Effect of a 22-day space flight on the lymphoid organs of rats

The effect of a 22-d space flight on the lymphoid organs of rats has been investigated. It has been shown that the flight leads to hypoplasia of lymphoid organs, the spleen and thymus weight decreasing very noticeably. Histological, morphometric, and cytological examinations have demonstrated that hypoplasia of the spleen occurs due to a reduction of the number of lymphocytes and erythroid cells and hypoplasia of the thymus and lymph nodes due to a decrease of the lymphocyte number. Changes found in the lymphoid organs of the flight rats are reversible and the structure of lymphoid organs recovers 27 d postflight. Pathogenetic mechanisms of the changes developing in lymphoid organs of rats under the influence of space flight are discussed. The animal data are compared with the results of postflight medical examinations of astronauts.