Enhancement of normal lymphocyte cytotoxicity by sera with high antibody titers against H-2 or virus-associated antigens.

The experiments reported in this paper were designed to investigate the in vitro interaction of immune sera with different antibody titers as determined by indirect mem brane immunofluorescence (MF) with normal or immune lymphoid cells in mediating target cell destruction. Target cells in these experiments were two Moloney sarcoma virus (MSV)-induced tumor cell lines derived from BALB/c and C57BL mice. The sera were collected from male BALB/c x DBA Fl mice hyperimmunized with MSVinduced tumor cells of C57BL origin (allogeneic serum), from BALB/c mice following the complete regression of MSV-induced tumors (regressor serum), and from BALB/c mice with progressively growing MSV-induced tumors (progressor serum). The in vitro investigations were per formed utilizing a 51Cr microcytotoxicity assay for demon strating cell-mediated cytotÃ2xicity against monolayer tar get cells which is described in this paper. The results demonstrated that sera with high MF anti body titers (allogeneic, regressor) directed against H-2 and/or MSV-induced antigens enhanced the cytotoxic activity of normal lymphoid cells for target cells carrying these antigens and this enhancing effect was directly re lated to the MF titer of the serum. Sera from mice with progressively growing MSV-induced tumors were gen erally ineffective in mediating this activity. The progres sor sera contained low antimembrane antibody titers. The enhancing factor in high-titered serum was removable by absorption with appropriate cells. The antibody-mediated lymphocyte cytotÃ2xicity was not as apparent with im mune cells as with normal lymphoid elements. The re lationship of these findings to those previously reported on the in vivo effects mediated by these same sera on tu mor growth is discussed.