Stress-Induced Changes In Immune Cell Populations In Mice Exposed To Hindlimb Unloading Restraint (45.19)

Abstract

Abstract 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).