Activation of neutrophil function via CD66: differential effects upon β2 integrin mediated adhesion

We investigated the potential role of transforming growth factor-beta (TGF-β) on spontaneous and cytokine-induced proliferation of B-cell chronic lymphocytic leukaemia (B-CLL) cells in vitro . Purified B lymphocytes from 21 B-CLL patients were cultured for 5 d in the presence of medium alone, IL-2 and/or IL-10, in the presence or absence of TGF-β, and proliferation was measured by ³H-thymidine incorporation. TGF-β inhibited B-cell proliferation in the majority of patients (15/21) but no inhibition was detected in 6/21 patients whatever the type of stimulant used. Addition of neutralizing antibodies to TGF-β increased spontaneous and cytokine-induced proliferation; this effect was dose dependent and specific because addition of an irrelevant chicken IgG had no effect on B-CLL proliferation. In resistant patients, neutralizing antibodies to TGF-β did not increase the proliferation. The expression of TGF-β receptors on B-CLL cells was significantly lower than the one observed on normal CD5⁺ B lymphocytes for which the sensitivity to TGF-β inhibition was more marked than in CLL. In addition, we found a strong correlation between the response of leukaemic B cells to TGF-β inhibitory action and the expression of TGF-β receptors on these cells. In summary, TGF-β appears to function in CLL as a negative regulator of B lymphocytes but loss of responsiveness to this factor accompanied by a decrease of TGF-β receptor expression, might provide a selective advantage to B-CLL lymphocytes.