| Summary: | –helper cells can be divided into two distinct subtypes of effector cells based on the profile of cytokines they produce. Th1 cells produce interferon– γ (IFN– γ) and tumor necrosis factor β (TNF– β), and are associated with cell– mediated responses, particularly with resistance to intracellular pathogens (bacteria, parasites, yeasts and viruses). In contrast, Th2 . cells produce IL– 4, IL– 5, IL– 9 and IL– 13. Th2 cells are involved in antibody responses and IgE production, as well as tissue fibrosis, and eosinophilia. Th2 responses are important in the resistance to infection with helminth parasites. Although both Th responses are protective against certain infectious pathogens, they can themselves be pathogenic: Th1 cell responses can mediate autoimmune diseases, whereas dysregulation of Th2 responses is implicated inatopic diseases (allergic rhinitis, asthma, atopic eczema, food allergy and anaphylaxis). The recent progress in our understanding of the mechanism of initiation and control of Th1 and Th2 cell responses will eventually lead to new therapeutic strategies.
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