Ultrastructural localization of S-1 00 protein in rat popliteal lymph nodes, and very slight proliferative activity of follicular dendritic cells

Abstract

The purposes of this study were to examine the tissue distribution of S-100 protein in rat lymph nodes at the ultrastructural level with respect to the relationship between follicular dendritic cells (FDCs) and antigen transporting cells (ATCs), and to determine whether FDCs increase after secondary stimulation with sheep red blood cells (SRBCs). We examined the ultrastructural localization of S-100 protein in rat popliteal lymph nodes, and the density of S-100 proteinpositive FDCs in lymphoid follicles, after secondary stimulation with SRBCs, on paraffin wax sections. We found S-100 protein expression in FDCs in al1 regions of lymphoid follicles, although FDCs in the central portion of lymphoid follicles showed stronger reactions than FDCs in the periphery. S-100 protein recognized ATCs weakly. At the border between the subsinus layer and the lymphoid follicles, ATCs were very close to FDCs. There were only two mitotic S-100 protein-positive cells in the lymphoid follicles of al1 specimens. The density of S- 100 protein-positive FDCs in the lymphoid follicles in secondary stimulated rats was significantly lower than in primary stimulated rats. We suggest that S-100 protein expression reflects FDC development and supports a close relationship between FDCs and ATCs. FDCs may have only very slight proliferative activity, though the FDC density in the lymphoid follicles decreased after secondary stimulation