The effectof a 10-day space flight on the function, phenotype, and adhesion molecule expression of splenocytes and lymph node lymphocytes

Previous studies have indicated that space flight affects the activation of lymphocytes from humans, monkeys, and rodents. In rats, where lymphocytes from blood, spleen, and lymph nodes have been tested, the accumulated data suggest that the effects of flight on various cells are lymphoid organ- specific. Thus, cells may be affectedby variations in trafficking brought about by fluid shifts in microgravity (<10⁻³ g). In this study we examined lymphocyteactivation (IL-2 production) as well as the expression of surface differentiation antigens and of adhesion molecules by splenocytes and lymph node lymphocytes (LNL) after a 10-day flight (Space Shuttle Mission STS-57). For splenocytes and LNL from flight (FLT) animals, IL-2 production decreased in response to the T cell receptor-independent mitogen 12-O- tetradecanoylphorbol-13-acetate plus ionomycin, but was not affected by stimulation with the T cell receptor-dependent mitogens Concanavalin A or phytohemagglutinin. In addition, thepercentage, as well as fluorescent intensity, of splenocytes which expressed CD8, CD4, or kappaincreased after flight. The percentage of LNL expressing CD2 also increased but those expressing CD5 decreased. The percentage of cells expressing theintegrins LFA-1 α and β increased with splenocytes from FLT animals but decreased for LNL. In contrast, FLT animals showed a decreasein the percentage of selectin-positive splenocytes. ICAM-1 expression did not change. In summary, these data are consistent with a model in which microgravity affects lymphocyte redistributionamong organs, which in turn influences the activationpotential of the cells.