Type II hypersensitivity
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What it means
Antibody (IgG/IgM) against a fixed cell-surface or matrix antigen → complement activation + opsonisation/ADCC, or receptor stimulation/blockade. Examples: autoimmune haemolytic anaemia, ITP, Goodpasture (anti-GBM), pemphigus vulgaris (anti-desmoglein), Graves (anti-TSHR, stimulatory), myasthenia gravis (anti-AChR, blocking), haemolytic disease of the newborn, ABO transfusion reactions.
Worked example
Direct antiglobulin (Coombs) test detects antibody/complement on the patient's own red cells → autoimmune haemolysis (a type II reaction).
In the exam
A patient develops anaemia; the direct Coombs test is positive, showing antibody bound directly to the surface of their own red cells.
What settles it
Type II antibody targets a CELL-BOUND antigen; type III involves SOLUBLE antigen–antibody complexes that deposit in tissues.
Classically confused with
Type III hypersensitivity
Source: StatPearls