What type of hypersensitivity reaction is mediated by cytotoxic antibodies?

The type of hypersensitivity reaction that is mediated by cytotoxic antibodies is Type II hypersensitivity. In this reaction, antibodies, typically IgG or IgM, bind to antigens on the surface of cells, leading to cell destruction or dysfunction. This binding triggers complement activation and recruitment of immune cells, resulting in lysis of the targeted cells due to various mechanisms including opsonization, phagocytosis, or the formation of membrane attack complexes.

Common examples of Type II hypersensitivity include autoimmune hemolytic anemia and Rh disease, where the immune system mistakenly attacks the body’s own cells or incompatible blood cells. In these cases, the cytotoxic antibodies directly damage the target cells, illustrating the characteristic mechanism of Type II hypersensitivity.

In contrast, Type I hypersensitivity involves IgE antibodies and is typically associated with allergic reactions, such as hay fever or anaphylaxis. Type III hypersensitivity is caused by immune complex deposition and is associated with conditions like systemic lupus erythematosus. Type IV hypersensitivity is delayed-type and T-cell mediated, as seen in contact dermatitis. Understanding these distinct mechanisms provides a clearer picture of how different immune responses contribute to various clinical scenarios.