JC virus antibody status underestimates infection rates.

Objective: JC virus (JCV) seropositivity is a risk factor for progressive multifocal leukoencephalopathy (PML) in patients on natalizumab. Accordingly, the JCV serological antibody test is of paramount importance in determining disease risk.

Methods: We tested the accuracy of the JCV serum antibody test by comparing the results of JCV serology to JCV viruria and viremia in 67 patients enrolled in a single-center, retrospective cohort study.

Disease-modifying drugs for multiple sclerosis and JC virus expression.

Natalizumab-associated progressive multifocal leukoencephalopathy in multiple sclerosis (MS) occurred in two individuals also treated with interferon β1a, raising concerns about the interaction of these disease-modifying agents and leading to the recommendation to avoid their concomitant administration. However, type I interferons are antiviral. Using a real-time quantitative polymerase chain reaction for the detection and quantification of the John Cunningham virus (JCV), DNA in peripheral blood mononuclear cells (PBMCs), and urine in MS patients, we tested the hypothesis that MS disease-modifying drugs (DMD) qualitatively and quantitatively alter JCV prevalence and viral copy numbers.