Immunoglobulin E (IgE) function: Which statement best describes the principal immunological role of IgE in humans?

Introduction / Context:
Different antibody isotypes specialize for distinct immune niches. IgE is tightly linked to antiparasitic defense and allergic responses via mast cells and basophils.

Given Data / Assumptions:

• IgE binds Fcε receptors on mast cells and basophils.
• Cross-linking by antigen triggers degranulation.
• Secretory dominance is associated with IgA, not IgE.

Concept / Approach:
IgE arms FcεRI-expressing cells. Upon exposure to helminth antigens or allergens, cross-linking causes mediator release (histamine, leukotrienes), promoting eosinophil recruitment and barrier responses helpful in anti-helminth immunity but also causing allergy symptoms.

Step-by-Step Solution:
Associate IgE with mast cells/basophils and eosinophils.Identify physiologic role: antiparasitic defense; pathologic role: immediate hypersensitivity.Exclude complement-dominant and secretory-dominant roles (belong to IgG/IgM and IgA).

Verification / Alternative check:
Elevated IgE and eosinophilia correlate with helminth infections; allergen skin testing depends on IgE-mediated mast cell degranulation.

Why Other Options Are Wrong:

• Complement killing/opsonization: Primarily IgG and IgM.
• Secretions: Predominantly dimeric IgA with secretory component.
• All of the above: Overgeneralizes beyond IgE’s niche.

Common Pitfalls:
Confusing isotype locations and effector mechanisms (IgA vs IgE).

Final Answer:
Immunity against some parasites (and mediation of immediate hypersensitivity).