Anomalous reactions of mouse alloantisera with cultured tumor cells. I. Demonstration of widespread occurrence using reference typing sera.

M0use alloantisera produced against different specificities of the K, I, and D regions of the H-2 gene complex reacted as immunogenetically anticipated with normal lymphoid target cells of different haplotypes in cytotoxicity and indirect immunofluorescence tests. These same alloantisera, however, produced anomalous positive reactions when tested on cultured MCA-induced sarcoma cells from B10 background H-2 congenic mice. Absorption experiments demonstrated that the anomalous activity in these sera was directed against a tumor membrane antigen(s) which was distinct from H-2 region specificities against which the reference alloantisera were produced, and which was shared in common by multiple cultured sarcoma lines. Similar anti-tumor antibody activity could be demonstrated in the serum of older (greater than 12 weeks) but not younger normal unimmunized mice of the strains used as recipients for alloantiserum production. It is suggested that the observed anamalous anti-tumor activity in these alloantisera may be due to the presence of antibodies reactive with envelope antigens of murine leukemia virus which are expressed on sarcoma cells maintained in culture.