Splenic Regulation Of Cell Mediated Immunity To Listeria Monocytogenes: Suppression Of Macrophages

Splenectomized mice are more resistant than normal mice to infection by Listeria monocytogenes. It has been suggested that splenectomized mice have increased phagocytic activity. The nature of splenic regulation of macrophage activity was investigated. To determine if suppression was cellular or humoral, splenectomized mice were reconstituted with normal syngeneic spleen cells and normal plasma from Listeria-stimulated normal donors. Mice receiving spleen cells showed no decreased resistance by mice receiving plasma showed decreased resistance as determined from bacterial numbers in the liver. The suppressive effect was found to be associated with plasma components having a molecular weight of less than 10,000. The data suggest that a macrophage suppressor factor is produced by spleen-associated cells in response to stimulation of the cell mediated immune system. This factor may act in the same manner as suppressor factors produced in response to tumor development and may modulate macrophage activation. The development of an in vitro model and the isolation and characterization of the factor and its cellular source await further investigation