Alteration in human mononuclear leucocytes following space flight

Reduced in vitro mitogen-stimulated proliferative responses have routinely been observed from astronauts' mononuclear leucocytes following space flight. This study investigated the effect of space flight on subpopulations of peripheral blood mononuclear cells from 30 shuttle astronauts prior to launch, upon landing and 3 days after flight. The total number of peripheral blood leucocytes, granulocytes and monocytes were increased after space flight (5.7 +/- 0.2 versus 7.0 +/- 0.2; 3.1 +/- 0.1 versus 5.0 +/- 0.1; and 0.16 +/- 0.02 versus 0.25 +/- 0.28 x 10(3) cells/mm3, respectively) whereas lymphocytes were decreased (2.2 +/- 0.1 versus 1.7 +/- 0.1 x 10(3) cells/mm3). Flow cytometry analysis on Ficoll-Hypaque isolated mononuclear cells upon landing revealed significant decreases in T-inducer (CD4+, Leu-8+; 32 +/- 2 versus 23 +/- 2%) and T-cytotoxic lymphocytes (CD8+, CD11b-; 17 +/- 1 versus 12 +/- 1%), and increases in monocytes (CD14+; 13 +/- 1 versus 21 +/- 1%) compared to pre-flight and post-flight samples whereas B cells (CD19+), T-helper (CD4+, Leu-8-) and T-suppressor (CD8+, CD11b+) populations did not change. Additional phenotypic analysis of these mononuclear leucocytes from 10 crew members upon landing revealed a reduction in natural killer (NK) cells (CD16+ or CD56+; 9 +/- 1 versus 3 +/- 1%) and an increase in monocytes that were negative for insulin and insulin-like growth factor-1 (IGF-1) receptor expression. Flow cytometric analysis indicated these hormone receptor negative monocytes were smaller and less granular than receptor positive monocytes. Therefore, a novel population of monocytes may be released into the peripheral blood during the stress of space flight or upon landing. These findings may explain some of the diverse in vitro immunological and endocrine changes observed in crew members following space flight.