SKELETAL UNLOADING CAUSES ORGAN-SPECIFIC CHANGES IN IMMUNE CELL RESPONSES

The effects of skeletal unloading using antiorthostatic tail suspensio n on the mouse immune system are tissue specific. This phenomenon was demonstrated by analyzing cells from the lymph nodes, spleen, and bone marrow. Phytohemagglutinin-induced T-cell proliferation was depressed in lymph nodes after 11 days of antiorthostatic suspension. In contra st, splenic T-cell proliferation in response to phytohemagglutinin was enhanced. Splenic natural killer cell cytotoxicity was unchanged afte r suspension, which demonstrated the organ- and cell-specific effects of skeletal unloading. Whereas antiorthostatic suspension induced mini mal changes in bone, there was a significant depression in the number of macrophage precursors in the bone marrow. Overall, skeletally unloa ded animals had slightly higher blood corticosterone levels than did c ontrol animals; however, it did not appear to be responsible for the o bserved changes. In conclusion, skeletal unloading produces organ- and cell-specific changes in the murine immune system rather than a gener alized immunosuppression.