Prenatal morphogenesis of compartments of the parenchyma of the lymph nodes of domestic cattle (Bos taurus)

The article analyzes the regularities of the formation and development of the lymphoid lobules of the parenchyma of the somatic (Limphonodi cervicales superficiales) and visceral (L. jejunales) lymph nodes in domestic cattle in the fetal period of ontogenesis. We used routine histological techniques and author's modification of the impregnation of total median sections with silver nitrate. Visualization of various zones of lymphoid lobules was carried out taking into account the specific for different cell zones architectonics of reticular fibers. It has been established that signs of morphological heterogeneity of parenchyma of lymph nodes are first found in three month-old fetuses, which is associated with the concentration of lymphoid tissue along the marginal sinus. Separation of lymphoid lobules and their structural and functional differentiation are first detected in five month fetuses. In the lymphoid lobules of five month-old fetuses all structural and functional cell zones are observable, among which the regions of clonal proliferation of T and B lymphocytes are the least developed, and regions of the transit corridors for lymphocytes migrating medullary and the cords (zone of potential accumulation of plasmocytes and antibody formation) are the most developed. Structural and functional transformations of compartments in the prenatal period of ontogenesis are accompanied by a predominantly moderate increase of the relative volume of specialized T- and B-dependent zones of lobules, against a background of a gradual decrease of the volume of transit corridors for lymphocytes migrating and zone of potential accumulation of plasmocytes and antibody formation. Due to the small volume and relatively low rates of development of the lymphocytes clonal proliferation zones, the quantitative ratios of the cellular zones in lymphoid lobules of the lymph nodes of domestic cattle in prenatal ontogenesis remain relatively stable, while maintaining the maximum indices of the development of transit corridors for lymphocytes migration and medullary cords. Among the zones of lymphocytes clonal proliferation throughout the fetal period, T-dependent zones predominate, the relative volume of which is 5.0–7.5 times greater than the volume of B-dependent zones. Lymphoid lobules in the lymph nodes of the domestic cattle fetuses of all age groups are arranged along the marginal sinus in one row and have a polar structure due to the formation of lymph nodes at one pole of the lobules in the interfollicular zone. In the visceral lymph nodes (L. jejunum) of 8–9 month-old fetuses, individual lymph nodes can form in paracortical strands, on the border with the interfollicular zone