B

Question 1

Key phases of infection

Answer 1

1. establishment of infection
2. induction phase - adaptive threshold
3. effector phase
4. Memory - threshold lowered when reencountered

Question 2

Why does adaptive immune response take time

Answer 2

requires cell to move, interact & produce cytokines: effector.
APC takes up antigen, travels from site of infection to lymph node: activates T cells -> activate B cells. Both return to site of infection via circulation

Question 3

where does T/B precursor rearrange receptor genes

Answer 3

Thymus: -ve & ive selection of naive cell

Question 4

Immature T cells can be

Answer 4

receive survival signals - if recognise MHC

clonal deletion: interact strongly w/self

Question 5

where do mature T/B cells encounter antigen

Answer 5

peripheral lymphoid: are activated

Question 6

MHC-I recognises which kind of cells

Answer 6

CD8+ intracellular antigens e.g. virus (endogenous)

- all of self except RBC can present to CD8+

Question 7

MHC-II recognises which kind of cell

Answer 7

CD4+ extracellular: extracellular bacteria, soluble antigens, virus particles. e.g. dendritic cells/ pinocytosis

Question 8

How does MHC polymorphism affect antigen recognition by T cells through

Answer 8

influencing peptide binding & contacts between T cell + MHC

Question 9

Th1 induces & is induced by

Answer 9

Macrophage activation & delayed type hypersensitivity

induced by: IL-12, IFNy, IL-18

Question 10

Th2 induces & is induced by

Answer 10

antibody production & allergic response.

induced by: IL-4, IL-5

Question 11

what signals do APC deliver to naive T cells

Answer 11

1. activation 2. survival 3. Differentiation

Question 12

B cell activation

Answer 12

Antigen recognised by BCR -> antigen internalised via receptor mediated endocytosis -> peptides presented to MHC
if CD4 also recognises antigen will provide help via CD4 & cytokines

Question 13

what provides flexibility to antibody

Answer 13

Hinge region of Ig when binding to multiple antigens

Question 14

what happens when IgE recognises antigen

Answer 14

variable region of IgE binds antigen & constant region binds FCeR1 - crosslinks receptors = degranulation of mast cells

Question 15

3 main functions of antibodies protection

Answer 15

1. neutralisation: antibody binds & blocks toxin from
   cell receptor
2. opsonisation: antibodies bind to bacterium, label it foreign. Fc region antibody binds Fc phagocytic cell & is digested.
3. complement: recognises certain features of microbial surfaces allowing it to be lysed and ingested.

Question 16

Central tolerance involves

Answer 16

occurs at young age
+ve selection: cells lacking affinity - dont receive survival signals
-ve: removes T cells which bind too strongly, ensure autoreactive deleted by apoptosis: clonal deletion
Fates: 1. death by neglect 2. +ve selection 3. clonal deletion

Question 17

describe Peripheral tolerance

Answer 17

occurs throughout lifetime in periphery
ensure self-reactive T&B cells which escaped central tolerance don’t cause autoimmune disease
e.g. antigens not present in thymic selection: sex hormones & food antigens, autoantigen, good bacteria

Question 18

which mechanisms of peripheral tolerance exist to ensure mature T cells don’t activate inappropriately

Answer 18

1. co stimulation signal & specific signals: activates T cell
2. specific signal alone (MHC bound) - T cell becomes anergic
3. co stim signal alone - no effect on T cell (no antigen)
   B. CTLA-4 binds to B7 more than CD8: inhibits T activity
   C. Treg: IL-10 & TGFb: inhibit self reactive T cells

Question 19

What happens if T cells escapes clonal deletion

Answer 19

can become activated

• to non harmful antigens: allergy
• to self antigens: autoimmunity

Question 20

What happens when tolerance fails

Answer 20

immunodeficiency (immune evasion by pathogens)
1y - genetically acquired
2y - infections, metabolic dysregulation, therapeutically induced