Michael T. Liu

IFN-gamma-inducible protein 10 (IP-10; CXCL10)-deficient mice reveal a role for IP-10 in effector T cell generation and trafficking.

IFN-γ-inducible protein 10 (IP-10, CXCL10), a chemokine secreted from cells stimulated with type I and II IFNs and LPS, is a chemoattractant for activated T cells. Expression of IP-10 is seen in many Th1-type inflammatory diseases, where it is thought to play an important role in recruiting activated T cells into sites of tissue inflammation. To determine the in vivo function of IP-10, we constructed an IP-10-deficient mouse (IP-10−/−) by targeted gene disruption. Immunological analysis revealed that IP-10−/− mice had impaired T cell responses. T cell proliferation to allogeneic and antigenic stimulation and IFN-γ secretion in response to antigenic challenge were impaired in IP-10−/− mice. In addition, IP-10−/− mice exhibited an impaired contact hypersensitivity response, characterized by decreased ear swelling and reduced inflammatory cell infiltrates. T cells recovered from draining lymph nodes also had a decreased proliferative response to Ag restimulation. Furthermore, IP-10−/− mice infected with a neurotropic mouse hepatitis virus had an impaired ability to control viral replication in the brain. This was associated with decreased recruitment of CD4+ and CD8+ lymphocytes into the brain, reduced levels of IFN-γ and the IFN-γ-induced chemokines monokine induced by IFN-γ (Mig, CXCL9) and IFN-inducible T cell α chemoattractant (I-TAC, CXCL11) in the brain, decreased numbers of virus-specific IFN-γ-secreting CD8+ cells in the spleen, and reduced levels of demyelination in the CNS. Taken together, our data suggest a role for IP-10 in both effector T cell generation and trafficking in vivo.

Cutting Edge: The T Cell Chemoattractant IFN-Inducible Protein 10 Is Essential in Host Defense Against Viral-Induced Neurologic Disease

The contribution of the T cell chemoattractant chemokine IFN-inducible protein 10 (IP-10) in host defense following viral infection of the CNS was examined. IP-10 is expressed by astrocytes during acute encephalomyelitis in mouse hepatitis virus-infected mice, and the majority of T lymphocytes infiltrating into the CNS expressed the IP-10 receptor CXCR3. Treatment of mice with anti-IP-10 antisera led to increased mortality and delayed viral clearance from the CNS as compared with control mice. Further, administration of anti-IP-10 led to a >70% reduction (p ≤ 0.001) in CD4+ and CD8+ T lymphocyte infiltration into the CNS, which correlated with decreased (p ≤ 0.01) levels of IFN-γ. These data indicate that IP-10 functions as a sentinel molecule in host defense and is essential in the development of a protective Th1 response against viral infection of the CNS.

A Central Role for CD4+ T Cells and RANTES in Virus-Induced Central Nervous System Inflammation and Demyelination

ABSTRACT Infection of C57BL/6 mice with mouse hepatitis virus (MHV) results in a demyelinating encephalomyelitis characterized by mononuclear cell infiltration and white matter destruction similar to the pathology of the human demyelinating disease multiple sclerosis. The contributions of CD4+ and CD8+ T cells in the pathogenesis of the disease were investigated. Significantly less severe inflammation and demyelination were observed in CD4−/− mice than in CD8−/− and C57BL/6 mice (P ≤ 0.002 andP ≤ 0.001, respectively). Immunophenotyping of central nervous system (CNS) infiltrates revealed that CD4−/− mice had a significant reduction in numbers of activated macrophages/microglial cells in the brain compared to the numbers in CD8−/− and C57BL/6 mice, indicating a role for these cells in myelin destruction. Furthermore, CD4−/−mice displayed lower levels of RANTES (a C-C chemokine) mRNA transcripts and protein, suggesting a role for this molecule in the pathogenesis of MHV-induced neurologic disease. Administration of RANTES antisera to MHV-infected C57BL/6 mice resulted in a significant reduction in macrophage infiltration and demyelination (P ≤ 0.001) compared to those in control mice. These data indicate that CD4+ T cells have a pivotal role in accelerating CNS inflammation and demyelination within infected mice, possibly by regulating RANTES expression, which in turn coordinates the trafficking of macrophages into the CNS, leading to myelin destruction.

Neutralization of the Chemokine CXCL10 Reduces Inflammatory Cell Invasion and Demyelination and Improves Neurological Function in a Viral Model of Multiple Sclerosis

Intracerebral infection of mice with mouse hepatitis virus (MHV) results in an acute encephalomyelitis followed by a chronic demyelinating disease with clinical and histological similarities with the human demyelinating disease multiple sclerosis (MS). Following MHV infection, chemokines including CXC chemokine ligand (CXCL)10 (IFN inducible protein 10 kDa), CXCL9 (monokine induced by IFN-γ), and CC chemokine ligand 5 (RANTES) are expressed during both acute and chronic stages of disease suggesting a role for these molecules in disease exacerbation. Previous studies have shown that during the acute phase of infection, T lymphocytes are recruited into the CNS by the chemokines CXCL10 and CXCL9. In the present study, MHV-infected mice with established demyelination were treated with antisera against these two chemokines, and disease severity was assessed. Treatment with anti-CXCL10 reduced CD4+ T lymphocyte and macrophage invasion, diminished expression of IFN-γ and CC chemokine ligand 5, inhibited progression of demyelination, and increased remyelination. Anti-CXCL10 treatment also resulted in an impediment of clinical disease progression that was characterized by a dramatic improvement in neurological function. Treatment with antisera against CXCL9 was without effect, demonstrating a critical role for CXCL10 in inflammatory demyelination in this model. These findings document a novel therapeutic strategy using Ab-mediated neutralization of a key chemokine as a possible treatment for chronic human inflammatory demyelinating diseases such as MS.

Expression of Mig (Monokine Induced by Interferon-γ) Is Important in T Lymphocyte Recruitment and Host Defense Following Viral Infection of the Central Nervous System

Induction of a Th1 immune response against viral infection of the CNS is important in contributing to viral clearance. The present studies demonstrate a role for the T cell chemoattractant chemokine Mig (monokine induced by IFN-γ) in contributing to a Th1 response against mouse hepatitis virus infection of the CNS. Analysis of the kinetics of Mig expression revealed mRNA transcripts present at days 7 and 12 postinfection (p.i.) but not early (day 2) or late (day 35) in the infection. To determine functional significance, mouse hepatitis virus-infected mice were treated with anti-Mig antisera, and the severity of disease was evaluated. Such treatment resulted in a marked increase in mortality that correlated with a >3 log increase in viral burden within the brains as compared with control mice treated with normal rabbit serum. Anti-Mig-treated mice displayed a significant decrease (p < 0.005) in CD4+ and CD8+ T cell recruitment into the CNS as compared with normal rabbit serum-treated mice. In addition, anti-Mig treatment resulted in a significant decrease (p < 0.05) in levels of IFN-γ and IFN-β that coincided with increased (p < 0.02) expression of the anti-inflammatory Th2 cytokine IL-10 within the CNS. Collectively, these data indicate that Mig is important in contributing to host defense by promoting a protective Th1 response against viral infection of the CNS.

Reducing inflammation decreases secondary degeneration and functional deficit after spinal cord injury

Injury to the spinal cord is followed by degeneration, which leads to progressive tissue loss and usually cystic cavitation. Cellular and humoral immune responses have been implicated as mediators of secondary degeneration, and the expression of leukocyte chemoattractants has been shown to precede immune cell influx. However, the relationship between the increased expression of chemoattractants, the invasion of lymphocytes, and overall lesion evolution is poorly understood. Here, we show that the T-lymphocyte chemoattractant CXCL10 is upregulated after dorsal hemisection injury to the adult mammalian spinal cord of C57/BL6 mice, and that antibody neutralization of CXCL10 beginning 1 day prior to injury dramatically reduces the T-lymphocyte invasion that normally occurs after trauma. Notably, this treatment resulted in a significant reduction of secondary tissue loss and functional deficit. We conclude that CXCL10 plays a critical role in recruitment of T lymphocytes to sites of spinal cord injury, and that a reduction of T-lymphocyte recruitment significantly enhances tissue preservation and functional outcome.

Antibody Targeting of the CC Chemokine Ligand 5 Results in Diminished Leukocyte Infiltration into the Central Nervous System and Reduced Neurologic Disease in a Viral Model of Multiple Sclerosis

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.

Reduced macrophage infiltration and demyelination in mice lacking the chemokine receptor CCR5 following infection with a neurotropic coronavirus

Abstract 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 CCR5−/− mice 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 CCR5−/− and CCR5+/+ mice was similar and both strains exhibited comparable viral titers, indicating that CCR5 expression is not essential for host defense. Following MHV infection of CCR5+/+ mice, greater than 50% of cells expressing CCR5 antigen were activated macrophage/microglia (determined by F4/80 antigen expression). In addition, infected CCR5−/− mice exhibited reduced (P ≤ 0.02) macrophage (CD45highF4/80+) infiltration, which correlated with a significant reduction (P ≤ 0.001) in the severity of demyelination compared to CCR5+/+ mice. These data indicate that CCR5 contributes to MHV-induced demyelination by allowing macrophages to traffic into the CNS.

Mouse hepatitis virus infection of the central nervous system: chemokine-mediated regulation of host defense and disease.

Infection of the central nervous system (CNS) of susceptible mice with mouse hepatitis virus (MHV), a positive-strand RNA virus that is a member of the Coronaviridae family, reproducibly results in an acute encephalomyelitis followed by a demyelinating disease similar to the human demyelinating disease multiple sclerosis (MS). MHV infection triggers a robust cell-mediated response in which both CD4+ and CD8+ T cells are essential in controlling viral replication and spread. However, viral clearance is incomplete and viral RNA and protein can persist within white matter tracts, areas of viral persistence are often associated with demyelinating lesions, and recent studies have indicated an important role for both T cells and macrophages in contributing to myelin destruction. The molecular mechanisms governing leukocyte trafficking and accumulation within the CNS of MHV-infected mice are just now being understood and recent studies indicate that chemokines and chemokine receptors have an important role in this process. This article will provide an overview on how these molecules regulate T cell and macrophage trafficking into the CNS of MHV-infected mice and illustrate the delicate balance that exists with regards to expression of chemokines and their receptors as it relates to both host defense and disease development.

The CXC chemokines IP-10 and Mig are essential in host defense following infection with a neurotropic coronavirus.

Chemokines represent an ever-growing family of secreted proteins that function as potent mediators of inflammation (for review, see Luster, 1998). These molecules have been classified depending on the number and spacing of the first two conserved amino terminal cysteine residues into the C, CC, CXC, and CX3C family. Studies have shown that chemokines target specific leukocyte populations during periods of inflammation (Luster, 1998; Lane et al., 2000; Biddison et al., 1998; Kolb et al, 1999). In addition, chemokines have been shown to be prominently expressed following viral infection of the CNS (Lane et al, 1998; Cheret et al., 1997, Asensio and Campbell, 1997; Hoffman et al., 1999). However, the functional significance of chemokine expression within this environment has not been fully defined.