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Flashcards in T Lymphocytes Deck (15):

Describe the structure of a TCR

Alpha and beta chain but some have beta and gamma
Fab and Fc regions
Part of the immunoglobulin family
Chains are not very long but are natively charged so interact with +ve charges in T


When antigen binds to TCR?

CD3 has long cytoplasmic tail
Phosphorylation of tyrosine when antigen binds
Triggers chemical cascade


How are the alpha and beta chains rearranged?

Beta is rearranged first VDJ
Alpha arranged next VJ


TCR checkpoint

If the TCR doesn’t recognise MHC= useless
If it binds to MHC even when there is no antigen = dangerous


Maturing T in the thymus

In the cortex, T cells express CD4, CD8 and preTCR
The preTCR then becomes TCR
Either CD4 or CD8 is expressed


T cell classes

Cytotoxic T = CD8 binds to MHC class I = kill
Helper T1 = CD4 binds to MHC class II = inflammatory response
Helper T2= CD4 binds to MHC class II = activate B


Structure of MHC class I

Alpha chain is heavy and variable
Beta microglobulin is light and the same in everyone
Part of the immunoglobulin family
Alpha 1,2,3 beta


Structure of MHC class II

Same as class I
BUT 2 polypeptides equal in size and both transmembranal
Alpha 1, beta 1, beta 2, alpha 2


MHC class I and II present which kinds of peptide?

Class I = 8-10 amino acids long
Class II = 13+ sticks out


How does a peptide bind to MHC

Parts of the peptide that are the same bind to binding pockets


What is HLA?

Humans leukocyte antigen = human MHC
Three types of class I =A,B,C
Three types of class II =DP, DQ, DR


Why do we have different responses to the same disease?

We have variation in the alleles that code for MHC


Endogenous and exogenous antigens?

Endogenous are inside a cell e.g. virus , presented by MHC class I for cytotoxic t
Exogenous= outside the cell e.g. phagocytosis, presented by class II to helper T



Viral proteins in cytoplasm
Processed by proteasome
Peptide moves into ER by TAP (transport associated with antigen processing)
MHC synthesised in ER and binds to chaperone protein
Go to Golgi and presented in surface



Protein taken into cell
Processed in endocytic vesicles
Class II enters ER
Binds to invariant chain so MHC doesn’t bind to a peptide
Invariant cain digested
= MHC and CLIP (class II associated invariant chain peptide)
Swap CLIP for antigen
Move to surface