Neutralizing and Binding Antibodies to Interferon Beta in Patients with Multiple Sclerosis: A Comparison of Assay Results from Three Italian Centres.

Interferon (IFN) beta therapy for multiple sclerosis (MS) is associated with the development of binding antibodies (BAbs) and neutralizing antibodies (NAbs) in a percentage of patients. This study investigated the reproducibility of results of two different antibody detection techniques using serum from 100 patients with MS who were receiving IFN beta therapy. Fifty samples were analysed using a commercially available kit-based BAb assay and a further 50 different samples were analysed using a widely used NAb cytopathic effect assay, at three different laboratories. All three centres agreed on the BAb status of all serum samples. However, only 84% agreement was reached on serum NAb status, and there was significant inter-laboratory variation in NAb titre values. Further analysis of these data revealed a correlation between the mean NAb titre and the coefficient of variation of serum samples, indicating greater discordance with higher NAb titres. A significant interlaboratory variation in NAb titres does exist; thus, caution is required when comparing titres from different centres. It is clear that validated detection assays are needed to accurately quantify NAb titres.