Type 1 T helper and type 2 T helper cells: functions, regulation and role in protection and disease.
Two very distinct cytokine secretion patterns have been defined among murine CD4+ T cells. Type 1 helper (TH1), but not type 2 helper (TH2), cells produce interleukin (IL)-2, gamma-interferon (IFN-gamma) and tumour necrosis factor-beta, whereas TH2, but not TH1, cells express IL-4, IL-5, IL-6 and IL-10. The different cytokine patterns lead to different functions of the two types of T cell. In general, TH2 cells are excellent helpers for B-cell antibody secretion, particularly IgE responses. On the other hand TH1 cells induce delayed-type hypersensitivity reactions. There is general agreement that the different functional subsets of TH cells arise post-thymically from a common pool of precursors and as a consequence of activation of antigen. However, the factors affecting differentiation of TH precursors into the TH1 or TH2 subsets are still unclear. Mutual cross-regulation between TH1 (via IFN-gamma) and TH2 (via IL-10) has also been reported. Recently, human T cell clones similar to murine TH1 and TH2 cells have been demonstrated. Most allergen- or helminthic antigen-specific CD4+ human T cell clones have a TH2 phenotype, whereas the majority of T-cell clones specific for mycobacterial antigens or antigens responsible for type IV hypersensitivity exhibit a TH1 phenotype. Human TH2 clones provide B-cell help for IgE synthesis, whereas most TH1 clones are cytolytic for antigen-presenting cells, including B lymphocytes. It is highly probable that the selective or preferential activation of CD4+ T-cell subsets secreting defined patterns of cytokines is of major importance in determining the class of immune effector function, thus influencing both protection and immunopathology.
Cattedra di Immunologia, Università degli Studi di Firenze, Florence, Italy.
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Romagnani
D000818:Animals; D000941:Antigens / Q000276:immunology; D001327:Autoimmune Diseases / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D002454:Cell Differentiation; D016207:Cytokines / Q000378:metabolism; D006373:Helminthiasis / Q000276:immunology; D006801:Humans; D006967:Hypersensitivity / Q000276:immunology; D007896:Leishmaniasis / Q000276:immunology; D008213:Lymphocyte Activation; D008211:Lymphocyte Cooperation; D051379:Mice / Q000276:immunology; D008954:Models, Biological; D010641:Phenotype; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology / Q000378:metabolism
D000941:Antigens; D016207:Cytokines