[Splenic lymphoid structures reorganization in gerbils after space flight].

To assess the effects of weightlessness on the organism of mammals, splenic lymphoid tissue was studied in 10 intact Mongolian gerbils and in 10 animals after a 12-days-long spaceflight. In experimental animals the body mass and splenic, thymic and adrenal mass indexes were sharply reduced. In the spleen, the red pulp area was significantly increased, there appeared the areas of fibrous tissue proliferation, and extensive hemorrhage. Lymphoid nodules with germinal centers disappeared, while periarterial lymphoid sheaths were depleted. Quantitative analysis of cellular content of the lymphoid structures of the spleen showed dramatic activation of cell destruction, lymphocytopoiesis suppression with the disappearance of mitotically dividing cells and a decrease in the number of blast cells. The absence of plasma cells indicates the suppression of the processes of the immunocytopoiesis. The complex of changes noted suggests the decrease of immunological barrier of lymphoid tissue in the spleen and in the whole organism, in gerbils under the conditions of weightlessness in the spaceflight.