REGULATION OF IMMUNE-RESPONSE TO TUMOR ANTIGENS .3. CHARACTERIZATION OF THYMIC SUPPRESSOR FACTORS(S) PRODUCED BY TUMOR-BEARING HOSTS

Abstract

Immunosuppressor T [thymus-derived] cells (IST), capable of inhibiting the rejection of a methycholanthrene-induced fibrosarcoma (S1509a) in A/Jax mice immune to this tumor, produced soluble factors with similar suppressive activity. The immunosuppressive factor(s) (ISF) was immunologically specific, as demonstrated by the complete loss of suppressive activity after absorption with S1509a cells, but not with cells of an unrelated syngeneic tumor. From its behavior on gel filtration, the size of ISF was deduced to be < 70,000 daltons. The ISF was not removed by passage through a rabbit anti-mouse F(ab'')2 reverse immunosorbent and, hence, was probably not an immunoglobulin. The (immunosuppressive) activity of ISF was destroyed by treatment with Pronase,but not with RNase. The ISF shared the antigenic determinant(s) of the product(s) of the K end of the major histocompatibility complex of the mouse. Antibodies to ISF were induced by immunization with ISF-tumor cell complexes. Thus, IST and their factor(s) may play an important role in the regulation of the immune response to tumor antigens.