6. Adaptive Antigen Recognition in the Immune System Flashcards
Since the TCR must bind to MHC to function, what counts as being self reactive for T Cells?
When both the TCR and the CD28 of the immature T Cell are engaged in binding to the mTEC
What contributes most of the serum IgM during the initial stages of infection?
B-1 Cells
Where are immature B-1 cells sent?
Into the peripheral tissues
What subset are most B Cells derived from fetal liver stem cells sorted into?
B-1 lineage
What two things does “avidity” of an antibody take into account?
Affinity of an antibody for its antigen
Valence of the antibody and antigen (how many binding sites are available on both the antibody and antigen, eg. IgM has 10 binding sites)
Where are immature B-2 cells sent?
Into the spleen to continue developing into mature B Cells
What changes in the production of secreted antibodies vs membrane bound antibodies?
Alternative splicing results in a secreted antibody that lacks a intercalating region for the plasma membrane
What determines whether a mature T Cell will present CD4 or CD8?
Initially they present both, then they interact by chance with either MHC I or MHC II in the Thymus. Whichever it contacts will be the associated CDx they preserve. (Eg. if it contacts MHC II CD4 will be preserved.)
What heavy chains are associated with each of the classes of antibodies?
IgD = Delta heavy chain
IgM = Mu
IgA = Alpha
IgG = Gamma
IgE = Epsilon
What is the total potential “repertoire” for BCR’s vs TCR’s?
BCR: 1011
TCR: 1016
TCRs are capable of interacting with a larger number of specific epitopes
What is the benefit of IgM having lower affinity than IgG?
IgM is able to recognize a wider range of epitopes, whereas IgG is more specific
What does papain do to antibodies?
Cleaves them at the heavy chain above the hinge region.
What is the primary mechanism of epitope specific diversity of BCR and TCRs?
DNA Chromosomal Rearrangement via Rag1 and Rag2 recombination enzymes
What compound is used to help fuse immunized mouse splenocytes with myeloma cells?
Polyethylene glycol
Where does T Cell negative selection occur, and by what cell type?
Occurs in the medulla (stroma)
Medullary Thymic Epithelial Cells (mTECs)
Why are B1 cells less diverse than B2 cells?
Because TdT is not expressed in the fetal liver, and as a result, we don’t get N regions added, and there is no junctional diversity.
What enzyme is responsible for adding additional variablility to the BCR or TCR after VDJ recombination through the addition of N regions?
Terminal Deoxynucleotidyl Transferase
On which chromosome do we find TCR beta?
Chromosome 7
TCRs have CD3 and zeta subunits with ITAMs to assist in intracellular signaling, what do BCRs have?
Immunoglobulin beta and alpha with ITAMs
(IGb IGa)
What two types of light chains are there?
Kappa and Lambda
Which subset of B Cells require T Cells to respond to an antigen?
Follicular B-2 Cells
What class or classes of immunoglobulins are expressed by every naive mature B Cell?
IgM and IgD
What motif do we see in the intracellular domains of the TCR and BCR complexes?
ITAMs
(Immunoreceptor Tyrosine-based Activation Motif)
If a B Cell is found to react to a self antigen, but does not yet need to go through apoptosis, what mechanism can it go through instead?
Light chain rearrangement
(Called receptor editing)
Which interleukin is essential for proliferation of the earliest lymphocytes?
IL-7
What subset of cells produce “natural antibodies?”
B-1 Cells
Which Igs do we find on Chromosome 14?
TCR alpha chain
IgH (Heavy chain)
In an antibody, how many CDRs are in the VH and VL chains?
Three in each
What is a haptan?
A small molecule that, when attached to a larger carrier, can elicit the production of antibodies that bind to the complex.
Which antibody is most present in serum?
IgG
What substances make up the HAT medium for monoclonal antibody formation?
Hypoxanthine, Aminopterin, Thymidine
Which subset of B-2 cells has more limited diversity?
Marginal Zone B-2 Cells
Where do memory cells reside between infections?
Primarily secondary lymphoid organs
What does a “trophic signal” cause in a young B Cell?
Confirms that the heavy chain was rearranged and generates a surrogate light chain.
(The surrogate light chain is invariate)
Which class of antibody is presented most in the body?
IgA
(Found on mucosal surfaces)
What is different about recombination of light chains vs heavy chains?
Light chain DNA doesn’t include a D region, just a VJC
What are the signal transducing subunits of the TCR complex?
CD3 and the two zeta subunits
Which terminus of the BCR or TCR binds the antigen and is highly variable?
The N Terminus
What about the BCR has an effector function?
The Fc region of the antibody
What subset are B Cells produced after birth in the bone marrow sorted into?
B-2 lineage
What is interesting about the inheritance of IgH, IgLambda, and IgKappa?
They are inherited codominantly
Which Ig do we find on Chromosome 22?
Ig lambda
Where are B1 cells found in adults?
In the peritoneum and mucosa
What does pepsin do to antibodies?
Cleaves the heavy chain below the hinge region.
What class of antibody has four subtypes?
What are these subtypes based upon?
IgG
Compliment fixation / not
How does the HAT medium kill myeloma cells?
Aminopterin blocks de novo purine synthesis, and myeloma cells lack hypoxanthine guanine phosphoribosyl transferase, so they can’t use a scavenger pathway to use the hypoxanthene in the medium. Hybrid cells can, so they survive.
What has a higher affinity for antigens, TLR’s or antibodies?
Antibodies, by far.
Which immunoglobulin is passed through the placenta?
IgG
What are the steps to VDJ recombination?
- DJ are chosen
- V is chosen
- C is chosen
- Check for productive rearrangement (no stop codons, 10% chance)
- Either paternal or maternal is expressed and recombination of the other allele is stopped.
What is interesting about the affinity of antigen bindind for antibodies vs TCRs?
Immunoglobulins increase their affinity to the antigen during immune response. TCRs stay the same.
Do antibodies from a primary response or a memory response typically have higher affinity?
Memory response (1000x higher)
What are CD86 and CD80?
Costimulatory molecules on mTECs that induce apoptosis when both the TCR and the CD28 of an immature T Cell bind to the self-peptide MHC on the mTEC.
What is the function of the intracellular part of the alpha and beta chains?
It functions as intracellular signaling
What subset of B-2 cells is independent of T Cell help?
Marginal Zone B2 Cells
What is allelic exclusion in B Cells and T Cells?
The process by which both parent’s alleles (for IgLambda IgKappa and IgHeavy in B Cells) are expressed in a given cell at first, but then whichever protein finishes first is the one presented for that cell, and the other allele is turned off.
Which subset of B Cells are capable of isotype switching and affinity maturation?
Follicular B2 Cells
What are P Nucleotides, and what is their function?
During an intermediate phase of VDJ recombination, sometimes overhangs in DNA are formed, and there are unpaired nucleobases. The complimentary nucleobases that are added in add to the diversity of the immunoglobulin or TCR, and are called P Nucleotides, as they are palindromic.
Where are the six CDRs in a TCR?
3 in Valpha
3 in Vbeta
Between which two regions is the hinge located on an antibody?
Between the CH1 and CH2 regions
Where does T Cell positive selection occur, and by what cell type?
Occurs in the cortex
Cortical Thymic Epithelial Cells (cTECs)
What is the name of the self antigens presented during T Cell education?
Tissue-Restricted Antigens (TRAs)
Why do we have such a sudden antibody mediated response to transfusions of mismatched blood types?
Because B-1 cells come preset with IgM antibodies to common microbial epitopes that cross react to non self blood types.
What determines the class of antibody?
The types of heavy chains involved.
On which chromosome do we find Ig kappa?
Chromosome 2
Which chain of the TCR is first to rearrange?
Beta chain first
What is the structure of an antibody, along with its different regions?
How do Rag1 and Rag2 initiate V(D)J recombination?
They introduce double strand breaks in the DNA coding for the antibody or TCR, and those breaks are resolved exclusively by non-homologous end joining so as to increase variability.
