Restricted activity of serum blocking factors related to a common tumour antigen in mice.

Mice of four different inbred strains (CBA, Balb/c, C57Bl/6 and DBA/2), bearing different transplanted tumours (methylcholanthrene-induced sarcomas, B16 melanoma and P-815 mastocytoma), were tested for cellular immune reactivity to the synthetic encephalitogenic peptide of human myelin basic protein by the leucocyte adherence inhibition (LAI) assay. All exhibited reactivity at about the same optimal concentration of peptide. Normal mice of all strains and pregnant CBA mice were non-reactive. Blocking of LAI was detected with serum obtained 10 or more days after tumour transplantation. Sera from mice bearing different transplanted tumours abrogated the adherence-inhibitory effect of peptide on sensitized syngeneic peritoneal leucocytes. The blocking factors were cross-reactive between different tumours only within the same mouse strain, indicating a requirement for genetic compatibility between donors of the reactive cells and the serum blocking factors.