True about type II hypersensitivity reaction is?
**Core Concept**
Type II hypersensitivity reaction is a form of immune-mediated cytotoxicity where antibodies bind to antigens on the surface of host cells, marking them for destruction. This process involves the activation of complement and the recruitment of effector cells such as neutrophils and macrophages.
**Why the Correct Answer is Right**
The type II hypersensitivity reaction is characterized by the formation of IgG and IgM antibodies against cell-bound antigens, which can be proteins or other molecules. These antibodies can activate the classical complement pathway, leading to the deposition of C3b fragments on the cell surface and the recruitment of immune effector cells. The binding of antibodies to the Fc receptors on neutrophils and macrophages triggers phagocytosis and the release of cytotoxic granules, resulting in cell lysis and tissue damage.
**Why Each Wrong Option is Incorrect**
**Option A:** This option might refer to a type I hypersensitivity reaction, which involves IgE antibodies and the release of histamine from mast cells, leading to allergic symptoms.
**Option B:** This option might refer to a type III hypersensitivity reaction, which involves the formation of immune complexes and the activation of the complement system, leading to inflammation and tissue damage.
**Option C:** This option might refer to a type IV hypersensitivity reaction, which involves T cell-mediated immunity and the release of cytokines, leading to delayed-type hypersensitivity reactions.
**Clinical Pearl / High-Yield Fact**
Remember that type II hypersensitivity reactions often involve the destruction of cells that express specific antigens on their surface, such as red blood cells in autoimmune hemolytic anemia or platelets in immune thrombocytopenic purpura.
**Correct Answer:** D