Which immunologic mechanism is usually involved in bronchial asthma?

Which immunologic mechanism is usually involved in bronchial asthma?

• A. Immediate hypersensitivity
• B. Antibody mediated cytotoxicity
• C. Immune complex deposition
• D. Delayed hypersensitivity

Answer: (A)

Bronchial asthma—especially the allergic form—is driven by an IgE-mediated immediate hypersensitivity reaction. When an inhaled allergen is encountered, a Th2-skewed response promotes production of IgE antibodies. These IgE molecules bind to high-affinity receptors on mast cells and basophils. On re-exposure, the allergen cross-links the bound IgE, triggering rapid degranulation of these cells and release of mediators such as histamine, leukotrienes, and prostaglandins. This mediator surge causes bronchial smooth muscle constriction (bronchoconstriction), increased mucus production, and airway edema within minutes—the hallmark of the immediate hypersensitivity reaction. Late-phase inflammation can follow, driven by eosinophils and cytokines, contributing to ongoing airway hyperresponsiveness, but the initial and most characteristic mechanism in asthma is IgE-mediated mast cell degranulation. The other immunologic mechanisms don’t fit asthma as described: antibody-mediated cytotoxicity involves antibodies targeting cell surfaces leading to cell lysis; immune complex deposition involves circulating antigen-antibody complexes causing tissue injury; and delayed hypersensitivity is T-cell–mediated, typically taking longer to develop and seen in conditions like contact dermatitis—not the primary driver of the classic allergic asthma response.

Bronchial asthma—especially the allergic form—is driven by an IgE-mediated immediate hypersensitivity reaction. When an inhaled allergen is encountered, a Th2-skewed response promotes production of IgE antibodies. These IgE molecules bind to high-affinity receptors on mast cells and basophils. On re-exposure, the allergen cross-links the bound IgE, triggering rapid degranulation of these cells and release of mediators such as histamine, leukotrienes, and prostaglandins. This mediator surge causes bronchial smooth muscle constriction (bronchoconstriction), increased mucus production, and airway edema within minutes—the hallmark of the immediate hypersensitivity reaction.

Late-phase inflammation can follow, driven by eosinophils and cytokines, contributing to ongoing airway hyperresponsiveness, but the initial and most characteristic mechanism in asthma is IgE-mediated mast cell degranulation.

The other immunologic mechanisms don’t fit asthma as described: antibody-mediated cytotoxicity involves antibodies targeting cell surfaces leading to cell lysis; immune complex deposition involves circulating antigen-antibody complexes causing tissue injury; and delayed hypersensitivity is T-cell–mediated, typically taking longer to develop and seen in conditions like contact dermatitis—not the primary driver of the classic allergic asthma response.