Role of follicular dendritic cells in the apoptosis of germinal center B cells

Follicular dendritic cells (FDCs) provide the most obvious source of antige ns, which are essential for the differentiation of GC B cells. It has been reported that most proliferating B cells in germinal centers undergo apopto sis. Quantitative histology shows macrophages with apoptotic debris through out the germinal center, the highest frequency of these cells bring found i n the dense FDC network. Based on these findings, we hypothesized that FDC may be involved in an apoptotic pathway of the germinal center B cells. To prove this hypothesis, we performed double immunohistochemical analysis usi ng anti-FDC mAb and peanut agglutinin (PNA), with their respective TUNEL ki ts. Collated data showed that a great proportion of the apoptotic cells, mo st of which were positive for PNA, were in close contact with FDC, which in dicated an interaction between FDC and B cells in the apoptotic pathway. Fu rther studies using double immunohistochemical staining and FACS analyses d emonstrated the expression of Fas-ligand (FasL) ill a subset of the FDC. Th ese results suggest that FDC may play a role in the apoptosis of germinal c enter B cells via Fas-FasL interaction. (C) 2000 Elsevier Science B.V. All rights reserved.