Spaceflight induces changes in splenocyte subpopulations: effectiveness ofground-based models

Spaceflight produces changes in the immune system. The mechanisms for the a lterations in immune function after spaceflight remain unclear due in part to the difficulties associated with conducting spaceflight research. The pu rpose of the following studies, therefore, was to create a groundbased prot ocol that can reproduce the immunological changes found after spaceflight, i.e., changes in splenic lymphocyte populations. Rats were exposed to eithe r flight aboard the Space Shuttle Endeavor (STS-77) or groundbased simulati ons of various components of the spaceflight experience. The ground-based m ock spaceflight was comprised of exposure to launch and landing loads and u nloading of the hindlimbs. In addition, each component of this groundbased mock spaceflight was tested separately. The results were that spaceflight r educed splenic CD4(+) T (helper/inducer) cells and CD11b(+) (neutrophils/ma crophages) cells. The ground-based simulations of spaceflight did not repro duce the same pattern of splenocyte changes. In fact, exposure to landing l oads alone increased splenic CD4(+) T (helper/inducer) cells. These finding s support the conclusion that the ground models tested did not induce simil ar changes in the immune system as did spaceflight. It is possible, therefo re, that stressors/factors unique to the spaceflight experience impact the immune system in ways that cannot be currently, fully modeled on the ground .