Antigen activation by T cells Flashcards
What do T cells recognize?
Host cells presenting antigens that look different from normal cells
What is the role of T cells in the immune system?
To recognize antigens presented on the surface of cells and activate immune responses or kill the infected cells
What are the two main types of T cells?
CD4 plus T cells helper T cells and CD8 plus T cells cytotoxic T lymphocytes
How do CD4 plus and CD8 plus T cells differ in recognition?
CD4 plus T cells recognize MHC Class II molecules while CD8 plus T cells recognize MHC Class I molecules
What is a T cell receptor TCR?
A glycoprotein on T cells that recognizes antigens presented by MHC molecules
What are the structural features of a TCR?
It has variable V and constant C regions consists of alpha and beta chains linked by a disulfide bond and is anchored in the cell membrane
What is the role of MHC molecules?
To present antigenic peptides to T cells for recognition
What are the two classes of MHC molecules?
MHC Class I recognized by CD8 plus T cells and MHC Class II recognized by CD4 plus T cells
What is the difference between antigens recognized by TCRs and antibodies?
TCRs recognize processed antigenic peptides presented by MHC while antibodies recognize whole folded proteins
What is the function of co-receptors CD4 and CD8?
They stabilize the interaction between TCRs and MHC molecules and play a role in T cell activation
What is ITAM and what is its role in TCR signaling?
ITAM Immune-receptor-Tyrosine-based Activation Motif is a motif in CD3 and zeta chains that initiates signaling when phosphorylated
What enzyme phosphorylates ITAMs?
Src-family kinase Lck which activates ZAP-70 and downstream signaling pathways
How is diversity in TCRs generated?
Through gene rearrangement of the TCR alpha and beta chain loci similar to immunoglobulin recombination
What enzymes are involved in TCR gene rearrangement?
Recombinase-activating genes RAG1 and RAG2 and other DNA repair enzymes
What is the role of recombination signal sequences RSS in TCR diversity?
They flank the TCR gene segments and guide RAG enzymes during gene rearrangement
How does the TCR compare to an antibody Fab fragment?
Both have variable and constant regions but TCRs are not secreted and are membrane-bound
Where are gamma delta TCRs found and what is their role?
In epithelial-rich tissues with roles in mucosal immunity and recognizing unconventional antigens
What happens after TCR recognizes MHC-antigen complexes?
ITAMs are phosphorylated ZAP-70 is activated and signaling pathways initiate T cell activation
Why is TCR diversity important?
It enables T cells to recognize a vast range of antigens from different pathogens
How does MHC Class I differ from MHC Class II?
MHC Class I is present on all nucleated cells and presents endogenous peptides while MHC Class II is on antigen-presenting cells and presents exogenous peptides
What is the role of CD3 and zeta chains in TCR function?
They transmit activation signals upon antigen recognition by the TCR
What are the main sources of TCR diversity?
Gene rearrangement junctional diversity and combinatorial pairing of alpha and beta chains
Can TCRs undergo somatic hypermutation or affinity maturation?
No TCR specificity and affinity are fixed once the receptor is expressed
What are the functions of CD4 plus T cells?
To help other immune cells by producing cytokines enhancing B cell antibody production and supporting macrophage activation
What are the functions of CD8 plus T cells?
To kill infected or abnormal cells by recognizing antigens presented on MHC Class I molecules
