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The prevention of spontaneous apoptosis of follicular lymphoma B cells by a follicular dendritic cell line: involvement of caspase-3, caspase-8 and c-FLIP

Department of Pathology and Groupe Interdisciplinaire de Génoprotéomique Appliqué (GIGA)-Research, CHU Sart Tilman, University of Liege, Liege, Belgium

Correspondence: Laurence de Leval MD, PhD, Department of Pathology, CHU Sart-Tilman B23 Tour de Pathologie (+1) B-4000 Liège, Belgium., E-mail:L.deLeval{at}ulg.ac.be

ABSTRACT

Background: Follicular lymphoma, the neoplastic counterpart of germinal center B cells, typically recapitulates a follicular architecture. Several observations point to the crucial role of the cellular microenvironment in the development and/or progression of follicular lymphoma cells in vivo. The aim of our study was to characterize the spontaneous apoptosis of follicular lymphoma cells in vitro, and the modulation of this apoptosis by follicular dendritic cells.

Design and Methods: We used a cell line derived from follicular dendritic cells (HK cells) to model the functional interactions of these cells and lymphoma cells in co-culture. Follicular lymphoma cells were isolated from tissue biopsies. Apoptosis was quantified by flow cytometry and apoptotic pathways were investigated by western blotting.

Results: The spontaneous apoptosis of follicular lymphoma cells in vitro involves the activation of cas-pases-3 and -8 but not of caspase-9, occurs despite persistent high levels of BCL-2 and MCL-1, and is associated with down-regulation of c-FLIP_L. Spontaneous apoptosis of FL cells is partially prevented by coculture with the HK cells, which prevents activation of caspase-8, caspase-3 and induces an upregulation of c-FLIP_L. Using neutralizing antibodies, we demonstrated that interactions involving CD54 (ICAM-1), CD106 (VCAM-1) and CD40 are implicated in this biological process.

Conclusions: HK cells constitute a useful tool to study the functional interactions between follicular lymphoma cells and follicular dendritic cells in vitro. Understanding the molecular mechanisms involved in these protective interactions may lead to the identification of therapeutic agents that might suppress the survival and growth of follicular lymphoma cells.

Key words: follicular lymphoma, HK cells, apoptosis.