Abstract
When mice were injected intraperitoneally with a ribonucleic acid (RNA) preparation extracted from the peritoneal mononuclear phagocytes (termed monocytes) of immunized mice, these macrophages developed cellular immunity and cellular antibodies. The peritoneal monocytes were obtained from normal mice and maintained in tissue culture bottles in a homogeneous cell population. When they were treated in vitro with an immune RNA preparation, they acquired cellular immunity, and cellular antibodies were detectable in such monocytes. These results suggest that the mononuclear phagocytic cell line constitutes a cell line responsible for antibody formation.