Wheal & flare reaction is what type of hypersensitivity recations?
First, I need to recall the different types of hypersensitivity. There are four main types: I, II, III, and IV. Type I is immediate, mediated by IgE, like in allergies. Type II involves IgG or IgM against cell surface antigens, such as in hemolytic anemia. Type III is immune complex-mediated, like in serum sickness. Type IV is delayed, T-cell mediated, like in contact dermatitis.
The wheal and flare reaction is a classic example of a local anaphylaxis reaction. It's the kind you see with histamine release, leading to vasodilation (flare) and increased vascular permeability (wheal). Histamine comes from mast cells and basophils, which are part of the IgE-mediated response. So this points to Type I hypersensitivity.
Now, the options aren't listed, but the correct answer is Type I. The other options would be Types II, III, IV. For each incorrect option, I need to explain why they don't fit. For example, Type II involves cell destruction, Type III has immune complexes, Type IV is T-cell driven. The clinical pearl here is that wheal and flare is a hallmark of Type I, often seen in skin tests like the intradermal test for allergies.
I should structure the explanation with the core concept being hypersensitivity types, explain why Type I is correct, address each wrong option, and end with a memorable fact. Make sure to use medical terms correctly and keep it concise within the character limit.
**Core Concept**
Wheal & flare reaction is a localized response to histamine release from mast cells/basophils, characteristic of **Type I hypersensitivity**. This IgE-mediated reaction involves antigen-antibody binding triggering degranulation, leading to vasodilation (flare) and fluid extravasation (wheal).
**Why the Correct Answer is Right**
Type I hypersensitivity is defined by IgE-mediated mast cell degranulation. When an allergen binds to IgE antibodies on mast cells, histamine is released, causing increased capillary permeability (wheal) and arteriolar dilation (flare). This occurs within minutes, as seen in hives, allergic rhinitis, or anaphylaxis. The reaction is mediated by IgE, not IgG/IgM (Type II/III) or T-cells (Type IV).
**Why Each Wrong Option is Incorrect**
**Option A:** Type II hypersensitivity involves IgG/IgM targeting cell surface antigens (e.g., Goodpasture’s disease), causing cytotoxic damage—not wheal/flare.
**Option B:** Type III hypersensitivity results from immune complex deposition (e.g., serum sickness), leading to inflammation days later, not immediate wheal/flare.
**Option C:** Type IV hypersensitivity is T-cell-mediated (e.g., contact dermatitis), peaking in 48–72 hours, unrelated to histamine.
**Clinical Pearl / High-Yield Fact**
**Type I = Immediate (minutes), IgE, mast cells, histamine.** In exams