Anti-interferon-β neutralising activity is not entirely mediated by antibodies

Many multiple sclerosis (MS) patients treated with interferon-β (IFNβ) develop anti-IFNβ antibodies (BAbs), which can interfere with both in vitro and in vivo bioactivity of the injected cytokine. Objective of this study was to correlate these measures. Among the 256 enrolled patients, 11 (4.3%) showed a significant inhibition of the IFNβ activity in vitro, but no measurable BAbs. As a whole, in vivo bioactivity was inhibited in 9/11 (82%) of these patients. A minority of IFNβ treated patients have a non-antibody mediated neutralising activity, which competitively inhibits the bioactivity both in vitro and in vivo.