Macrophage function in senescence.

Although the parenteral injection of dextran sulfate 500 (DS 500; 50 mg/kg body weight) into 22-month-old NMRI mice resulted in a complete loss of resistance when administered 1 day before the sublethal (4.5 X 10(3)) infection with Listeria monocytogenes, the consequences in aged animals were less dramatic than in young adult (2- to 3-month-old) controls. This was documented by prolonged survival times as well as reduced numbers of Listeriae in spleen. This indicates that aged mice possess an increased paghocytic capacity, as compared to young adult animals. In aged mice the DS 500-induced loss of resistance could be completely abolished by pretreatment with 3 X 10(9) heat-killed Bordetella pertussis organisms 4 days before the DS 500 injection, i.e., 5 days before listeric infection. This indicates that aged NMRI mice possess remarkable reserves in phagocytic activity.