T cell antiviral effector function is not dependent on CXCL10 following murine coronavirus 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-gamma 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.     

The dynamics of mouse cytomegalovirus-specific CD4 T cell responses during acute and latent infection

The dynamics of mouse cytomegalovirus (MCMV)-specific CD4 T cell responses and the mechanisms by which these cells contribute to viral control are not well understood, mainly due to lack of appropriate tools to characterize MCMV-specific CD4 T cells. We therefore generated MCMV-specific CD4 T cell hybridomas, then used an MCMV expression library and overlapping peptides to identify CD4 T cell epitopes. We used these novel tools to study the long-term kinetics and organ distribution of MCMV-specific CD4 T cells in comparison to MCMV-specific CD8 T cell responses. We demonstrate that the overall MCMV-specific CD4 T cell response stabilizes during the latent stage, which stands in contrast to subpopulations of MCMV-specific CD8 T cells and HCMV-specific CD4 T cells which accumulate over the course of CMV latency. Furthermore, MCMV-specific CD4 T cells displayed a Th1 phenotype, secreting high levels of IFN-gamma and TNF-alpha and to some extent IL-2, cytokines which are involved in protection from CMV disease.     

Cutting edge: murine cytomegalovirus induces a polyfunctional CD4 T cell response

CD4 T lymphocytes regulate the adaptive immune response to most viruses, both by providing help to CD8 T cells and B cells as well as through direct antiviral activity. Currently, no mouse cytomegalovirus (MCMV)-specific CD4 T cell responses are known. In this study, we identify and characterize 15 I-A(b)-restricted CD4 T cell responses specific for MCMV epitopes. CD4 T cells accumulate to high levels in the spleen and lungs during acute infection and produce multiple cytokines (IFN-gamma, TNF, IL-2, IL-10, and IL-17). Interestingly, IL-17 and IFN-gamma production within epitope-specific cells was found to be mutually exclusive. CD4 T cells recognizing a peptide derived from m09 were only detectable at later times of infection and displayed a unique cytokine production profile. In total, this study reveals that the MCMV-specific CD4 T cell response is complex and functionally diverse, highlighting its important role in controlling this persistent pathogen.     

CXCL10 is the key ligand for CXCR3 on CD8+ effector T cells involved in immune surveillance of the lymphocytic choriomeningitis virus-infected central nervous system

IFN-gamma-inducible protein 10/CXCL10 is a chemokine associated with type 1 T cell responses, regulating the migration of activated T cells through binding to the CXCR3 receptor. Expression of both CXCL10 and CXCR3 are observed during immunopathological diseases of the CNS, and this receptor/ligand pair is thought to play a central role in regulating T cell-mediated inflammation in this organ site. In this report, we investigated the role of CXCL10 in regulating CD8(+) T cell-mediated inflammation in the virus-infected brain. This was done through analysis of CXCL10-deficient mice infected intracerebrally with lymphocytic choriomeningitis virus, which in normal immunocompetent mice induces a fatal CD8(+) T cell-mediated meningoencephalitis. We found that a normal antiviral CD8(+) T cell response was generated in CXCL10-deficient mice, and that lack of CXCL10 had no influence on the accumulation of mononuclear cells in the cerebrospinal fluid. However, analysis of the susceptibility of CXCL10-deficient mice to lymphocytic choriomeningitis virus-induced meningitis revealed that these mice just like CXCR3-deficient mice were partially resistant to this disease, whereas wild-type mice invariably died. Furthermore, despite marked up-regulation of the two remaining CXCR3 ligands: CXCL9 and 11, we found a reduced accumulation of CD8(+) T cells in the brain parenchyma around the time point when wild-type mice succumb as a result of CD8(+) T cell-mediated inflammation. Thus, taken together these results indicate a central role for CXCL10 in regulating the accumulation of effector T cells at sites of CNS inflammation, with no apparent compensatory effect of other CXCR3 ligands.     

Both CXCR3 and CXCL10/IFN-inducible protein 10 are required for resistance to primary infection by dengue virus

We examined the extent to which CXCR3 mediates resistance to dengue infection. Following intracerebral infection with dengue virus, CXCR3-deficient (CXCR3(-/-)) mice showed significantly higher mortality rates than wild-type (WT) mice; moreover, surviving CXCR3(-/-) mice, but not WT mice, often developed severe hind-limb paralysis. The brains of CXCR3(-/-) mice showed higher viral loads than those of WT mice, and quantitative analysis using real-time PCR, flow cytometry, and immunohistochemistry revealed fewer T cells, CD8(+) T cells in particular, in the brains of CXCR3(-/-) mice. This suggests that recruitment of effector T cells to sites of dengue infection was diminished in CXCR3(-/-) mice, which impaired elimination of the virus from the brain and thus increased the likelihood of paralysis and/or death. These results indicate that CXCR3 plays a protective rather than an immunopathological role in dengue virus infection. In studies to identify critical CXCR3 ligands, CXCL10/IFN-inducible protein 10-deficient (CXCL10/IP-10(-/-)) mice infected with dengue virus showed a higher mortality rate than that of the CXCR3(-/-) mice. Although CXCL10/IP-10, CXCL9/monokine induced by IFN-gamma, and CXCL11/IFN-inducible T cell alpha chemoattractant share a single receptor and all three of these chemokines are induced by dengue virus infection, the latter two could not compensate for the absence of CXCL10/IP-10 in this in vivo model. Our results suggest that both CXCR3 and CXCL10/IP-10 contribute to resistance against primary dengue virus infection and that chemokines that are indistinguishable in in vitro assays differ in their activities in vivo.     

Role of the indigenous microbiota in maintaining the virus-specific CD8 memory T cells in the lung of mice infected with murine cytomegalovirus

The potent role of indigenous microbiota in maintaining murine CMV (MCMV)-specific memory T cells, which were measured by multimer staining, was investigated using germfree (GF) mice. When the BALB/c mice bred under specific pathogen-free (SPF) conditions were i.p. infected with 0.2 LD(50) of MCMV, high frequencies of CD69(+)/CD44(+) MCMV-specific CD8 T cells were noted in the lungs even at 6-12 mo after infection (11.1 +/- 3.2 and 9.8 +/- 0.9%, respectively). In contrast, even though the viral load and expression levels of mRNA of such cytokines as IL-2, IL-7, IL-15, and IFN-gamma in the lungs of MCMV-infected GF mice were comparable to those of infected SPF mice, the frequencies of MCMV-specific CD8 T cells in the lungs of infected GF mice were kept lower than 1% at 6-12 mo after infection. In addition, the reconstitution of microbiota of MCMV-infected GF mice by orally administering a fecal suspension prepared from SPF mice restored the frequencies of both CD8(+)/multimer(+) and CD8(+)/multimer(-) T cells to levels similar to those found in SPF mice. These results suggested the indigenous microbiota to play a crucial role in the expansion and maintenance of viral-specific CD8 memory T cells, probably by cross-reactivity between the antigenic epitope of the MCMV-specific memory T cells and the variety of peptides derived from the members of the microbiota. Such cross-reactivity may thus be a major feature of those cells.     

Severe disease, unaltered leukocyte migration, and reduced IFN-gamma production in CXCR3-/- mice with experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a CD4(+) Th1 T cell-mediated disease of the CNS, used to study certain aspects of multiple sclerosis. CXCR3, the receptor for CXCL10, CXCL9, and CXCL11, is preferentially expressed on activated Th1 T cells and has been proposed to govern the migration of lymphocytes into the inflamed CNS during multiple sclerosis and EAE. Unexpectedly, CXCL10-deficient mice were susceptible to EAE, leaving uncertain what the role of CXCR3 and its ligands might play in this disease model. In this study, we report that CXCR3(-/-) mice exhibit exaggerated severity of EAE compared with wild-type (CXCR3(+/+)) littermate mice. Surprisingly, there were neither quantitative nor qualitative differences in CNS-infiltrating leukocytes between CXCR3(+/+) and CXCR3(-/-) mice with EAE. Despite these equivalent inflammatory infiltrates, CNS tissues from CXCR3(-/-) mice with EAE showed worsened blood-brain barrier disruption and more von Willebrand factor-immunoreactive vessels within inflamed spinal cords, as compared with CXCR3(+/+) mice. Spinal cords of CXCR3(-/-) mice with EAE demonstrated decreased levels of IFN-gamma, associated with reduced inducible NO synthase immunoreactivity, and lymph node T cells from CXCR3(-/-) mice primed with MOG(35-55) secreted less IFN-gamma in Ag-driven recall responses than cells from CXCR3(+/+) animals. CXCR3(-/-) lymph node T cells also showed enhanced Ag-driven proliferation, which was reduced by addition of IFN-gamma. Taken with prior findings, our data show that CXCL10 is the most relevant ligand for CXCR3 in EAE. CXCR3 does not govern leukocyte trafficking in EAE but modulates T cell IFN-gamma production and downstream events that affect disease severity.     

Protection from lethal infection by adoptive transfer of CD8 T cells genetically engineered to express virus-specific innate immune receptor

CMV infection is one of the most common complications in immunocompromised individuals, such as organ and bone marrow transplant patients. Both innate and adaptive immune responses are required for defense against CMV infection. In murine CMV (MCMV) infection, strains harboring the MCMV-specific NK cell activation receptor, Ly49H (Klra8), are resistant. In contrast, MCMV infection of mice lacking Ly49H gene causes early mortality due to uncontrolled viral replication. In this study, we report the successful protection of mice from lethal MCMV infection with gene-transferred polyclonal CD8 T cells. CD8 T cells expressing a chimeric receptor comprising Ly49H extracellular and CD3zeta cytoplasmic domains are capable of killing target cells expressing the MCMV protein, m157. CD8 T cells expressing the chimeric receptor protect mice in vivo from lethality in the acute phase of MCMV infection, leading to the establishment of long-term protection. These data provide proof-of-principle evidence that a novel strategy for harnessing CD8 cytolytic function through TCR-independent yet pathogen-specific receptor can result in effective protection of hosts from pathogens.     

The Function of the Chemokine Receptor CXCR6 in the T Cell Response of Mice against Listeria monocytogenes

The chemokine receptor CXCR6 is expressed on different T cell subsets and up-regulated following T cell activation. CXCR6 has been implicated in the localization of cells to the liver due to the constitutive expression of its ligand CXCL16 on liver sinusoidal endothelial cells. Here, we analyzed the role of CXCR6 in CD8⁺ T cell responses to infection of mice with Listeria monocytogenes. CD8⁺ T cells responding to listerial antigens acquired high expression levels of CXCR6. However, deficiency of mice in CXCR6 did not impair control of the L. monocytogenes infection. CXCR6-deficient mice were able to generate listeria-specific CD4⁺ and CD8⁺ T cell responses and showed accumulation of T cells in the infected liver. In transfer assays, we detected reduced accumulation of listeria-specific CXCR6-deficient CD8⁺ T cells in the liver at early time points post infection. Though, CXCR6 was dispensable at later time points of the CD8⁺ T cell response. When transferred CD8⁺ T cells were followed for extended time periods, we observed a decline in CXCR6-deficient CD8⁺ T cells. The manifestation of this cell loss depended on the tissue analyzed. In conclusion, our results demonstrate that CXCR6 is not required for the formation of a T cell response to L. monocytogenes and for the accumulation of T cells in the infected liver but CXCR6 appears to influence long-term survival and tissue distribution of activated cells.     

Chemotactic responses of IL-4-, IL-10-, and IFN-gamma-producing CD4+ T cells depend on tissue origin and microbial stimulus

Th1- and Th2-polarized immune responses are crucial in the defense against pathogens but can also promote autoimmunity and allergy. The chemokine receptors CXCR3 and CCR4 have been implicated in differential trafficking of IFN-gamma- and IL-4-producing T cells, respectively, but also in tissue and inflammation-specific homing independent of cytokine responses. Here, we tested whether CD4+ T cells isolated from murine tissues under homeostatic or inflammatory conditions exhibit restricted patterns of chemotactic responses that correlate with their production of IFN-gamma, IL-4, or IL-10. In uninfected mice, IL-4-producing T cells preferentially migrated to the CCR4 ligand, CCL17, whereas IFN-gamma-expressing T cells as well as populations of IL-4+ or IL-10+ T cells migrated to the CXCR3 ligand, CXCL9. All cytokine-producing T cell subsets strongly migrated to the CXCR4 ligand, CXCL12. We assessed chemotaxis of T cells isolated from mice infected with influenza A virus or the nematode Nippostrongylus brasiliensis, which induce a strong Th1 or Th2 response in the lung, respectively. Unexpectedly, the chemotactic responses of IL-4+ T cells and T cells expressing the immunosuppressive cytokine IL-10 were influenced not only by the strongly Th1- or Th2-polarized environments but also by their anatomical localization, i.e., lung or spleen. In contrast, IFN-gamma+ T cells exhibited robust chemotaxis toward CXCL9 and had the most consistent migration pattern in both infection models. The results support a model in which the trafficking responses of many effector and regulatory T cells are regulated as a function of the infectious and tissue environments.     

Role of IP-10/CXCL10 in the progression of pancreatitis-like injury in mice after murine retroviral infection

Exocrinopathy and pancreatitis-like injury were developed in C57BL/6 (B6) mice infected with LP-BM5 murine leukemia virus, which is known to induce murine acquired immunodeficiency syndrome (MAIDS). The role of chemokines, especially CXCL10/interferon (IFN)-gamma-inducible protein 10 (IP-10), a chemokine to attract CXCR3+ T helper 1-type CD4+ T cells, has not been investigated thoroughly in the pathogenesis of pancreatitis. B6 mice were inoculated intraperitoneally with LP-BM5 and then injected every week with either an antibody against IP-10 or a control antibody. Eight weeks after infection, we analyzed the effect of IP-10 neutralization. Anti-IP-10 antibody treatment did not change the generalized lymphadenopathy and hepatosplenomegaly of mice with MAIDS. The treatment significantly reduced the number of IP-10- and CXCR3-positive cells in the mesenteric lymph nodes (mLNs) but not the phenotypes and gross numbers of cells. In contrast, IP-10 neutralization reduced the number of mononuclear cells infiltrating into the pancreas. Anti-IP-10 antibody treatment did not change the numbers of IFN-gamma+ and IL10+ cells in the mLN but significantly reduced their numbers, especially IFN-gamma+ and IL-10+ CD4+ T cells and IFN-gamma+ Mac-1+ cells, in the pancreas. IP-10 neutralization ameliorated the pancreatic lesions of mice with MAIDS probably by blocking the cellular infiltration of CD4+ T cells and IFN-gamma+ Mac-1+ cells into the pancreas at least at 8 wk after infection, suggesting that IP-10 and these cells might play a key role in the development of chronic autoimmune pancreatitis.     

Kinetics of ocular and systemic antigen-specific T-cell responses elicited during murine cytomegalovirus retinitis

Cytomegalovirus (CMV) reactivation in the retina of immunocompromized patients is a cause of significant morbidity as it can lead to blindness. The adaptive immune response is critical in controlling murine CMV (MCMV) infection in MCMV-susceptible mouse strains. CD8(+) T cells limit systemic viral replication in the acute phase of infection and are essential to contain latent virus. In this study, we provide the first evaluation of the kinetics of anti-viral T-cell responses after subretinal infection with MCMV. The acute response was characterized by a rapid expansion phase, with infiltration of CD8(+) T cells into the infected retina, followed by a contraction phase. MCMV-specific T cells displayed biphasic kinetics with a first peak at day 12 and contraction by day 18 followed by sustained recruitment of these cells into the retina at later time points post-infection. MCMV-specific CD8(+) T cells were also observed in the draining cervical lymph nodes and the spleen. Presentation of viral epitopes and activation of CD8(+) T cells was widespread and could be detected in the spleen and the draining lymph nodes, but not in the retina or iris. Moreover, after intraocular infection, antigen-specific cytotoxic activity was detectable and exhibited kinetics equivalent to those observed after intraperitoneal infection with the same viral dose. These data provide novel insights of how and where immune responses are initiated when viral antigen is present in the subretinal space.     

CXCR3 mediates region-specific antiviral T cell trafficking within the central nervous system during West Nile virus encephalitis

Regional differences in inflammation during viral infections of the CNS suggest viruses differentially induce patterns of chemoattractant expression, depending on their cellular targets. Previous studies have shown that expression of the chemokine CXCL10 by West Nile virus (WNV)-infected neurons is essential for the recruitment of CD8 T cells for the purpose of viral clearance within the CNS. In the current study we used mice deficient for the CXCL10 receptor, CXCR3, to evaluate its role in leukocyte-mediated viral clearance of WNV infection within various CNS compartments. WNV-infected CXCR3-deficient mice exhibited significantly enhanced mortality compared with wild-type controls. Immunologic and virologic analyses revealed that CXCR3 was dispensable for control of viral infection in the periphery and in most CNS compartments but, surprisingly, was required for CD8 T cell-mediated antiviral responses specifically within the cerebellum. WNV-specific, CXCR3-expressing T cells preferentially migrated into the cerebellum, and WNV-infected cerebellar granule cell neurons expressed higher levels of CXCL10 compared with similarly infected cortical neurons. These results indicate that WNV differentially induces CXCL10 within neuronal populations and suggest a novel model for nonredundancy in chemokine-mediated inflammation among CNS compartments.     

A nonstructural viral protein expressed by a recombinant vaccinia virus protects against lethal cytomegalovirus infection.

The nonstructural immediate-early protein pp89 of murine cytomegalovirus (MCMV) is the first viral protein synthesized after infection and has a regulatory function in viral gene expression. Despite its localization in the nucleus of infected cells, pp89 is also the dominant antigen recognized by MCMV-specific cytolytic T lymphocytes. The recombinant vaccinia virus MCMV-ieI-VAC, which expresses pp89, was used to study the capacity of this protein to induce protective immunity in BALB/c mice. Vaccination with MCMV-ieI-VAC induced a long-lasting immunity that protected mice against challenge with a lethal dose of MCMV but did not prevent infection and morbidity. In vivo depletion of CD8+ T lymphocytes before challenge completely abrogated the protective immunity. CD8+ T lymphocytes derived from MCMV-ieI-VAC-primed donors and adoptively transferred into sublethally irradiated and MCMV-infected recipients were found to limit viral replication in host tissues, whereas CD4+ T lymphocytes and pp89-specific antiserum had no protective effect. The data demonstrate for the first time that a single nonstructural viral protein can confer protection against a lethal cytolytic infection and that this immunity is entirely mediated by the CD8+ subpopulation of T lymphocytes.     

Chemokine Transfer by Liver Sinusoidal Endothelial Cells Contributes to the Recruitment of CD4+ T Cells into the Murine Liver

Leukocyte adhesion and transmigration are central features governing immune surveillance and inflammatory reactions in body tissues. Within the liver sinusoids, chemokines initiate the first crucial step of T-cell migration into the hepatic tissue. We studied molecular mechanisms involved in endothelial chemokine supply during hepatic immune surveillance and liver inflammation and their impact on the recruitment of CD4⁺ T cells into the liver. In the murine model of Concanavalin A-induced T cell-mediated hepatitis, we showed that hepatic expression of the inflammatory CXC chemokine ligands (CXCL)9 and CXCL10 strongly increased whereas homeostatic CXCL12 significantly decreased. Consistently, CD4⁺ T cells expressing the CXC chemokine receptor (CXCR)3 accumulated within the inflamed liver tissue. In histology, CXCL9 was associated with liver sinusoidal endothelial cells (LSEC) which represent the first contact site for T-cell immigration into the liver. LSEC actively transferred basolaterally internalized CXCL12, CXCL9 and CXCL10 via clathrin-coated vesicles to CD4⁺ T cells leading to enhanced transmigration of CXCR4⁺ total CD4⁺ T cells and CXCR3⁺ effector/memory CD4⁺ T cells, respectively in vitro. LSEC-expressed CXCR4 mediated CXCL12 transport and blockage of endothelial CXCR4 inhibited CXCL12-dependent CD4⁺ T-cell transmigration. In contrast, CXCR3 was not involved in the endothelial transport of its ligands CXCL9 and CXCL10. The clathrin-specific inhibitor chlorpromazine blocked endothelial chemokine internalization and CD4⁺ T-cell transmigration in vitro as well as migration of CD4⁺ T cells into the inflamed liver in vivo. Moreover, hepatic accumulation of CXCR3⁺ CD4⁺ T cells during T cell-mediated hepatitis was strongly reduced after administration of chlorpromazine. These data demonstrate that LSEC actively provide perivascularly expressed homeostatic and inflammatory chemokines by CXCR4- and clathrin-dependent intracellular transport mechanisms thereby contributing to the hepatic recruitment of CD4⁺ T-cell populations during immune surveillance and liver inflammation.     

Chemokine gene expression during fatal murine cerebral malaria and protection due to CXCR3 deficiency

Cerebral malaria (CM) can be a fatal manifestation of Plasmodium falciparum infection. Using murine models of malaria, we found much greater up-regulation of a number of chemokine mRNAs, including those for CXCR3 and its ligands, in the brain during fatal murine CM (FMCM) than in a model of non-CM. Expression of CXCL9 and CXCL10 RNA was localized predominantly to the cerebral microvessels and in adjacent glial cells, while expression of CCL5 was restricted mainly to infiltrating lymphocytes. The majority of mice deficient in CXCR3 were found to be protected from FMCM, and this protection was associated with a reduction in the number of CD8+ T cells in brain vessels as well as reduced expression of perforin and FasL mRNA. Adoptive transfer of CD8+ cells from C57BL/6 mice with FMCM abrogated this protection in CXCR3-/- mice. Moreover, there were decreased mRNA levels for the proinflammatory cytokines IFN-gamma and lymphotoxin-alpha in the brains of mice protected from FMCM. These data suggest a role for CXCR3 in the pathogenesis of FMCM through the recruitment and activation of pathogenic CD8+ T cells.     

Viral interference with antigen presentation does not alter acute or chronic CD8 T cell immunodominance in murine cytomegalovirus infection

Both human CMV and murine CMV (MCMV) elicit large CD8 T cell responses, despite the potent effects of viral genes that interfere with the MHC class I (MHC I) pathway of Ag presentation. To investigate the impact of immune evasion on CD8 T cell priming, we infected mice with wild-type (wt) MCMV or a mutant lacking its MHC I immune evasion genes, Deltam4+m6+m152 MCMV. In acute infection, the two viruses elicited a CD8 T cell response to 26 peptide epitopes that was virtually identical in total size, kinetics, and immunodominance hierarchy. This occurred despite results demonstrating that primary DCs are susceptible to the effects of MCMV's MHC I immune evasion genes. Eight months later, responses to both wt and mutant MCMV displayed the same CD8 T cell "memory inflation" and altered immunodominance that characterize the transition to chronic MCMV infection in C57BL/6 mice. Taken together, these findings suggest either that cross-priming dominates over direct CD8 T cell priming in both acute and chronic MCMV infection, or else that the MHC I immune evasion genes of MCMV are unable to alter direct CD8 T cell priming in vivo. At 2 years postinfection, differences in CD8 T cell immunodominance emerged between individual mice, but on average there were only slight differences between wt and mutant virus infections. Overall, the data indicate that the presence or absence of MHC I immune evasion genes has remarkably little impact on the size or specificity of the MCMV-specific CD8 T cell response over an entire lifetime of infection.     

GammadeltaT cells initiate acute inflammation and injury in adenovirus-infected liver via cytokine-chemokine cross talk

Emerging studies suggest an important role for the innate immune response in replication-defective adenovirus (Ad)-mediated acute liver toxicity. Specifically, classical innate immune cells (including NK cells, neutrophils, and Kupffer cells) have all been implicated in the development of Ad-mediated acute liver toxicity. The nonclassical innate immune T cell, the gammadeltaT cell, has been implicated in the pathophysiology of several viral infections that predominantly affect the mucosa and brain, but the specific role in the pathology of AdLacZ-mediated acute liver inflammation and injury as well as accompanying vector clearance is largely unknown. In the present study, we demonstrated that a CXCL9-CXCR3-dependent mechanism governed the accumulation of gammadeltaT cells in the livers of mice infected with Ad expressing the Escherichia coli LacZ gene (AdLacZ). We also showed a critical role for gammadeltaT cells in initiating acute liver toxicity after AdLacZ administration, driven in part by the ability of gammadeltaT cells to promote the recruitment of the conventional T cell, the CD8(+) T cell, into the liver. Furthermore, reduced hepatic injury in AdLacZ-infected gammadeltaT-cell-deficient mice was associated with lower hepatic levels of gamma interferon (IFN-gamma) and CXCL9, an IFN-gamma-inducible chemokine. Finally, our study highlighted a key role for IFN-gamma and CXCL9 cross talk acting in a feedback loop to drive the proinflammatory effects of gammadeltaT cells during AdLacZ-mediated acute liver toxicity. Specifically, intracellular IFN-gamma produced by activated hepatic gammadeltaT cells interacts with hepatocytes to mediate hepatic CXCL9 production, with the consequent accumulation of CXCR3-bearing gammadeltaT cells in the liver to cause acute liver damage without vector clearance.     

CXCR6+CD4+ T cells promote mortality during Trypanosoma brucei infection

Liver macrophages internalize circulating bloodborne parasites. It remains poorly understood how this process affects the fate of the macrophages and T cell responses in the liver. Here, we report that infection by Trypanosoma brucei induced depletion of macrophages in the liver, leading to the repopulation of CXCL16-secreting intrahepatic macrophages, associated with substantial accumulation of CXCR6⁺CD4⁺ T cells in the liver. Interestingly, disruption of CXCR6 signaling did not affect control of the parasitemia, but significantly enhanced the survival of infected mice, associated with reduced inflammation and liver injury. Infected CXCR6 deficient mice displayed a reduced accumulation of CD4⁺ T cells in the liver; adoptive transfer experiments suggested that the reduction of CD4⁺ T cells in the liver was attributed to a cell intrinsic property of CXCR6 deficient CD4⁺ T cells. Importantly, infected CXCR6 deficient mice receiving wild-type CD4⁺ T cells survived significantly shorter than those receiving CXCR6 deficient CD4⁺ T cells, demonstrating that CXCR6⁺CD4⁺ T cells promote the mortality. We conclude that infection of T. brucei leads to depletion and repopulation of liver macrophages, associated with a substantial influx of CXCR6⁺CD4⁺ T cells that mediates mortality.     

CXCR3 and IFN protein-10 in Pneumocystis pneumonia

We have previously shown that Tc1 CD8(+) T cells have in vitro and in vivo effector activity against Pneumocystis (PC) infection in mice. Because these cells have preferential expression of CXCR3, we investigated whether CXCR3 was required for host defense activity against PC. Mice deficient in CXCR3 but CD4(+) T cell intact, showed an initial delay but were able to clear the infectious challenge, indicating that CXCR3 signaling is not essential for clearance of PC. CD4-depleted mice had lower levels of monokine induced by IFN-gamma, IFN protein-10 (IP-10), and IFN-inducible T cell alpha-chemoattractant at day 7 of infection and are permissive to PC infection. Overexpression of IP-10 in the lungs by adenoviral gene transfer did not accelerate clearance of infection in control mice but accelerated clearance by day 28 in mice depleted of CD4(+) T cells. This effect was associated with increased recruitment of CD8(+) T to the lungs with higher CXCR3(+) expression levels and enhanced IFN-gamma secretion upon in vitro activation compared with control mice. These results indicate that the CXCR3 chemokines are part of the host defense response to PC, and that IP-10 can direct Tc1 CD8(+) T cell recruitment to the lungs and contribute to host defense against PC even in the absence of CD4(+) T cells.