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Cell-mediated immunity is an immune response that does not involve antibodies, but rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.
Historically, the immune system was separated into two branches: humoral immunity, for which the protective function of immunization could be found in the humor (cell-free bodily fluid or serum) and cellular immunity, for which the protective function of immunization was associated with cells. CD4 cells or helper T cells provide protection against different pathogens. Cytotoxic T cells cause death by apoptosis without using cytokines; therefore in cell-mediated immunity cytokines are not always present.
Cellular immunity protects the body by:
- T-cell mediated immunity or T-cell immunity : activating antigen-specific cytotoxic T cells that are able to induce apoptosis in body cells displaying epitopes of foreign antigen on their surface, such as virus-infected cells, cells with intracellular bacteria, and cancer cells displaying tumor antigens;
- activating macrophages and natural killer cells, enabling them to destroy pathogens; and
- stimulating cells[clarification needed] to secrete a variety[clarification needed] of cytokines that influence the function of other cells[clarification needed] involved in adaptive immune responses and innate immune responses.
Cell-mediated immunity is directed primarily at microbes that survive in phagocytes and microbes that infect non-phagocytic cells. It is most effective in removing virus-infected cells, but also participates in defending against fungi, protozoans, cancers, and intracellular bacteria. It also plays a major role in transplant rejection.
- Cell-mediated immunity (Encyclopædia Britannica)
- Chapter 8:T Cell-Mediated Immunity Immunobiology: The Immune System in Health and Disease. 5th edition.