What characterizes a type I hypersensitivity reaction?

What characterizes a type I hypersensitivity reaction?

• A. IgE cross-linking on mast cells releases mediators causing an allergic reaction
• B. Anti-Fya antibodies destroy fetal red cells
• C. Immune complex deposition on glomeruli leads to renal failure
• D. T cells release lymphokines causing localized inflammation

Answer: (A)

A type I hypersensitivity reaction is characterized primarily by the involvement of IgE antibodies. When a person who is sensitized to an allergen is exposed to that allergen again, the IgE antibodies that are bound to mast cells cross-link. This cross-linking triggers the mast cells to degranulate and release various mediators such as histamine, leukotrienes, and prostaglandins. These mediators lead to the symptoms associated with allergic reactions, such as itching, swelling, and bronchoconstriction. This rapid immune response is typically immediate, occurring within minutes of exposure to the allergen. The other choices relate to different mechanisms of immune responses. The destruction of fetal red cells by anti-Fya antibodies pertains to hemolytic disease of the newborn and involves IgG, not IgE. Immune complex deposition leading to renal failure relates to type III hypersensitivity reactions, which involve the formation of immune complexes, not mast cell activation or IgE involvement. The role of T cells releasing lymphokines describes type IV hypersensitivity reactions, which are delayed-type and mediated by T cells rather than antibodies.

A type I hypersensitivity reaction is characterized primarily by the involvement of IgE antibodies. When a person who is sensitized to an allergen is exposed to that allergen again, the IgE antibodies that are bound to mast cells cross-link. This cross-linking triggers the mast cells to degranulate and release various mediators such as histamine, leukotrienes, and prostaglandins. These mediators lead to the symptoms associated with allergic reactions, such as itching, swelling, and bronchoconstriction. This rapid immune response is typically immediate, occurring within minutes of exposure to the allergen.

The other choices relate to different mechanisms of immune responses. The destruction of fetal red cells by anti-Fya antibodies pertains to hemolytic disease of the newborn and involves IgG, not IgE. Immune complex deposition leading to renal failure relates to type III hypersensitivity reactions, which involve the formation of immune complexes, not mast cell activation or IgE involvement. The role of T cells releasing lymphokines describes type IV hypersensitivity reactions, which are delayed-type and mediated by T cells rather than antibodies.