Type I hypersensitivity vs Non-IgE hypersensitivity patterns
How to tell Type I hypersensitivity and Non-IgE hypersensitivity patterns apart when a board question makes them look alike.
Type I is immediate IgE mast-cell allergy; non-IgE patterns are type II fixed-antigen antibody, type III immune complexes, or type IV delayed T cells.
Side by side
Type I hypersensitivity is immediate IgE-mediated mast-cell degranulation with urticaria, anaphylaxis, allergic rhinitis, asthma, and eosinophil late phase.
Type II is antibody against cell or matrix; type III is immune-complex deposition; type IV is delayed T-cell-mediated inflammation.
Allergen cross-links IgE bound to Fc epsilon RI on mast cells, releasing histamine, leukotrienes, and cytokines.
IgG/IgM can target cells, immune complexes can deposit in tissues, or sensitized T cells can activate macrophages/cytotoxic injury.
Minutes after exposure, wheals, bronchospasm, anaphylaxis, high IgE, and eosinophils support type I.
Coombs hemolysis supports type II; serum sickness/Arthus supports type III; contact dermatitis or TB test supports type IV.
The trap
Allergic-looking rash is not always type I; timing, antibody target, immune complexes, and T-cell delay decide.
The repair move
For hypersensitivity, name the immune effector first: IgE mast cell, fixed-antigen antibody, immune complex, or T cell.
Try a free question
CoreA 24-year-old man with a known peanut allergy ingests a peanut-containing cookie. Within 10 minutes, he develops urticaria, lip swelling, wheezing, hypotension, and a sense of impending doom. Tryptase levels are elevated. Which hypersensitivity reaction is this?
Show answer and explanation
Answer: A. Type I. Type I hypersensitivity is immediate IgE-mediated mast cell degranulation: preformed IgE bound to mast cell Fc-epsilon-RI is cross-linked by allergen, triggering release of histamine, tryptase, leukotrienes, prostaglandins, and cytokines. Anaphylaxis with hypotension and bronchospasm is the severe form. Treat with intramuscular epinephrine.
Why the other choices are tempting
- B. Type II involves antibody (IgG/IgM) against fixed cell-surface or matrix antigens (autoimmune hemolytic anemia, Goodpasture), not immediate mast cell degranulation.
- C. Type III involves immune complex deposition (serum sickness, Arthus reaction, lupus nephritis), not immediate IgE.
- D. Type IV is delayed T-cell-mediated (contact dermatitis, TB skin test, transplant rejection cellular), not immediate IgE.
- E. Type V (anti-receptor) is now usually classified as a subtype of type II (e.g., Graves disease TSH receptor stimulation).
Flashcards
Tap a card to flip it.
What clue supports Type I hypersensitivity?
Choose Type I hypersensitivity when the stem gives this pattern: Type I hypersensitivity is immediate IgE-mediated mast-cell degranulation with urticaria, anaphylaxis, allergic rhinitis, asthma, and eosinophil late phase.
What clue supports Type II, III, and IV hypersensitivity?
Choose Type II, III, and IV hypersensitivity when the stem gives this contrasting pattern: Type II is antibody against cell or matrix; type III is immune-complex deposition; type IV is delayed T-cell-mediated inflammation.
Quick answers
What is the fastest way to tell Type I hypersensitivity from Non-IgE hypersensitivity patterns?
Type I is immediate IgE mast-cell allergy; non-IgE patterns are type II fixed-antigen antibody, type III immune complexes, or type IV delayed T cells.
What is the key clue for Type I hypersensitivity?
Type I hypersensitivity is immediate IgE-mediated mast-cell degranulation with urticaria, anaphylaxis, allergic rhinitis, asthma, and eosinophil late phase.
What is the key clue for Non-IgE hypersensitivity patterns?
Type II is antibody against cell or matrix; type III is immune-complex deposition; type IV is delayed T-cell-mediated inflammation.
What is the common trap with Type I hypersensitivity vs Non-IgE hypersensitivity patterns?
Allergic-looking rash is not always type I; timing, antibody target, immune complexes, and T-cell delay decide.