Splenic regulation of cell-mediated immunity to Listeria monocytogenes

Splenectomized mice are more resistant than normal mice to infection by Listeria monocytogenes. The nature of splenic regulation of cell mediated immunity to Listeria was investigated. Splenectomized mice were reconstituted with normal syngeneic spleen cells and normal plasma from Listeria-stimulated normal donors to determine if suppression of resistance in normal mice was cellular or humoral. Mice receiving spleen cells showed no decreased resistance, but mice receiving plasma showed decreased resistance as determined from bacterial numbers in the liver. The suppressive effect was associated with plasma components having a molecular weight less than 10,000. The data suggest that a suppressor factor is produced by spleen associated cells in response to stimulation of the cell-mediated immune system.