Altered cytokine production by specific human peripheral blood cell subsets immediately following space flight

In this study, flow cytometry was used to positively identify the specific lymphocyte subsets exhibiting space flight-induced alterations in cytokine production. Whole blood samples were collected from 27 astronauts at three points (one preflight, two postflight) surrounding four space shuttle missi ons. Assays performed included serum/urine stress hormones, white blood cel l (WBC) phenotyping, and intracellular cytokine production following mitoge nic stimulation. Absolute levels of peripheral granulocytes were significan tly elevated following space flight, but the levels of circulating lymphocy tes and monocytes were unchanged. Lymphocyte subset analysis demonstrated a decreased percentage of T cells, whereas percentages of B cells and natura l killer (NK) cells remained unchanged after flight. Nearly all the astrona uts exhibited an increased CD4/CD8 T cell ratio. Assessment of naive (CD45R A(+)) vs. memory (CD45RO(+)) CD4(+) T cell subsets was ambiguous, and subje cts tended to group within specific missions. Although no significant trend was seen in absolute monocyte levels, a significant decrease in the percen tage of the CD14(+)CD16(+) monocytes was seen following space flight in all subjects tested. T cell (CD3(+)) production of interleukin-2 (IL-2) was si gnificantly decreased after space flight, as was IL-2 production by both CD 4(+) and CD8(+) T cell subsets. Production of interferon-gamma (IFN-gamma) was not altered by space flight for the CD8(+) cell subset, but there was a significant decrease in IFN-gamma production for the CD4(+) T cell subset. Serum and urine stress hormone analysis indicated significant physiologic stresses in astronauts following space flight. Altered peripheral leukocyte subsets, altered serum and urine stress hormone levels, and altered T cell cytokine secretion profiles were all observed postflight. In addition, the re appeared to be differential susceptibility to space flight regarding cyt okine secretion by T cell subsets. These alterations may be the result of e ither microgravity exposure or the physiologic stresses of landing and read aptation to unit gravity. Future studies, including in-flight analysis or s ampling, will be necessary to determine the cause of these alterations.