Antigen activation by T cells

Question 1

What do T cells recognize?

Answer 1

Host cells presenting antigens that look different from normal cells

Question 2

What is the role of T cells in the immune system?

Answer 2

To recognize antigens presented on the surface of cells and activate immune responses or kill the infected cells

Question 3

What are the two main types of T cells?

Answer 3

CD4 plus T cells helper T cells and CD8 plus T cells cytotoxic T lymphocytes

Question 4

How do CD4 plus and CD8 plus T cells differ in recognition?

Answer 4

CD4 plus T cells recognize MHC Class II molecules while CD8 plus T cells recognize MHC Class I molecules

Question 5

What is a T cell receptor TCR?

Answer 5

A glycoprotein on T cells that recognizes antigens presented by MHC molecules

Question 6

What are the structural features of a TCR?

Answer 6

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

Question 7

What is the role of MHC molecules?

Answer 7

To present antigenic peptides to T cells for recognition

Question 8

What are the two classes of MHC molecules?

Answer 8

MHC Class I recognized by CD8 plus T cells and MHC Class II recognized by CD4 plus T cells

Question 9

What is the difference between antigens recognized by TCRs and antibodies?

Answer 9

TCRs recognize processed antigenic peptides presented by MHC while antibodies recognize whole folded proteins

Question 10

What is the function of co-receptors CD4 and CD8?

Answer 10

They stabilize the interaction between TCRs and MHC molecules and play a role in T cell activation

Question 11

What is ITAM and what is its role in TCR signaling?

Answer 11

ITAM Immune-receptor-Tyrosine-based Activation Motif is a motif in CD3 and zeta chains that initiates signaling when phosphorylated

Question 12

What enzyme phosphorylates ITAMs?

Answer 12

Src-family kinase Lck which activates ZAP-70 and downstream signaling pathways

Question 13

How is diversity in TCRs generated?

Answer 13

Through gene rearrangement of the TCR alpha and beta chain loci similar to immunoglobulin recombination

Question 14

What enzymes are involved in TCR gene rearrangement?

Answer 14

Recombinase-activating genes RAG1 and RAG2 and other DNA repair enzymes

Question 15

What is the role of recombination signal sequences RSS in TCR diversity?

Answer 15

They flank the TCR gene segments and guide RAG enzymes during gene rearrangement

Question 16

How does the TCR compare to an antibody Fab fragment?

Answer 16

Both have variable and constant regions but TCRs are not secreted and are membrane-bound

Question 17

Where are gamma delta TCRs found and what is their role?

Answer 17

In epithelial-rich tissues with roles in mucosal immunity and recognizing unconventional antigens

Question 18

What happens after TCR recognizes MHC-antigen complexes?

Answer 18

ITAMs are phosphorylated ZAP-70 is activated and signaling pathways initiate T cell activation

Question 19

Why is TCR diversity important?

Answer 19

It enables T cells to recognize a vast range of antigens from different pathogens

Question 20

How does MHC Class I differ from MHC Class II?

Answer 20

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

Question 21

What is the role of CD3 and zeta chains in TCR function?

Answer 21

They transmit activation signals upon antigen recognition by the TCR

Question 22

What are the main sources of TCR diversity?

Answer 22

Gene rearrangement junctional diversity and combinatorial pairing of alpha and beta chains

Question 23

Can TCRs undergo somatic hypermutation or affinity maturation?

Answer 23

No TCR specificity and affinity are fixed once the receptor is expressed

Question 24

What are the functions of CD4 plus T cells?

Answer 24

To help other immune cells by producing cytokines enhancing B cell antibody production and supporting macrophage activation

Question 25

What are the functions of CD8 plus T cells?

Answer 25

To kill infected or abnormal cells by recognizing antigens presented on MHC Class I molecules