Suppression of the immune response to Listeria monocytogenes. I. Immune complexes inhibit resistance

Murine infection with the facultative intracellular pathogen Listeria monocytogenes was studied as a model of cell-mediated immunity. Overwhelming lethal infection with Listeria developed when mice were given a secondary challenge with a protein antigen at the same time as Listeria infection. Three days after infection, mice immunized with ovalbumin and then challenged with Listeria and ovalbumin had up to 2.1(10)⁶ times as many viable Listeria organisms in their spleens as mice challenged only with Listeria. The suppressive effect of secondary challenge with a protein antigen was found to be antigen-specific, transient, and not dependent on route of challenge with either Listeria or ovalbumin. Secondary challenge with a protein antigen suppressed both the primary and the secondary responses to Listeria. Immune serum, or affinity-purified antibody, was found to transfer the suppressive effect to nonimmune mice. These findings demonstrate that acute formation of immune complexes causes a transient state of high susceptibility to infection with an intracellular pathogen. Possible mechanisms for, and implications of, these findings are discussed.