Lymphocyte Ontogeny And Lymphopoiesis Flashcards
What processes enable diversity in TCR and BCR?
What third process further diversifies Ig in B Cells? What cells aid this process?
Combinatorial diversity and junctional diversity in TCR and BCR
Somatic hypermutation in B cell IgG
What gene segments and enzyme complexes are crucial for VDJ rearrangement?
Recombination signal sequences (RSS)
Recombination-activating gene (RAG) enzyme complexes
RAG1 and RAG2 recognize and bind to RSS’s adjacent to different V,D, and J segments
Which receptors only use V and J rearrangement?
TCR alpha chain
BCR (Ig) light chain
(BCR heavy chain uses V, D, and J rearrangements)
What is the role of DNA protein kinase in combinatorial diversity?
DNA-PK reanneals the cut ends (by RAG enzymes) in complex with Artemis nuclear and DNA ligaments IV
(Foals lacking DNA-PK have SCID)
Which T cell subset display decreased antigenic diversity?
Gamma-delta (yd) T-cells, due to reduced diversity in V-segments
What is the role of terminal deoxynucleotidyl transferase (TdT) in junctional diversity?
TdT is a DNA polymerase that adds variable number of nucleotides to the V,D, and J exons during rearrangement. These additional nucleotides are called N regions
What happens if a TCR or Ig chain fails to form?
If on the first chromosome, then rearrangement moves to the second chromosome. If both fail, then apoptosis occurs
How does TdT expression change as B-cell’s mature?
TdT expression decreases during maturation, and does not increase light-chain diversity
Where does somatic hypermutation occur?
Somatic hypermutation occurs in proliferating B cells that have been activated by antigen-bearing Th cells. It is restricted to the BCR genes in the complementarity determining regions (CDR) that bind the antigen.
How does activation-induced deaminase (AID) mediate somatic hypermutation?
AID delaminates cytosine to uracil, resulting in a U:G mismatch.
These mismatches are removed by base-excision repair enzymes.
These removals are repaired by DNA polymerases that create mutations in one or a few nucleotides surrounding the mismatch.
Where does B-cell lymphopoeisis occur in different animal groups?
Mammals - fetal liver, transitions to bone marrow
Birds - bursa of fabricius
Fish - kidneys
Amphibians - spleen, bone marrow, kidney
What is the initial antibody isotype (the initial BCR) expressed by all developing mammalian B-cells?
IgM
What interleukin is important in initial proliferation of B-cell progenitors?
IL-7
Explain the sequence of VDJ rearrangement in developing B-cells
Heavy chain D-J segments recombine first, followed by V segments to the rearranged DJ segment
The recombined heavy chain is tested to see if it can bind to a surrogate light chain. (First checkpoint)
If not, the second chromosome is recombined
If so, then the BCR is checked for self-reactivity (second checkpoint)
What is the third checkpoint in BCR production?
After the light chain is recombined and if it can bind the heavy chain, the newly formed BCR is exposed to self-antigen (and those with affinity are deleted)
When do B-cell precursors start to express CD21?
As cytoplasmic IgM is exported to the surface membrane
B-cells initially express which Ig isotypes?
IgM (because C mu is the first constant region) and some IgD
Will exhibit class switching later after antigen and T-helper activation in the periphery
B-1 B cells express which cell surface marker? Where do they mostly reside?
CD5
Reside in pleural and peritoneal cavities
Which species do B-1 cells make up the majority of B-cells?
Ruminants and rabbits
Why is there less BCR diversity in B-1 B cells? What is their antigen specificity honed to?
They lack TdT expression and do not undergo somatic hypermutation, and they have fewer possible DJ and VDJ permutations
Their specificity is honed to bacterial polysaccharides and lipids
What is an inflammatory response advantage that B-1 B cells have over B-2 B cells?
They are capable of activation independent of Th-cells
Where do marginal zone B-cells reside? How are they similar to B-1 B cells?
They residency in the marginal zone of the spleen
They can respond to antigen in a T-helper independent manner
Initial T-cell precursors are produced from CLP then migrate to the ____ for maturation
Thymus
What signaling pathway driven by thymic stromal cells drives T-cell development and is essential for T-cell vs. B-cell fate decision?
Notch signaling
In most species, 90% of T-cells have what type of TCR?
Alpha-beta (vs. gamma-delta)
ab TCR are only capable of recognizing antigen when complexed with ______
MCH I or MHCII molecules
What are two characteristics of yd TCRs?
Capable of recognizing antigen not associated with MHC
Narrow range, capable of binding to lipid antigens, phosphorylated ligands, and heat shock proteins
What are the earliest T cell progenitors in the thymus?
Double negative (lack expression of CD4 or CD8)
After a functional beta TCR is produced, TCRa rearrangement occurs in what cells?
CD4+/CD8+ (double positive cells)
Double positive CD3 T-cells are selected through their interaction with ____
MHC
Cells that interact with MHCII cells will become CD4 T cells (Th1, Th2, Th17, poss Treg)
Cells that interact with MCH I will become CD8 T cells (Cytotoxic T-cells)
Which cells produce peripheral antigens to enable negative selection of T-cells? What gene is required?
Thymic medullary epithelial and dendritic cells
AIRE (an auto immune regulatory gene)
Natural killer cells are a subpopulation of what T-cells?
alpha-beta T-cells
NK cells may express what cell markers?
NK1.1
Variable CD4/CD8 expression
CD16, CD56
Produce granzyme
NK cells recognize antigen presented in what molecules?
CD1d
(Enhanced ability to recognize lipid and glycolipid antigen)
What receptors do NK cells lack? What do they express?
Lack TCR, BCR, and CD3
Express NK-receptors, which are not recombined but are constitutively expressed
What are two mechanisms that NK cells may recognize altered host cells?
Normal cell surface proteins with structural modifications (secondary to intracellular stress or viral infection)
Altered MHC 1 expression (normal MHC-1 expression may inhibit cell killing)
