Isolation of an immunosuppressive fraction in ultrafiltrate from uremic sera

An improved purification method for isolating an immunosuppressive fraction from uremic ultrafiltrates was described. Lyophilized ultrafiltrates were fractionated on Sephadex G-15 and the active fraction was further purified using high-performance liquid chromatography. The inhibitory effect of eluates on in vitro lymphocyte proliferation was assessed at the different steps of purification. Results obtained after enzyme treatment suggested that the substance(s) responsible for the immunosuppressive activity is (are) of peptidic nature. This peptide appears to be different from the other peptides previously reported, which have a much lesser activity in the lymphocyte proliferation assay.