Abstract
Tumor culture toxohormone (TCT) obtained from cultures of MBQA mouse tumor cells, a line derived from a methylcholanthrene-induced fibrosarcoma (CBA/J origin), suppressed the mitogenic responsiveness of mouse spleen cells (PHA [phytohemagglutinin], LPS [lipopolysaccharide]) as well as the antibody formation to SRBC [sheep red blood cells] in vitro. The immunosuppressive activity of toxohormone was readily inactivated by heating at 100.degree. C or treatment with trypsin, but not by DNase and RNase treatment.