lecture 3 immunology (week 1)

Question 1

describe t cells

Answer 1

central players in cell mediated immunity

recognise antigens presented by mhc molecules on the surface of infected or abnormal cells

cd8 kill infected or cancerous cells

cd4 coordinate immune response by activating other immune cells through cytokine release

Question 2

describe b cells

Answer 2

key components of humoral immunity

produce antibodies that bind to antigens on pathogens or toxins, neutralizing them or marking them for destruction by other immune cells

upon activation, b cells differentiate (help from cd4) into plasma cells (antibody factories) and memory cells

Question 3

how do tcrs and antibodies differ and what similarities do they share?

Answer 3

similarities -

tcr resembles a memrane bound fab fragment

fab fragment of an antibody molecule is a disulphide linked heterodimer, each chain of which contains one antibody c domain and one v domain: tcr (alpha/beta) antibody (heavy/light)

both are formed through v, d, j, and c regions

differences -

tcrs are membrane bound - no soluble form

antibodies hace effector functions via their fc regions, tcrs are only for antigen recognition

Question 4

what is the structure of the tcr molecule?

Answer 4

tcr composed of two trasmembrane glycoprotein chains (alpha/beta)

extracellular portion of each chain consists of 2 domains, resembling antibody V and C domains

both chains have carbohydrate side chains attached to each domain

a short stalk segment, analogous to an antibody hinge region, connects the Ig-like domains to the membrane and contains the cysteine residue that forms the interchain disulphide bond

Question 5

how does tcr recognise antigens?

Answer 5

recognise protein antigens

recognises peptide epitope derived from a partially degraded protein, but only if the peptide is bound to mhc

no secreted form of the t cell receptor, functions to signal that the t cell has bound its antigen

Question 6

how is tcr diversity generated?

Answer 6

alpha and beta chains are composed of discrete segments joined by somatic recombination in thymus

functional alpha and beta chain genes are generated with the aid of RAG-1/2

alpha chain; Va gene segment rearranges to a Jα gene segment to create a functional V-region exon, that is transcribed and spliced to join to Cα

beta chain: the variable domain is encoded in three gene segments, Vβ, Dβ, and Jβ. Rearrangement generates a functional VDJβ V-region exon that is transcribed and spliced to join to Cβ

for both, the resulting mRNA is translated and the α and β chains pair soon after their synthesis to yield the α:β TCR heterodimer