In chicken spleen the ellipsoid‐associated cells are precursors of follicular dendritic cells

Abstract

Splenic ellipsoid associated cells (EAC) are of hemopoietic origin, and the antigens expressed by them can be identified by monoclonal antibodies, designated 68.2 (reticular cell marker) and E5G12 (EAC and chicken dendritic cells). Follicular dendritic cells (FDC) express E5G12 but not 68.2 antigens. This observation is taken together with earlier histological findings - namely the EAC after endocytosis detach from the ellipsoid and migrate to the T dependent region, periarterial lymphoid sheath (PALS) - raised the question; if EAC could be precursors of FDC. Beta galactosidase (Gal) was intravenously injected into four week old birds and sampled at different intervals. 45 minutes after injection Gal was exclusively localized in the splenic EAC, but not in the Kupffer cells. One day later Gal positive cells appeared in the PALS and selected germinal centers (GC). In the PALS the Gal positive cells formed small clusters, which were enlarged by day two. The continuous migration of Gal positive cells and accumulation of B cells around them resulted in enlargement of the clusters, which histological appeared as GC. Double staining (Gal histochemistry and 68.2 or E5G12 immunochemistry) proved that EAC carry the Gal. Because Gal and E5G12 positive cells are present in the GC but not 68.2, therefore this antigen is shut down on the EAC during their migration. Double positive (Gal+E5G12) cells around the ellipsoid (EAC) and in the GC (FDC) clearly indicates that the EAC carried the Gal to the follicles and PALS. These experiments provided evidence for the origin of FDC in the spleen. Sponsored by OTKA:T04558