Hypersensitivity Reactions

Question 1

Type I

Answer 1

MAST CELLS

Pre-sensitized mast cells or basophils (must see it b/f) bind antigen –> crosslink IgE –> histamine release at post-cap venules

Delayed phase = from cytokines released from mast cells and basophils

Question 2

Type II

Answer 2

ANTIBODIES

Antibody binds to cell surface antigen …

1- destroys cells (opsonization, phagocytosed or killed w/ NK cells)

2- induces inflammation (complement activation)

3- cell dysfunction (block or amp downstream paths)

Question 3

Type III

Answer 3

IMMUNE COMPLEX (antigen - IgG)

This complex then binds complement –> neutrophils(C5a) –> lysosomal enzymes

Often seen in vasculitis

Question 4

Type IV

Answer 4

T CELLS

CD8+ kills cells OR delayed type (sensitized CD4+ cells release cytokines –> inflammation and macrophage activation)

Question 5

Serum Sickness v Arthus Reaction

Answer 5

Serum Sickness - most systemic; exposed to antigen or drug and develop immune complexes (takes 5 -10 days) then these complexes deposit in membranes and lead to complement - mediated tissue destruction (arthralgias, fever, itchy, proteinuria, lymphadenopathy)

Arthus - LOCAL; inject antigen then pre-made IgG binds and immune complexes in skin (edema and necrosis)