In type II hypersensitivity reactions, target cell destruction is primarily mediated by the binding of antibodies (usually IgG or IgM) to antigens on the surface of the target cells. This binding can lead to cell destruction through several mechanisms:
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Complement Activation: The bound antibodies can activate the complement system, which leads to the formation of the membrane attack complex (MAC) that can directly lyse the target cells.
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Antibody-Dependent Cellular Cytotoxicity (ADCC): Natural killer (NK) cells or other immune effector cells can recognize the Fc portion of the bound antibodies on the target cell surface. This interaction can lead to the destruction of the target cell through the release of cytotoxic substances.
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Phagocytosis: Immune cells like macrophages and neutrophils can recognize and bind to the antibodies on the surface of the target cells. Once bound, these immune cells can engulf and destroy the target cells through phagocytosis.
These mechanisms highlight how type II hypersensitivity reactions can lead to cellular damage and tissue injury through antibody-mediated responses.