Effect of alpha-fetoprotein and other serum factors derived from hepatoma-bearing rats on the mixed lymphocyte response.

Serum alpha-globulin fractions isolated by physiocochemical techniques from normal adult Buffalo rats suppressed lymphocyte proliferation in vitro. The factors responsible for mixed lymphocyte culture suppression appeared to be strain specific since they were not demonstrable in the same fractions from normal LBN rat serum. Similar fractionation of the serum from Buffalo rats bearing the Morris Hepatoma 7777 obtained from two different sources also yielded suppressive protein fractions that differed both chemically and functionally. Both variants of this hepatoma produced high serum concentrations of alpha-fetoprotein (AFP), providing an opportunity to study the possible immunoregulatory role of their fetal-associated globulins. Fractions rich in AFP that lacked other serum alpha-globulins were obtained by gel filtration chromatography and were devoid of any in vitro immunosuppressive activity. When AFP that was further purified by immunoabsorption was added to mixed lymphocyte cultures, no effect was observed at doses below 400 mug/ml. The MLC response was augmented with higher doses, similar to albumin purified by the same methods.