[CHARACTERISTICS OF THE REACTIONS OF THE SPLEEN LYMPHOID STRUCTURES IN MICE IN A TERRESTRIAL EXPERIMENT AND AFTER A PROLONGED SPACEFLIGHT].

Morphometric methods were used to examine the cell composition of the germinal centers of lymphoid nodules and periarteriolar lymphoid sheaths (PALS) in male C57/b16 mice aged 19-20 weeks after 30-day-long space flight, simulation of space flight factors in a terrestrial experiment and in vivarium control group. After a ground-based experiment, compared to vivarium control, the functional activity of morphological zone of T lymphocyte maturation was decreased in PALM. In the germinal centers of lymphoid nodules of mice subjected to a ground-based experiment, lymphocytopoiesis and cell blast transformation, that characterize the morpho-functional activity of this zone and humoral immunity, remained unchanged. After a spaceflight, as compared with ground-based experiment, the changes of cell composition were less expressed in PALS than in the in the germinal centers of lymphoid nodules. It is concluded that PALS are more stable morphological zones, while the germinal centers of lymphoid nodules in the spleen are specific "target zones", most sensitive to a variety of factors of a space flight.