Reduced Macrophage Infiltration and Demyelination in Mice Lacking the Chemokine Receptor CCR5 Following Infection with a Neurotropic Coronavirus William G. Glass,* Michael T. Liu,* William A. Kuziel, and Thomas E. Lane*,1 *Department of Molecular Biology and Biochemistry, Reeve-Irvine Research Center, University of California, Irvine, California 92697-3900; and Section of Molecular Genetics and Microbiology and Institute for Cellular and Molecular Biology, University of Texas, Austin, Texas 78712 Received April 6, 2001; returned to author for revision May 21, 2001; accepted June 5, 2001 Studies were performed to investigate the contributions of the CC chemokine receptor CCR5 in host defense and disease development following intracranial infection with mouse hepatitis virus (MHV). T cell recruitment was impaired in MHV-infected CCR52/2mice at day 7 postinfection (pi), which correlated with increased (P # 0.03) titers within the brain. However, by day 12 pi, T cell infiltration into the CNS of infected CCR52/2and CCR51/1mice was similar and both strains exhibited comparable viral titers, indicating that CCR5 expression is not essential for host defense. Following MHV infection of CCR51/1mice, greater than 50% of cells expressing CCR5 antigen were activated macrophage/microglia (determined by F4/80 antigen expression). In addition, infected CCR52/2mice exhibited reduced (P # 0.02) macrophage (CD45highF4/801) infiltration, which correlated with a significant reduction (P # 0.001) in the severity of demyelination compared to CCR51/1mice. These data indicate that CCR5 contributes to MHV-induced demyelination by allowing macrophages to traffic into the CNS. 2001 Academic Press Key Words: chemokine; chemokine receptor; demyelination; multiple sclerosis; macrophage; neuroimmunology. INTRODUCTION CCR5 is a member of the CC chemokine receptor family that is expressed on various hematopoietic cells, including lymphocytes and macrophages (Raport et al., 1996). Che- mokines that are capable of binding to CCR5 include CCL3 (MIP-1a), CCL4 (MIP-1b), and CCL5 (RANTES) (Boring et al., 1996; Meyer et al., 1996; Raport et al., 1996; Zlotnik and Yoshie, 2000). Recent studies have impli- cated CCR5 as an important molecule in regulating the immune response as well as leukocyte trafficking follow- ing microbial infection. Mice deficient in CCR5 (CCR52/2) exhibit altered T cell activity and impaired macrophage function (Sato et al., 1999; Zhou et al., 1998). Furthermore, macrophage trafficking in response to antigen is impaired in CCR52/2mice, indicating that CCR5 is required for mi- gration of this population of cells (Huffnagle et al., 1999). Mouse hepatitis virus (MHV) is a positive-strand RNA virus that is a member of the Coronaviridae family. MHV infection of the CNS results in an acute encephalomyeli- tis followed by a chronic demyelinating disease that is similar to the pathology observed in the human demyeli- nating disease multiple sclerosis (MS) (Houtman and Flemming, 1996; Lane and Buchmeier, 1997). A robust expression of chemokine genes occurs within the brains and spinal cords of MHV-infected mice which precedes then accompanies leukocyte infiltration (Lane et al., 1998). Among the chemokines expressed within the CNS of MHV-infected mice are the CCR5 ligands CCL3, CCL4, and CCL5, suggesting an important role for these che- mokines in attracting leukocytes into the CNS. In support of this are studies demonstrating that treatment of MHV- infected mice with neutralizing antisera specific for CCL5 resulted in reduced lymphocyte infiltration into the brain and enhanced viral recovery (Lane et al., 2000). More- over, anti-CCL5 treatment resulted in decreased macro- phage infiltration, which correlated with a significant decrease in the severity of demyelination. Therefore, these data suggested that CCL5 contributes to demyeli- nation in MHV-infected mice by attracting macrophages into the CNS following binding and signaling of chemo- kine receptors expressed on the surface of these cells. The present study was undertaken in order to better understand how CCR5 contributes to disease following MHV infection of the CNS. To this end, we have evalu- ated the severity of neurologic disease following MHV infection of CCR52/2mice (Andres et al., 2000). The results presented indicate that MHV infection of the CNS of CCR52/2mice results in the development of an effec- tive immune response, as characterized by cytokine and chemokine gene expression and clearance of virus from the CNS. However, both macrophage infiltration and de- myelination was significantly reduced in MHV-infected CCR52/2mice compared to CCR51/1mice, indicating that CCR5 contributes to the pathogenesis of MHV-induced demyelination by attracting macrophages into the CNS. 1To whom correspondence and reprint requests should be ad- dressed at Department of Molecular Biology and Biochemistry, Biolog- ical Sciences II, University of California, Irvine, CA 92697-3900. Fax: