HUMAN TH1 AND TH2 CELLS - FUNCTIONAL-PROPERTIES, REGULATION OF DEVELOPMENT AND ROLE IN AUTOIMMUNITY

Evidence has accumulated suggesting the existence in humans of polariz ed T helper (Th) cell subsets, coded as Th1 and Th2, with defined cyto kine secretion profiles. Immune responses to intracellular bacteria an d viruses result in the preferential development of the Th1 cell subse t. Th1 cells express cytolytic activity against antigen-presenting cel ls and provide helper function for IgM, IgG and IgA synthesis only at low T/B cell ratios. In contrast, Th2 cells develop in response to all ergens or helminth antigens, provide help for all immunoglobulin class es, including IgE, and lack cytolytic potential. The cytokine milieu i n the microenvironment plays a fundamental role in determining the fun ctional phenotype of the subsequent antigen-specific Th1 or Th2 respon ses. In recent years it has become clear that Th1 and Th2 cells play d ifferent roles not only in protection against exogenous offending agen ts, but also immunopathology. Th2 cells are involved in immunopatholog y induced by helminths and are responsible for the initiation and main tenance of allergic disorders. Th1 cells seem to be involved in contac t dermatitis, acute allograft rejection and organ-specific autoimmunit y, such as thyroid autoimmune disorders, diabetes mellitus or multiple sclerosis, whereas less polarized patterns of Th cells are detectable in target organs of patients with rheumatoid arthritis. Sjogren's syn drome or systemic lupus erythematosus.