EFFECT OF SLS-2 SPACEFLIGHT ON IMMUNOLOGICAL PARAMETERS OF RATS

During the Spacelab Life Sciences-2 mission, rats were dissected in sp ace and biosamples were returned to Earth for analysis, Immunologic st udies addressed the kinetics of T lymphocyte proliferative responses, cytotoxic activity of natural killer cells, and cytokine production. E xperiments were performed by using spleen and bone marrow of rats diss ected before flight, during flight, immediately after landing of the s pace shuttle (R + O), or 14 days after landing (R + 14), as well as th ose of respective control animals. Each group consisted of five male S prague-Dawley rats. It was demonstrated that T lymphocyte activity of rats dissected in flight was significantly decreased compared with the controls. This was observed during 48-, 72-, and 96-h cultivation and stimulation with the following mitogenic stimuli: concanavalin A (Con A; 0.1, 1.0, and 10.0 mg/ml), phytohemagglutinin (PHA; 2.5 mg/ml), an d interleukin-2 (IL-2; 1 U/ml). The cell proliferation rate in rats di ssected immediately after landing did not decrease, whereas that in ra ts dissected at R + 14 increased. The activity of spleen natural kille r cells was reduced in response to Cr-51-labeled target cells during f light (YAC-1 and K-562) and after flight (YAC-1). At R + 14, their act ivity returned to normal. Another technique employed to measure natura l cytotoxicity, using [H-3]uridine-labeled target cells and ribonuclea se, did not reveal any differences between control and experimental gr oups. In bone marrow, the activity of natural killer cells did not var y significantly. The production of IL-1, IL-2, tumor necrosis factor ( TNF)-alpha, and TNF-beta in spleen cell cultures of the flight rats wa s reduced. At R + O, IL-1 and TNF-P levels remained lowered, whereas T NF-alpha was increased. At R + O, interferon-alpha and interferon-gamm a levels were diminished. In summary, cell-mediated immunity in rats w as significantly suppressed during flight. The lime course variation o f immune parameters after flight suggests that tile changes may truly indicate a response of the immune system to spaceflight conditions tha t could increase over time.