Cellemediert

Cellemediert, known in English as cell-mediated immunity, refers to the arm of the adaptive immune system that is primarily driven by T lymphocytes rather than by antibodies. It protects against intracellular pathogens, virus-infected cells, some bacteria and parasites, as well as neoplastic or transplanted cells, through T cell–dependent mechanisms.

Activation begins when antigen-presenting cells display peptide fragments via MHC molecules to T cells. CD4+ helper T cells coordinate the response by secreting cytokines that activate other immune cells, while CD8+ cytotoxic T lymphocytes recognize antigens presented on MHC class I and directly kill target cells using perforin and granzymes, Fas/FasL interactions, or other cytotoxic pathways. Macrophages are activated by Th1-derived cytokines, such as interferon-γ, enhancing their antimicrobial activities.

Clonal expansion generates effector and memory T cells, which provide rapid and robust responses upon re-exposure. Delayed-type hypersensitivity reactions and cytotoxic responses are characteristic functional manifestations of cell-mediated immunity. This arm works in concert with humoral immunity, with B cells and antibodies playing complementary roles in defense.

Clinical relevance: impaired T cell function can lead to increased susceptibility to intracellular infections and to tumor progression. Graft rejection is a classic consequence of cell-mediated immune responses. Vaccines and immunotherapies often aim to elicit robust CMI, and laboratory techniques such as ELISPOT or intracellular cytokine staining are used to assess T cell activity.