Ppt 4 Antigen recognition in the adaptive immune syst Flashcards
How do B cells recognize antibodies?(in other words, what kind ofreceptor do they use?)
they use membrane bound or secreted antibody receptors
What receptor do T lymphocytes use to recognize antigen?
T cell receptor on its membrane (MEMBRANE BOUND)
What is the principal function of antigen receptors in the immunesystem?
to detect and trigger a response against it
How are antigenreceptors distributed?(are they clonal or non-clonal?)What does this mean?
they are clonalwhich means that the clones are all different for a specific antigen
Antigen receptors are differentfor different antigens, yet, what is still the same among their functionality?
theantigen receptors transmit biochemical signals fundamentallythe same which are unrelated to specificity.
What 2 things makeup the structure of a antigen receptor in a lymphocyte? (generally speaking)
1) Varibale region2) Constant region
What is the variable region?
this is the part that recognizes antigen
What is the constant region?
give structural integrity and effectorfunctions
What structure remains unchanged in a antigen receptor clones?
Constant region
What gives the variable region the ability to detect different antigens?
genes thatvary the polypeptides that detect antigenin the variable region
T cell receptors will recognize what kind of microbes?
cell-associated microbes bound to the MHC molecule of APC’s and must bepeptides
Inside the variable region, what specifically binds to antigens and contains the actual variability?
the hypervariable region or CDR (complementarity-determining region)
what forms the entire structure of the B cell receptor and the T cell receptor?
the antigen receptor (constant and variable region) and the signaling proteins found in the inside of the cell
What is the T cell receptor complex?
when you have the:T cell receptor (variable and constant regions found outside) + the internal signaling molecules for t cells (CD3 andζ chains)
what are the internal signaling molecules for T cells?
CD3 andζ chain
How do you activate the signaling proteins in both T/B cell receptor complex?
you need to cross link 2 or more receptors in order to bring the singaling proteins together- that way they will cause phosphorylation of other proteins inside the lymphocyte and activate transcription
what are the effector molecules of the humoral immunity?
antibodies
where do you find antibodies secreted?
blood and mucosa
what do membrane bound and secreted immunoglobins use to recognize antigen?
they use variable domains
What other 2 cells use receptors thatrecognizesecreted antibody constant regions in order to eliminate microbes?
1) Fc receptor in phagocytes2) C1 proteins of complement
what part of the secreted antibody’s structure can be used by other cells to eliminate microbes?
the constant region on secreted antibodies
What is the function of membrane bound antibodies on B cells?
to bind antigen and initiate a response
what is the function of secreted antibodies?
to neutralize microbes before they colonize
What is the structure of an antibody?
2 heavy chains2 light chains
each Heavy chain and ligh chain contains individual what?
variable and constant regions
to what is the light chain attached?
to the heavy chain
to what is the heavy chain attached?
to the other heavy chain using disulfide bond
How many V domains does the light chain have?
1 V domain
How many V domains does a Heavy chain have?
1 V domain
How many C domains does the light chain have?
1 C domain
How many C domains does a heavy chain have?
3 or 4 C domains
how many hypervariable regions does each Heavy and Light chain have?
3 CDR or hypervariable regions
which hypervariable region contains the most variability? (which CDR is highly polymorphic?)
it is CDR 3 or Hypervariable region 3
where is the CDR 3 located?
in the junction of the V and C region
which hypervariable region contributes the most to antigen binding?
CDR 3 because its the most polymorphic
what is found between the Fab region and the Fc region?
the flexible hinge region
What is the top box?
the Fab regions (there are 2)
what is the bottom box?
the Fc region, only 1
who generates 1F(ab)2 region capable of binding antigen and bridging?
Pepsin
What does Papain generate?
2 Fab fragments and 1 Fc fragment
what is the differene in the production of Fab regions by papain and pepsin?
papain generates Fab regions that are monovalentpepsin generates Fab regions that are divalent
what is the Fab region?
fragment of antigen binding- its a light chain attached to the V and C domain of a constant region
how many Fab regions are in an immunoglobulin?
2 identical one’s
What are the 5isotypes of antibodies?
Ig G/M/E/A/D
what is the heavy chain for IgE
epsilon (e)
what is the heavy chain for IgA?and for IgG?and for IgM?and for IgD?
IgA = alphaIgG = gamma (y)IgM = mew (µ)IgD = delta
what does IgA do?
mucosal immunity
what does IgM do?
its a naive B cell antigen receptor
what does IgE do?
its used for Mast cell degranulation and defends against parasites
what does IgG do?
its coats microbe for opsonization and also serves for ADCC
what 2 antibodies are found always as monomers?
IgG and IgE
What antibody is always found as a pentamer?
IgM
what antibody is not secreted?
IgD
what antibody do we find as a dimer, monomer or trimer?
IgA
what antibodies lasts a long time after it is secreted?
IgG
what antibody is removed fast after it has done its function?
IgE
what antibodies have 2 antigen binding sites?
IgG, IgE, IgD
how many antigens can IgA bind?
4
how many antigens can IgM bind?
10
what is avidity?
the total strenght which an antibody binds an antigen
what is cross reaction?
when an antibody binds another antigen that looks similar to the one it was initially going to bind
what are the 2 types of light chains?
kappa and lambda
How does the kappa and lambda light chains differ?
they have different C regions
how are kappa and lamda light chains similar?
they have the same function
can B cells express both kappa and lambda chains?
no
what is different about the heavy chains of each antibody?
they all have different C regions
Can light chains join or complex with any type of heavy chain?
yes
naive B cells have what 2 antibody isotypes in their membrane?
IgM, IgD
what other cell helps B cells differentiate?
helper T cells
what antibody do naive B cells secrete?
IgM
what process or mechanism allows B cells to produce other heavy chains different than IgM or IgD?
heavy chain class switching
in isotype switching or heavy chain switching, do B cells chainge their specificity or their V chains?
No, they remain specific for an antigen and their V region does not change
What makes up the signaling proteins in the B cell receptor?
Ig (alpha) and Ig (beta)
What are Ig alpha and Ig beta involved with when antigen is recognized?
B cell activation
what are the parts of antigens recognized by antibodies?
the epitopes
what is another name for the antigen epitopes?
determinants
how are different different antigens recognized? (based on their epitopes)
because epitopes may be sequential or conformational(AKA: they are linear or with a shape)
what is the term used for the strenght of the antigen binding surface to the epitope?What is the symbol used for this term?
affinity; Kd
what does a low Kd mean?
there is a high affinity for that antigen epitope
what is affinity maturation?
when antibodies become adapt to binding to a specific antigens epitopes. Usually by repeated expossure
what is a monoclonal antibody?
its a antibody that has been fused with a myeloma cell causing it to last very long and secrete a specific antibody
what is a myeloma cell?
a tumor cell of plasma cells
what is a hybridoma?
the cell that forms when a B cell is fused with a myeloma cell
how do you make monoclonal antibodies?
1) immunise a mouse2) he now makes antibodies3) fuse those plasma cells with myeloma cells4) select the hybridomas of choice
can monoclonal antibodies be repeatedly injected into humans? why?
NO, because our immune system will see the mouse Immunoglobulin as foreign and will attack it
how can you inject monoclonal antibodies repeatedly into humans?
by replacing the Ig part of the antibodies with human Ig
besides replacing the Ig part of antibodies, how else can you make monoclonal antibodies suitable for injection into humans?
through DNA recombination
the t cell receptor for antigen is a membrane bound receptor, is it made a heterodimer or homodimer?
it is a heterodimer
What chainsmakes up the T cell recpetor dimers?
the alpha and beta chains
how many Variable and Constant regions to T cell alpha and beta chains have?
1 variable and 1 constant
how many hypervariable regions does each variable chain have?
3 CDR
which CDR in the T cell variable chain is the most…variable or polymorphic?
CDR 3
do t cell receptors undergo affinity maturation or isotype switching?
No!!
how to t cells differentiate between complex microbes?
detecting amino acid sequences in the immuno-dominant epitopes
are gamma delta T cell receptors structurally the same as alpha beta receptors?
yes
how to Alpha Beta TCR differ from Gamma Delta TCR?
Gamma Delta TCR will recognize protein and non-protein antigens and theydon’thave to be displayed by MHC molecules
where are gamma delta TCR found in the body?
in the epithelium
what subunits in the TCR variable region make up the antigen binding part?
Va (alpha) and Vb (beta)
What subunits compose the TCR constant regions?
Ca (alpha) and Cb (beta)
When transmiting signals to the inside of the cell, besides CD3 andζ, what else is needed to fully activate a T cell response?
engagement of the co-receptor molecules CD4 and CD8
what do CD8 and CD4 molecules recognize in the MHC molecules?
the nonpolymorphic portions of the MHC
maturation of lymphocytes in the bone marrow consists of 3 processes:
1) proliferation of immature cells2) expression of the antigen receptor genes3) selecting the lymphocytes that express the full antigen receptor
how are lymphocytes selected during the maturation process?
those that express the antigen receptor and are able to recognize only the antigen (not self cells)
what happens to lymphocytes that do not express the full antigen receptor?
they die through apoptosis
how is diversity of B/T receptors achieved?
recombining the receptor genes during the maturation process
what is the main goal in the maturation process?
to express diverse amounts of antigen receptors
what process do B/T cells after the end of the maturation process?
they undergo Positive and Negative selection
Is the generation of useful antigenreceptors aefficient or inefficient process? Why?
A highly inefficient process, because it involves random genetic recombination events that fail more often than not
What does IL-7 do?
expands the number of T cellprogenitors before they express antigen receptors
When does IL-7 stop being the signal to proliferate in maturing precursor lymphocytes?
when they acquire the first antigen receptor
What receptor is defective in SCID?
IL-7
Where does positive selection occur?
in the thymus
What is positive selection?
When immature T cells are selected to reacognize self MHC molecules
What do mature T cells need find after positive selection in order to get activated?
The same MHC molecules they wherepresented during positive selection
What 2things are needed to pass positive selection?
1) recognition of MHC molecules2) expression of survival and proliferation signal
What is Negative selection?What does it prevent?
Selectionagainst high-affinity recognition of self antigens in the bone marrow andthymus.It prevents self reactiveantigens
How is the expression of B and T lymphocyte antigen receptors is initiated? what is generated during this process?
Bysomatic recombination of gene segments that code for the variableregions of the receptors.Somatic recombination generates diversity
early lymphoid progenitor cells in the bone marrow contain what genes needed for the maturation process?
Immunoglobulin and TCR genes already in the germline
Do early lymphoid progenitor cells alreadycontain the Ig heavy chain and light chain?
yes
Do early lymphoid progenitor cells that have the TCR already have the alpha/beta chain?
yes
How many variable region genesdo each beta and alpha chains of the early lymphoid progenitor T cell contain?
multiple variable region genes
How many constant region genesdo each beta and alpha chains of the early lymphoid progenitor T cell contain?
few
between the V and C region genes in the early lymphoid progenitor cells there are what?
J(joining) and D (diversity) gene segments
Of the VCJD genes found:which do we find in the antigen receptor gene loci?Which do we find in Immunoglobulin heavy chain?Which do we find in the TCR beta chain?
VJCVDJCVDJC
How do we know the early lymphoid progenitor cell is commited to becoming a B cell?
because there will be recombination of the Varible heavy chain in the Immunoglobulin with the D or J segment
What do we find in a developing B cell gene loci for the heavy chain locus?
a recombined VDJ gene in the heavy chain locus
The VDJ gene in the heavy chain locus gets spliced into the C region and thentranslated, what will it produce?
the µ mRNA
what will the µ mRNA produce?
the µ Heavy chainthe first Ig proteinin B cell maturation
what are the 2 recombination events for the production of the immunoglobulins heavy chain?Who will cause the recombination between VDJ?who activates VDJ recombinase?
D-J gene segments joining and then joining the V regionVDJ recombinaseRAG-1 and RAG-2
what gives the antigen receptor its diversity?
1)combinatorial diversity:different combination of the V D J gene segments2) Junctional diversity: inserting nucleotides at the junctions of V D and J
combinatorial and junctional diversity will increase diversity in what part of the antigen receptor?
the CDR 3 of the variable region
what are 3 ways to do junctional diversity?
- exonucleases: removes nuclotides from VDJ when recombining
- TdT (terminal deoxyribonucleotidyl transferase): it add random nucleotides during recombination of VDJ
- P-nucleotides: during VDJ recombination, breaks are formed and the p-nucleotides fill the overhangs with nucleotides
where do B lymphocytes mature?
in the bone marrow
how are progenitor cell committed to becoming B cell called?What chains do they have?
pro-B cellsIg alpha and Ig beta
afer pro-B cells, what are the next committed cells called?what is characteristic of these cells?
pre-B cells and they have- cytoplasmic µ (the heavy chain protein)- surrogate light chains
what forms the pre-B cell receptor complex?
the µ chain and surrogate light chain associated with the Ig alpha and Ig beta
what are the 2surrogate light chains?
1) lambda 52) VpreB
What is the first checkpoint in B cell formation?
the expression of the B cell receptor complex
what happens if the µ chain is not produced?
the cell is not selected and it dies
what areother two processes that theµ chain and BCR complex will signal?
1) stops recombination of the Ig heavy chain genes- allows to only express 1 Ig gene from the 2 given by parents2) recombination of the Ig light chain locus
when the light chain is produced, it associates with what? What will it produce?
the µ chain and produces IgM antigen receptor
What does the IgM receptor do?What is special about the IgM receptor expression?
provide signal of survival and proliferationIgM receptor expression is the 2nd checkpoint in the B cell maturation
what do we call the IgM expressing B cell?
immature b cell
immature B cells will do what?
leave the bone marrow and enter the spleen
what is the final step in the maturation of B cells?
coexpression of IgM and IgD
why does coexpression of IgM and IgD occur?
because the recombined VDJ heavy chain RNA is spliced onto CµRNA and CδRNA- you end up with:µRNA orδRNA
what do we call a B cell expressing both IgM and IgD?
Mature B cell
What happens in negative selection of B cells?
if B cell binds to antigen strongly in bone marrow it is killed or undergoes receptor editing
what is receptor editing?
when B cell fails negative selection and the VDJ recombinase is activated to make a new light chain to change the specificity of the antigen receptor
what are the progenitor cells that are committed to become T cell called?
pro-T cells or double negative T cells
why are progenitor cells that will become T cells calleddouble negative T cells?
because they dont express CD4 or CD8
for double negative progenitor t cells to proliferate and survive, what must be expressed?
IL-7
some double negative progenitor T cells will undergo what process on their TCR beta gene? What will it result in?
TCR beta gene recombination using VDJ recombinasea beta chain will be produced and expressed in the surface in association with pre-Talpha
what does the pre-Talpha and the newly made beta chain produce?
a pre-TCR complex in pro-T cells
what 3 things will the pre-TCR complex provide?
the first checkpoint: the pre-TCR now provides1) survival and proliferation signal2) TCR alpha gene recombination3) inhibition of VDJ recombination in the second Beta chain locus
cells that survive by expressing the pre-TCR will also express what receptors?
CD4 and CD8 co-receptors
when the pro-Tcells express the co-receptors for CD4/8 and have the pre-TCR, what are these cell now called?
double positive T cells
how to double positive t cells pass positive selection?
it must recognize the MHC molecule in the thymus
what happens to double positive T cells that do not recognize MHC molecules in the thymus?
they do not pass positive selection and undergo apoptosis
in positive selection, double positive t cells that recognize MHC 1 remain whith what co-receptor?and which is lost?
CD8 remainsCD4 is lost
in positive selection, double positive t cells that recognize MHC 2remain whith what co-receptor?and which is lost?
CD4 remains and CD8 is lost
immature t cells that remain with CD8 co-receptor can become what?
CTL’s
immature t cells that remain with CD4co-receptor can become what?
Helper T cells
if a double positive T cell recognized MHC too strongly, what happens to it?What is this process called?
it is killedthis is negative selection
if the double positive cell recognizes the MHC molecule with low avidity, the result is?
positive selection
if the double positive cell recognizes the MHC molecule with high avidity, the result is?
negative selection
