Ontogenic development of T and B cells and non-lymphoid cells in the white pulp of human spleen.

The ontogenic development of lymphoid and non-lymphoid cells in human splenic white pulp was studied histologically with immunoperoxidase technique, together with that of lymphoid cells from fetal liver, bone marrow and thymus by membrane immunofluorescence assay. The primitive white pulp, which appeared as small accumulations of lymphocytes around arterioles at 14 weeks of gestation (g.w.), was mainly composed of B1 antigen-positive B cells. After the appearance of follicular structure accompanied by follicular dendritic cells (FDC) stained with anti-DRC1 antibody at 26 g.w., these perivascular structures of B cells were located in the periphery of the white pulp areas. A large number of B cells composing the perivascular structure had surface IgM (sIgM) and IgD (sIgD) from the earliest stage (14 g.w.), although this type of B cell with mature phenotype was seldom observed in fetal liver or bone marrow at this stage. It was suggested that the spleen is an important site for B-cell maturation from sIg-negative B cells observed in 10-14 g.w. fetal liver, and that FDC are not involved in this development of B cells. The organization of 9.6 antigen-positive T cells around arterioles developed 4 weeks later than that of B cells, at 18 g.w., although 11 g.w. fetal thymocytes already showed a phenotype very similar to that of infants. Interdigitating reticulum cells (IDC) stained with anti-S-100 protein serum appeared from 14 g.w. before the T-cell organization, suggesting that IDC may play an essential role in the homing of T cells.