Effect of Spleen Cells on Cytotoxicity by Immune Lymph Node Cells: Cell-Mediated Immune Suppression (? Enhancement) in Vitro

Abstract

Abstract The reactivity of spleen cells (SP) from C57BL mice immunized with BP8 ascites tumor was assessed in an in vitro assay system for cell-mediated immunity. In this system it has been shown previously that immune lymph node cells (ILNC) obtained 5 to 7 days after subcutaneous immunization are capable of killing the tumor cells. The activity of these ILNC could be blocked completely by microliter amounts of hyperimmune sera possessing enhancing activity in vivo. Normal C47BL SP, normal C3H SP, SP from C3H mice bearing the ascites tumor, and SP from C57BL mice immunized with Freund's adjuvant were all incapable of killing the tumor cells in culture. SP obtained from C57BL mice 5 to 7 days post-immunization were inactive. Hypotonic treatment did not modify these results. Lymphocyte-mediated cytotoxicity (LCT) was observed with SP obtained 9 days or longer after subcutaneous immunization. In contrast, more direct stimulation of the spleen with intravenous immunization produced evidence of immune reactivity in SP obtained 5 days after immunization. None of the various SP capable of LCT were able to effect 100% cytotoxicity of the tumor cells. Most significantly, SP obtained 5 to 7 days after subcutaneous immunization were able to block completely the LCT of ILNC obtained from the same animals. These results suggest that a portion of the SP population is producing cells capable of LCT while another part of the population consists of cells which antagonize this effect. This antagonistic sub-population may act by interfering with ILNC-tumor cell contact or by elaborating substances which act on the ILNC. These substances could be “enhancing antibodies” or non-antibody molecules.