A two-chain tumour-related suppressor factor specific for a sequence antigen.

Suppressor factors in the serum of CBA mice bearing transplanted methylcholanthrene-induced tumours suppressed the leukocyte adherence inhibition reaction between tumour-sensitized peritoneal cells and a sequenced antigen, myelin basic protein (MBP). Chromatography on Sephacryl S-200 columns demonstrated suppressive activity in low molecular weight fractions (40-50 kDa) derived from whole serum. The factors were absorbed from serum by MBP, but not by lysozyme, coupled to Sepharose gel. Cleavage with sodium dodecyl sulphate (SDS) and absorption with either MBP or anti-I-J antibody on Sepharose gels yielded inactive supernatants that regained suppressive activity when combined. Elution of these gels with acidic buffer yielded eluates that were inactive alone but suppressive when combined. These results indicate that the tumour-related suppressor factors consist of two chains separable by detergent action; one chain is antigen (MBP)-binding and the other contains an I-J determinant.