Effect of acute nutritional deprivation on immune function in mice. II. Response to sublethal radiation.

Previous studies from this laboratory indicated that mice starved for 48 or 72 hr were resistant to the intracellular pathogen, Listeria monocytogenes. In the present experiments, we investigated the possibility that rapidly proliferating monocytes were responsible for the early protective effect observed in these mice. Confirming previous studies, the numbers of L. monocytogenes in livers and spleens of starved mice were 2-3 logs lower than those of fed mice 72 hr after inoculation of bacteria. The early protective effect of starvation could be eliminated completely by nonlethal doses of radiation (200-900 rads). Organ bacterial counts in starved-irradiated mice were similar to those of fed mice. Correlative histopathologic studies were carried out on all three groups of mice. Seventy-two hours after challenge with L. monocytogenes, the livers of fed mice had multiple microabscesses with cental necrosis and a poor mononuclear response. In contrast, livers of starved mice had fewer infectious foci, less necrosis, and a more prominent monocyte/macrophage inflammatory response. Similar to fed mice, the livers of starved-irradiated mice had marked necrosis and few monocytes/macrophages. In addition, the number of peripheral blood monocytes in starved mice was increased 72 hr after inoculation compared to fed and starved-irradiated mice. The data from these experiments suggest that a proliferating population of monocytes is responsible for resistance of starved mice against L. monocytogenes.