A CHANGE IN THE LOCALIZATION OF THE REGION TRAPPING IMMUNE-COMPLEXES IN RAT POPLITEAL LYMPH-NODES DURING DEVELOPMENT OF GERMINAL-CENTERS, WITH REGARD TO THE DISTRIBUTION OF FOLLICULAR DENDRITIC CELLS

A study was conducted to clarify changes in the relationship between t he region of immune complex (IC) trapping by follicular dendritic cell s (FDCs) and the distribution of FDC during reaction of germinal cente rs (GCs), and to examine the relationship between the tridimensional s hape of the IC-trapping regions and their two-dimensional shape. Five- week-old rats were given footpad injections of sheep red blood cells, and then their popliteal lymph nodes were excised between days 0 and 4 2, 24 h after injection of peroxidase-antiperoxidase complex (PAP) as an IC. The specimens were immunostained for PAP trapping on serial par affin sections, and for S-100 protein as a marker of FDCs. It was foun d that during the GC reaction, PAP trapping became weak and then disap peared on the basal side of developing GCs where S-100 protein-positiv e FDCs were still present. All of the 1933 lymph follicles examined we re found to trap PAP. Whereas the tridimensional shapes of the trappin g regions showed similar patterns according to the development of lymp h follicles, their two-dimensional shapes varied. We suggest that FDCs in primary follicles may differentiate into FDCs in the light zone an d FDCs in the dark zone in secondary follicles. To evaluate each of th e compartments of a lymph follicle more accurately, investigators shou ld pay attention to the tridimensional shape of the compartment.