CMV Infection Attenuates the Disease Course in a Murine Model of Multiple Sclerosis Istvan Pirko1*, Rhonda Cardin2, Yi Chen 3 , Anne K. Lohrey3, Diana M. Lindquist4, R. Scott Dunn4, Robert Zivadinov5, Aaron J. Johnson3 1 Department of Neurology, Mayo Clinic, Rochester, Minnesota, United States of America, 2 Division of Infectious Diseases, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, United States of America, 3 Department of Neurology and Immunology, Mayo Clinic, Rochester, Minnesota, United States of America, 4 Imaging Research Center, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, United States of America, 5 Department of Neurology and Buffalo Neuroimaging Analysis Center, University of Buffalo, Buffalo, New York, United States of America Abstract Recent evidence in multiple sclerosis (MS) suggests that active CMV infection may result in more benign clinical disease. The goal of this pilot study was to determine whether underlying murine CMV (MCMV) infection affects the course of the Theiler’s murine encephalitis virus (TMEV) induced murine model of MS. A group of eight TMEV-infected mice were co- infected with MCMV at 2 weeks prior to TMEV infection while a second group of TMEV-infected mice received MCMV two weeks post TMEV. We also used 2 control groups, where at the above time points MCMV was replaced with PBS. Outcome measures included (1) monthly monitoring of disability via rotarod for 8 months; (2) in vivo MRI for brain atrophy studies and (3) FACS analysis of brain infiltrating lymphocytes at 8 months post TMEV infection. Co-infection with MCMV influenced the disease course in mice infected prior to TMEV infection. In this group, rotarod detectable motor performance was significantly improved starting 3 months post-infection and beyond (p#0.024). In addition, their brain atrophy was close to 30% reduced at 8 months, but this was only present as a trend due to low power (p = 0.19). A significant reduction in the proportion of brain infiltrating CD3+ cells was detected in this group (p = 0.026), while the proportion of CD45+ Mac1+ cells significantly increased (p = 0.003). There was also a strong trend for a reduced proportion of CD4+ cells (p = 0.17) while CD8 and B220+ cell proportion did not change. These findings support an immunomodulatory effect of MCMV infection in this MS model. Future studies in this co-infection model will provide insight into mechanisms which modulate the development of demyelination and may be utilized for the development of novel therapeutic strategies. Citation: Pirko I, Cardin R, Chen Y, Lohrey AK, Lindquist DM, et al. (2012) CMV Infection Attenuates the Disease Course in a Murine Model of Multiple Sclerosis. PLoS ONE 7(2): e32767. doi:10.1371/journal.pone.0032767 Editor: Steven Jacobson, National Institutes of Health, United States of America Received September 19, 2011; Accepted January 30, 2012; Published February 29, 2012 Copyright: 2012 Pirko et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was funded by the National MS Society, by intramural funds at the University of Cincinnati’s Waddell Center for Multiple Sclerosis, and by the National Institutes of Heatlh (NINDS R01 NS058698). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: Pirko@mayo.edu Introduction Multiple sclerosis (MS) is the most common inflammatory demyelinating disease of the central nervous system (CNS). MS is the leading cause of non-traumatic disability among young adults in their most productive years [1]. Although the exact cause of MS remains elusive, it is widely accepted that the pathology of MS is mediated by the immune system in genetically susceptible hosts [2]. In addition to genetic risk factors, which determine the susceptibility and may influence disease severity, environmental factors are also suspected to contribute as disease initiating events [3]. Infections, especially of viral etiology, have long been suspected as environmental factors that may contribute to the development of MS in addition to environmental variables including vitamin-D deficiency [4]. Several viruses have been suspected as MS triggers. Currently, the most commonly studied virus which appears to be associated with MS is Epstein-Barr Virus (EBV), a member of the Herpesviridae family [5]. EBV establishes a persistent infection in B cells. Interestingly, EBV is also suspected to play a role in the pathogenesis of several classic autoimmune diseases, including polymyositis, SLE, anti-phospho- lipid antibody syndrome, rheumatoid arthritis, pemphigus vul- garis, giant cell arthritis, Wegener’s granulomatosis, and polyar- teritis nodosa [6]. A second herpes virus, human cytomegalovirus (HCMV), has also been proposed as a potential MS trigger [7]. However, more recent studies with extensive case ascertainment failed to demonstrate such an association [5]. Among systemic autoimmune conditions, elevated HCMV IgG titers were observed only in the sera of SLE patients [6]. In a recent study analyzing the role of active HCMV infection in MS cases, multiple analyses demonstrated a clear association between antibody positivity against HCMV and better clinical and MRI outcomes [8]. These analyses indicated that patients positive for antibodies against HCMV had significantly older age of disease onset, lower lifetime relapse rate, higher brain parenchymal fraction (BPF)on volumetric MRI, suggesting less brain atrophy. HCMV-positive patients who had higher antibody titer presented with lower T2 weighted lesion load and higher BPF compared to patients with lower levels. Of note, this doesn’t mean that the antibody itself would be responsible for the protective effect; instead, it implies that recent active infection overall has a protective role, via a mechanism that can’t be directly clarified in PLoS ONE | www.plosone.org 1 February 2012 | Volume 7 | Issue 2 | e32767