Murine natural anti-tumor antibodies. I. Rapidin vivo binding of natural antibody by tumor cells in syngeneic mice

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Abstract
A competitive radioimmunoassay (RIA) for the detection of cell-bound antibody was used to study the in vivo acquisition of immunoglobulin (Ig) by tumor cells. Several tumor lines acquired Ig rapidly between 3 and 18 h after intraperitoneal implantation into normal syngeneic mice and this Ig was recovered by elution with basic or acid buffers. The Ig eluted from the L5178Y lymphoma showed higher binding to the L5178Y than to thymocytes, bone-marrow cells, 1509a sarcoma and P-815-X2 mastocytoma. In addition, binding of the eluates to the L5178Y was specifically inhibited by L5178Y cells or by solubilized membrane antigens of the L5178Y. The in vivo acquisition of Ig by the L5178Y could also be blocked by the IV and IP injections of tumor antigen although both L5178Y and 1509a solubilized membrane antigens were effective. Some of the Ig acquired by the tumor cells was found to be complement-fixing antibody since normal rabbit complement lysed 80% of L5178Y cells obtained from the peritoneal cavity of syngeneic mice 18 h after implantation, but did not lyse in vitro L5178Y cells. The in vivo binding of the complement-fixing antibodies was also inhibited by tumor antigens in the same way as the acquisition of Ig detected by RIA. It was shown that the acquisition of Ig during the first 18 h of IP growth was a T-independent phenomenon because tumor cells acquire as much Ig in AT × BM mice as in sham-thymectomized controls. In a study with 11 different clones derived from the L5178Y lymphoma, a high correlation (r = 0.75, pvivo implantation and the amount of Ig bound to the cells after in vitro incubation with normal syngeneic serum. It is suggested that the rapid in vivo acquisition of Ig was due to the in vivo binding of natural antibodies to tumor cells.