Microgravity Inhibits Resting T Cell Immunity in an Exposure Time-Dependent Manner

Background: Decline immune function is well documented after spaceflights. Microgravity is one of the key factors directly suppressing the function of immune system. Though T cell immune response was inhibited by microgravity, it is not clearly whether activation would be inhibited after a pre-exposure of microgravity on T lymphocytes at the resting state. Methods: We herein investigated the response ability of resting CD4(+) and CD8(+) T cells experiencing pre-exposure of modeled microgravity (MMg) for 0, 8, 16 and 24 hrs to concanavalin A (ConA) stimulation. The phenotypes and subsets of immune cells were determined by flow cytometry. Results: Both CD4(+) and CD8(+) T cells with an MMg pre-exposure exhibited decreased expressions of activation-markers including CD25, CD69 and CD71, inflammatory cytokine secretion and cell proliferation in response to ConA compared with T cells with 1g controls in an MMg exposure time- dependent manner. Moreover, short term MMg treatment caused more severe decreased proliferation in CD4(+ )T cells than in CD8(+) T cells. Conclusions: MMg can directly impact on resting T cell subsets. CD4(+ )T cells were more sensitive to the microgravity inhibition than CD8(+) T cells in respect of cell proliferation. These results offered new insights for the MMg-caused T cell functional defects.