Differential Neutralizing Activity of Human Antibodies in Interferon Antiviral and Natural Killer Cell Bioassays

Abstract

The ability of interferon-α (IFN-α) to augment the cytotoxicity of human natural killer (NK) cells was used to probe the neutralization capacity of human antibodies to IFN-α. Sera from patients treated with IFN-α were tested for antibodies that could bind to IFN-α, neutralize IFN-α antiviral activity, or neutralize IFN-α-mediated augmentation of NK cytolytic activity. The NK-augmenting activity of IFN-α was measured in a chromium-release cytotoxicity assay using K562 targets and human peripheral blood mononuclear cells in the presence of a constant amount of antibody from patients treated with IFN-α. Neutralization of IFN-α-mediated antiviral activity did not correlate with neutralization of NK augmentation. However, all sera that neutralized a biologic activity of IFN-α also bound IFN-α. Conversely, sera that did not bind to IFN-α also did not neutralize either biologic activity. The data suggest that some immunogenic epitopes of IFN-α reside in distinct domains that mediate different biologic activities of-IFN-α. The identification of neutralizing antibodies for the NK immunomodulating function of IFN-α but not antiviral function suggests that assessment of antiviral neutralization alone may be an incomplete evaluation of the potential significance of binding antibodies that occur subsequent to the administration of therapeutic IFNs.