[Antenatal and early postnatal development of the organs of immunogenesis]

In order to reveal temporal interrelations between the lymphoid organs (the thymus, spleen, lymphatic nodes) in embryogenesis and early postnatal period, the investigation has been performed on Wistar rats. The stromal and lymphoid cells have been studied by means of general histological, histochemical methods and electron microscopically. In the antenatal period, and development of the lymphoid organs goes through several stages which continues in the early postnatal period. Three stages have been distinguished in embryogenesis: I - firm germ; II - loosening of its stroma; III - migration of lymphoid cells. Formation of the stroma of the lymphoid organs precedes their functional differentiation. Migration of the lymphoid cells into the stroma takes place only after its loosening and does not occur simultaneously in different organs. The thymus is the first to develop; the greatest proliferative activity of its all cells is observed in the second half of the intrauterine development. The mitotic index has two peaks - on the 16th and 21st days of embryogenesis. B-zones have not been revealed in the lymph nodes and spleen of the newborn rats. They form during the postnatal period.