Tumor-associated blocking factors: isolation from sera of tumor-bearing mice

An isolation and partial purifications of tumor-associated blocking factors from the sera of tumor-bearing mice is described. Columns for affinity chromatography were prepared by coupling syngeneic tumor-immune antibodies to Sepharose 4B. Passage of serum through such immunoadsorbent columns removed all blocking activity from tumor-bearers' sera; subsequent elution of the absorbent with 3 M NaSCN recovered the activity. The blocking material was further purified on Sephadex G-200. The data provide evidence for the presence of antigen in tumor-associated blocking factors and are compatible with the hypothesis that blocking factors often consist of antigen and antibodies in the form of immune complexes.