Naturally occurring mouse antibodies against T-cell-secreted chondroitin sulphate proteoglycan.

Stimulated T lymphocytes and certain T-cell hybridomas secrete molecules capable of inducing B-lymphocyte proliferation and differentiation. It has been shown recently that one such B-cell stimulatory factor is associated with chondroitin sulphate proteoglycan (CSPG) and was designated T-cell proteoglycan fraction, or T-PGF. We report here that mouse spleen cells cultured at high densities or stimulated with lipopolysaccharide (LPS) at low cell densities secrete antibodies directed against T-PGF. Such antibodies react primarily with the CSPG component of T-PGF and can inhibit the induction of plaque-forming cells (PFC) by T-PGF. By fusing high-density cultures of unstimulated mouse spleen cells with the myeloma P3 x 63AG8.653, several anti-T-PGF (CSPG) hybridomas were derived that exhibited activities identical to anti-T-PGF (CSPG) obtained from high-density spleen cell culture supernatants. The role that these spontaneously secreted autoantibodies may play in immunoregulation is discussed.