigen processing
- requires APC
- MHC restricted
Surface molecules of T cells
- TCR, CD3
- CD4 if MHC class II
- CD8 if MHC class I
What does a double negative T cell have on its surface?
TCR, CD3
What does a double positive T cell have on its surface?
- Both CD4 and CD8 expressed —TCR increases
What does a single positive cell have on its surface?
TCR, CD3, and their choice of CD4 or CD8
What happens to single positive cells after they become single positives?
go to lymphoid tissue waiting to be stimulated by APC; die is not stimulated by immunogen
What happens in negative selection?
makes sure that t cells are not auto immune; don’t want it to attack self; if it does, it becomes anergic and die
What is the major product from T cells?
cytokine; NOT the same thing as antibody
structure of TCR
- α chain and β chain (like heavy and light chain in Ig)
- variable and constant domain
- variable region contribute to antigen binding site
- monovalent and monospecific
- anchored by transmembrane protein
With respect to antigen binding site, what is the difference between α β chains and γ δ chains?
- α β chain bind to peptide
- γ δ chain pick up patterns / classes of antigen; link between innate and acquired immunity
What is the importance of CD3 in the TCR complex?
it’s the wiring; you have to have all four chains in order for signal transduction to occur
T cell acticvation
- MHC class II binds to receptor -> first signal
- dendritic cell upregulates B7 -> T cell brings in CD28 to attach to B7 -> second signal -> proliferation and differentiation
What happens without B7?
no costimulation -> no proliferation -> cell becomes anergic -> shuts off due to lack of signal
Superantigen pathology
immunostimulation -> dendritic cells release cytokines -> cytokine storm -> toxic shock
Profound paradoxical immunosuppression
patient survives toxic shock but is super immunosuppressed; t cells shut off
MHC II Presentation
- antigen endocytosed
- chopped up
- associated with MHC in the cell
- goes to surface of cell
MHC I Presentation
- protein gets chopped up in the cell
- goes to golgi
- associates with MHC
- goes to cell surface
How does T cell interact with APC?
- adhesion molecules
- all T cells express LFA-1
- all dendritic cells present ICAM-1
- LFA and ICAM interact and change conformation to increase affinity
CTLA-4
when B7 tries to stimulate a T cell that’s already been stimulated, CTLA-4 is upregulated; CD28 looks for overstimulation in order to suppress itself by making suppressive cytokines
suppression binding affinity
CTLA-4 bind to B7 twenty times the affinity than it does to CD28
What are the results of T cell cell-cell interaction?
- CD8 kills viral cell
- CD4 stimulates macrophage to make cytokines
- TH2 (also CD4) causes B cell to produce cytokines and also to differentiate into plasma cell
TH1
- mainly antiviral
- can be anti-tumor, anti-fungal, and anti-parasite
- can activate macrophages to fight bacteria
TH2
- mainly anti-parasitic
- also involved in allergies
- promote basophil, eosinophil, mast cell proliferation, class switch to IgE, B cell proliferation, Ig production, humoral immunity
Treg
- mucosal immunity
- anti-inflammatory
- broadly immunosupressant
- inhibit response so that you stay healthy without having inflammatory response
- suppress other effector T cells
- protective role in autoimmunity; pathogenic role in cancer
TH17
- inflammatory T cell response
- associated with fungal and mycobacterial surviellience
- main effector in auto-immune disease
- enhance neutrophil response
What can TH0 cells differentiate to?
- TH1
- TH2
- Treg
- TH17
Balance between TH1 and TH2
- TH1 cells make cytokines that inhibit TH2 responses
- TH2 cells make cytokines that inhibit TH1 responses
γδ T cells
- majority in lymphoid tissue
- doesn’t use CD4 or CD8
- doesn’t need MHC
- ligands are not short peptides
- help tissue repair
- main function is homeostasis
- cytotoxic to tumor cells
Natural killer cells
- 10-15% of circulating lymphocytes
- contain lots of inhibitory receptors
- possess Fcγ receptors—ADCC [can bind Fc portion of IgG]
- antiviral first line of defense
pleiotropy
when cytokines have different biological effects on different target cells
redundant (with respect to cytokines)
when two or more cytokines have the same effect on a target cell
Since cytokines have a wide range of activities, how do you keep specificity in the immune response?
- Regulation of cytokine receptor expression.
- Limited radius of effectiveness.
- Short half lives.
Clinical signs of inflammation
- redness
- swelling
- heat
- pain
- loss of function
What happens during initiation of inflammatory response?
- increased blood supply
- increased vascular permeability
- migration of leukocytes out of capillaries into the area
What are the stages of inflammatory response?
- initiation
- amplification
- termination
What happens during amplification of inflammatory response?
Activated immune system cells secrete cytokines and chemokines that amplify the response.
What is the difference between acute and chronic inflammatory response?
- acute: accumulation of innate immune cells; toxins cleared; response terminated
- chronic: persistent presence of T cell and macrophage
Principle cellular mediators. What are the tissue residents and what do they recruit?
- Tissue: mast cells, macrophages
- Recruit: neutrophils, eosinophils, basophils, lymphocytes, monocytes
What are the first type of leukocytes that leave circulation to go to site if injury and what do they do?
neutrophils; they spit out their chromatin to trap bacteria which keeps infection local
Macrophages’ role in inflammation
- secrete cytokines
- activate other leukocytes
- phagocytose microbes
- present antigen to T cells
- secrete factors that are important in regulating fibroblasts and endothelial cells
What are the main transcription factors for production of inflammatory mediators?
AP-1 and NF-kB
What are the soluble inflammatory mediators?
- cytokines
- complement components
- chemokines
- C-Reactive Protein
- histamine
- platelet activating factor (PAF)
- arachidonic acid metabolites
complement components as an inflammatory mediator
Found in serum. C5a and C3a are “anaphylatoxins.” Activate mast cells to release histamines. C5a is a chemoattractant.
C-Reactive Protein as an inflammatory mediator
CRP is made in liver in response to TNFa, IL-1, and IL-6. Binds to LPS in bacterial cell walls and acts as opsonin. Binds to C1q and activates complement.
histamine as an inflammatory mediator
Released by mast cells and causes vasodilation, vascular permeability, and release of arachidonic acid.
platelet activating factor as an inflammatory mediator
Causes platelets to release serotonin (similar to histamine in effects). PAF is a strong chemoattractant for neutrophils.
arachidonic acid metabolites as an inflammatory mediator
- Leukotrienes and prostaglandins: cause capillary endothelial leakiness and edema during inflammation
- Thromboxanes: vasoconstrictors
- Prostacylins: vasodilators
Define margination
Leukocytes adhere to vascular endothelium (via selectin and integrin binding) near sites of infection or injury.
Define transmigration
Leukocytes migrate through the endothelium. Vasodilation aids this process.
Define chemotaxis
Leukocytes follow a gradient of chemical attractants to the site of infection or injury.
Selectin-mediated adhesion
weak; allows neutrophil to roll along the vascular endothelial surface
What causes chronic inflammation?
- genetic traits
- autoimmunity due to improper lymphocyte development
- persistent irritation or injury
Characteristics of chronic inflammation
- Persistence of T cell and macrophage activity
- Presence of high levels of inflammatory cytokines
- Pain
- Swelling
- Unnecessary scarring
- High levels of matrix metalloproteinases (MMPs)
- Elevated levels of reactive oxygens
- Tissue destruction
What are the types of chronic inflammation?
- cellular mediated immunity: psoriasis, RA
- immune complexes: glomerulonephritis, uveoretinitis
What does it mean if a T cell has CD4 on its surface?
- makes up 65% of T cells
- it is a T helper cell
- helps TCR interact with MHC class II
- doesn’t recognize antigen
What does it mean if a T cell has CD8 on its surface?
- makes up 35% of T cells
- it is a T killer cell / cytotoxic T lymphocyte
- helps stabilize complex between TCR and MHC class I
Response of T cell vary depending on what?
- type of APC
- type of T cell
Superantigen properties
- Bacterial toxins and retroviral proteins
- Specific for Vb
- Activate 1-10%
- Leads to toxic shock syndrome
- Cross link TCRβ and MHC II
What happens after APC activation?
cytokine production
Tfh
- activate B cells
- maturation of antibody response
