Intracerebral infection of mice with mouse hepatitis virus, a member of the Coronaviridae family, reproducibly results in an acute encephalomyelitis that progresses to a chronic demyelinating disease. The ensuing neuropathology during the chronic stage of disease is primarily immune mediated and similar to that of the human demyelinating disease multiple sclerosis. Secretion of chemokines within the CNS signals the infiltration of leukocytes, which results in destruction of white matter and neurological impairment. The CC chemokine ligand (CCL)5 is localized in white matter tracts undergoing demyelination, suggesting that this chemokine participates in the pathogenesis of disease by attracting inflammatory cells into the CNS. In this study, we administer a mAb directed against CCL5 to mice with established mouse hepatitis virus-induced demyelination and impaired motor skills. Anti-CCL5 treatment decreased T cell accumulation within the CNS based, in part, on viral Ag specificity, indicating the ability to differentially target select populations of T cells. In addition, administration of anti-CCL5 improved neurological function and significantly (p ≤ 0.005) reduced the severity of demyelination and macrophage accumulation within the CNS. These results demonstrate that the severity of CNS disease can be reduced through the use of a neutralizing mAb directed against CCL5 in a viral model of demyelination.

The CXC chemokine ligand 10 (CXCL10) is a non-ELR CXC chemokine that exerts a potent chemotactic effect on activated T cells through binding the receptor CXCR3 (5). CXCL10 is expressed within tissues following viral infection, suggesting an important role for this chemokine in host defense by contributing to lymphocyte activation, extravasation, and accumulation of virus-specific T cells within sites of infection. Indeed, recent studies with antibody-mediated targeting of CXCL10 and CXCL10 Ϫ/Ϫ mice demonstrated that the absence of CXCL10 function results in increased mortality accompanied by increased viral titers and reduced T-cell infiltration within the brains of mice infected intracerebrally with a murine coronavirus (mouse hepatitis virus [MHV]) (8,20). In addition, CXCL10 expression modulates the pathogenesis of liver disease in adenovirus-infected mice and transgenic mice capable of replicating hepatitis B virus by attracting CD8 ϩ T lymphocytes into the liver (2, 11).These studies indicate that CXCL10 functions as a sentinel molecule in host defense and is important in the development of a protective T-cell response following viral infection. Recent findings have also illustrated an important role for chemokines in innate defense following viral infection. For example, in addition to its chemotactic effect on T cells, CXCL10 has also been shown to induce natural killer (NK) cell migration following viral infection (2, 11, 22, 23). Expression of both CXCL10 and CXC chemokine ligand 9 (CXCL9) has been found to contribute to antiviral immune responses in the absence of T and B cells (24). Although these chemokines have a demonstrated direct antimicrobial effect (6), their protective effect following vaccinia virus infection was a result of enhanced NK cell trafficking and activation (24).Our laboratory is interested in the functional contributions of chemokines and chemokine receptors in both host defense and disease progression within the context of coronavirus infection of the central nervous system (CNS). Intracerebral infection of susceptible strains of mice with MHV results in an acute encephalomyelitis followed by a chronic immune-mediated demyelinating disease that is similar in pathology to the human demyelinating disease multiple sclerosis (16). A robust expression of chemokine genes occurs within the CNS following MHV infection that precedes and accompanies leukocyte entry (18).Although NK cells can be readily detected within the CNS early following MHV infection, their precise contributions to antiviral immune responses within the CNS have not been well established. Furthermore, CXCL10 is prominently expressed as early as day 1 postinfection, suggesting that this molecule may function in enhancing innate immune responses by attracting NK cells into the CNS. Therefore, to further understand the relationship between CXCL10 and the innate immune response to viral infection of the CNS, we constructed a recombinant MHV capable of expressing mouse CXCL10. Intracerebral infection of RAG1 Ϫ/Ϫ mice with t...

Infection of susceptible mice with the Colombiana strain of Trypanosoma cruzi results in an orchestrated expression of chemokines and chemokine receptors within the heart that coincides with parasite burden and cellular infiltration. CC chemokine receptor 5 (CCR5) is prominently expressed during both acute and chronic disease, suggesting a role in regulating leukocyte trafficking and accumulation within the heart following T. cruzi infection. To better understand the functional role of CCR5 and its ligands with regard to both host defense and/or disease, CCR5؊/؊ mice were infected with T. cruzi, and the disease severity was evaluated. Infected CCR5؊/؊ mice develop significantly higher levels of parasitemia (P < 0.05) and cardiac parasitism (P < 0.01) during acute infection that correlated with reduced survival. Further, we show that CCR5 is essential for directing the migration of macrophages and T cells to the heart early in acute infection with T. cruzi. In addition, data are provided demonstrating that CCR5 does not play an essential role in maintaining inflammation in the heart during chronic infection. Collectively, these studies clearly demonstrate that CCR5 contributes to the control of parasite replication and the development of a protective immune response during acute infection but does not ultimately participate in maintaining a chronic inflammatory response within the heart.

The expression of chemokines within the heart during experimental infection of susceptible mice with the Colombiana strain of Trypanosoma cruzi was characterized in an attempt to determine a functional role for these molecules in both host defense and disease. Analysis of chemokine transcripts revealed that CXC chemokine ligand 9 (CXCL9) and CXCL10, as well as CC chemokine ligand 2 (CCL2) and CCL5, were prominently expressed during acute disease, whereas transcripts for CXCL9, CXCL10, and CCL5 remained elevated during chronic infection. Inflammatory macrophages present within the heart were the primary cellular source of these chemokines following T. cruzi infection. Peak chemokine expression levels coincided with increased gamma interferon expression and inflammation within the heart, suggesting a role for these molecules in both host defense and disease. Indeed, simultaneous treatment of T. cruzi-infected mice with neutralizing antibodies specific for CXCL9 and CXCL10 resulted in an increased parasite burden that was sustained out to 50 days p.i. Antibody targeting either CXCL10 or CCL5 did not change either T. cruzi burden within the heart nor attenuate the severity of cardiac inflammation at any time point examined, while targeting CXCL9 in combination with CXCL10 resulted in increased parasite burden. Collectively, these studies imply that CXCL9 and CXCL10 signaling enhances immune responses following parasite infection. However, antibody targeting of CXCL9 and CXCL10, or CXCL10 alone, or CCL5 alone does not directly modulate the inflammatory response within the heart, suggesting that other proinflammatory factors are able to regulate inflammation in this tissue in response to T. cruzi infection.

The chemokine CXCL10 is expressed within the CNS in response to intracerebral infection with mouse hepatitis virus (MHV). Blocking CXCL10 signaling results in increased mortality accompanied by reduced T cell infiltration and increased viral titers within the brain suggesting that CXCL10 functions in host defense by attracting T cells into the CNS. The present study was undertaken to extend our understanding of the functional role of CXCL10 in response to MHV infection given that CXCL10 signaling has been implicated in coordinating both effector T cell generation and trafficking. We show that MHV infection of CXCL10+/+ or CXCL10−/− mice results in comparable levels of T cell activation and similar numbers of virus-specific CD4+ and CD8+ T cells. Subsequent analysis revealed no differences in T cell proliferation, IFN-γ secretion by virus-specific T cells, or CD8+ T cell cytolytic activity. Analysis of chemokine receptor expression on CD4+ and CD8+ T cells obtained from MHV-immunized CXCL10+/+ and CXCL10−/− mice revealed comparable levels of CXCR3 and CCR5, which are capable of responding to ligands CXCL10 and CCL5, respectively. Adoptive transfer of splenocytes acquired from MHV-immunized CXCL10−/− mice into MHV-infected RAG1−/− mice resulted in T cell infiltration into the CNS, reduced viral burden, and demyelination comparable to RAG1−/− recipients of immune CXCL10+/+ splenocytes. Collectively, these data imply that CXCL10 functions primarily as a T cell chemoattractant and does not significantly influence T cell effector response following MHV infection.