Thrush - T lymphocytes Flashcards
Gamma delta T cells are not traditional T cells and are found in low amounts in our body. They can recognize ____protein Ag. They dont use classical MHC, they use ____ molecules which are associated with ____ microglobulin. Lipids from M. _____ and M. _____ are found to be presented with CD1. _____ cells may also recognize Ag with CD1
non; such as lipids and sugars.
CD1; MHC like molecule ; beta II.
TUberculosis; Leprae
natural killer
NK cells express class ____MHC proteins
I
T cell receptors (TCR) are only ____bound. TCRs recognize Ag only in association with the _____. TCRs are restricted to _____MHC
cell; they are not secreted ever; MHC; self –>we dont want our immune ssytem to recognize our own cells.
How does MHC molecules work with target cell
MHC molecules that T cell expreses will rec Ag on target cell thats expressing same MHC molecules. If you have a match, you get a killing
When do you have no killing?
TCR recognizes a specific Ag, but when you put a diff Ag you dont get a killing (diff epitope)
When do you have self restriction?
It recognizes proper Ag, but with wrong MHC. The T cell in recognizing its Ag, needs to do so when target cell is expressing same MHC molecules
Describe T cell receptor structure
Heterodimer:
- alpha beta or delta gamma chains (similar to Fab)
- disulfide bond and membrane anchor holds together
- hinge region next to membrane
- variable and constant region
- three CDRS (hypervariable regions) - CDR3 most impt in contacting Ag
TCR has _____rearrangement similar to Ig gene rearrangment. _____ complex serves as a signaling function. TCRs are members of the ____ gene superfamily.
gene; CD3; Ig
What is the difference between TCR and Ab
TCR constant region doesnt have extra effector functions. If Ab binds Ag, Ab can activate complement, opsination, cross placenta, or mucous membranes due to heavy chain. TCR dont do this. They produce cytokines which are the effector function of the T cell.
What is the key distinction between alpha beta and gamma delta T cells
alpha beta recognize: classical MHC. Peptide Ag. Large TCR gene diversity. Majority represent the CD4 helper T cells. Need Ag peptide and MHC
gamma delta: non classical MHC. Sometimes non peptide Ag. Small TCR diversity. No MHC restriction. Use phospholipid Ag (from bacteria and parasites)
CD3 is the signaling molecule for ____.
TCR
Diversity in T cells and B cells is bc we have multiple diff gene segments that together one is selected to express to produce TCR polypeptide to be able to interact with _____.. ____locus is within the alpha locus. Beta and ____ loci are separated
Ag; delta; gamma
During gene rearrangement, a T cell will be either alpha beta, or gamma ___. Cant have both bc in order to exp alpha chain genes, the intervening DNA is cut out and thrown away.
delta
the diversity of ____ cells is higher than B cells.
T
Where does TCR gene rearrangement occur? TCRs use ____ sequences as well as the 12/23 bp seq like B cells. They also use ____ and RAG2 genes/enzymes that recognize signal sequences. Without RAG enzymes you can’t rearrange Ab genes or TCR genes. These ind’s have SCID, that affect B cells and T cells. No immune response and solely rely on innate defenses. They have a ____process. 3 diff genes rerranging at the same time: ____, ____ and delta chain. It depends on who reaches the cell surface first. If gamme delta have complete reararngement first, then it will be gamma delta T cell.
thymus; RSS; RAG 1.
beta; gamma
Why are most of our T cells alpha beta? What happens when beta is first?
beta has only 1 set of genes to rearrange. Gamma delta have to rearrange both of their alleles. If beta is first, it deletes the delta locus, and the T cell will be alpha beta T cell.
What type of allelic exclusion to T cells express?
functional allelic exclusion; sometimes one alpha associates with beta better/stronger, this is the one that will be usually functional
why is the diversity of TCR higher than B cells?
- Combinatorial joining; higher number of J regions = more diversity
- alternative joining of D segments: can have VDDJ rearrrangment unlike B cells.
- junctional flexibility: random addition of bases during joining of cut DNA during rearrangment (imprecise cutting and joining of seq together)
- P nucleotides: palindromic bases added.
- N nucleotides: Tdt expressed throughout entire gene rearrangement process (unlike B cells who only did this on heavy chain).
Unlike B cells, T cells dont have _____ hypermutation
somatic; we dont need to increase affinity for Ag. Bc TCR is on T cell we have other molecules to hold T cell and TCR on antigen to keep in close proximity, unlike Ab.
If randomly mutating, we might have a self reactive TCR. We cannot have loose binding to self MHC
There are fewer ____ region genes in TCR’s bc we have limited amt of MHC in our bodies. ____ and ____ interact with MHC. Higher number of ___ regions because these are the areas that have higher contact with Ag peptides (CDR3)
V; CDR1; CDR2; J
