T Lymphocyte Responses: Development

AbstractThe function of T cells is to recognize specific ‘non‐self’ antigens and to generate against them specific responses to protect the body from different diseases. In particular, a subset of T lymphocytes, named T‐helper cells, produces cytokines that orchestrate the immune response, whereas another subset, named cytotoxic T cells is able to kill the pathogen‐infected cells.Two population of T‐helper lymphocytes exist: T‐effector cells, devoted to respond to foreign antigens and to protect the body from infection and tumours, and T‐regulatory cells, whose main function is to suppress T‐effector responses and to avoid the development of atoimmune diseases.T‐effector lymphocytes can be divided, according to their cytokines production profile in TH1, TH2 and TH17 cells, whereas T‐regulatory cells can be distinguished, on the basis of their origin, in natural and adaptive.Key ConceptsT‐ and B cells are the major cellular components of the adaptive immune response.CD4+ T‐helper lymphocytes produce cytokines that orchestrate the immune response, whereas CD8+ T cytotoxic lymphocytes kill the target cells.T‐helper lymphocytes can be distinguished in effector cells, which protect the body from pathogens, and regulatory T cells, that suppress effector responses, when they may become dangerous for the host.Effector T‐helper cells can be distinguished, according to the cytokines they are able to produce, in TH1, TH2, and TH17 cells.TH1 cells play an important role in the protection against intracellular pathogens, but they could be involved in the pathogenesis of autoimmune and inflammatory disorders, when Treg cells fail to control autoreactive clones.TH2 cells are mainly involved in the protection against parasitic helminths, but they also play a central role in the development of allergic disorders.TH17 cells favour the clearance of extracellular pathogens, and play a pathogenic role in autoimmune and other chronic inflammatory disorders, particularly when they acquire the ability to produce IFNγ, thus becoming TH17/TH1 cells.Treg cells can be distinguished in natural Treg cells, a population already planned to suppress the response against self‐antigens since its birth in thymus, and adaptive Treg cells which acquires their suppressive activity in the periphery.