Effects of long duration spaceflight on human T lymphocyte and monocyte activity

Experiments were performed on blood samples from 5 cosmonauts in order to investigate the effects of long duration spaceflight (26 to 166 days) on immune activity. The experiments were performed on cultured mononuclear cells purified from blood samples collected during the preflight period and 24 h after landing. The production of interleukin 2, which is the major cytokine involved in T lymphocyte proliferation, was found to be enhanced after flight in some individuals, whereas the ability of mitogen-stimulated cells to express interleukin 2 receptor was impaired 24 h after flight for two cosmonauts out of five. Normal interleukin 2 receptor expression was obtained in all cases when lymphocytes were directly activated by a protein kinase C activating phorbol ester. On the other hand, no significant changes were observed in interleukin 1 production by cultured peripheral blood mononuclear cells. Lastly, the distribution of T lymphocytes subsets was examined in peripheral blood sampled 24 h after landing and was found to be within normal values.