Concomitant induction of an inflammatory response and immunosuppression by an extract from Listeria monocytogenes

An immunosuppressive agent (ISA) present in an aqueous extract from Listeria monocytogenes diminished the immune response in vivo to subsequently injected heterologous antigen. Intraperitoneal injection of ISA induced an inflammatory response and activation of the reticuloendothelial system, both of which coincided with the period of immune hyporesponsiveness. Mice treated with ISA exhibited increased accumulation of labelled antigen to phagocytic peritoneal cells but decreased delivery of labelled antigen to the spleen. Both delivery of antigen to spleen and the immune response could be improved by injecting either ISA or antigen or both intravenously, or by increasing the dose of antigen. The response of ISA-treated animals could also be improved by intraperitoneal injection of latex beads, colloidal carbon, or carrageenan shortly (60 min) before immunization. Spleen cells from ISA-treated mice adoptively transferred to irradiated syngeneic recipients were able to mount a normal immune response. These results suggest that ingestion of antigen by the enlarged population of phagocytes in peritoneal cavities of ISA-treated mice prevented antigen delivery to the spleen and was partly responsible for the observed immunosuppression.