Immunosuppressive factors in porcine vitreous body.

High molecular (designated Sv, greater than 3K) and low molecular (designated Sv, less than 3K) fractions were prepared by filtration of porcine vitreous extracts through a membrane filter with a molecular weight cut-off of 3,000 daltons. Both fractions inhibited mitogen-stimulated proliferation of lymphocytes from rat spleen, as determined by [3H]-thymidine incorporation. The inhibitory activity of Sv, greater than 3K was markedly enhanced by acid treatment and abolished almost completely by incubation with anti-transforming growth factor beta (TGF-beta) antibody. The major immunosuppressive factor in Sv, greater than 3K was therefore concluded to be TGF-beta. On the other hand, the inhibitory activity of Sv, less than 3K was not affected by acid treatment or by incubation with anti-TGF-beta antibody but was decreased by proteolytic treatment. From these results the immunosuppressive factor in Sv, less than 3K was attributed to a low molecular substance which is probably a peptide structurally unrelated to TGF-beta. The inhibitory effects of both Sv, greater than 3K and Sv, less than 3K were reversible and therefore not cytotoxic. Both factors seemed to suppress lymphoproliferation without affecting the expression of Interleukin-2 receptor, CD4 and CD8 on the cell surface of cultured lymphocytes.