Immune effector responses

Question 1

Humoral and cell-mediated effector responses

Answer 1

Humoral responses are mediated by antibodies

Cell mediated responses rely on NK cells, macrophages, neutrophils, CTLs, Th cells

Question 2

Antibody-mediated effector functions

Answer 2

Neutralisation
Agglutination
Opsonisation
Complement activation
Antibody dependent cell mediated cytotoxicity
Degranulation

Question 3

Antibody isotypes

Answer 3

Differ in Fc region and hinge
Different effector functions depending on which Fc receptor they bind
IgM produced first during infection
IgG abundant in blood
IgA at mucosal sites
IgE against worm infections and allergies

Question 4

Fc receptors

Answer 4

Have extracellular immunoglobulin domains that recognise Fc domains of antibodies

FcgammaRI (expressed on macrophages, DCs and granulocytes) binds IgG
FceRI (expressed on eosinophils, mast cells and basophils) binds IgE

Question 5

Opsonisation

Answer 5

IgG/A bind to FcR on macrophages, inducing phagocytosis

Question 6

Complement fixation

Answer 6

IgG/M recognised by C1 complement complex, leading to activation of the classical complement pathway.

Induces opsonisation and membrane attack complex

Question 7

ADCC

Answer 7

Antibody dependent cell mediated cytotoxicity

IgG on the surface of infected cells binds FcyRIIIa on NK cells, inducing degranulation (perforins and granzymes)

Question 8

Granulocyte activation

Answer 8

IgE bound to parasites/allergens causes degranulation of mast cells, eosinophils and basophils.

Induces histamine and other inflammatory mediator release

Question 9

Cytotoxic effector cells

Answer 9

Natural Killer cells (innate)
CD8+ cytotoxic T Lymphocytes (adaptive)
Natural killer T cells (innate and adaptive)

Induce cell death by apoptosis

Question 10

Sequential activation of CTLs

Answer 10

APC licensed via interaction with pathogen (PRR) or with activated Th1 cell (MHCII)

licensed APC interacts (MHCI) with naive CD8+ T cell leading to activation and differentiation into CTL

Question 11

Simultaneous activation of CTLs

Answer 11

APC simultaneously interacts with active Th1 cell and CD8+ T cell.
APC licensing and CTL activation occur at the same time
IL-2 from Th1 promotes CTL differentiation

Question 12

Action of CTLs

Answer 12

CTL forms immunological synapse with target cell
Granules trafficked along microtubules
Granules fuse with presynaptic membrane and released
Perforins assemble into a pore on the membranes and granzymes enter, cleaving proteins and causing apoptosis

Question 13

Non-functional perforins

Answer 13

Associated with protracted viral infections.

Polymorphism in PRF gene encodes perforin dysfunction

Question 14

NKT cells

Answer 14

Natural Killer T cells
Develop in thymus and undergo TCR gene rearrangement but have invariant alphabeta TCR
Can be CD4+ or CD4- and can act as both Th and CTLs