The sneezing, watery eyes and swelling of an allergic reaction are caused mainly by
Correct answer: B. histamine released from mast cells
- A. complement proteins puncturing the cell membrane
- B. histamine released from mast cells
- C. cytotoxic T cells destroying the airway lining
- D. the pathogen's own toxins
Explanation
An allergen binds IgE already attached to mast cells, which then release histamine, and histamine dilates blood vessels and makes capillaries leaky, producing swelling, redness and mucus secretion. Antihistamine drugs work precisely by blocking its receptors. Allergy is thus an immune response out of proportion to a harmless substance rather than damage done by a pathogen.
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About Specific Defense Mechanism
Specific defense mechanisms provide targeted immunity through B lymphocytes, T lymphocytes, antibodies and memory cells that recognize particular antigens. Questions cover humoral and cell mediated responses, clonal selection, primary and secondary immune responses, vaccination and passive immunity, while distinguishing adaptive defenses from the immediate, non specific innate response.
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