The proliferation site of B-lymphocytes and the role of follicular dendritic cell in secondary lymphoid follicle of the tonsil.

The proliferation site of B lymphocytes in secondary lymphoid follicle of the tonsil was evaluated. Five follicles were selected to detect histon H3 mRNA as marker of cells in S-phase of the cell cycle by in situ hybridization. Moreover, 11 follicles were selected and stained immunohistochemically with serial frozen sections with cyclin B1 as a G2-M phase marker, p34cdc2 as a marker mainly of G2-M phase, cyclin E as a marker mainly of late G1 phase, and Ki-67 as a marker of cells in the cell cycle. Secondary lymphoid follicles were divided into five zones by the HE stain and the expression of CD23 (Fc e receptor II) to calculate the positive rate of histon H3 mRNA and these proteins. The positive rates of histon H3 mRNA, cyclin B1, and p34cdc2 were the highest in the dark and the outer zones. The result implies that the outer zone as well as the dark zone is a proliferatation site of B cells.Nextly, the phase of the cell cycle of B cells in the follicular dendritic cell (FDC)-lymphocytes clusters, which were obtained from the germinal center of the secondary lymphoid follicle of human tonsils, is evaluated. The rate of cyclin B1-positive lymphocytes in the cluster (4.6%) is lower than that of the lymphocytes out of the cluster in germinal center (27.7%) and, moreover, the rate of Ki-67-positive cells in the cluster (35.9%) is lower than that of cells out of clusters (61.5%). The result shows that few G2-M phase lymphocytes are retained in the FDC-lymphocytes clusters and support that the B lymphocytes actively do not proliferate in the clusters.