Increased resistance and depressed delayed-type hypersensitivity to Listeria monocytogenes induced by pretreatment with lipopolysaccharide.

Intravenous injection of a small dose of lipopolysaccharide 24 h before infection with Listeria monocytogenes enhanced the resistance of mice to this organism. This protective effect of lipopolysaccharide related to the ability of nonimmune macrophages to inhibit bacterial proliferation in livers and spleens. Surprisingly, lipopolysaccharide-treated mice exhibited inferior acquired immunity, as measured by adoptive transfer of immunity to normal mice, delayed-type hypersensitivity to Listeria antigens, and uptake of tritiated thymidine by lymphocytes in the spleen. These results support the view that lipopolysaccharide stimulates a highly effective anti-Listeria immunity via the macrophage component, despite interference with the lymphocyte component.