IV immunoglobulin confounds JC virus antibody serostatus determination

OBJECTIVE To determine the impact of therapeutic infusion of IV immunoglobulin (IVIg) on John Cunningham virus antibody (JCV Ab) serostatus and level in serum. METHODS We carried out a retrospective analysis of serum levels of JCV Ab among STRATIFY-2 trial enrollees from 2 multiple sclerosis centers who were exposed to IVIg during the trial. For the subset of eligible patients, we estimated mean linear trends while on IVIg and after stopping IVIg with a linear mixed-effects model. RESULTS The JCV Ab seropositivity rate in the group of patients that was recently exposed to IVIg was 100%, which is significantly higher than in the IVIg-naive population (58%, p < 0.001). The seropositivity rate in the patient group with remote IVIg exposure was similar to that in the IVIg-naive population (67%, p = 0.68, Fisher exact test). The slope of the linear trend line after stopping IVIg decreased significantly by -0.310 units per 100 days (95% confidence interval, -0.611 to -0.008; p = 0.04). CONCLUSIONS Recent IVIg exposure is invariably associated with JCV Ab seropositivity. After stopping IVIg, JCV Ab levels tend to decrease with time, and seroreversion to innately Ab-negative status can occur.