Effector function of hepatocytes and Kupffer cells in the resolution of systemic bacterial infections.

It has been suggested that mononuclear phagocytes serve as the principal site of replication for a number of intracellular pathogens including Listeria monocytogenes. To determine the role of the tissue macrophages (Kupffer cells) in the proliferation of Listeria taken up in the liver, the hepatic cell populations were purified and the associated bacteria were quantified at periodic intervals postinfection. Here we report that the bulk of Listeria injected intravenously into nonimmune mice replicated within hepatocytes rather than Kupffer cells. Whereas a 200-fold increase in the number of hepatocyte-associated Listeria occurred during the first 3 days following infection, a relatively small (less than 2-fold) increase in number of Kupffer cell-associated Listeria was observed. The Listeria injected intravenously into immune animals, on the other hand, were eliminated rapidly from the hepatocyte as well as the Kupffer cell population. The latter findings suggest that uptake and elimination of pathogenic organisms by "non-professional phagocytes" in the liver (i.e., hepatocytes) may be an important effector mechanism in host defenses.

Acute starvation in mice reduces the number of T cells and suppresses the development of T-cell-mediated immunity.

Experiments were performed to determine the effect of starvation on T-cell mediated host defences. In mice starved for 72 hr, the number of thymocytes fell by 98%, spleen cells by 82% and peripheral blood cells by 44%. By 7 days after the end of starvation, values had returned to within 50% of baseline. The percentage of L3T4 and Lyt-2 antigen-bearing cells fell in the thymus, but the percentage of Thy-1.2-positive cells did not change. Starvation decreased the percentage of lymphocytes in peripheral blood but increased the percentage of granulocytes. During starvation, the cellularity in thymuses, spleens and peripheral blood was preserved in adrenalectomized mice compared to normal or sham-adrenalectomized mice. Confirming previous results of ours, starved mice were resistant to i.v. challenge with Listeria monocytogenes immediately after starvation. However, when starved mice were immunized with a sublethal dose of Listeria immediately after starvation and challenged 3-4 weeks later, they were less resistant to Listeria than fed, immunized mice. Similarly, spleen cells of starved, immunized mice had a reduced capacity to transfer immunity passively to non-immune mice. Increasing the immunizing dose of Listeria in starved mice increased the level of immunity that developed. These data indicate that starved mice have a marked reduction in T-cell cellularity, possibly related to corticosteroid production during the stress of starvation. Although starved mice were relatively resistant to Listeria immediately after starvation, they had a reduced capacity to develop T-cell mediated immunity to Listeria. This deficiency could be partly overcome by increasing the immunizing dose of Listeria.

Analysis of colony-stimulating factors and macrophage progenitor cells in mice immunized against Listeria monocytogenes by adoptive transfer.

Experiments were performed to elucidate the role of colony-stimulating factors in host defenses to the intracellular pathogen Listeria monocytogenes. Mice were protected against Listeria sp. by adoptive transfer of immune spleen cells and were then challenged with listeriae intravenously. Control mice were injected with spleen cells from uninfected mice. Adoptively immunized (immune) mice had significantly fewer listeriae in spleens and livers 2 and 4 days after Listeria challenge than did control mice. During acute infection, colony-stimulating activity in serum was increased earlier (10 h) in immune mice than in controls. Concentrations of colony-stimulating activity were equal at 24 h. By 48 h, values were decreased in immune mice, but were elevated in control mice. Similar changes were noted when a specific colony-stimulating factor, macrophage colony-stimulating factor, was measured in serum by using a radioimmunoassay. The changes in serum colony-stimulating activity in mice adoptively immunized with immune spleen cells were eliminated if spleen cells were first treated with anti-Thy-1.2 monoclonal antibodies. The number of macrophage progenitor cells in bone marrow and spleen were also determined as measures of the hemopoietic potential in these organs. The number of macrophage progenitor cells in bone marrow was higher in immune animals than control animals at 1, 2, and 4 days of infection. Similarly, the number of these cells in spleens was higher during the early stages of infection in immune mice. These results indicate that both the regulation of leukocyte production and the transfer of specific cellular immunity by spleen cells are associated, and they therefore suggest that hemopoietic regulatory factors play a role in immune host defenses.

Effect of acute nutritional deprivation on macrophage colony-stimulating factor and macrophage progenitor cells in mice.

The effect of short-term nutritional deprivation on host defenses and on the parameters of macrophage production was determined in outbred mice. Confirming previous data from this laboratory, initial experiments demonstrated that starved mice were relatively resistant to infection by Listeria monocytogenes as determined by spleen and liver bacterial counts. The number of macrophage progenitor cells in bone marrow rose slightly during a 72-h starvation period and returned to normal during refeeding. By contrast, the number of progenitor cells in spleens fell to 12% of the base line during starvation. The concentration of the macrophage colony-stimulating factor in serum decreased during starvation and returned to normal during refeeding. Additional experiments were performed to determine whether starved mice had increased parameters of macrophage production during listerial infection. The number of progenitor cells in the bone marrow and spleens of starved mice had increased compared with that of fed mice early in infection. Macrophage colony-stimulating factor levels in starved mice rose early and remained elevated during infection but were not as high as in fed mice. These data document the changes in the parameters of monocyte production during starvation and suggest that the number of macrophage progenitor cells may be related to increased resistance to L. monocytogenes.

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.

Effect of acute nutritional deprivation on immune function in mice. I. Macrophages.

This study was designed to explore the effects of acute nutritional deprivation (starvation) on macrophage function in mice. In vivo macrophage activity was increased by starvation, as determined by multiplication of Listeria monocytogenes in both spleens and livers after intravenous injection. Similarly, in vitro studies revealed that the capacity of peritoneal macrophages to kill listeria was enhanced by starvation. This function was increased further by the addition of small concentrations of lipopolysaccharide (LPS; 10-100 ng/ml). The bactericidal activity of macrophages from starved mice, however, did not reach the levels observed with macrophages from BCG-infected mice. Furthermore, LPS did not appear to be an important second signal for macrophage activation in vivo, as LPS-unresponsive mice (C3H/HeJ and A/J) were protected by starvation. In contrast to these results we found that starved mice were not protected against Toxoplasma gondii infection and that macrophages from starved mice were unable to prevent multiplication of toxoplasma trophozoites in vitro. In toto, these experiments suggest that macrophage function is enhanced by starvation, but that this enhancement is not sufficient to fulfill all criteria for macrophage activation.