Human herpesvirus 6 and 7 reactivation and disease activity in multiple sclerosis

Recent studies have focused on the associations between human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7), and multiple sclerosis (MS). The aim of this study was to investigate the associations between HHV-6 and HHV-7 reactivation and MS disease activity, and interleukin 12 (IL-12) and tumor necrosis factor α (TNF-α) production. Material and Methods. The frequency of plasma viremia by nested polymerase chain reaction and transcription of viral mRNA in peripheral blood mononuclear cells by reverse transcriptasepolymerase chain reaction (RT-PCR) of 14 relapsing/remitting (RR) and 14 secondary progressive (SP) MS patients were studied in comparison with clinical manifestation of the disease. Serum concentrations of cytokines IL-12 and TNF-α were analyzed by enzyme-linked immunosorbent assay. Results. Plasma samples from 25 of the 28 MS patients with estimated latent/persistent HHV-6 and/or HHV-7 infection were examined during relapse and remission/relative remission. HHV-6 reactivation was found in 4 of the 7 RRMS and 4 of the 7 SPMS patients, and HHV-7 reactivation was identified in 3 of the 7 RRMS and 1 of the 7 SPMS patients (all in relapse). In 2 of the 3 RRMS patients without viremia in relapse, HHV-6 mRNA transcription was detected. In RRMS and SPMS patients with active HHV-6 and HHV-7 infection in relapse, the serum concentrations of IL-12 and TNF-α were significantly higher than in those with latent virus infection. Conclusions. HHV-6 and HHV-7 reactivation could be implicated in the exacerbation of MS via activation of Th1 lymphocyte subsets.