Cytokine-related genes play critical roles in extrafollicular growth of follicular lymphoma cells

Follicular lymphoma (FL) is a germinal center-derived B-cell lymphoma that is known to proliferate in the intrafollicular region. However, lymphoma cells can be identified in the extrafollicular regions, which are related to disease dissemination. We purified the intrafollicular and extrafollicular regions of FL cells by laser microdissection and conducted microarray analysis in order to characterize the gene expression profiles of FL cells from both regions. BCL2 and genes of germinal B-cell markers clearly separated intrafollicular and extrafollicular regions of reactive follicular hyperplasia, suggesting the adequacy of the current analysis. In FL cases, cytokine-related genes were significantly enriched in extrafollicular regions compared with those in the intrafollicular regions. In intrafollicular regions of FL, cell-cycle–related genes were enriched. We found that the FL cells in the extrafollicular region more strongly expressed IL3RA and CXCL12 than those of intrafollicular regions. The cytokines might be also derived from stroma cells in the extrafollicular regions, which may initiate activation and migration of the tumor cells to this region. Our results suggest that FL cell interaction with surrounding stroma cells plays an important role in the pathophysiology of FL and that such interactions should be a good target for therapy.