Autoimmune mice develop antibodies to thymic hormone: production of anti-thymulin monoclonal autoantibodies from diabetic (db/db) and B/W mice.

Monoclonal autoantibodies specific for the thymic hormone thymulin (FTS-Zn) were obtained by cell fusion with the use of spleen cells from nonimmunized autoimmune B/W or diabetic (db/db) mice and myeloma cells. Culture supernatants were screened for their ability to inhibit in vitro and in vivo the biologic activity of synthetic and natural hormone and to bind specifically to thymic epithelial cells in indirect immunofluorescence. This binding was completely abolished by preincubation of the antibodies with the synthetic hormone. These monoclonal autoantibodies were shown by double labeling experiments to bind the same thymic epithelial cells as the antithymulin monoclonal antibodies prepared by immunization with thymic epithelial cells. These autoantibodies directed against the low m.w. thymic hormone thymulin do not explain the low thymulin serum level found in those mice because there is a concomitant decrease in the number of thymulin-containing cells in the thymus, but they could play a role in the maintenance of T lymphocyte defects observed in these mice.