Non-clinical sciences/Immunology · Hypersensitivity

Type III hypersensitivity

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What it means

Soluble antigen–antibody (immune) complexes deposit in tissues (skin, joints, kidney, vessels) → complement activation → neutrophil-driven inflammation. Examples: SLE, post-streptococcal glomerulonephritis, serum sickness, extrinsic allergic alveolitis (farmer's lung), polyarteritis nodosa.

Worked example

SLE flare: low C3/C4 (consumed), raised anti-dsDNA, immune-complex glomerulonephritis.

In the exam

Two weeks after a streptococcal throat infection a child develops haematuria, periorbital oedema and hypertension with low complement.

What settles it

Type III = circulating SOLUBLE complexes deposit; type II = antibody binds a FIXED tissue antigen directly.

Classically confused with

Type II hypersensitivity

Source: StatPearls