The measurement of antibodies binding to IFNβ in MS patients treated with IFNβ

The intensity of the antibody response to injected interferons (IFNs) depends on many factors: route of injection, dose injected, frequency of injections, and duration of treatment. The optimal assay or approach for testing for anti-IFN antibodies has not been determined. Neutralizing antibody (NAb) determinations are most commonly used but have intrinsic problems when used as clinical assays. They are time consuming, expensive, and only indirectly measure antibodies. Thus, false-positive results can occur because of other serum factors. In contrast, binding assays measure antibodies directly; they are mainly used as an initial screen to detect NAbs. ELISA methodologies for binding antibodies have been used, but direct adhesion of the antigen (i.e., IFNβ) to the plate has resulted in false-negative and false-positive results, presumably because of changes in antigenicity.1 This limitation is circumvented by using the capture ELISA in which a first antibody is used to capture the antibody and hold it in an antigenic position, mimicking that of IFNβ in its natural state. Radioimmunoprecipitation assays (RIPAs) are used routinely to measure pathogenic autoantibodies, including antibodies to the acetylcholine receptor and voltage-gated calcium and potassium channels, with good sensitivity and specificity. The RIPA also has been used to measure antibodies to another biologic substance, botulinum toxin, in patients treated with this toxin. The experience of groups in the United States (University of Medicine and Dentistry of New Jersey) and Canada (University of British Columbia) with improved ELISAs and in the United Kingdom (Oxford University) with RIPA is summarized below. ### Direct ELISA. The assay has been previously described.2,3⇓ In brief, IFNβ was directly coated onto an ELISA plate, followed by serial incubations with serum, conjugate, and substrate, with washes in between. ### Capture ELISA.  #### United States. The assay has been previously described.1 Experience with this assay in a broad spectrum of patients with MS has recently …