The follicular dendritic cell network in secondary follicles of human palatine tonsils and spleens

Abstract

The structure of germinal centres (GCs) in human secondary lymphatic organs has not been thoroughly investigated until now. We stained follicular dendritic cells (FDCs) in serial sections of human hyperplastic tonsils and spleens to compare the morphology of GCs in fulminant immune reactions and quiescence. Detection of CD35, CD21, CD23 and the target of mAb CNA.42 confirmed that full-blown human tonsil GCs may consist of four regions, the dark zone, the basal and apical light zone and the outer zone. The outer zone was, however, not a constant feature of tonsillar GCs and existed only in a minority of follicles in most specimens. Thus, between 3 and 60% of tonsil GCs with a CD23⁺ apical light zone exhibited an outer zone in individual specimens. FDCs in tonsil GCs appeared to be extremely sensitive to mechanical stress during surgery. In contrast to tonsils, seven of the eight adult spleens did not exhibit asymmetric polarized GCs, but only symmetric GCs without dark and light zones or follicles with few GC B cells. Some specimens apparently only contained primary follicles after conventional staining, but on closer inspection a homogenous hyaline extracellular material deposited among the FDCs indicated that a GC had been present. Our study demonstrates that the structure of GCs varies in different human secondary lymphatic organs most likely depending on the local antigenic challenge.