Suppression of the humoral immune response by particulate material extracted from spleen cell subpoulations of MOPC-315 tumor-bearing mice.

Particulate extracts were prepared from MOPC-315 plasmacytoma cells, from whole spleen cells or from splenic macrophages of MOPC-315 tumor-bearing mice. These preparations, when injected into normal mice, inhibited their primary humoral immune response to sheep red blood cells (SRBC). At the same time, particulate extracts from whole spleens or splenic macrophages of normal mice and T cell extracts from spleens of MOPC-315 tumor-bearing mice had no effect on the primary immune response to SRBC. The results suggest that phagocytic spleen cells of tumor-bearing mice contain immunosuppressive particles which originate from the tumor cells.