Localization of splenic cells with antigen-transporting capability in the chicken

The objective of the present study is to investigate the migration pattern of the splenic dendritic cell of the chicken named the ellipsoid-associated cell (EAC) from the site of initial location at the periphery of the ellipsoid to the splenic T- and B-dependent areas.

Bovine serum albumin bound to biotin and conjugated to gold particles was used as a histochemically identifiable antigen detected as a peroxidase reaction. The antigen was intravenously injected, and subsequently its pattern of distribution in a time sequence and within the tissue was examined at the light and electron microscopy levels. In addition, an hour prior to sacrifice, the chickens received a single injection of the thymidine analogue 5-bromo-2'-deoxyuridine, in order to quantify the number of DNA synthesizing cells and to establish a relationship between the migrating EAC and the rate of mitosis in the white pulp.

The observations showed that between 12 hours and 3 days after the second antigen administration the labeled EAC, which was first located around the ellipsoid, progressively reached further areas with time towards the periarteriolar lymphoid sheaths, where newly formed germinal centers appeared. Furthermore, the rate of cell proliferation within the white pulp was associated with the arrival of the antigen-transporting EAC.

The results suggest that migrating EAC have a role as both antigen-transporting cell and antigen-presenting cell in the T- and B-dependent areas, as a result of which migrating EAC is transiently found in periellipsoidal white pulp, then periarteriolar lymphoid sheaths, and finally germinal centers, where it may function as an interdigitating cell or as a follicular dendritic cell, depending on its location. Thus, we conclude that the EACs are precursors of both interdigitating and follicular dendritic cells.