Hypersensitivity - Types 2 (Cytotoxic) & 3 (Immune Complexes)

Question 1

ADCC

Answer 1

Ab-dependent cellular cytotoxicity: the Fc region of IgG bound to surface antigens on cells (e.g. infected cells) binds to FcγRIII on NK —> NK releases cytotoxic granules

Question 2

C3a, C5a

Answer 2

Complement components known as “anaphylotoxins” which bind to C’ receptors on both mast cells and endothelial cells resulting in blood vessels leakage and edema. C5a is also chemotactic for neutrophils.

Question 3

immune complex

Answer 3

complex of antigen + Ab + C”

when small, they lodge into tight places and cause local inflammatory response and mediator release initiated by immune-complex deposition —> fever, urticaria (hives), lymphadenitis, arthritis, glomerulonephritis, carditis, and neuritis

when large enough (by 8th day in Serum sickness) they are removed by macrophages (also RBCs?)

Question 4

HDN (erythroblastosis fetalis)

Answer 4

Hemolytic dz of newborn —

RH(-) mom

1st preg w/ RH(+) fetus: some fetal blood get in mom’s bloodstream = sensitization

Subsequent preg w/ RH(+) fetus —> maternal anti-RH IgG cross placenta —> hemolysis in fetus —> fetal demise

paradox: Decreased likelihood when ABO mismatched, too

Question 5

CLICKER QUESTION: Which type(s) of antibody is(are) able to activate complement with Ab only?

Answer 5

IgM b/c it is pentameric and you need 2 Fc regions close to each other in order to connect with C1Q molecule.

Question 6

Why is it unlikely that maternal immune system will attack ABO mismatch fetus?

Answer 6

B/c anti-A and anti-B Abs are IgM (T-independent) and IgM is so big that it cannot cross the placenta.