Abstract
Summary
Immunosuppression induced by mastocytoma cells is related to a soluble factor present both in the supernatants of tumor cell cultures and in tumor cell extracts and ascites fluid of tumor-bearing animals. In the present study culture supernatants of mastocytoma cells growing in serum-free medium contained an 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 to 5000. The immunosuppressive activity of the culture supernatants, the concentrated dialysates, and the post-void volume Sephadex fractions were stable to heating at 56° for 30 min but was inactivated when heated at 80°. Furthermore, the 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.
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