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The hindlimb unloading (HU) rodent model was developed to simulate some of the aspects of spaceflight conditions. Our previous studies showed that exposure to HU for 48 h (h) followed by bacterial challenge, reduces the ability of mice to resist infection. The purpose of this study was to investigate the physiological changes in mice during the 48 h of exposure to HU to understand the mechanisms involved in the increased susceptibility to infection observed in mice subjected to these conditions. Female Swiss Webster mice were hindlimb-unloaded during 48 h. Blood samples, spleen and peritoneal cells were removed before and after 18 or 48 h of HU-exposure. Leukocyte subset analysis was performed in spleen and peritoneal cells by flow cytometry, and catecholamine levels were measured in plasma and whole spleen by a catecholamine enzyme immunoassay. Catecholamine levels measured in plasma and spleen were significantly greater in mice exposed to HU compared to control. This increase coincided with significant ...

Toxoplasma gondii often migrates to the central nervous system in immunocompromised patients, where it induces a severe inflammation referred to as Toxoplasma encephalitis. The mechanisms involved in control of parasite multiplication and prevention of Toxoplasma encephalitis remain unclear. The objective of the present study was to characterize the inflammatory response in the brains of mice during acute T. gondii infection, with emphasis on the expression of chemokine receptors. Susceptible C57BL/6 mice were orally infected with 10 cysts of the low-virulent ME49 strain of T. gondii. Levels of cytokines (TNF-alpha, IFN-gamma, IL-10, IL-6, and IL-12p70) and chemokines (CCL/2MCP-1) were measured in plasma at 5, 10, 15, 20, and 30 days after infection. In addition, the mRNA expression of chemokines (CCL5/RANTES, CCL2/MCP-1, CCL4/MIP-1beta) and chemokine receptors (CCR1, CCR2, CCR5, CCR7, CCR8, CXCR4, and CXR5) were measured in brain tissues at the same time points. Plasma levels of IFN-gamma and CCL2/MCP-1 were highly expressed at day 5, whereas TNF-alpha had a moderate increase at day 5, peaked at day 10, and returned to normal levels by day 30. Plasma levels of IL-10, IL-6, and IL-12p70 were not detected throughout the study. Analyses of mRNA expression of chemokines and chemokine receptors in the brain showed that CCL5/ RANTES, CCR7, CXCR4, and CXCR5 were upregulated, peaking after 10 days of T. gondii infection. IgM-specific antibody levels increased at day 5 and peaked at days 10 and 30, whereas IgG levels increased at day 10 and continued to increase thereafter, reaching maximum levels at day 30 postinfection (PI). Our results suggest that T. gondii infection is controlled at local and systemic levels, and that proinflammatory proteins and their receptors may be acting coordinately to induce stage conversion and prevent parasite multiplication and development of Toxoplasma encephalitis. The early production of IFN-gamma and the delayed expression of CXCR4 and CXCR5 indicate that T. gondii induces an early robust cellular immune response, followed by a strong and sustained antibody-mediated immunity.

Hindlimb unloading (HU) is a rodent model that has been successfully used to simulate some of the aspects of space flight including alterations of the immune system. We have shown in previous studies that exposure of mice to HU results in significantly increased plasma norepinephrine levels, decreased IL-6 and TNF-α from LPS stimulated spleen cell supernatants, and increased susceptibility to bacterial infection compared to control mice. The purpose of this study was to examine the populations of immune cells affected by HU to better understand the mechanisms by which HU induced changes in susceptibility to infection. Spleens from HU or control normally caged mice were asceptically removed after 18 or 48 hours of HU exposure, weighed, and analyzed for cell antigen marker expression. Spleen weights were significantly reduced in the HU group with no significant changes in body weights. Flow cytometric analyses revealed that the percentage of splenic CD19+ B cells in mice exposed to HU was significantly reduced at both 18 and 48 hr following HU commencement compared to controls. CD4:CD8 ratios declined from control 2.3 to 2.2 with 18 hr HU and to 1.9 with 48 hr HU. These results suggest that lymphocyte sub-population changes may contribute to the dysregulation of immunity in mice exposed to HU and the subsequent reduced ability of these mice to resist infections. Funded in part by a grant from the Amino Up Chemical Company (Sapporo, Japan).

In spite of the use of modern techniques, infection continues to be a leading cause of death in patients subjected to severe trauma and surgical wounds. Previous studies have shown that AHCC, a natural compound, increases survival and prolongs the time to death in a murine model of surgical wound infection. This model simulates some of the conditions that occur after trauma or surgical procedures including systemic infection and food deprivation. To better understand the mechanisms involved in this model, food-deprived mice receiving either AHCC or the excipient were infected with sub-lethal doses of Klebsiella pneumoniae. Organ bacterial load, plasma levels of cytokines, and differential white blood cell counts were determined at different time points after infection. In contrast to control mice, which did not clear bacteria from organs, mice receiving AHCC had significantly reduced numbers of bacteria at day 5 and cleared bacteria entirely from the system at day 6. Levels of IL-12, TNF-α, and IL-6 peaked earlier in this group (day 3) compared with controls (day 5). AHCC also induced a significant increase of numbers of macrophages at day 2 and lymphocytes at day 3. Additional studies indicated that AHCC improved the function of peritoneal cells as measured by nitric oxide production and spleen cell proliferation affected by food deprivation in this model. Taken together, these results suggest that AHCC protects mice restoring the immune system and promoting effective clearance of bacteria and, consequently, a rapid recovery. Funded in part by a grant from the Amino Up Chemical Company, Sapporo, Japan.