Evidence for multiple binding sites for several components of human lymphoblastoid interferon-alpha

The antiproliferative and competitive binding activities of 20 purified components of human lymphoblastoid interferon (IFN)-alpha were compared with that of recombinant human IFN-alpha 2b on Daudi and AU937 cells. We observed broad ranges of antiproliferative activities of the IFN-alpha components on these cell lines. Daudi cells were more sensitive to the IFN-alpha components than AU937 cells; the concentrations of the components that resulted in 50% inhibition of cell growth ranged from 0.003 ng/ml to > 10 ng/ml on Daudi cells and 0.05 ng/ml to > 200 ng/ml on AU937 cells. Component o was the most active human IFN-alpha on both cell lines. Scatchard analysis demonstrated that the number of IFN-alpha 2b binding sites is greater on Daudi cells (12,700 binding sites/cell) than AU937 cells (3,300 binding sites/cell); however, their receptor affinities were similar. Component o, which exhibited high antiproliferative activity on both cell lines, had low affinity for the IFN-alpha 2b binding site on AU937 and Daudi cells. Several human IFN-alpha s (components b', b", and e) appeared to have high affinity binding sites but low antiproliferative activity on both Daudi and AU937 cells. These data suggest that there may be more than one binding site or receptor for human IFN-alpha, and/or there may be a multicomponent receptor involved in the biological actions of these molecules.