• Olivier Outteryck, Hélène Zéphir, Julia Salleron, Jean-Claude Ongagna, Ana Etxeberria, Nicolas Collongues, Arnaud Lacour, Marie-Céline Fleury, Frédéric Blanc, Marianne Giroux, Jérôme de Seze, and Patrick Vermersch.
• Department of Neurology, Université Lille Nord de France (EA2686), France olivier.outteryck@chru-lille.fr.
• Mult. Scler. 2014 Jun 1; 20 (7): 822-9.

AimThe objectives of this study were to evaluate the rate of JC virus (JCV) seroconversion/seroreversion in a French cohort of multiple sclerosis (MS) patients receiving natalizumab (NTZ), describe the characteristics of this population, identify risk factors for JCV seropositivity and analyse the additional value of quantitative JCV serology results in this context.MethodsMS patients from two French MS centres, whose JCV serological status in 2011 while receiving NTZ was known (n=357; first-generation enzyme-linked immunosorbent assay (ELISA) test (Gen1)), were proposed for inclusion in this study. We evaluated the rate of JCV seroconversion over a period of one year with a second-generation ELISA test (Gen2; n=303) and analysed the quantitative results. Multivariate analysis was performed to identify risk factors for JCV seropositivity.ResultsAmong the patients with Gen2 JCV serology (n=303) that had been JCV-seronegative one year before (n=165), the rate of JCV seroconversion was 26.67% (44/165). We observed a higher proportion of anti-JCV antibody seroconverters (14.5%) than expected (≤3%) but also increasing index values of anti-JCV antibody over time.ConclusionOur data suggest that JCV reactivation occurs during NTZ therapy and leads to an increase in the anti-JCV antibodies titre, thus making them more easily detectable by the second-generation ELISA test.© The Author(s) 2013.

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