Antibody to activated lymphocytes in patients with systemic lupus erythematosus.

: IgG antilymphocyte antibodies preferentially reacting with phytohemagglutinin (PHA) activated peripheral blood lymphocytes (PBL) and an adult T cell leukemia cell line were detected in 70.6% sera from patients with systemic lupus erythematosus (SLE), using a fluorescence activated cell sorter (FACS). In the sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis, 2 major peaks with an apparent molecular weight 60,000 to 65,000 Da and about 40,000 Da were observed in the membrane glycoprotein fractions of both PHA activated PBL and an adult T cell leukemia cell line. From the result of sequential coprecipitation analysis of SDS-PAGE between SLE serum, antiinterleukin-2 (IL-2) receptor antibody (anti-Tac antibody) and anti-Ia antibody, the reactive antigen on the activated PBL and an adult T cell leukemia cell line proved to be an identical molecule of the IL-2 receptor on these cells. The role of this autoantibody in the modulation of T cell mediated immunity in patients with SLE is discussed.