[Development of the lymphatic follicles and the differentiation of splenic lymphocytes in the human fetus].

Spleens of more than 100 human fetuses at the age of 5-34 weeks of development have been studied by means of immunofluorescent methods to identify T- and B-lymphocytes. The spleen lymphatic follicles are detected at the 12th-14th weeks of the embryonal development. Within the same range of time in the mononuclear suspension of the organ T- and B-lymphocytes are defined. The critical period is stated when certain density of lymphocytes and the portion of T- and B-lymphocytes is established in the organ and it is not changed up to the end of embryogenesis. After the 22nd week, the reticular stroma of the lymphatic follicle acquires a complex structure. The following zones can be determined in it: the periarterial where thymus-dependent cells are situated, the zone where thymus-independent cells are situated and the marginal zone surrounding the whole lymphatic follicle.