[Changes in the lymphoid organs of rats during space flight]

The thymus, spleen and inguinal lymphatic nodes of rats flown for 19.5 and 22.5 days on board of the Earth artificial satellites Cosmos-605 and Cosmos-782 were examined histologically. It was shown that prolonged space flights brought about accidental involution of lymph organs due to a decrease of the lymphocytes amount. It is suggested that hypoplasia of lymph organs resulted from stress effects of space flight factors. The mass disintegration of lymphocytes and accumulation of nuclear detritus in the thymus as well as neutrophil infiltration of the spleen can be attributed to the acute stress of the reentry and weightlessness--1 g transition stages. It is emphasized that inhibition of erythroid hemopoiesis in the spleen cannot be ascribed to stress effects of space flight factors. Possible contribution of the changes found in lymph organs to the immunological state of the animal body is discussed.