Leukocyte subsets and neutrophil function after short-term spaceflight

Changes in leukocyte subpopulations and function after spaceflight have bee n observed but the mechanisms underlying these changes are not well defined . This study investigated the effects of short-term spaceflight (8-15 days) on circulating leukocyte subsets, stress hormones, immunoglobulin levels, and neutrophil function. At landing, a 1.5-fold increase in neutrophils was observed compared with preflight values; lymphocytes were slightly decreas ed, whereas the results were variable for monocytes. No significant changes were observed in plasma levels of immunoglobulins, cortisol, or adrenocort icotropic hormone. In contrast, urinary epinephrine, norepinephrine, and co rtisol were significantly elevated at landing. Band neutrophils were observ ed in 9 of 16 astronauts. Neutrophil chemotactic assays showed a 10-fold de crease in the optimal dose response after landing. Neutrophil adhesion to e ndothelial cells was increased both before and after spaceflight. At landin g, the expression of MAC-1 was significantly decreased while L-selectin Tva s significantly increased. These functional alterations may be of clinical significance on long-duration space missions.