Antiviral immune response in patients with multiple sclerosis, healthy siblings and twins.

In their paper, Comabella et al. identify IgG responses to the latent Epstein–Barr virus (EBV)-encoded nuclear antigen-I (EBNA-1) as associated with disease in patients with multiple sclerosis (MS) compared with healthy siblings raised in the same family household. We would like to contribute the results of a similar study that we performed on MS-discordant monozygotic (MZ) twins, a setting that further decreases the possibility of heritable and non-heritable confounders. In 20 pairs of MS-discordant monozygotic twins, selected as described previously, we evaluated the humoral responses to the viruses investigated by Comabella et al. (EBV, human herpesvirus-6 [HHV6], human cytomegalovirus [CMV], measles virus [MV]) plus four additional pathogens: varicella zoster (VZV), herpes simplex-1 (HSV-1), HSV-2 and Bordetella pertussis (Bp). The study was approved by the local ethics committee and all participating subjects gave written informed consent. The following commercially available kits were used: Captia EBNA-1 IgG, VCA (P-18) IgG and Captia EA-D IgG for EBV, IgG EIA Panbio for HHV-6, IgG EIA Serion Gmbh for CMV, IgG EIA Serion Gmbh for MV, IgG EIA Serion Gmbh for VZV, IgG EIA Serion Gmbh for HSV 1-2 and IgG EIA Serion Gmbh for Bp. The results were interpreted according to the manufacturers’ criteria. The mean age in this series was 36.5 8.3 years. None of the affected individuals had ever taken diseasemodifying therapies. All of the samples were obtained at least 3 months after the last steroid therapy. Overall, in disease discordant MZ twins the humoral responses to the above pathogens did not correlate with the MS status (Mann–Whitney U-test). Surprisingly, however, in 7 out of 20 pairs, the healthy twins were EBV-seronegative according to the manufacturer’s guidelines and to generally accepted criteria. At a different time point, 1 year apart from the first, EBV serology was repeated on three of the seven MZ pairs that had a seronegative healthy individual and on three pairs where both co-twins were seropositive. In all subjects the result did not vary substantially compared with the first time point. To further verify the reliability of the results (EBV is a ubiquitous infection and therefore a discordant serological EBV status in MZ co-twins is unexpected) a different laboratory reassayed aliquots of the same sera of 9 of the 20 twin pairs, including 4 of the pairs with a seronegative healthy twin, using a different antiviral assay as described previously (anti-EBV VCA and EBNA-1 IgG and IgM, Wampole Laboratories). This time the EBV-seronegative status of the healthy individuals was not confirmed. Commercially available EBV enzyme immunoassays can differ considerably in performance. This may explain the discrepancies in our results and those between previous studies on twins, thus stressing the importance of validating the data with different assays. Variable results may also be expected on the basis of possible components of heterogeneity at the population level in the cause of MS. For these reasons, and given the positive results of Comabella et al., the association between MS status and EBV serology that emerged in some of the tests that we have performed should not be overlooked, also considering the lack of substantial genetic, epigenetic and transcriptome variations in identical twins discordant for MS.