Follicular dendritic cells protect malignant B cells from apoptosis induced by anti-Fas and antineoplastic agents

The observation that follicular dendritic cells (FDC) reduce apoptosis in B cells prompted the hypothesis that FDC might enhance tumor cell survival by protecting malignant B cells from apoptotic death. To test this notion, apoptosis was induced in B cell lymphomas by anti-Fas or various antineoplastic agents in the presence and absence of FDC. Apoptosis was detected and quantified by TUNEL analysis. Induction of apoptosis with anti-Fas, etoposide, cyclophosphamide, and busulfan was markedly antagonized by FDC at FDC to B cell ratios of >/=1:16. For example, treatment with 10 ng/ml anti-Fas caused 60-90% of A20 cells to undergo apoptosis in 6 h, whereas addition of FDC reduced apoptosis to background levels (3-15%). Similarly, treatment with busulfan induced apoptosis in 55-80% of A20 cells, whereas addition of FDC reduced B cell death to