Induction of IgM secretion by chronic B-lymphocytic leukaemia cells in serum-free medium: effects of interferon-alpha, -gamma and phorbol ester.

Serum-free culture conditions would be preferable when studying the cellular and molecular regulation of B lymphocyte activation, proliferation and differentiation. We describe here the morphological and functional differentiation of chronic B-lymphocytic leukaemia (B-CLL) cells from 10 patients cultured in serum-free medium. When exposed to the phorbol ester TPA, cells from 8/10 cases expressed blastoid morphology and secreted significant levels of monoclonal IgM. The addition of 0.5% newborn calf serum to the serum-free medium increased both the spontaneous and TPA-induced IgM secretion of B-CLL cells by a factor of 6 and 7, respectively. Compared with TPA, significant but lower levels of IgM secretion and morphological differentiation were observed with native purified leucocyte interferon-alpha (IFN-alpha) (6/8 patients), some batches of recombinant IFN-alpha 2 (5/8 patients) and recombinant IFN-gamma (4/8 patients) in a dose-dependent and specific manner. Preactivation of B-CLL cells with TPA or anti-mu antibody was not necessary for the IFN-induced functional maturation. Significant DNA synthesis was not observed with any of the inducers used. These studies show that B-CLL cells can be induced to differentiate under serum-free conditions in response to physiological and non-physiological ligands.