iLite® IFN beta 1a (950 IU/mL), is a stock solution of recombinant IFN beta 1a, for use as a stimulator of iLite® Type I IFN Assay Ready Cells, after appropriate dilution. Interferon beta (IFNβ) is well established as first line therapy in relapsing/remitting multiple sclerosis. The occurrence of NAbs and binding antibodies (BAbs) to IFNβ has been widely reported. Subjects with NAbs have shown reduced response to treatment with IFNβ, having higher relapse rates, increased MRI activity and higher risk of disease progression. The frequencies and titers of NAbs vary depending on the preparation used, dose and frequency of administration and also the assay used to quantify them.