Selective inhibitory effect of Hu-IFN-γ on the agarose clonability of tumor-derived lymphoid cell lines

Recombinant human Interferon alpha (IFN-α) and Interferon gamma (IFN-γ) were compared for their ability to influence the proliferative capacity of tumor-derived cell lines and of normal B lymphocytes infected in vitro by Epstein-Barr virus (EBV). EBV-induced B-cell proliferation was supressed almost completely when 10² U/ml IFN-α were added to the culture medium while the same dose of IFN-γ had significantly lower inhibitory activity. The pure IFNs differed in their ability to influence the growth of three Burkitt lymphoma-derived cell lines, Raji, Daudi, and Namalwa, depending on whether the cells were propagated in suspension or in semisolid cultures. IFN-α inhibited cell proliferation under both culture conditions with thresholds of sensitivity characteristics for each cell line. In contrast, IFN-γ had no effect on the growth in suspension but it abolished the clonogenic potential of tumor cell lines in semisolid agarose. The results suggest that the two IFN types may exert their growth inhibitory activity through different mechanisms of action.