Abstract
Two receptors for tumor necrosis factor (TNF) with different molecular weight (75-Kd and 55-Kd) and binding affinity have been recently discovered. To investigate the distribution and the functional role of these receptors on leukemic B cells from hairy cell leukemia (HCL) and B-cell chronic lymphocytic leukemia (B-CLL) patients, we evaluated: (1) the cytofluorimetric pattern of uncultured and cultured leukemic B cells incubated with utr-1 and htr-9 monoclonal antibodies (MoAbs), which specifically recognize the 75-Kd and 55-Kd TNF receptors (TNFR), respectively; (2) the effect of TNF-alpha and TNF-beta on leukemic B cells in an in vitro proliferation assay; (3) the role of anti-TNFR MoAbs on TNF-alpha and TNF-beta-driven B-cell growth; and (4) the proliferative effect of utr-1 and htr-9 MoAbs on in vitro cultured leukemic cells. Our study shows that the high affinity (75-Kd) but not the low affinity (55-Kd) TNFR molecules are expressed on freshly isolated leukemic B cells recovered from HCL and B-CLL patients. The expression of these receptors was neither upregulated nor downregulated by different stimuli, including TNF-alpha, TNF-beta, B-cell growth factor, and interleukin-2. TNF-alpha efficiently triggers the proliferation of HC and, to a lesser extent, the growth of B-CLL cells. TNF-beta was also able to transduce the proliferative signal in HCL, but not in B-CLL patients. TNF-alpha- and TNF-beta-driven B-cell proliferation was inhibited by the preincubation of leukemic B cells with utr-1 but not htr-9 MoAb. Moreover, anti-75-Kd, but not anti-55-Kd TNFR MoAb, was able to trigger the proliferation of leukemic B cells, and in particular of HC. These results show that leukemic B cells from patients with HCL and B-CLL are equipped with a fully functional high affinity TNFR.
