Matrix metalloproteinase 9 facilitates West Nile virus entry into the brain

West Nile virus (WNV) is the most-common cause of mosquito-borne encephalitis in the United States. Invasion of the brain by WNV is influenced by viral and host factors, and the molecular mechanism underlying disruption of the blood-brain barrier is likely multifactorial. Here we show that matrix metalloproteinase 9 (MMP9) is involved in WNV entry into the brain by enhancing blood-brain barrier permeability. Murine MMP9 expression was induced in the circulation shortly after WNV infection, and the protein levels remained high even when viremia subsided. In the murine brain, MMP9 expression and its enzymatic activity were upregulated and MMP9 was shown to partly localize to the blood vessels. Interestingly, we also found that cerebrospinal fluid from patients suffering from WNV contained increased MMP9 levels. The peripheral viremia and expression of host cytokines were not altered in MMP9(-/-) mice; however, these animals were protected from lethal WNV challenge. The resistance of MMP9(-/-) mice to WNV infection correlated with an intact blood-brain barrier since immunoglobulin G, Evans blue leakage into brain, and type IV collagen degradation were markedly reduced in the MMP9(-/-) mice compared with their levels in controls. Consistent with this, the brain viral loads, selected inflammatory cytokines, and leukocyte infiltrates were significantly reduced in the MMP9(-/-) mice compared to their levels in wild-type mice. These data suggest that MMP9 plays a role in mediating WNV entry into the central nervous system and that strategies to interrupt this process may influence the course of West Nile encephalitis.     

CD22 Is Required for Protection against West Nile Virus Infection

West Nile virus (WNV) is a RNA virus of the family Flaviviridae and the leading cause of mosquito-borne encephalitis in the United States. Humoral immunity is essential for protection against WNV infection; however, the requirements for initiating effective antibody responses against WNV infection are still unclear. CD22 (Siglec-2) is expressed on B cells and regulates B cell receptor signaling, cell survival, proliferation, and antibody production. In this study, we investigated how CD22 contributes to protection against WNV infection and found that CD22 knockout (Cd22^−/−) mice were highly susceptible to WNV infection and had increased viral loads in the serum and central nervous system (CNS) compared to wild-type (WT) mice. This was not due to a defect in humoral immunity, as Cd22^−/− mice had normal WNV-specific antibody responses. However, Cd22^−/− mice had decreased WNV-specific CD8⁺ T cell responses compared to those of WT mice. These defects were not simply due to reduced cytotoxic activity or increased cell death but, rather, were associated with decreased lymphocyte migration into the draining lymph nodes (dLNs) of infected Cd22^−/− mice. Cd22^−/− mice had reduced production of the chemokine CCL3 in the dLNs after infection, suggesting that CD22 affects chemotaxis via controlling chemokine production. CD22 was not restricted to B cells but was also expressed on a subset of splenic DCIR2⁺ dendritic cells that rapidly expand early after WNV infection. Thus, CD22 plays an essential role in controlling WNV infection by governing cell migration and CD8⁺ T cell responses.     

Caspase 3-dependent cell death of neurons contributes to the pathogenesis of West Nile virus encephalitis

West Nile virus (WNV) is a neurotropic, arthropod-borne flavivirus that has become a significant global cause of viral encephalitis. To examine the mechanisms of WNV-induced neuronal death and the importance of apoptosis in pathogenesis, we evaluated the role of a key apoptotic regulator, caspase 3. WNV infection induced caspase 3 activation and apoptosis in the brains of wild-type mice. Notably, congenic caspase 3(-/-) mice were more resistant to lethal WNV infection, although there were no significant differences in the tissue viral burdens or the kinetics of viral spread. Instead, decreased neuronal death was observed in the cerebral cortices, brain stems, and cerebella of caspase 3(-/-) mice. Analogously, primary central nervous system (CNS)-derived neurons demonstrated caspase 3 activation and apoptosis after WNV infection, and treatment with caspase inhibitors or a genetic deficiency in caspase 3 significantly decreased virus-induced death. These studies establish that caspase 3-dependent apoptosis contributes to the pathogenesis of lethal WNV encephalitis and suggest possible novel therapeutic targets to restrict CNS injury.     

The Bacteriostatic Protein Lipocalin 2 Is Induced in the Central Nervous System of Mice with West Nile Virus Encephalitis

Lipocalin 2 (Lcn2) is a bacteriostatic factor produced during the innate immune response to bacterial infection. Whether Lcn2 has a function in viral infection is unknown. We investigated the regulation and function of Lcn2 in the central nervous system (CNS) of mice during West Nile virus (WNV) encephalitis. Lcn2 mRNA and protein were induced in the brain by day 5, and this induction increased further by day 7 postinfection but was delayed compared with the induction of the toll-like receptor 3 (TLR3) gene, retinoic acid-inducible gene 1 (RIG-I), and melanoma differentiation-associated protein 5 (MDA5) gene. The Lcn2 mRNA and protein were both found at high levels in the choroid plexus, vascular endothelium, macrophage/microglia, and astrocytes. However, some neuronal subsets contained Lcn2 protein but no detectable mRNA. In Lcn2 knockout (KO) mice, with the exception of CXC motif chemokine 5 (CXCL5), which was significantly more downregulated than in wild-type (WT) mice, expression levels of a number of other host response genes were similar in the two genotypes. The brain from Lcn2 and WT mice with WNV encephalitis contained similar numbers of infiltrating macrophages, granulocytes, and T cells. Lcn2 KO and WT mice had no significant difference in tissue viral loads or survival after infection with different doses of WNV. We conclude that Lcn2 gene expression is induced to high levels in a time-dependent fashion in a variety of cells and regions of the CNS of mice with WNV encephalitis. The function of Lcn2 in the host response to WNV infection remains largely unknown, but our data indicate that it is dispensable as an antiviral or immunoregulatory factor in WNV encephalitis.     

IL-12, but not IL-18, is critical to neutrophil activation and resistance to polymicrobial sepsis induced by cecal ligation and puncture

Sepsis is a systemic inflammatory response resulting from local infection due, at least in part, to impaired neutrophil migration. IL-12 and IL-18 play an important role in neutrophil migration. We have investigated the mechanism and relative role of IL-12 and IL-18 in polymicrobial sepsis induced by cecal ligation and puncture (CLP) in mice. Wild-type (WT) and IL-18(-/-) mice were resistant to sublethal CLP (SL-CLP) sepsis. In contrast, IL-12(-/-) mice were susceptible to SL-CLP sepsis with high bacteria load in peritoneal cavity and systemic inflammation (serum TNF-alpha and lung neutrophil infiltration). The magnitude of these events was similar to those observed in WT mice with lethal CLP sepsis. The inability of IL-12(-/-) mice to restrict the infection was not due to impairment of neutrophil migration, but correlated with decrease of phagocytosis, NO production, and microbicidal activities of their neutrophils, and with reduction of systemic IFN-gamma synthesis. Consistent with this observation, IFN-gamma(-/-) mice were as susceptible to SL-CLP as IL-12(-/-) mice. Moreover, addition of IFN-gamma to cultures of neutrophils from IL-12(-/-) mice restored their phagocytic, microbicidal activities and NO production. Mortality of IL-12(-/-) mice to SL-CLP was prevented by treatment with IFN-gamma. Thus we show that IL-12, but not IL-18, is critical to an efficient host defense in polymicrobial sepsis. IL-12 acts through induction of IFN-gamma and stimulation of phagocytic and microbicidal activities of neutrophils, rather than neutrophil migration per se. Our data therefore provide further insight into the defense mechanism against this critical area of infectious disease.     

PKR and RNase L contribute to protection against lethal West Nile Virus infection by controlling early viral spread in the periphery and replication in neurons

West Nile virus (WNV) is a neurotropic, mosquito-borne flavivirus that can cause lethal meningoencephalitis. Type I interferon (IFN) plays a critical role in controlling WNV replication, spread, and tropism. In this study, we begin to examine the effector mechanisms by which type I IFN inhibits WNV infection. Mice lacking both the interferon-induced, double-stranded-RNA-activated protein kinase (PKR) and the endoribonuclease of the 2',5'-oligoadenylate synthetase-RNase L system (PKR(-/-) x RL(-/-)) were highly susceptible to subcutaneous WNV infection, with a 90% mortality rate compared to the 30% mortality rate observed in congenic wild-type mice. PKR(-/-) x RL(-/-) mice had increased viral loads in their draining lymph nodes, sera, and spleens, which led to early viral entry into the central nervous system (CNS) and higher viral burden in neuronal tissues. Although mice lacking RNase L showed a higher CNS viral burden and an increased mortality, they were less susceptible than the PKR(-/-) x RL(-/-) mice; thus, we also infer an antiviral role for PKR in the control of WNV infection. Notably, a deficiency in both PKR and RNase L resulted in a decreased ability of type I IFN to inhibit WNV in primary macrophages and cortical neurons. In contrast, the peripheral neurons of the superior cervical ganglia of PKR(-/-) x RL(-/-) mice showed no deficiency in the IFN-mediated inhibition of WNV. Our data suggest that PKR and RNase L contribute to IFN-mediated protection in a cell-restricted manner and control WNV infection in peripheral tissues and some neuronal subtypes.     

Pulmonary immune cells and inflammatory cytokine dysregulation are associated with mortality of IL-1R1-/-mice infected with influenza virus (H1 N1)

Respirovirus infection can cause viral pneumonia and acute lung injury (ALI).The interleukin-1 (IL-1) family consists of proinflammatory cytokines that play essential roles in regulating immune and inflammatory responses in vivo.IL-1 signaling is associated with protection against respiratory influenza virus infection by mediation of the pulmonary anti-viral immune response and inflammation.We analyzed the infiltration lung immune leukocytes and cytokines that contribute to inflammatory lung pathology and mortality of fatal H1N1 virus-infected IL-1 receptor 1 (IL-1R1) deficient mice.Results showed that early innate immune cells and cytokine/chemokine dysregulation were observed with significantly decreased neutrophil infiltration and IL-6,TNF-α,G-CSF,KC,and MIP-2 cytokine levels in the bronchoalveolar lavage fluid of infected IL-1R1-/-mice in comparison with that of wild type infected mice.The adaptive immune response against the H1N1 virus in IL-1R1-/-mice was impaired with downregulated anti-viral Th1 cell,CD8+ cell,and antibody functions,which contributes to attenuated viral clearance.Histological analysis revealed reduced lung inflammation during early infection but severe lung pathology in late infection in IL-1R1-/-mice compared with that in WT infected mice.Moreover,the infected IL-1R1-/-mice showed markedly reduced neutrophil generation in bone marrow and neutrophil recruitment to the inflamed lung.Together,these results suggest that IL-1 signaling is associated with pulmonary anti-influenza immune response and inflammatory lung injury,particularly via the influence on neutrophil mobilization and inflammatory cytokine/chemokine production.     

Maximal adjuvant activity of nasally delivered IL-1α requires adjuvant-responsive CD11c(+) cells and does not correlate with adjuvant-induced in vivo cytokine production

IL-1 has been shown to have strong mucosal adjuvant activities, but little is known about its mechanism of action. We vaccinated IL-1R1 bone marrow (BM) chimeric mice to determine whether IL-1R1 expression on stromal cells or hematopoietic cells was sufficient for the maximal adjuvant activity of nasally delivered IL-1α as determined by the acute induction of cytokine responses and induction of Bacillus anthracis lethal factor (LF)-specific adaptive immunity. Cytokine and chemokine responses induced by vaccination with IL-1α were predominantly derived from the stromal cell compartment and included G-CSF, IL-6, IL-13, MCP-1, and keratinocyte chemoattractant. Nasal vaccination of Il1r1(-/-) (knock-out [KO]) mice given wild-type (WT) BM (WT→KO) and WT→WT mice with LF + IL-1α induced maximal adaptive immune responses, whereas vaccination of WT mice given Il1r1(-/-) BM (KO→WT) resulted in significantly decreased production of LF-specific serum IgG, IgG subclasses, lethal toxin-neutralizing Abs, and mucosal IgA compared with WT→KO and WT→WT mice (p < 0.05). IL-1α adjuvant activity was not dependent on mast cells. However, the ability of IL-1α to induce serum LF-specific IgG2c and lethal toxin-neutralizing Abs was significantly impaired in CD11c-Myd88(-/-) mice when compared with WT mice (p < 0.05). Our results suggest that CD11c(+) cells must be directly activated by nasally administered IL-1α for maximal adjuvant activity and that, although stromal cells are required for maximal adjuvant-induced cytokine production, the adjuvant-induced stromal cell cytokine responses are not required for effective induction of adaptive immunity.     

Tumor necrosis factor alpha protects against lethal West Nile virus infection by promoting trafficking of mononuclear leukocytes into the central nervous system

West Nile virus (WNV) is a neurotropic flavivirus that has emerged globally as a significant cause of viral encephalitis in humans, especially in immunocompromised individuals. Previous studies have shown essential protective roles for antiviral cytokines (e.g., alpha interferon [IFN-alpha] and IFN-gamma) against WNV in mice. However, studies using cell culture offer conflicting answers regarding whether tumor necrosis factor alpha (TNF-alpha) has an anti-WNV function. To test the biological significance of TNF-alpha against WNV in vivo, experiments were performed with TNF receptor-1 (TNF-R1)-deficient and TNF-alpha-depleted C57BL/6 mice. TNF-R1(-/-) mice had enhanced mortality and decreased survival time after WNV infection compared to congenic wild-type mice. Consistent with this, administration of a neutralizing anti-TNF-alpha monoclonal antibody also decreased survival after WNV infection. Relatively small differences in viral burdens in peripheral tissues of TNF-R1(-/-) mice were observed, and this occurrence correlated with a modest antiviral effect of TNF-alpha on primary macrophages but not dendritic cells. In contrast, the viral titers detected in the central nervous systems of TNF-R1(-/-) mice were significantly increased compared to those of wild-type mice, although TNF-alpha did not have a direct antiviral effect in primary neuron cultures. Whereas no defect in priming of adaptive B- and T-cell responses in TNF-R1(-/-) mice was observed, there were significant reductions in accumulations of CD8+ T cells and macrophages in the brain. Our data are most consistent with a model in which interaction of TNF-alpha with TNF-R1 protects against WNV infection by regulating migration of protective inflammatory cells into the brain during acute infection.     

Fas ligand interactions contribute to CD8+ T-cell-mediated control of West Nile virus infection in the central nervous system

West Nile virus (WNV) is a neurotropic flavivirus that causes encephalitis, most frequently in elderly and immunocompromised humans. Previous studies demonstrated that CD8+ T cells utilize perforin-dependent cytolytic mechanisms to limit WNV infection. Nonetheless, the phenotype of perforin-deficient CD8+ T cells was not as severe as that of an absence of CD8+ T cells, suggesting additional effector control mechanisms. In this study, we evaluated the contribution of Fas-Fas ligand (FasL) interactions to CD8+ T-cell-mediated control of WNV infection. Notably, the cell death receptor Fas was strongly upregulated on neurons in culture and in vivo after WNV infection. gld mice that were functionally deficient in FasL expression showed increased susceptibility to lethal WNV infection. Although antigen-specific priming of CD8+ T cells in peripheral lymphoid tissues was normal in gld mice, increased central nervous system (CNS) viral burdens and delayed clearance were observed. Moreover, the adoptive transfer of WNV-primed wild-type but not gld CD8+ T cells to recipient CD8(-/-) or gld mice efficiently limited infection in the CNS and enhanced survival rates. Overall, our data suggest that CD8+ T cells also utilize FasL effector mechanisms to contain WNV infection in Fas-expressing neurons in the CNS.     

Alpha/beta interferon protects against lethal West Nile virus infection by restricting cellular tropism and enhancing neuronal survival

West Nile virus (WNV) is a mosquito-borne flavivirus that is neurotropic in humans, birds, and other animals. While adaptive immunity plays an important role in preventing WNV spread to the central nervous system (CNS), little is known about how alpha/beta interferon (IFN-alpha/beta) protects against peripheral and CNS infection. In this study, we examine the virulence and tropism of WNV in IFN-alpha/beta receptor-deficient (IFN- alpha/betaR-/-) mice and primary neuronal cultures. IFN-alpha/betaR-/- mice were acutely susceptible to WNV infection through subcutaneous inoculation, with 100% mortality and a mean time to death (MTD) of 4.6 +/- 0.7 and 3.8+/- 0.5 days after infection with 10(0) and 10(2) PFU, respectively. In contrast, congenic wild-type 129Sv/Ev mice infected with 10(2) PFU showed 62% mortality and a MTD of 11.9 +/- 1.9 days. IFN-alpha/betaR-/- mice developed high viral loads by day 3 after infection in nearly all tissues assayed, including many that were not infected in wild-type mice. IFN-alpha/betaR-/- mice also demonstrated altered cellular tropism, with increased infection in macrophages, B cells, and T cells in the spleen. Additionally, treatment of primary wild-type neurons in vitro with IFN-beta either before or after infection increased neuronal survival independent of its effect on WNV replication. Collectively, our data suggest that IFN-alpha/beta controls WNV infection by restricting tropism and viral burden and by preventing death of infected neurons.     

IL-21 promotes the pathologic immune response to pneumovirus infection

IL-21 is a cytokine with pleiotropic actions, promoting terminal differentiation of B cells, increased Ig production, and the development of Th17 and T follicular helper cells. IL-21 is also implicated in the development of autoimmune disease and has antitumor activity. In this study, we investigated the role of IL-21 in host defense to pneumonia virus of mice (PVM), which initiates an infection in mice resembling that of respiratory syncytial virus disease in humans. We found that PVM-infected mice expressed IL-21 in lung CD4(+) T cells. Following infection, Il21r(-/-) mice exhibited less lung infiltration by neutrophils than did wild-type (WT) mice and correspondingly had lower levels of the chemokine CXCL1 in bronchoalveolar lavage fluid and lung parenchyma. CD8(+), CD4(+), and γδ T cell numbers were also lower in the lungs of PVM-infected Il21r(-/-) mice than in infected WT mice, with normal Th17 cytokines but diminished IL-6 production in PVM-infected Il21r(-/-) mice. Strikingly, Il21r(-/-) mice had enhanced survival following PVM infection, and moreover, treatment of WT mice with soluble IL-21R-Fc fusion protein enhanced their survival. These data reveal that IL-21 promotes the pathogenic inflammatory effect of PVM and indicate that manipulating IL-21 signaling may represent an immunomodulatory strategy for controlling PVM and potentially other respiratory virus infections.     

Joint production of IL-22 participates in the initial phase of antigen-induced arthritis through IL-1β production

IntroductionRheumatoid arthritis (RA) is a chronic autoimmune disease characterized by neutrophil articular infiltration, joint pain and the progressive destruction of cartilage and bone. IL-22 is a key effector molecule that plays a critical role in autoimmune diseases. However, the function of IL-22 in the pathogenesis of RA remains controversial. In this study, we investigated the role of IL-22 in the early phase of antigen-induced arthritis (AIA) in mice.MethodsAIA was induced in C57BL/6, IL-22^−/−, ASC^−/− and IL-1R1^−/− immunized mice challenged intra-articularly with methylated bovine serum albumin (mBSA). Expression of IL-22 in synovial membranes was determined by RT-PCR. Articular hypernociception was evaluated using an electronic von Frey. Neutrophil recruitment and histopathological analyses were assessed in inflamed knee joint. Joint levels of inflammatory mediators and mBSA-specific IgG concentration in the serum were measured by ELISA.ResultsThe IL-22 mRNA expression and protein levels in synovial tissue were increased during the onset of AIA. In addition, pharmacological inhibition (anti-IL-22 antibody) and genetic deficiency (IL-22^−/− mice) reduced articular pain and neutrophil migration in arthritic mice. Consistent with these findings, recombinant IL-22 joint administration promoted articular inflammation per se in WT mice, restoring joint nociception and neutrophil infiltration in IL-22^−/− mice. Moreover, IL-22-deficient mice showed reduced synovitis (inflammatory cell influx) and lower joint IL-1β levels, whereas the production of IL-17, MCP-1/CCL2, and KC/CXCL1 and the humoral immune response were similar, compared with WT mice. Corroborating these results, the exogenous administration of IL-22 into the joints induced IL-1β production in WT mice and reestablished IL-1β production in IL-22^−/− mice challenged with mBSA. Additionally, IL-1R1^−/− mice showed attenuated inflammatory features induced by mBSA or IL-22 challenge. Articular nociception and neutrophil migration induced by IL-22 were also reduced in ASC^−/− mice.ConclusionsThese results suggest that IL-22 plays a pro-inflammatory/pathogenic role in the onset of AIA through an ASC-dependent stimulation of IL-1β production.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0759-2) contains supplementary material, which is available to authorized users.     

Mycobacterial infection-induced miR-206 inhibits protective neutrophil recruitment via the CXCL12/CXCR4 signalling axis

Pathogenic mycobacteria actively dysregulate protective host immune signalling pathways during infection to drive the formation of permissive granuloma microenvironments. Dynamic regulation of host microRNA (miRNA) expression is a conserved feature of mycobacterial infections across host-pathogen pairings. Here we examine the role of miR-206 in the zebrafish model of Mycobacterium marinum infection, which allows investigation of the early stages of granuloma formation. We find miR-206 is upregulated following infection by pathogenic M. marinum and that antagomir-mediated knockdown of miR-206 is protective against infection. We observed striking upregulation of cxcl12a and cxcr4b in infected miR-206 knockdown zebrafish embryos and live imaging revealed enhanced recruitment of neutrophils to sites of infection. We used CRISPR/Cas9-mediated knockdown of cxcl12a and cxcr4b expression and AMD3100 inhibition of Cxcr4 to show that the enhanced neutrophil response and reduced bacterial burden caused by miR-206 knockdown was dependent on the Cxcl12/Cxcr4 signalling axis. Together, our data illustrate a pathway through which pathogenic mycobacteria induce host miR-206 expression to suppress Cxcl12/Cxcr4 signalling and prevent protective neutrophil recruitment to granulomas.     

Role of two distinct gammadelta T cell subsets during West Nile virus infection.

gammadelta T cells respond rapidly following West Nile virus (WNV) infection, limiting viremia and invasion of the central nervous system and thereby protecting the host from lethal encephalitis. Here, we investigated the role of two major subpopulations of peripheral gammadelta T cells, Vgamma1(+) and Vgamma4(+) cells, in host immunity against WNV infection. We found initially that aged mice were more susceptible to WNV infection than young mice. Following WNV challenge, Vgamma1(+) cells in young mice expanded significantly whereas Vgamma4(+) cells expanded modestly. In contrast, aged mice exhibited a slower and reduced response of Vgamma1(+) cells but maintained a higher content of Vgamma4(+) cells. Vgamma1(+) cells were the major gammadelta subset producing IFN-gamma during WNV infection. Mice depleted of Vgamma1(+) cells had an enhanced viremia and higher mortality to WNV encephalitis. Vgamma4(+) cells had a higher potential for producing tumor necrosis factor-alpha (TNF-alpha), a cytokine known to be involved in blood-brain barrier compromise and WNV entry into the brain. Depletion of Vgamma4(+) cells reduced TNF-alpha level in the periphery, accompanied by a decreased viral load in the brain and a lower mortality to WN encephalitis. These results suggest that Vgamma1(+) and Vgamma4(+) cells play distinct roles in protection and pathogenesis during WNV infection.     

Icam-1 participates in the entry of west nile virus into the central nervous system

Determining how West Nile virus crosses the blood-brain barrier is critical to understanding the pathogenesis of encephalitis. Here, we show that ICAM-1(-/-) mice are more resistant than control animals to lethal West Nile encephalitis. ICAM-1(-/-) mice have a lower viral load, reduced leukocyte infiltration, and diminished neuronal damage in the brain compared to control animals. This is associated with decreased blood-brain barrier leakage after viral infection. These data suggest that ICAM-1 plays an important role in West Nile virus neuroinvasion and that targeting ICAM-1 signaling may help control viral encephalitis.     

Endogenous tissue-type plasminogen activator is protective during Escherichia coli-induced abdominal sepsis in mice

Sepsis is associated with enhanced production of tissue-type plasminogen activator (tPA). We investigated the function of endogenous tPA in the immune responses to Escherichia coli-induced abdominal sepsis using tPA gene-deficient (tPA(-/-)) and normal wild-type (WT) mice. tPA(-/-) mice demonstrated an impaired defense against E. coli peritonitis as indicated by higher bacterial loads at the primary site of the infection, enhanced dissemination, and reduced survival. The protective function of tPA was independent of plasmin since plasminogen gene-deficient (Plg(-/-)) mice were indistinguishable from WT mice. Relative to WT mice, tPA(-/-) mice demonstrated similar neutrophil counts in the peritoneal cavity despite much higher bacterial loads and higher local concentrations of neutrophil attracting chemokines, suggesting a reduced migratory response. In line, tPA(-/-) mice demonstrated a reduced thioglycolate-induced neutrophil influx into the peritoneal cavity and i.p. injection of WT mice with a replication-defective adenoviral vector expressing tPA caused an enhanced cell migration to the peritoneal cavity during E. coli peritonitis. These findings identify a novel protective function of tPA in abdominal sepsis caused by E. coli that seems independent of its role in the generation of plasmin.     

Interleukin-21 Receptor Signalling Is Important for Innate Immune Protection against HSV-2 Infections

Interleukin (IL) -21 is produced by Natural Killer T (NKT) cells and CD4⁺ T cells and is produced in response to virus infections, where IL-21 has been shown to be essential in adaptive immune responses. Cells from the innate immune system such as Natural Killer (NK) cells and macrophages are also important in immune protection against virus. These cells express the IL-21 receptor (IL-21R) and respond to IL-21 with increased cytotoxicity and cytokine production. Currently, however it is not known whether IL-21 plays a significant role in innate immune responses to virus infections. The purpose of this study was to investigate the role of IL-21 and IL-21R in the innate immune response to a virus infection. We used C57BL/6 wild type (WT) and IL-21R knock out (KO) mice in a murine vaginal Herpes Simplex Virus type 2 (HSV-2) infection model to show that IL-21 – IL-21R signalling is indeed important in innate immune responses against HSV-2. We found that the IL-21R was expressed in the vaginal epithelium in uninfected (u.i) WT mice, and expression increased early after HSV-2 infection. IL-21R KO mice exhibited increased vaginal viral titers on day 2 and 3 post infection (p.i.) and subsequently developed significantly higher disease scores and a lower survival rate compared to WT mice. In addition, WT mice infected with HSV-2 receiving intra-vaginal pre-treatment with murine recombinant IL-21 (mIL-21) had decreased vaginal viral titers on day 2 p.i., significantly lower disease scores, and a higher survival rate compared to infected untreated WT controls. Collectively our data demonstrate the novel finding that the IL-21R plays a critical role in regulating innate immune responses against HSV-2 infection.