Background:
The association between multiple sclerosis (MS) and Epstein-Barr virus (EBV) is well known. Previously, it’s been shown that antibodies to EBV protein BFRF3 cross-react with the self-antigen cytoplasmic protein septin-9, suggesting that EBV may contribute to CNS damage via molecular mimicry. Ocrelizumab, an anti-CD20 monoclonal antibody, has shown efficacy in MS treatment. Through B cell depletion, ocrelizumab should reduce the EBV viral load and allow B cells to regain self-tolerance, reducing the progression of CNS damage.
Objectives:
To investigate ocrelizumab’s effect on antibody responses to BFRF3 and its known cross-reactive human protein, septin-9, to evaluate the mechanism by which EBV plays in the pathogenesis of MS.
Methods:
Plasma samples from 36 MS patients were taken at three times: before treatment with ocrelizumab, 6 months and 12 months post treatment. 26 received treatment with ocrelizumab while 10 patients were on other treatments. EBV and human proteins produced by transfected bacteria were used as antigens for ELISA and Western Blots. Total IgG and BFRF3 concentration was measured at the 3 time points using ELISA assay with a standard curve for quantitative results. Intra-assay coefficients of variation were <10%. Antibody response to septin-9 was evaluated by quantitative Western blots and calculated by densitometry. The magnitude of change in antibody response between the three categories were compared. Data was analyzed and comparisons were made using a One-Sample Signed Rank Test in SigmaPlot version 11.0.
Results:
Total IgG: The mean percent change from baseline to 12 months showed an 8% decrease, with a mean percent interquartile interval of -18.4% and a mean percent third quartile of 9.2%. The 95 percent confidence interval (CI) for the population median was -13.3% to 7.84% with no significant difference between the two medians (p = 0.537). BFRF3: The mean percent change over 12 months showed an 8.9% decrease, with a mean percent interquartile interval of -49.8% and a mean percent third quartile of 24.7%. The CI for the population median was -17.9% to -3.6% with no significant difference between the two medians (p = 0.247). Septin-9: The mean percent change over 12 months showed a 3% decrease, with a mean percent interquartile interval of -30.4% and a mean percent third quartile of 39.8%. The CI for the population median was -23.8% to 32.1%. No significant difference between the two medians (p = 0.808).
Conclusions:
There was no significant change in antibody response to EBV protein BFRF3 and its cross-reactive protein septin-9 after ocrelizumab treatment. A time period greater than 12 months may be necessary to show a significant change in antibody levels and a larger sample size would have benefited this study, increasing its statistical power. In the future, it could be valuable to measure antibody levels to more EBV antigens (EBNA-1, BRRF2) and their known cross-reactive self proteins (HNRNPL and DLST).
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