Classify the hypersensitivity reactions, give an example for each reaction and describe the pathophysiological processes of each reaction.

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College Answer

A tabular format is a very desirable format for a response to this question. Again candidates
who struggled to provide an organised response also failed to provide sufficient and succinct
detail in their answer. A good answer would have included the following features.

Mechanisms of Immunological Injury
Mechanism Pathophysiology Disease types

Type I
Immediate
hypersensitivity
IgE mediated

· basophil & mast cell
degranulation
· histamine, SRSA, ECFA, NCF
· immediate weal & flare

· anaphylaxis
· atopy

Type II
cell cytotoxicity
IgG, IgM mediated

· direct phagocytosis or cell lysis
· activation of complement,
classical
· tissue deposition of complement

· blood transfusions
· Goodpasteur's
syndrome
· autoimmune
cytopaenias

Type III
Immune complex
IgG, IgM, IgA mediated

· tissue deposition of Ag-Ab
complexes
· accumulation of PMN's,
macrophages & complement

· SLE
· serum sickness
· necrotising vasculitis

Type IV
Delayed
hypersensitivity
T-cell mediated

· T-cell induced mononuclear cell
accumulation
· release of lymphokines &
monokines
· often with granuloma formation

· TB, sarcoid
· Wegener's
granulomatosis
· granulomatous
vasculitis