Modulation of the immune response in vitro and in vivo by splenocytes from tumor-bearing mice.

Immunosuppression in mice infected with either a leukemia virus (Friend virus) or bearing a rapidly growing transplantable tumor (either a plasmacytoma or mastocytoma) was studied at the level of individual immunocytes to sheep erythrocytes both in vivo and in vitro. Immunization of mice with progressing tumors showed markedly depressed hemolytic antibody plaque responses in the spleen. Furthermore, spleen cell cultures derived from immunodepressed mice with the tumors revealed the continued impairment of antibody formation in vitro. Relatively small numbers of splenocytes from the tumor-bearing mice suppressed larger numbers of normal spleen cells from control mice. Immunosuppression in all three tumor systems could be related to subcellular factors in that cell-free extracts of the spleens and tumor bearing mice or even ascites fluid or plasma could suppress the normal antibody responsiveness of normal spleen cell cultures. The virus per se or a virus associated factor seemed important in the leukemia virus model but non-virus tumor associated or related substances seemed to be involved in the immunosuppression induced by the plasmacytoma or mastocytoma. Such results support the view that tumor related subcellular factors may be important mediators of immunologic impairment of a host's immune defense mechanism to a neoplasm.