[Structural and immunomorphological characteristics of the human thymus in embryogenesis].

The thymus glands from one hundred of 4--34-week-old human fetuses were studied by the histologic, histochemical, immunomorphologic and electron microscopic methods. The development of the organ is described from the standpoint of systemogenesis. The laying of the gland is defined at the 5th week of the fetus development, and it reflects the features of the epithelium of the head intestine organs. The differentiation of the reticuloepithelium, the population of the gland by lymphocytes and emergence of antigenic specificity on their surface state at the age of 7--8 weeks. The growth zone of the thymus reticuloepithelium, the significance of Hassal's bodies, the appearance and quantitative dynamics of two subpopulations of T-lymphocytes are described. From 11--12 till 34 weeks of fetal development the percentage of T-lymphocytes forming rosettes with sheep red blood cells virtually does not change (70--90%), while the percentage of lymphocytes forming rosettes with their own red cell increases during the same period from 23 to 70%.