[Superantigens and their implication in autoimmune diseases]

Superantigens, unlike conventional antigens, are capable of stimulating cell growth and differentiation of a large proportion of T cells (10 -40%). There are two types of superantigens: endogenous retroviral superantigens (described only in mice) and bacterial superantigens. Bacterial superantigens are heat-resistant enterotoxins responsible for Staphylococcus food poisoning or toxic shock syndromes. T lymphocyte proliferation is associated with production of large quantities of cytokines, including interleukin-1, 2, 4, 6 and tumour necrosis factor which induce the symptoms observed in toxic syndromes. These superantigens form trimolecular complexes with the beta chains on the outer peptide pouch of class II HLA molecules and with certain families of V beta chains of the T-cell receptors on CD4 and CD8 lymphocytes. Unlike conventional antigens, superantigens do not have to be processed in small-sized peptides before presentation to T-cell receptors by the class II HLA molecules. The late consequences of T-cell activation by superantigens are either a deletion of the T-lymphocytes carrying V beta chains in families specific for a superantigen, or an anergy. The oligoclonal characteristic of T-lymphoid populations infiltrating the central nervous system, the synovial membrane or the salivary glands suggests that superantigens are implicated in the pathogenesis of certain autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, and Sjögren's syndrome. Certain Staphylococcus superantigens could be the cause of Kawasaki's syndrome.