Inhibition of apoptotic cell death in B-CLL by interferon gamma correlates with clinical stage

Apoptosis was evaluated in B cells from 41 patients with B-CLL and 20 healthy aged-matched controls. B cells were cultured with and without γ-IFN and other cytokines ; apoptosis was quantified at regular intervals throughout a 5-day culture period. According to Rai's criteria, 17 patients were classified as good risk, 16 as intermediate and eight as high risk. In vitro, purified B cells from B-CLL patients were evaluated for apoptosis. Maximal apoptosis (44.12%) was observed at day 5 in cells from patients with poor prognosis. The addition of γ-IFN to the culture media prevented apoptosis in a dose-dependent manner. Maximal inhibition of apoptosis was achieved with 100 IU/ml of γ-IFN. The degree of inhibition of apoptosis by γ-IFN was greater in cells from the high-risk group patients than in those from the intermediate and good prognosis group (P < 0.0001). The expression of γ-IFN receptors in B-CLL cells was evaluated using a MnAb against the extracellular domain of γ-IFN receptor. After 4 days in culture with γ-IFN, only cells from the intermediate- and high-risk groups showed an increase in the density of γ-IFN receptors (P < 0.001). γ-IFN was not detected in the sera of our study patients. However γ-IFN was detectable in the media from both normal B cells and B-CLL cells in culture ; there was no difference in the amount of γ-IFN released by cells from the three groups of patients studied. Our results show that in vivo γ-IFN inhibits apoptosis of B cells from B-CLL patients. The inhibitory effect of γ-IFN on apoptosis correlates directly with the severity of the disease and this is likely explained by a marked upregulation of γ-IFN receptors in cells from patients in the high-risk group.