Origin of follicular dendritic cell in the chicken spleen.

The ellipsoid-associated cell (EAC) is a blood-borne phagocytic cell, residing in the antigen trapping zone of the chicken spleen. Binding and endocytosis of betaGalactosidase (betaGal) are independent from the Fc and complement receptors, because sulfated polysaccharides, in a concentration manner, inhibit the bacterial antigen uptake. The betaGal-positive cells migrate to the periarterial lymphatic sheath (PALS), the preexisting germinal centers (GC), and form clusters with B- and T-cells. betaGal, E5G12 double positive cells on the surface of the ellipsoid and in the PALS, GC and clusters prove that the EACs carry the enzyme. The EAC and the follicular dendritic cell (FDC) express, 68.2 and E5G12 and, 74.3 and E5G12, antigens, respectively. During migration the cessation of 68.2 and expression of 74.3 indicate the differentiation of EAC to FDC. By day 14 the clusters had disappeared, and in several GC the presence of double positive cells (74.3 and betaGal; E5G12 and betaGal) showed that the clusters had developed to GC. The presence of betaGal(+) cells in the PALS, where interdigitating dendritic cells (IDC) cooperate with the T-cells, suggests that in the spleen alternate routes exist for the EAC differentiation to FDC: EAC to FDC: betaGal-loaded cells in the preexisting GC; and EAC through IDC to FDC: betaGal(+) EAC in the PALS and clusters. The EAC-FDC axis works exclusively inside the spleen; therefore; this system may be operated in pneumococcus infection.