title: Cytotoxic T cells.
abstract: The immune system is a complex arrangement of cells and molecules that preserve the integrity of the organism by elimination of all elements judged dangerous. Within the immune system, a humoral and a cellular as well as an innate and an adaptive arm can be differentiated. The key players of adaptive cellular immune responses are T lymphocytes in general and, for the effector function, cytotoxic T lymphocytes (CTLs) in particular. T lymphocytes arise in the bone marrow and migrate to the thymus for maturation. During this process, T cells somatically rearrange gene segments, eventually leading to the expression of a unique antigen-binding molecule, the T-cell receptor (TCR). This receptor allows them to monitor all cells of the body, ready to destroy any cell posing a threat to the organism. Cytotoxicity is exerted directly through the Fas or perforin pathway and/or indirectly by the release of cytokines. Obviously, the activity of such a potent cell is tightly regulated. Indeed, a predominance of stimulatory over inhibitory signals is required for effective immune responses to pathogens, and a predominance of inhibitory over stimulatory signals is required for maintenance of self-tolerance. Still, several situations occur in which an inappropriate CTL response leads to either autoimmune disease or persistence of pathogens.
authors.affiliation: Tumor Immunology Group, Institute of Cancer Biology, Danish Cancer Society, Copenhagen, Denmark.
authors.forename: Mads Hald
authors.initials: MH
authors.lastname: Andersen
authors.forename: David
authors.initials: D
authors.lastname: Schrama
authors.forename: Per
authors.initials: P
authors.lastname: Thor Straten
authors.forename: Jürgen C
authors.initials: JC
authors.lastname: Becker
mesh_terms: D001327:Autoimmune Diseases / Q000276:immunology; D015415:Biomarkers / Q000032:analysis; D003602:Cytotoxicity, Immunologic; D006801:Humans; D006968:Hypersensitivity, Delayed / Q000276:immunology; D007157:Immunologic Surveillance; D008213:Lymphocyte Activation; D009369:Neoplasms / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
chemical_list: D015415:Biomarkers; D011948:Receptors, Antigen, T-Cell