IFNbeta bioavailability in multiple sclerosis patients: MxA versus antibody-detecting assays

Anti-IFNbeta antibodies are related to IFNbeta bioavailability loss in multiple sclerosis. We investigated the reliability of radioimmunoprecipitation and cytopathic assays in detecting binding (BAbs) and neutralizing (NAbs) antibodies and the correlation of these antibodies to MxA mRNA production. Eleven percent of IFNbeta-treated patients showed a lack of MxA induction, with an inverse correlation between MxA mRNA and the presence of BAbs and NAbs. Some patients had contemporary MxA induction in the presence of high NAb titres, thus calling into question the reliability of cytopathic assay. Since anti-IFNbeta antibodies well correlated with MxA induction loss, MxA assay is an appropriate test to determine IFNbeta bioavailability.