Table 2.

Revised Gell and Coombs classification of hypersensitivity reactions. Adapted from Pichler.³,⁴

Type of reaction	Immune reactant	Antigen	Effector	Clinical symptoms
Type I-immediate	IgE	Soluble antigen	Mast cells, basophils	Pruritus Angioedema, Urticaria, Bronchospasm
Type II- cytotoxic	IgG	Cell or matrix associated antigen	FcR positive cells (phagocytes, NK cells)	Thrombocytopaenia, Haemolytic anaemia
Type III- immune complex	IgG	Soluble antigen	FcR positive cells complement	Serum sickness
Type IV- delayed	T-cell mediated
	IVa	Antigen presented by cells, or direct T-cell stimulation	(IVa)Macrophage	Contact dermatitis
	IVb		(IVb) Eosinophils	DRESS/DIHS/HSS
	IVc		(IVc) T-cells	SJS/TEN, DILI
	IVd		(IVd) Neutrophils	AGEP

Ig: immunoglobulin, FcR: Fc receptor, NK cells: natural killer cells, SJS: Stevens-Johnson syndrome, TEN: toxic epidermal necrolysis, DRESS: drug reaction with eosinophilia and systemic symptoms, DIHS: drug-induced hypersensitivity syndrome, HSS: Hypersensitivity syndrome, AGEP: acute generalised exanthematous pustulosis, DILI: Drug induced liver injury.