Hypersensitivity: the four types compared !

Topic

An immune response that harms the body. There are four types, named by what does the damage: IgE, antibodies on cells, immune complexes or T cells.

Updated 2026-11-01

What it is

Hypersensitivity is the normal adaptive immune machinery aimed at the wrong target or switched on too hard. The Gell and Coombs scheme sorts it into four types by the effector that causes the injury. Types I to III are driven by antibodies and start within minutes to days; type IV is driven by T cells and takes two to three days or longer. One disease can mix types, and drugs can trigger any of the four.

Key facts

Low complement points to type III (and to some type II diseases); type I and IV reactions usually do not consume it.
A positive direct Coombs test means antibody or complement on red cells: a type II signature.
Graves disease and myasthenia gravis are type II without cell death: the antibody switches a receptor on or blocks it.

The four hypersensitivity types side by side

Type	Effector	Timing	How it injures	Classic examples
I · Immediate	IgE bound to mast cells and basophils	Minutes (late phase hours later)	Allergen cross-links IgE, cells degranulate: histamine, tryptase, leukotrienes	Anaphylaxis, allergic asthma, allergic rhinitis, urticaria, food allergy
II · Cytotoxic	IgG or IgM against a cell-surface or matrix antigen	Hours to days	Complement lysis, opsonization, ADCC, or receptor stimulation or blockade	Acute hemolytic transfusion reaction, hemolytic disease of the newborn, Graves, myasthenia gravis, anti-GBM disease, rheumatic fever
III · Immune complex	Circulating antigen–antibody complexes	Hours (Arthus) to 1–2 weeks (serum sickness)	Complexes lodge in small vessels, activate complement and draw in neutrophils	Serum sickness, Arthus reaction, lupus nephritis, post-streptococcal glomerulonephritis
IV · Delayed	CD4 Th1 cells and macrophages, or CD8 cytotoxic T cells	48–72 hours or longer	Cytokines activate macrophages (granulomas) or T cells kill target cells	Tuberculin skin test, contact dermatitis, tuberculosis granuloma, Stevens–Johnson syndrome

Test yourself

Think of the answer, then tap the question to see it.

Which hypersensitivity type is the only one not mediated by antibody?

Type IV (delayed). T cells and macrophages do the damage, so it appears after 48–72 hours and cannot be passed on with serum.

A patient develops fever, rash, joint pain and low C3 about 10 days after receiving an animal-derived antivenom. Which type is this?

Type III: serum sickness. Antibodies to the foreign protein form complexes that deposit in vessels and consume complement.

Why is Graves disease classified as type II if the thyroid cells are not destroyed?

Because an IgG antibody binds a fixed cell antigen, the TSH receptor, and stimulates it. Type II includes receptor-stimulating and receptor-blocking antibodies.

Which type explains a wheal and itching within minutes of a bee sting?

Type I: venom cross-links IgE on sensitized mast cells, which release histamine and other mediators at once.

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← All of immunology

Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.

Sources: Type II Hypersensitivity Reaction (StatPearls Publishing (NCBI Bookshelf), 2025); Type III Hypersensitivity Reaction (StatPearls Publishing (NCBI Bookshelf), 2025); Type IV Hypersensitivity Reaction (StatPearls Publishing (NCBI Bookshelf), 2025); Atopy (StatPearls Publishing (NCBI Bookshelf), 2024).

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