Human Th1 and Th2 lymphocytes: their role in the pathophysiology of atopy.
In human beings, as in mice, two distinct patterns of cytokine secretion have been defined among CD4+ helper T-cell clones. Human type 1 helper (Th1), but not type 2 helper (Th2), cells produce interleukin-2 (IL-2), gamma-interferon (IFN-gamma), and tumor necrosis factor-beta, whereas Th2, but not Th1, cells secrete IL-4 and IL-5, but not IL-2 or IFN-gamma. Other cytokines, such as IL-3, IL-6, GM-CSF, or TNF-alpha, are produced by both Th1 and Th2 cells. Th0 cells, a third Th subset, show combined production of Th1- and Th2-type cytokines. The different cytokine patterns are associated with different functions. In general, Th2 cells provide an excellent helper function for B-cell antibody production, particularly of the IgE class. On the other hand, Th1 cells are responsible for delayed type hypersensitivity reactions and are cytolytic for autologous antigen-presenting cells, including B cells. Most allergen- or helminth-antigen-specific human CD4+ T-cell clones exhibit a Th2 phenotype, whereas most clones specific for bacterial antigens show a Th1 profile. Allergen-specific Th2 cells seem to play a crucial role in atopy. These cells induce IgE production via IL-4 and favor the proliferation, differentiation, and activation of eosinophils via IL-5. In addition, Th2-derived IL-3 and IL-4 are mast-cell growth factors that act in synergy, at least in vitro. Recent evidence indicates that allergen-specific Th2 cells are selectively enriched in tissues affected by allergic inflammation, such as the bronchial mucosa of subjects with allergic asthma.(ABSTRACT TRUNCATED AT 250 WORDS)
Del Prete
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Division of Clinical Immunology and Allergology, University of Florence, Italy.
D000485:Allergens / Q000276:immunology; D016207:Cytokines / Q000096:biosynthesis / Q000276:immunology; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000276:immunology / Q000503:physiopathology*; D007073:Immunoglobulin E / Q000096:biosynthesis / Q000276:immunology; D007371:Interferon-gamma / Q000096:biosynthesis / Q000276:immunology; D015847:Interleukin-4 / Q000276:immunology; D008407:Mast Cells / Q000276:immunology; D010641:Phenotype; D016176:T-Lymphocyte Subsets / Q000276:immunology; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology*
D000485:Allergens; D016207:Cytokines; D015847:Interleukin-4; D007073:Immunoglobulin E; D007371:Interferon-gamma