Type I (immediate) hypersensitivity is mediated mainly by:

Correct answer: (d) IgE

Explanation

Type I (immediate) hypersensitivity is allergy. It is mediated by IgE antibodies:

• on first exposure to an allergen (such as pollen, dust mites or certain foods), the body makes IgE, which sticks to mast cells and basophils;
• on the next exposure, the allergen binds this IgE, and the mast cells release histamine and other chemicals within minutes.

This causes hay fever, asthma, hives and, at worst, anaphylactic shock.

• IgA guards mucous surfaces (saliva, tears, breast milk).
• IgG is the most common antibody and crosses the placenta.
• IgM is the first antibody made in an infection.