Immunology lecture 2

Question 1

Recognition of foreign Ag (T cells)

Answer 1

• Important in adaptive immune response
• T cell = leukocyte
• Activated T cells by recognition of specific ligand through TCR

Question 2

TCR

Answer 2

• Composed of 2 chains, a and B, 40-50kD

- Peptide binding to MHC recognised by TCR

Question 3

TCR diversity

Answer 3

• Problem with diversity (diverse ligands, MHC polymorphic, peptide to MHC binding is degenerate)
• Solution (TCRs differ in membrane distal portion, 10^9 versions of TCR)
• Generating diversity (a+b composed of various regions encoded by separate genes, a = v,j,c b = v,j,c,d, randomly combine v,j,c,d, excise intervening DNA, a pairs w/ b → 10^9-10^16 different TCRs

Question 4

T cell types

Answer 4

• CTL = made in thymus, express TCR + CD8, recognise MHCI, needed for defence against IC pathogens
• Th1 = responds to IC pathogens, has CD4+, secretes IL-2 that activates macropgage
• Th2 CD4+, humeral immunity, EC organisms, produces activation signals like IL-10 to proceed Ab

Question 5

CTL response

Answer 5

1. Secretion of cytokines (TNFa + IFNy)
2. Production + release of cytotoxic granules
   - Perforin + granzymes
3. Destruction of infected cells w/ Fas/FasL (activated CD8+ express FasL, binds Fas → Fas trimerises → caspase cascade, CD8+ express Fas + FasL so can kill each other in contraction phase)

Question 6

Immunoglobulin

Answer 6

• Bridges adaptive + immune system
• V(D)J recombination, need to recognise ↑ Ag
• Heavy chain of Ig = v,d,j,c light chain = v,j,c
• Somatic hypermutation, clonal expansion, changes affinity

Question 7

Immunoglobulin repsonse

Answer 7

1. Neutralisation
2. Opsonisation (coat pathogen w/ complement factors, assists phagocyte binding, or fab portion of igG Ab binds to Ag, Fc of Ab binds FCR which traps organism at surface + stimulates phagocytosis)
3. Complement fixation (innate defence, classical = triggered by activation of C1 by C1q binding to Ch3 of IgM or Ch2 of IgG, C1q binds at least 2 Ig Fc)