T-box-expressed-in-T-cells (T-bet) expression by the tumor cells of hairy-cell leukemia correlates with interferon-gamma production.

Hairy cell leukemia (HCL) is an uncommon B-cell malignancy with unknown pathogenesis. In an earlier study, we demonstrated that HCL cells highly express the transcription factor T-box-expressed-in-T-cells (T-bet). T-bet is the master regulator of the T-helper (Th)1 cell response regulating interferon gamma (IFN-gamma) production and also plays a central role in the T-cell independent Th1-like B-cell response. Here, we demonstrate by fluorescence activated cell sorting (FACS) analysis that neoplastic cells from the peripheral blood of five patients with HCL showed an enhanced expression of IFN-gamma after stimulation. Additionally, a comparison with 55 healthy individuals revealed a significant elevation of IFN-gamma in the sera of patients with HCL. Based on our recent findings that a non-neoplastic B-cell subset, the monocytoid B-cells, are T-bet positive and produce IFN-gamma, we propose that monocytoid and hairy B-cells have a similar function and that the T-bet-IFN-gamma axis is involved in the pathogenesis of HCL.