Increased natural resistance to Listeria monocytogenes in senescent mice correlates with enhanced macrophage bactericidal activity.

Natural resistance to Listeria monocytogenes is increased in aging (18-22-month-old) AB6F1 mice when compared to their younger counterparts. We have investigated several parameters of macrophage function of old AB6F1 mice to establish what macrophage characteristics determine their enhanced resistance to Listeria. Senescent mice had an increased number of macrophages present in unstimulated peritoneal cavity. These macrophages exhibited enhanced bactericidal activity and H2O2 production. Old mice showed a diminished subcutaneous inflammatory response. Kupffer cells obtained from normal uninfected old mice had good levels of listericidal activity, but Kupffer cells obtained from normal young mice could not kill Listeria. The increased natural resistance to Listeria monocytogenes seen in old AB6F1 mice could be the result of enhanced macrophage bactericidal activities in the liver prior to the infection.