6 - T lymphocytes and antigen recognition

Question 1

The alpha and beta chains of the TCR have short cytoplasmic tails. How is the signal delivered to the T-lymphocyte occur?

Answer 1

• there are charged residues in the transmembrane region of the alpha and beta that interact with the oppositely charged residues in the transmembrane region of the CD3 polypeptides
• CD polypeptide have long cytoplasmic tails and are important in the delivery of the signal to the cells
• the tails have motifs called tyrosine motifs
• when the TCR meets the antigen, PHOSPHORYLATION OF TYROSINE IN THE MOTFS OCCURS
• this triggers several other chemical cascades

Question 2

What are the 2 major populations of T-cells?

Answer 2

CD4 (T-helper)

CD8 (cytotoxic)

Question 3

What do T-helper cells do?

Answer 3

• secrete cytokines
• recruit effector cells (activate macrophages)
• help and activate CTL and B cell responses

Question 4

What do CTLs do?

Answer 4

kill target cells

induce apoptosis in target cells

Question 5

What are CD4 and CD8 and how do they help in terms of antigen and TCR binding?

Answer 5

they are co-receptors
they bind to the side of the MHC molecule
(they do not bind to the antigen presented by the MHC, that is the role of the TCR)

Question 6

define the Major Histocompatibility Complex

Answer 6

a group of tightly linked genes that are important in specific immune responses

Question 7

What is interesting about the MHC gene in the human genome?

Answer 7

the most polymorphic gene in the human genome

Question 8

Which MHC classes are endogenous and exogenous?

Answer 8

Class I - endogenous (viral)

Class II - exogenous

Question 9

Which antigen are presented by which MHC molecules to which cells?

Answer 9

• short endogenous antigens are presented via MHC Class I to CD8 T-cells
• longer exogenous antigens are presented via MHC class II to CD4 T-cells