An Evolutionary Insertion in the Mxra8 Receptor-Binding Site Confers Resistance to Alphavirus Infection and Pathogenesis

Alphaviruses are emerging, mosquito-transmitted RNA viruses with poorly understood cellular tropism and species selectivity. Mxra8 is a receptor for multiple alphaviruses including chikungunya virus (CHIKV). We discovered that while expression of mouse, rat, chimpanzee, dog, horse, goat, sheep, and human Mxra8 enables alphavirus infection in cell culture, cattle Mxra8 does not. Cattle Mxra8 encodes a 15-amino acid insertion in its ectodomain that prevents Mxra8 binding to CHIKV. Identical insertions are present in zebu, yak, and the extinct auroch. As other Bovinae lineages contain related Mxra8 sequences, this insertion likely occurred at least 5 million years ago. Removing the Mxra8 insertion in Bovinae enhances alphavirus binding and infection, while introducing the insertion into mouse Mxra8 blocks CHIKV binding, prevents infection by multiple alphaviruses in cells, and mitigates CHIKV-induced pathogenesis in mice. Our studies on how this insertion provides resistance to CHIKV infection could facilitate countermeasures that disrupt Mxra8 interactions with alphaviruses.

Antigen-specific antibody Fc glycosylation enhances humoral immunity via the recruitment of complement

HIV-specific broadly neutralizing antibodies (bNAbs) confer protection after passive immunization, but the immunological mechanisms that drive their development are poorly understood. Structural features of bNAbs indicate that they originate from extensive germinal center (GC) selection, which relies on persistent GC activity. However, why a fraction of infected individuals are able to successfully drive more effective affinity maturation is unclear. Delivery of antigens in the form of antibody-immune complexes (ICs), which bind to complement receptors (CRs) or Fc receptors (FcRs) on follicular dendritic cells, represents an effective mechanism for antigen delivery to the GC. We sought to define whether IC-FcR or CR interactions differ among individuals who develop bNAb responses to HIV. Enhanced Fc effector functions and FcR/CR interactions, via altered Fc glycosylation profiles, were observed among individuals with neutralizing antibody responses to HIV compared with those without neutralizing antibody activity. Moreover, both polyclonal neutralizer ICs and monoclonal IC mimics of neutralizer antibodies induced higher antibody titers, higher-avidity antibodies, and expanded GC B cell reactions after immunization of mice via accelerated antigen deposition within B cell follicles in a complement-dependent manner. Thus, these data point to a direct role for altered Fc profile/complement interactions in shaping the maturation of the humoral immune response, providing insights into how GC activity may be enhanced to drive affinity maturation in next-generation vaccine approaches.

Core-shell patterning of synthetic hydrogels via interfacial bioorthogonal chemistry for spatial control of stem cell behavior

A new technique is described for the patterning of cell-guidance cues in synthetic extracellular matrices (ECM) for tissue engineering applications. Using s-tetrazine modified hyaluronic acid (HA), bis-trans-cyclooctene (TCO) crosslinkers and monofunctional TCO conjugates, interfacial bioorthogonal crosslinking was used to covalently functionalize hydrogels as they were synthesized at the liquid-gel interface. Through temporally controlled introduction of TCO conjugates during the crosslinking process, the enzymatic degradability, cell adhesivity, and mechanical properties of the synthetic microenvironment can be tuned with spatial precision. Using human mesenchymal stem cells (hMSCs) and hydrogels with a core-shell structure, we demonstrated the ability of the synthetic ECM with spatially defined guidance cues to modulate cell morphology in a biomimetic fashion. This new method for the spatially resolved introduction of cell-guidance cues for the establishment of functional tissue constructs complements existing methods that require UV-light or specialized equipment.

Mxra8 is a receptor for multiple arthritogenic alphaviruses

Arthritogenic alphaviruses comprise a group of enveloped RNA viruses that are transmitted to humans by mosquitoes and cause debilitating acute and chronic musculoskeletal disease 1 . The host factors required for alphavirus entry remain poorly characterized 2 . Here we use a genome-wide CRISPR-Cas9-based screen to identify the cell adhesion molecule Mxra8 as an entry mediator for multiple emerging arthritogenic alphaviruses, including chikungunya, Ross River, Mayaro and O'nyong nyong viruses. Gene editing of mouse Mxra8 or human MXRA8 resulted in reduced levels of viral infection of cells and, reciprocally, ectopic expression of these genes resulted in increased infection. Mxra8 bound directly to chikungunya virus particles and enhanced virus attachment and internalization into cells. Consistent with these findings, Mxra8-Fc fusion protein or anti-Mxra8 monoclonal antibodies blocked chikungunya virus infection in multiple cell types, including primary human synovial fibroblasts, osteoblasts, chondrocytes and skeletal muscle cells. Mutagenesis experiments suggest that Mxra8 binds to a surface-exposed region across the A and B domains of chikungunya virus E2 protein, which are a speculated site of attachment. Finally, administration of the Mxra8-Fc protein or anti-Mxra8 blocking antibodies to mice reduced chikungunya and O'nyong nyong virus infection as well as associated foot swelling. Pharmacological targeting of Mxra8 could form a strategy for mitigating infection and disease by multiple arthritogenic alphaviruses.

Immune-Mediated Protection and Pathogenesis of Chikungunya Virus

Chikungunya virus (CHIKV) is a re-emerging alphavirus that causes debilitating acute and chronic arthritis. Infection by CHIKV induces a robust immune response that is characterized by production of type I IFNs, recruitment of innate and adaptive immune cells, and development of neutralizing Abs. Despite this response, chronic arthritis can develop in some individuals, which may be due to a failure to eliminate viral RNA and Ag and/or persistent immune responses that cause chronic joint inflammation. In this review, based primarily on advances from recent studies in mice, we discuss the innate and adaptive immune factors that control CHIKV dissemination and clearance or contribute to pathogenesis.

Modified mRNA Vaccines Protect against Zika Virus Infection

The emergence of ZIKV infection has prompted a global effort to develop safe and effective vaccines. We engineered a lipid nanoparticle (LNP) encapsulated modified mRNA vaccine encoding wild-type or variant ZIKV structural genes and tested immunogenicity and protection in mice. Two doses of modified mRNA LNPs encoding prM-E genes that produced virus-like particles resulted in high neutralizing antibody titers (∼1/100,000) that protected against ZIKV infection and conferred sterilizing immunity. To offset a theoretical concern of ZIKV vaccines inducing antibodies that cross-react with the related dengue virus (DENV), we designed modified prM-E RNA encoding mutations destroying the conserved fusion-loop epitope in the E protein. This variant protected against ZIKV and diminished production of antibodies enhancing DENV infection in cells or mice. A modified mRNA vaccine can prevent ZIKV disease and be adapted to reduce the risk of sensitizing individuals to subsequent exposure to DENV, should this become a clinically relevant concern.

Collective Approach to Complex Food System Issues, the Case of The Ohio State University

Urban universities are uniquely positioned to make powerful and lasting contributions to the grand challenge of food security. To better understand the various dimensions related to the university’s role in food systems, this case study explores intentional linkages, significant developments, natural tensions, and emerging impacts at the Ohio State University. Discoveries from this analysis can guide urban university decision makers as they confront complex food system challenges. 

University Influence in Urban Food Systems

This themed issue of Metropolitan Universities journal illustrates how urban universities lead and contribute to food system teaching and learning; research and innovation; outreach and engagement; and resource stewardship. Common themes emerging in this issue include the essential approach of collaboration; the value of diverse voices and perspectives; the influence of distinct urban contexts; and the complexity of food security and other system issues.

Neutralizing human antibodies prevent Zika virus replication and fetal disease in mice

Zika virus (ZIKV) is an emerging mosquito-transmitted flavivirus that can cause severe disease, including congenital birth defects during pregnancy. To develop candidate therapeutic agents against ZIKV, we isolated a panel of human monoclonal antibodies from subjects that were previously infected with ZIKV. We show that a subset of antibodies recognize diverse epitopes on the envelope (E) protein and exhibit potent neutralizing activity. One of the most inhibitory antibodies, ZIKV-117, broadly neutralized infection of ZIKV strains corresponding to African and Asian-American lineages. Epitope mapping studies revealed that ZIKV-117 recognized a unique quaternary epitope on the E protein dimer-dimer interface. We evaluated the therapeutic efficacy of ZIKV-117 in pregnant and non-pregnant mice. Monoclonal antibody treatment markedly reduced tissue pathology, placental and fetal infection, and mortality in mice. Thus, neutralizing human antibodies can protect against maternal-fetal transmission, infection and disease, and reveal important determinants for structure-based rational vaccine design efforts.

Pathogenic Chikungunya Virus Evades B Cell Responses to Establish Persistence

Chikungunya virus (CHIKV) and related alphaviruses cause epidemics of acute and chronic musculoskeletal disease. To investigate the mechanisms underlying the failure of immune clearance of CHIKV, we studied mice infected with an attenuated CHIKV strain (181/25) and the pathogenic parental strain (AF15561), which differ by five amino acids. Whereas AF15561 infection of wild-type mice results in viral persistence in joint tissues, 181/25 is cleared. In contrast, 181/25 infection of μMT mice lacking mature B cells results in viral persistence in joint tissues, suggesting that virus-specific antibody is required for clearance of infection. Mapping studies demonstrated that a highly conserved glycine at position 82 in the A domain of the E2 glycoprotein impedes clearance and neutralization of multiple CHIKV strains. Remarkably, murine and human antibodies targeting E2 domain B failed to neutralize pathogenic CHIKV strains efficiently. Our data suggest that pathogenic CHIKV strains evade E2 domain-B-neutralizing antibodies to establish persistence.

Pathogenic chikungunya virus evades B cell responses to establish persistence

Chikungunya virus (CHIKV) causes large outbreaks of acute and chronic musculoskeletal disease. To investigate mechanisms of CHIKV clearance and persistence, we performed studies in mice with an attenuated CHIKV strain (181/25) and its pathogenic parent strain (AF15561). Whereas AF15561 infection of WT mice resulted in viral persistence in joint-associated tissue, 181/25 was cleared within 4 weeks. In contrast to WT mice, 181/25 infection of Rag1−/−mice resulted in viral persistence in joint tissue at levels similar to that detected in AF15561-infected Rag1−/− mice, suggesting an important role for adaptive immunity in the clearance of 181/25 infection. Indeed, 181/25 infection of B cell-deficient μMT mice or B cell receptor transgenic mice that cannot produce virus-specific antibody resulted in viral persistence that was equivalent to AF15561-infected WT and immunodeficient mice. In WT mice, 181/25 infection resulted in a higher quality neutralizing antibody response at early times post-infection. In addition, detailed mapping studies demonstrated that the amino acid at position 82 in the A domain of the E2 glycoprotein influenced clearance and serum neutralization of CHIKV. Neutralization assays revealed that inhibition of AF15561 by monoclonal antibodies specifically targeting E2 domain B was impaired relative to that observed with 181/25. Collectively, our data suggest that virus-specific antibody responses contribute to the clearance of 181/25 infection and that AF15561 evades this response by minimizing the impact of B domain neutralizing antibodies to establish persistent infection.

Isolation and Characterization of Broad and Ultrapotent Human Monoclonal Antibodies with Therapeutic Activity against Chikungunya Virus

Chikungunya virus (CHIKV) is a mosquito-transmitted RNA virus that causes acute febrile infection associated with polyarthralgia in humans. Mechanisms of protective immunity against CHIKV are poorly understood, and no effective therapeutics or vaccines are available. We isolated and characterized human monoclonal antibodies (mAbs) that neutralize CHIKV infectivity. Among the 30 mAbs isolated, 13 had broad and ultrapotent neutralizing activity (IC50 < 10 ng/ml), and all of these mapped to domain A of the E2 envelope protein. Potent inhibitory mAbs blocked post-attachment steps required for CHIKV membrane fusion, and several were protective in a lethal challenge model in immunocompromised mice, even when administered at late time points after infection. These highly protective mAbs could be considered for prevention or treatment of CHIKV infection, and their epitope location in domain A of E2 could be targeted for rational structure-based vaccine development.

Neutralizing Monoclonal Antibodies Block Chikungunya Virus Entry and Release by Targeting an Epitope Critical to Viral Pathogenesis

We evaluated the mechanism by which neutralizing human monoclonal antibodies inhibit chikungunya virus (CHIKV) infection. Potently neutralizing antibodies (NAbs) blocked infection at multiple steps of the virus life cycle, including entry and release. Cryo-electron microscopy structures of Fab fragments of two human NAbs and chikungunya virus-like particles showed a binding footprint that spanned independent domains on neighboring E2 subunits within one viral spike, suggesting a mechanism for inhibiting low-pH-dependent membrane fusion. Detailed epitope mapping identified amino acid E2-W64 as a critical interaction residue. An escape mutation (E2-W64G) at this residue rendered CHIKV attenuated in mice. Consistent with these data, CHIKV-E2-W64G failed to emerge in vivo under the selection pressure of one of the NAbs, IM-CKV063. As our study suggests that antibodies engaging the residue E2-W64 can potently inhibit CHIKV at multiple stages of infection, antibody-based therapies or immunogens that target this region might have protective value.

Broadly Neutralizing Alphavirus Antibodies Bind an Epitope on E2 and Inhibit Entry and Egress

We screened a panel of mouse and human monoclonal antibodies (MAbs) against chikungunya virus and identified several with inhibitory activity against multiple alphaviruses. Passive transfer of broadly neutralizing MAbs protected mice against infection by chikungunya, Mayaro, and O'nyong'nyong alphaviruses. Using alanine-scanning mutagenesis, loss-of-function recombinant proteins and viruses, and multiple functional assays, we determined that broadly neutralizing MAbs block multiple steps in the viral lifecycle, including entry and egress, and bind to a conserved epitope on the B domain of the E2 glycoprotein. A 16 Å resolution cryo-electron microscopy structure of a Fab fragment bound to CHIKV E2 B domain provided an explanation for its neutralizing activity. Binding to the B domain was associated with repositioning of the A domain of E2 that enabled cross-linking of neighboring spikes. Our results suggest that B domain antigenic determinants could be targeted for vaccine or antibody therapeutic development against multiple alphaviruses of global concern.

Interferon Lambda Upregulates IDO1 Expression in Respiratory Epithelial Cells After Influenza Virus Infection

Influenza infection causes an increase in indoleamine 2, 3-dioxygenase (IDO) activity in the lung parenchyma. IDO catabolizes tryptophan into kynurenine, leading to immune dampening. Multiple cell types express IDO, and while IFN-γ upregulates IDO in dendritic cells and macrophages, it is unclear how IDO is affected in respiratory epithelial cells during influenza infection. In this study, the role of IFN-λ in IDO regulation was investigated after influenza infection of respiratory epithelial cells. IDO1 expression increased concurrently with IFN-λ expression. In differentiated NHBE cells, the IDO metabolite was released basolaterally. Recombinant IFN-λ upregulated IDO1 activity, and silencing of IFN-λ decreased IDO1 expression during influenza infection. During IFN-λ stimulation, most differentiated cell types are able to express IDO but during influenza infection, IDO is primarily expressed in uninfected cells. These studies show a role for IDO in the host response to influenza infection, and they provide insights into novel approaches for enhancing vaccine responses and therapeutic approaches.

Chikungunya viral arthritis in the United States: a mimic of seronegative rheumatoid arthritis

OBJECTIVE

Chikungunya virus (CHIKV) is an arthritogenic mosquito-transmitted alphavirus that spread to the Caribbean in 2013 and to the US in 2014. CHIKV-infected patients develop inflammatory arthritis that can persist for months or years, but little is known about the rheumatologic and immunologic features of CHIKV-related arthritis in humans, particularly as compared to rheumatoid arthritis (RA). The purpose of this study was to describe these features in a group of 10 American travelers who were nearly simultaneously infected while visiting Haiti in June 2014.

METHODS

Patient history was obtained and physical examination and laboratory tests were performed. All patients with CHIKV-related arthritis had detectable levels of anti-CHIKV IgG. Using cytometry by time-of-flight (CyTOF), we analyzed peripheral blood mononuclear cells in CHIKV-infected patients, healthy controls, and patients with untreated, active RA.

RESULTS

Among 10 CHIKV-infected individuals, 8 developed persistent symmetric polyarthritis that met the American College of Rheumatology/European League Against Rheumatism 2010 criteria for (seronegative) RA. CyTOF analysis revealed that RA and CHIKV-infected patients had greater percentages of activated and effector CD4+ and CD8+ T cells than healthy controls.

CONCLUSION

In addition to similar clinical features, patients with CHIKV infection and patients with RA develop very similar peripheral T cell phenotypes. These overlapping clinical and immunologic features highlight a need for rheumatologists to consider CHIKV infection when evaluating patients with new, symmetric polyarthritis.

Drug analog inhibition of indoleamine 2,3-dioxygenase (IDO) activity modifies pattern recognition receptor expression and proinflammatory cytokine responses early during influenza virus infection

Influenza virus is recognized by PRRs, which are critical in the early response to virus infection and induction of proinflammatory cytokines. IDO is increased in the lung of mice immediately following influenza infection, and the presence of IDO has been shown to mediate immune suppression through depletion of trp and reduction in IL-6 production. To determine the role of IDO activity in the early immune response to influenza infection, IDO activity was inhibited using the synthetic analog, 1MT. The results show that IDO inhibition enhanced proinflammatory cytokine gene and protein expression at 24 and 48 h postinfection, respectively, compared with control-treated mice and affected PRR expression. The enhanced proinflammatory response in the presence of 1MT was attributed to macrophages in the airways, as Raw264.7 and primary AMs showed enhanced production of IFN-β, IL-1β, IL-6, and TNF-α in the presence of 1MT. These findings provide important knowledge for the role of IDO during initial host response to influenza infection.

Indoleamine 2,3-dioxygenase (IDO) activity during the primary immune response to influenza infection modifies the memory T cell response to influenza challenge

The generation of a heterosubtypic memory T cell response is important for cross-protective immunity against unrelated strains of influenza virus. One way to facilitate the generation of the memory T cell population is to control the activity of immune modulatory agents. The enzyme, indoleamine 2,3-dioxygenase (IDO), is upregulated during influenza infection by the interferon response where IDO activity depletes tryptophan required in T cell response. In this study, IDO activity was pharmacologically inhibited with 1-methyl-tryptophan (1MT) during the primary response to influenza virus infection and the effect on the memory T cell response was evaluated. 1MT treatment improved the memory T cell response to influenza virus challenge by increasing interferon gamma expression by CD4 and CD8 T cells, and numbers of lung virus-specific CD8+ T cells, and increased the Th1 response as well as modifying the immunodominance hierarchy to increase the number of subdominant epitope specific CD8+ T cells, a feature which may be linked to decreased regulatory T cell function. These changes also accompanied evidence of accelerated lung tissue repair upon virus challenge. These findings suggest that modulation of IDO activity could be exploited in influenza vaccine development to enhance memory T cell responses and reduce disease burden.

Subsisting H1N1 influenza memory responses are insufficient to protect from pandemic H1N1 influenza challenge in C57BL/6 mice

The 2009 swine-origin pandemic H1N1 (pH1N1) influenza virus transmitted and caused disease in many individuals immune to pre-2009 H1N1 influenza virus. Whilst extensive studies on antibody-mediated pH1N1 cross-reactivity have been described, few studies have focused on influenza-specific memory T-cells. To address this, the immune response in pre-2009 H1N1 influenza-immune mice was evaluated after pH1N1 challenge and disease pathogenesis was determined. The results show that despite homology shared between pre-2009 H1N1 and pH1N1 strains, the effector memory T-cell response to pre-2009 H1N1 was generally ineffective, a finding that correlated with lung virus persistence. Additionally, pH1N1 challenge generated T-cells reactive to new pH1N1 epitopes. These studies highlight the importance of vaccinating against immunodominant T-cell epitopes to provide for a more effective strategy to control influenza virus through heterosubtypic immunity.

Inhibition of indoleamine 2,3-dioxygenase enhances the T-cell response to influenza virus infection

Influenza infection induces an increase in the level of indoleamine 2,3-dioxygenase (IDO) activity in the lung parenchyma. IDO is the first and rate-limiting step in the kynurenine pathway where tryptophan is reduced to kynurenine and other metabolites. The depletion of tryptophan, and production of associated metabolites, attenuates the immune response to infection. The impact of IDO on the primary immune response to influenza virus infection was determined using the IDO inhibitor 1-methyl-D,L-tryptophan (1MT). C57BL/6 mice treated with 1MT and infected with A/HKx31 influenza virus had increased numbers of activated and functional CD4⁺ T-cells, influenza-specific CD8⁺ T-cells and effector memory cells in the lung. Inhibition of IDO increased the Th1 response in CD4⁺ T-cells as well as enhanced the Th17 response. These studies show that inhibition of IDO engenders a more robust T-cell response to influenza virus, and suggests an approach for enhancing the immune response to influenza vaccination by facilitating increased influenza-specific T-cell response.

Renal impairment is associated with coronary heart disease in HIV-positive men

BACKGROUND

Chronic kidney disease is a risk factor for coronary heart disease (CHD). The association between renal impairment and CHD in HIV-positive patients remains poorly described.

OBJECTIVE

To describe the CHD incidence in a cohort of HIV-positive patients and to examine the relationship between reduced estimated glomerular filtration rate (eGFR) and incident CHD.

METHODS

We studied 7,828 HIV-positive patients who were followed up at 3 South London clinics between January 2004 and December 2009. CHD events were identified from electronic records and through elevated troponin levels. Multivariate Poisson regression analysis was used to identify factors associated with CHD among HIV-positive men.

RESULTS

The incidence of CHD among men was 1.2 (95% CI, 0.8-1.8) per 1,000 person-years of follow-up, with 28 patients (0.4%) having experienced 32 CHD events. In adjusted analyses, older age (incidence rate ratios [IRR], 2.81; 95% CI, 1.51-5.25) and hepatitis C virus (HCV) status (IRR, 3.94; 95% CI, 1.00-15.5) were significantly associated with CHD. Although eGFR as a continuous variable was not associated with CHD, an eGFR <75 mL/min remained associated with incident CHD (IRR, 4.30; 95% CI, 1.33-14.5) after adjustment for age. No association between CHD and abacavir exposure was observed (IRR, 0.94; 95% CI, 0.30-2.99).

CONCLUSIONS

The incidence of CHD in this ethnically diverse cohort was low. Our data suggest that impaired renal function identifies patients at increased risk of CHD events in whom management of traditional CHD risk factors should be prioritized.

Isospora troglodytes n. sp. (Apicomplexa: Eimeriidae), a new coccidian species from wrens of Costa Rica

Nineteen (91%) of 21 rufous-and-white wrens (Thryothorus rufalbus) and five (71%) of seven plain wrens (Cantorchilus modestus) sampled from Costa Rica were positive for a new species of Isospora. Oocysts have a thin, smooth, double, colorless wall and measure 20.1 ± 1.4 × 23.4 ± 1.5 μm (18-24 × 20-26 μm) with an average length-width ratio of 1.2 μm. Sporocysts are ovoid, measure 9.5 ± 0.9 × 15.5 ± 1.1 μm (7-12 × 12-18 μm) with an average length-width ratio of 1.6 μm. A nipple-like steida body continuous with the sporocyst wall and a prominent oval-shaped substeida body are present. In addition to the four sporozoites, a single compact sporocyst residuum was present in each sporocyst. This is the first description of an Isospora species from the family Troglodytidae and the first report of Isospora from the rufous-and-white wren and plain wren.

Interferon type I response in porcine reproductive and respiratory syndrome virus-infected MARC-145 cells

Infection by porcine reproductive and respiratory syndrome virus (PRRSV) results in a weak induction of the innate immune response. There are many genes that collectively comprise this response and the extent to which each gene responds to PRRSV infection is unclear and warrants further investigation. To this end, we have utilized real-time PCR using SYBR Green I dye-based detection to quantify transcript abundance of the type I interferons (IFN-α and -β) and IFN-β transcriptional enhanceasome genes. In MARC-145 cells, both IFN-α and -β transcript abundance were unaffected by PRRSV infection. However, stimulation of MARC-145 cells by exogenous double-stranded RNA, resulted in significant increases in transcript abundance of both IFN-α and -β as well as IFN-β enhanceasome components, indicating that a type I IFN response could be induced in these cells. The double-stranded RNA induction of type I IFN transcription was significantly inhibited by dual-exposure with PRRSV. These results suggest that PRRSV infection directly interferes with type I IFN transcriptional activation early in its pathway, at the level of IFN-β gene transcription.