The mechanism by which the immune system destroys or damages foreign or abnormal cells. Immunologic cytotoxicity may lead to complete loss of viability of the target cells (cytolysis) or an inhibition of the ability of the cells to continue growing (cytostasis). Immunologic cytotoxicity can be manifested against a wide variety of target cells, including malignant cells, normal cells from individuals unrelated to the responding host, and normal cells of the host that are infected with viruses or other microorganisms. In addition, the immune system can cause direct cytotoxic effects on some microorganisms, including bacteria, parasites, and fungi.
Immunologic cytotoxicity is a principal mechanism by which the immune response copes with, and often eliminates, foreign materials or abnormal cells. Cytotoxic reactions are frequently observed as a major component of an immune response that develops following exposure to foreign cells or microorganisms. In addition, there is increasing evidence that cytotoxic reactions represent a major mechanism for natural immunity and resistance to such materials. In most instances, cytotoxicity by immune components involves the recognition of particular structures on the target cells; also, the targets need to be susceptible to attack by the immune components. Some cells are quite resistant to immunologic cytotoxicity, and this appears to represent a major mechanism by which they can escape control by the immune system.
There are a variety of mechanisms for immunologic cytotoxicity. The two main categories are antibody- and cell-mediated cytotoxicity. Within cell-mediated cytotoxicity, there is a multiplicity of effector cell types and mechanisms that can be involved, including cytotoxic T lymphocytes, macrophage-mediated cytotoxicity, natural killer cells, granulocyte cytoxicity, and antibody-dependent cell-mediated cytotoxicity. See Immunology