# DBT JRF 2022 — Question 29

Exam: DBT JRF 2022 · Section: B · Topic: Immunology › Immunoglobulins & Allergic Reactions · Difficulty: Medium

## Question

Which one of the following Immunoglobulins cause type 1 allergic reaction?

## Options

- **A.** IgG
- **B.** IgM
- **C.** IgE
- **D.** IgA

## Answer

Option C

## Explanation

Immunoglobulin responsible for Type I (immediate) allergic reactions: Type I hypersensitivity (immediate / anaphylactic type) is mediated exclusively by IgE: 1. First exposure: allergen stimulates B cells to produce IgE antibodies. 2. IgE binds to FcεRI (high-affinity IgE receptor) on mast cells and basophils — 'sensitisation'. 3. Second exposure: allergen cross-links IgE on mast cells → degranulation: • Releases histamine, leukotrienes, prostaglandins • Causes vasodilation, bronchoconstriction, mucus secretion 4. Clinical manifestations: allergic rhinitis, asthma, urticaria, anaphylaxis Other immunoglobulin classes are NOT involved in Type I hypersensitivity: • IgG: Type II (cytotoxic) and Type III (immune complex) hypersensitivity • IgM: agglutination, complement activation • IgA: mucosal immunity Answer: IgE (Option 3).

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