Differences in the germinal centres of palatine tonsils and lymph nodes.

The germinal centres of human palatine tonsils typically have four clearly recognizable compartments. The dark zone is identified by the presence of centroblasts and a thin follicular dendritic cell (FDC) network. The dense FDC network is divided into a CD23(low/-) portion adjacent to the dark zone (the basal light zone) and a CD23(high) portion, the apical light zone). The outer zone, which lies between the apical light zone and the follicular mantle, has only fine CD23- FDC processes. While these compartments were seen in 48 follicles from eight tonsils, the compartmental structure of 54 germinal centres in lymph nodes from 11 individuals was markedly different. The CD23+ FDC network in lymph node follicles extended into part of the dark zone and the inner part of the follicular mantle, and consequently no outer zone or basal light zone was identified. In both the lymph nodes and tonsils most T cells were CD4+ and located outside the dark zone; the concentration of these cells at the edge of germinal centres was typical of tonsil centres but was noted only occasionally in lymph nodes. The substantial minority of T cells that were CD4,CD57+ were located mainly in the dense FDC network.