Antiviral potential of chemokines

Interleukin-15 mediates potent antiviral responses via an interferon-dependent mechanism

Interleukin-15 (IL-15) is a potent growth factor for activated T and natural killer (NK) cells, stimulator of memory T cells and plays an important role in viral immunity. To investigate mechanisms underlying the antiviral activity of IL-15, a recombinant vaccinia virus (rVV) encoding murine IL-15 (VV-IL-15) was constructed. Following infection of mice with VV-IL-15, virus titres in the ovaries were significantly reduced compared to mice infected with control VV. Growth of VV-IL-15 was also reduced in nude athymic mice, indicating the antiviral activity of IL-15 does not require T cells. Additionally, VV-IL-15 augmented the cytolytic activity of natural NK cells in the spleen and enhanced interferon (IFN) mRNA expression and transcription factors associated with IFN induction. Using knockout mice and antibody depletion studies, we showed for the first time that the control of VV-IL-15 replication in mice is dependent on NK cells and IFNs and, in their absence, the protective role of IL-15 is abolished.

Pediatric measles vaccine expressing a dengue antigen induces durable serotype-specific neutralizing antibodies to dengue virus

Dengue disease is an increasing global health problem that threatens one-third of the world's population. Despite decades of efforts, no licensed vaccine against dengue is available. With the aim to develop an affordable vaccine that could be used in young populations living in tropical areas, we evaluated a new strategy based on the expression of a minimal dengue antigen by a vector derived from pediatric live-attenuated Schwarz measles vaccine (MV). As a proof-of-concept, we inserted into the MV vector a sequence encoding a minimal combined dengue antigen composed of the envelope domain III (EDIII) fused to the ectodomain of the membrane protein (ectoM) from DV serotype-1. Immunization of mice susceptible to MV resulted in a long-term production of DV1 serotype-specific neutralizing antibodies. The presence of ectoM was critical to the immunogenicity of inserted EDIII. The adjuvant capacity of ectoM correlated with its ability to promote the maturation of dendritic cells and the secretion of proinflammatory and antiviral cytokines and chemokines involved in adaptive immunity. The protective efficacy of this vaccine should be studied in non-human primates. A combined measles–dengue vaccine might provide a one-shot approach to immunize children against both diseases where they co-exist.

Dengue is a tropical emerging disease that threatens one-third of the world's population, mainly children under the age of 15. The development of an affordable pediatric vaccine that could provide long-term protection against all four dengue serotypes remains a global public health priority. To address this challenge, we evaluated a strategy based on the expression of a minimal dengue antigen by live attenuated measles vaccine (MV), one of the most safe, stable, and effective human vaccines. As a proof-of-concept, we constructed a MV vector expressing a secreted dengue antigen composed of the domain III of the envelope glycoprotein (EDIII), which contains major serotype-specific neutralizing epitopes, fused to the ectodomain of the membrane protein (ectoM) from DV-1, as an adjuvant. This vector induced in mice durable serotype-specific virus-neutralizing antibodies against DV1. The remarkable adjuvant capacity of ectoM to EDIII immunogenicity was correlated to its capacity to mature dendritic cells, known to initiate immune response, and to activate the secretion of a panel of cytokines and chemokines determinant for the establishment of specific adaptive immunity. Such strategy might offer pediatric vaccines to immunize children simultaneously against measles and dengue in areas of the world where the diseases co-exist.

Suppression of NF-κB and AP-1 activation in monocytic cells persistently infected with measles virus

A major cause of the high morbidity and mortality associated with measles infection is attributed to virus-mediated immunosuppression. In this report, we present evidence for a novel strategy of immunosuppression by the measles virus. We observed a marked suppression of lipopolysaccharide (LPS)-induced IL-8, RANTES, TNF-alpha and IL-6 production and NF-kappaB activation in human monocytic cell lines persistently infected with measles virus. This effect was not observed in human epithelial cells lines persistently infected with measles virus. There were no significant differences in expression levels of Toll-like receptors (TLRs) and their associated molecules, or other intracellular signaling molecules of the NF-kappaB signaling pathway in measles-virus-infected monocytic cells compared to uninfected cells. Infected monocytic cells exhibited decreased LPS-induced DNA binding of NF-kappaB and phosphorylation of JNK, namely activation of transcription factors NF-kappaB and AP-1. NF-kappaB was constitutively activated in human epithelial cells persistently infected with measles virus, and LPS treatment resulted in further activation. The cell-type-specific suppression of NF-kappaB activation represents a potential strategy of escape from the host immune system by measles virus via induced immunological silencing in infected cells.

Interferons and viruses: signaling for supremacy

Interferon (IFN)-α and IFN-β are critical mediators of host defense against microbial challenges, directly interfering with viral infection and influencing both the innate and adaptive immune responses. IFNs exert their effects in target cells through the activation of a cell-surface receptor, leading to a cascade of signaling events that determine transcriptional and translation regulation. Understanding the circuitry associated with IFN-mediated signal transduction that leads to a specific biological outcome has been a major focus of our laboratory. Through the efforts of graduate students, postdoctoral fellows, a skilled research technologist, and important collaborations with investigators elsewhere, we have provided some insights into the complexity of the IFN system—and the elegance and simplicity of how protein-protein interactions define biological function.

Ross River virus: Molecular and cellular aspects of disease pathogenesis

Ross River virus (RRV) is a mosquito-borne alphavirus indigenous to Australia and the Western Pacific region and is responsible for several thousand cases of human RRV disease (RRVD) per annum. The disease primarily involves polyarthritis/arthralgia, with many patients also presenting with rash, myalgia, fever, and/or lethargy. The symptoms can be debilitating at onset, but they usually resolve within 3-6 months. Recent insights into the RRV-host relationship, associated pathology, and molecular biology of infection have generated a number of potential avenues for improved treatment. Although vaccine development has been proposed, the small market size and potential for antibody-dependent enhancement (ADE) of disease make this approach unattractive. Recent insights into the molecular basis of RRV-ADE and the virus's ability to manipulate host inflammatory and immune responses create potential new opportunities for therapeutic invention. Such interventions should overcome virus-induced dysregulation of protective host responses to promote viral clearance and/or ameliorate inflammatory immunopathology.

Perturbation of chemokine networks by gene deletion alters the reinforcing actions of ethanol

Microarray analysis of human alcoholic brain and cultured cells exposed to ethanol showed significant changes in expression of genes related to immune or inflammatory responses, including chemokines and chemokine receptors. To test the hypothesis that chemokines exhibit previously undiscovered pleiotropic effects important for the behavioral actions of ethanol, we studied mutant mice with deletion of the Ccr2, Ccr5, Ccl2 or Ccl3 genes. Deletion of Ccr2, Ccl2 (females) or Ccl3 in mice resulted in lower preference for alcohol and consumption of lower amounts of alcohol in a two-bottle choice test as compared with wild-type mice. Ethanol treatment (2.5 g/kg, i.p.) induced stronger conditioned taste aversion in Ccr2, Ccl2 or Ccl3 null mutant mice than in controls. Ccr2 and Ccr5 null mutant mice did not differ from wild-type mice in ethanol-induced loss of righting reflex (LORR), but mice lacking Ccl2 or Ccl3 showed longer LORR than wild-type mice. There were no differences between mutant strains and wild-type mice in severity of ethanol-induced withdrawal. Genetic mapping of chromosome 11 for the Ccl2 and Ccl3 genes (46.5 and 47.6 cM, respectively) revealed that an alcohol-induced LORR QTL region was contained within the introgressed region derived from 129/SvJ, which may cause some behavioral phenotypes observed in the null mice. On the contrary, known QTLs on Chr 9 are outside of 129/SvJ region in Ccr2 and Ccr5 (71.9 and 72.0 cM, respectively) null mutant mice. These data show that disruption of the chemokine network interferes with motivational effects of alcohol.

Codelivery of CCR7 ligands as molecular adjuvants enhances the protective immune response against herpes simplex virus type 1

Humoral and cellular immunity, associated with long-term protective immunological memory, defines the efficacy of a given vaccine formulation. However, few vaccines achieve this target without the aid of a suitable adjuvant. Molecular adjuvants in vaccination against infectious agents offer a noninvasive means of enhancing the immune response against target antigens. To examine the potency of two beta-chemokines as immunomodulators, plasmid DNA encoding beta-chemokines CCL19 and CCL21 (CCR7L) was codelivered intranasally with plasmid DNA or recombinant vaccinia virus encoding herpes simplex virus (HSV) gB (HSV-gB) in a prime-and-boost vaccination strategy. This vaccination regimen increased serum and vaginal immunoglobulin G (IgG) and IgA, respectively, as well as the numbers of HSV-gB(498-505) peptide-specific gamma interferon-producing CD8(+) T cells. Distinctively, a high number of cytotoxic T lymphocytes was achieved when pCCR7L was applied at both prime and boost as opposed to omission of pCCR7L. A rapid-recall response was induced in the genital tract upon challenge with the HSV McKrae strain, affording a high level of protection and survival of vaccinated mice. Our results demonstrate that high innate immune kinetics and distribution of adaptive response induced in the nasal mucosa appears to be key factors in generating protective memory responses against HSV. Thus CCR7L expressed ectopically may serve as a molecular adjuvant to boost the immune response to a codelivered antigen in mucosal surfaces.

Subversion of the chemokine world by microbial pathogens

It is well known that microbial pathogens are able to subvert the host immune system in order to increase microbial replication and propagation. Recent research indicates that another arm of the immune response, that of the chemokine system, is also subject to this sabotage, and is undermined by a range of microbial pathogens, including viruses, bacteria, and parasites. Currently, it is known that the chemokine system is being challenged by a number of mechanisms, and still more are likely to be discovered with further research. Here we first review the general mechanisms by which microbial pathogens bypass mammalian chemokine defences. Broadly, these can be grouped as viral chemokine interacting proteins, microbial manipulation of host chemokine and chemokine receptor expression, microbial blockade of host chemokine receptor signalling, and the largely hypothetical mechanisms of microbial enhancement of host anti-chemokine networks (including digestion, antagonism, and neutralisation of host chemokines and chemokine receptors). We then discuss the potential results of these interactions in terms of outcome of infection.

Double-stranded RNA cooperates with interferon-gamma and IL-1 beta to induce both chemokine expression and nuclear factor-kappa B-dependent apoptosis in pancreatic beta-cells: potential mechanisms for viral-induced insulitis and beta-cell death in type 1 diabetes mellitus

Viral infections may trigger the autoimmune assault leading to type 1 diabetes mellitus. Double-stranded RNA (dsRNA) is produced by many viruses during their replicative cycle. The dsRNA, tested as synthetic poly(IC) (PIC), in synergism with the proinflammatory cytokines interferon-gamma (IFN-gamma) and/or IL-1 beta, results in nitric oxide production, Fas expression, beta-cell dysfunction, and death. Activation of the transcription nuclear factor-kappa B (NF-kappa B) is required for PIC-induced inducible nitric oxide synthase expression in beta-cells, and we hypothesized that this transcription factor may also participate in PIC-induced Fas expression and beta-cell apoptosis. This hypothesis, and the possibility that PIC induces expression of additional chemokines and cytokines (previously reported as NF-kappa B dependent) in pancreatic beta-cells, was investigated in the present study. We observed that the PIC-responsive region in the Fas promoter is located between nucleotides -223 and -54. Site-directed mutations at the NF-kappa B and CCAAT/enhancer binding protein-binding sites prevented PIC-induced Fas promoter activity. Increased Fas promoter activity was paralleled by enhanced susceptibility of PIC + cytokine-treated beta-cells to apoptosis induced by Fas ligand. beta-Cell infection with the NF-kappa B inhibitor AdI kappa B((SA)2) prevented both necrosis and apoptosis induced by PIC + IL-1 beta or PIC + IFN-gamma. Messenger RNAs for several chemokines and one cytokine were induced by PIC, alone or in combination with IFN-gamma, in pancreatic beta-cells. These included IP-10, interferon-gamma-inducible protein-10, IL-15, macrophage chemoattractant protein-1, fractalkine, and macrophage inflammatory protein-3 alpha. There was not, however, induction of IL-1 beta expression. We propose that dsRNA, generated during a viral infection, may contribute for beta-cell demise by both inducing expression of chemokines and IL-15, putative contributors for the build-up of insulitis, and by synergizing with locally produced cytokines to induce beta-cell apoptosis. Activation of the transcription factor NF-kappa B plays a central role in at least part of the deleterious effects of dsRNA in pancreatic beta-cells.

Molecular determinants for CC-chemokine recognition by a poxvirus CC-chemokine inhibitor

Poxviruses express a family of secreted proteins that bind with high affinity to chemokines and antagonize the interaction with their cognate G protein-coupled receptors (GPCRs). These viral inhibitors are novel in structure and, unlike cellular chemokine receptors, are able to specifically interact with most, if not all, CC-chemokines. We therefore sought to define the structural features of CC-chemokines that facilitate this broad-spectrum interaction. Here, we identify the residues present on human monocyte chemoattractant protein-1 (MCP-1) that are required for high-affinity interaction with the vaccinia virus 35-kDa CC-chemokine binding protein (VV-35kDa). Not only do these residues correspond to those required for interaction with the cognate receptor CCR2b but they are also conserved among many CC-chemokines. Thus, the results provide a structural basis for the ability of VV-35kDa to promiscuously recognize CC-chemokines and block binding to their receptors.