Characterization of a Dialyzable Immunosuppressive Fraction from Mastocytoma Culture Supernatants

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Abstract
Immunosuppression induced by mastocytoma cells is related to a soluble factor present in the supernatants of tumor cell cultures and tumor cell extracts and ascites fluid of tumor-bearing mice. In the present study culture supernatants of mastocytoma cells growing in serum-free medium contained immunosuppressive material which was readily dialyzed. The concentrated dialysates from the culture supernatants were fractionated by Sephadex gel filtration. The postvoid volume fraction from Sephadex G-10 columns contained most of the immunosuppressive activity present in the dialysates. The material in the active fractions had a molecular weight in the range of 1000-5000. The immunosuppressive activity of the culture supernatants, concentrated dialysates and postvoid volume Sephadex fractions was stable to heating at 56.degree. C for 30 min but was inactivated when heated at 80.degree. C. Immunosuppressive activity was inhibited by treatment with trypsin in vitro but was resistant to treatment with DNase or RNase. These results suggest that a relatively small molecular weight dialyzable material, possibly polypeptide in nature, is responsible for the immunosuppressive activity of mastocytoma cells.