Interferon inhibitory activity in patients with multiple sclerosis.
BACKGROUND: Interferon inhibitory activity (IIA) is a logical candidate for explaining neutralizing antibody-negative partial responsiveness to interferon beta in multiple sclerosis (MS), but its role has not been evaluated. OBJECTIVE: To investigate the role of IIA and soluble interferon-alpha/beta receptor (sIFNR) in determining response of patients with MS to interferon beta therapy. DESIGN: Parallel-group, open-label study. SETTING: Baird Multiple Sclerosis Center, Buffalo, NY. Patients Blood was obtained before and 24 hours after injection of interferon beta-1a from 38 anti-interferon beta neutralizing antibody-negative patients with relapsing-remitting MS and 16 untreated healthy controls. On the basis of clinical parameters of response to interferon beta therapy, the patients were divided into stable or good-responder (n = 20) and active or partial-responder (n = 18) groups. MAIN OUTCOME MEASURES: Quantitative analyses of magnetic resonance imaging were obtained; the IIA and sIFNR levels were measured using bioassay and enzyme-linked immunosorbent assay, respectively. RESULTS: The IIA and sIFNR levels were elevated in MS patients compared with controls (P<.001). The IIA levels were higher in active or partial responders compared with stable or good responders (P<.001); the sIFNR levels were not different between groups. The Extended Disability Status Score and T2 lesion volumes were higher in the active or partial-responder group compared with the stable or good-responder group. Interferon beta-1a did not have short-term effects on the IIA and sIFNR levels. In univariate general linear model and stepwise regression analyses, IIA levels were associated with T2 lesion volume. CONCLUSION: The levels of IIA are associated with increased MS disease activity and with responsiveness to interferon beta therapy in anti-interferon beta neutralizing antibody-negative MS patients.