Functional property of Ia-positive T cells in peripheral blood from patients with systemic lupus erythematosus.

Ia-positive (Ia+) T cells in peripheral blood and their functional property were examined in patients with systemic lupus erythematosus (SLE). Binding of specific monoclonal antibodies was assessed by indirect immunofluorescence. Functional study of Ia+ T cells was carried out in coculture experiments by measuring the IgG secreted into the culture supernatant. We found that the percentage of Ia+ T cells in peripheral blood from patients with SLE was raised and the rise correlated positively with serum gamma globulin and IgG level. The elevation was further increased after stimulation with DNA in vitro, indicating the presence of DNA-sensitive T cells. Functionally, Ia+ T cells acted as helper cells in spontaneous IgG synthesis of SLE B cells, and were enriched in the OKT4 subset. These results indicate that SLE T cells are activated in vivo and that the Ia+ T cells may play a crucial role in the immunoregulatory function. Accordingly, demonstration of Ia antigens on T cells by monoclonal antibody may provide a useful tool for the measurement of immunological activity in patients with SLE.