Effects of spaceflight and PEG-IL-2 on rat physiological and immunological responses

1 Division of Biology, Kansas State University, Manhattan, Kansas 66506; 2 BioServe Space Technologies, Department of Aerospace Engineering, University of Colorado, Boulder, Colorado 80309; 3 Department of General Surgery Research, Carolinas Medical Center, Charlotte, North Carolina 28232; 4 Medical Immunotherapy Program, Texas Tech University Health Science Center School of Pharmacy, Amarillo, Texas 79106; and 5 Chiron Corporation, Emeryville, California 94608 Sprague-Dawley rats were subjected to two 8-day spaceflights on the space shuttle. Rats housed in the National Aeronautics and Space Administration's animal enclosure were injected (iv or sc) with pegylated interleukin-2 (PEG-IL-2) or a placebo. We tested the hypothesis that PEG-IL-2 would ameliorate some of the effects of spaceflight. We measured body and organ weights; blood cell differentials; plasma corticosterone; colony-forming units (macrophage and granulocyte macrophage); lymphocyte mitogenic, superantigenic, and interferon- responses; bone marrow cell and peritoneal macrophage cytokine secretion; and bone strength and mass. Few immunological parameters were affected by spaceflight. However, some spaceflight effects were observed in each flight. Specifically, peritoneal macrophage spontaneous secretion of tumor necrosis factor- occurred in the first but not in the second flight. A significant monocytopenia and lymphocytopenia were detected in the second but not in the first flight. The second mission produced bone changes more consistent with past spaceflight investigations. PEG-IL-2 did not appear to be beneficial; however, this was mostly due to the lack of spaceflight effects. These studies reflect the difficulty in reproducing experimental models by using current space shuttle conditions. pegylated interleukin-2; animal enclosure module; space shuttle; bone; lymphocyte; macrophage