Characterization of antigens on murine tumor cells reacting with alloantisera against foreign H-2 specificities: analysis by absorption with purified murine leukemia virus and normal lymphoid cells of different H-2 haplotypes.

A spontaneous T cell lymphoma of DBA/2 (H-2-d) mice, SL2, was found to react with anti H-2 typing sera raised against certain foreign haplotypes as well as with anti H-2d sera. The cytotoxic anti-SL2 activity of the anti-foreign H-2 sera was detected in a newly developed microradioassay, not however, in a conventional 51Cr release test. Upon culture in vitro the reactivity of the tumor cells with the anti H-2 sera decreased. The anomalous cytotoxic anti-tumor activity of the anti-foreign H-2 sera appeared to be distinct from anti-murine leukemia virus activity, since it was not removed by absorption with either Friend of AKR leukemia virus. Partial absorption was observed with normal lymphoid cells carrying the respective foreign H-2 antigens, but not with cells of unrelated H-2 haplotypes. In each serum tested, the anti-tumor activity could also be absorbed with syngeneic H-2d lymphoid cells. These results show that the anomalous anti-tumor reactivity of certain anti H-2 typing sera, in particular of sera raised in recipients differing in H-2 from the tumor host strains, is not due to the presence of foreign (derepressed) H-2 molecules on the tumor cells. The differences observed between the tumor cells and normal cells seem to be due to unexpected antibodies in the sera reacting with public H-2 specificities which are better exposed on the tumor cells than on normal cells.