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

Abstract

A study was conducted to clarify changes in the relationship between the region of irnrnune complex (IC) trapping by follicular dendritic cells (FDCs) and the distribution of FDC during reaction of germinal centers (GCs), and to examine the relationship between the tridiniensional shape 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 O and 42, 24 h after injection of peroxidase-antiperoxidase complex (PAP) as an IC. The specimens were immunostained for PAP trapping on serial paraffin sections, and for S-100 protein as a marker of FDCs. It was found that during the GC reaction, PAP trapping became weak and then disappeared on the basal side of developing GCs where S-100 protein-positive FDCs were still present. Al1 of the 1933 lymph follicles examined were found to trap PAP. Whereas the tridiniensional shapes of the trapping regions showed similar pattems according to the development of lymph follicles, their two-dimensional shapes varied. We suggest that FDCs in primary follicles may differentiate into FDCs in the light zone and FDCs in the dark zone in secondary follicles. To evaluate each of the compartments of a lymph follicle more accurately, investigators should pay attention to the tridimensional shape of the compartment.