Gr-1+ cells, but not neutrophils, limit virus replication and lesion development following flank infection of mice with herpes simplex virus type-1

T-cell acute lymphoblastic leukemia progression is supported by inflammatory molecules including hepatocyte growth factor

T-cell acute lymphoblastic leukemia (T-ALL) is a malignant hematological disorder characterized by an increased proliferation of immature T lymphocytes precursors. T-ALL treatment includes chemotherapy with strong side effects, and patients that undergo relapse display poor prognosis. Although cell-intrinsic oncogenic pathways are well-studied, the tumor microenvironment, like inflammatory cellular and molecular components is less explored in T-ALL. We sought to determine the composition of the inflammatory microenvironment induced by T-ALL, and its role in T-ALL progression. We show in two mouse T-ALL cell models that T-ALLs enhance blood neutrophils and resident monocytes, accompanied with a plasmatic acute secretion of inflammatory molecules. Depleting neutrophils using anti-Ly6G treatment or resident monocytes by clodronate liposomes treatment does not modulate plasmatic inflammatory molecule secretion and mice survival. However, inhibiting the secretion of inflammatory molecules by microenvironment with NECA, an agonist of adenosine receptors, diminishes T-ALL progression enhancing mouse survival. We uncovered Hepatocyte Growth Factor (HGF), T-ALL-driven and the most decreased molecule with NECA, as a potential therapeutic target in T-ALL. Altogether, we identified a signature of inflammatory molecules that can potentially be involved in T-ALL evolution and uncovered HGF/cMET pathway as important to target for limiting T-ALL progression.

Interferon lambda restricts herpes simplex virus skin disease by suppressing neutrophil-mediated pathology

Type III interferons (IFN-λ) are antiviral and immunomodulatory cytokines that have been best characterized in respiratory and gastrointestinal infections, but the effects of IFN-λ against skin infections have not been extensively investigated. We sought to define the skin-specific effects of IFN-λ against the highly prevalent human pathogen, herpes simplex virus (HSV). We infected mice lacking the IFN-λ receptor (Ifnlr1-/-), both the IFN-λ and the IFN-α/β receptors (Ifnar1-/-Ifnlr1-/-), or IFN-λ cytokines (Ifnl2/3-/-) and found that IFN-λ restricts the severity of HSV-1 and HSV-2 skin lesions without affecting viral loads. We used RNAseq to define IFN-λ- and IFN-β-induced transcriptional responses in primary mouse keratinocytes. Using conditional knockout mice, we found that IFN-λ signaling in both keratinocytes and neutrophils was necessary to control HSV-1 skin lesion severity and that IFN-λ signaling in keratinocytes suppressed CXCL9-mediated neutrophil recruitment to the skin. Furthermore, depleting neutrophils or blocking CXCL9 protected against severe HSV-1 skin lesions in Ifnlr1-/- mice. Altogether, our results suggest that IFN-λ plays an immunomodulatory role in the skin that restricts neutrophil-mediated pathology during HSV infection and suggests potential applications for IFN-λ in treating viral skin infections.IMPORTANCEType III interferons (IFN-λ) have been shown to have antiviral and immunomodulatory effects at epithelial barriers such as the respiratory and gastrointestinal tracts, but their effects on the skin have not been extensively investigated. We used mice lacking IFN-λ signaling to investigate the skin-specific effects of IFN-λ against the herpes simplex virus (HSV), which targets epithelial tissues to cause cold sores and genital herpes. We found that IFN-λ limited the severity of HSV skin lesions without affecting viral load and that this protective effect required IFN-λ signaling in both keratinocytes and neutrophils. We found that IFN-λ signaling in keratinocytes suppressed neutrophil recruitment to the skin and that depleting neutrophils protected against severe HSV skin lesions in the absence of IFN-λ. Altogether, our results suggest that IFN-λ plays an immunomodulatory role in the skin that restricts neutrophil-mediated pathology during HSV infection and suggests potential applications for IFN-λ in treating viral skin infections.

Interferon lambda restricts herpes simplex virus skin disease by suppressing neutrophil-mediated pathology

Type III interferons (IFN-λ) are antiviral and immunomodulatory cytokines that have been best characterized in respiratory and gastrointestinal infections, but the effects of IFN-λ against skin infections have not been extensively investigated. We sought to define the skin-specific effects of IFN-λ against the highly prevalent human pathogen herpes simplex virus (HSV). We infected mice lacking the IFN-λ receptor (Ifnlr1-/-), both the IFN-λ and the IFN-αβ receptor (Ifnar1-/- Ifnlr1-/-), or IFN-λ cytokines (Ifnl2/3-/-) and found that IFN-λ restricts the severity of HSV-1 and HSV-2 skin lesions, independent of a direct effect on viral load. Using conditional knockout mice, we found that IFN-λ signaling in both keratinocytes and neutrophils was necessary to control HSV-1 skin lesion severity, and that IFN-λ signaling in keratinocytes suppressed CXCL9-mediated neutrophil recruitment to the skin. Furthermore, depleting neutrophils or blocking CXCL9 protected against severe HSV-1 skin lesions in Ifnlr1-/- mice. Altogether, our results suggest that IFN-λ plays an immunomodulatory role in the skin that restricts neutrophil-mediated pathology during HSV infection, and suggest potential applications for IFN-λ in treating viral skin infections.

Pellino Proteins in Viral Immunity and Pathogenesis

Pellino proteins are a family of evolutionarily conserved ubiquitin ligases involved in intracellular signaling in a wide range of cell types. They are essential for microbe detection and the initiation of innate and adaptive immune responses. Some viruses specifically target the Pellino proteins as part of their immune evasion strategies. Through studies of mouse models of viral infections in the central nervous system, heart, lungs, and skin, the Pellino proteins have been linked to both beneficial and detrimental immune responses. Only in recent years have some of the involved mechanisms been identified. The objective of this review is to highlight the many diverse aspects of viral immunity and pathogenesis that the Pellino proteins have been associated with, in order to promote further research into their functions. After a brief introduction to the cellular signaling mechanisms involving Pellino proteins, their physiological roles in the initiation of immune responses, pathogenesis through excess inflammation, immune regulation, and cell death are presented. Known viral immune evasion strategies are also described. Throughout, areas that require more in-depth investigation are identified. Future research into the functions of the Pellino protein family may reveal fundamental insights into how our immune system works. Such knowledge may be leveraged in the fight against viral infections and their sequala.

Pellino1 Restricts Herpes Simplex Virus Infections in the Epidermis and Dissemination to Sebaceous Glands

Nearly all adults are infected with one or more herpes viruses. The most common are herpes simplex virus (HSV)-1 and HSV-2, which upon reactivation can cause painful skin and mucosal erosions. Patients who are immune compromised often experience frequent, atypical, or chronic lesions and thus a greatly diminished QOL. Pellino1 is a ubiquitin ligase involved in IL-1 and toll-like receptor signaling; however, the role of Pellino1 in skin immunity against HSV is unknown. In this study, using the mouse-flank HSV-1 skin infection model, we show that Pellino1 has several critical functions during active viral replication. Peli1‒/‒ mice succumb more than wild-type mice to systemic disease and develop larger zosteriform skin lesions along affected dermatomes. In Pellino1-deficient mice, the virus spread extensively through the epidermis and follicular infundibulum into sebaceous glands where sebocytes were found positive for the virus. The latter did not appear to involve a shift in how the virus migrated through the nervous system. Immunohistochemistry revealed delayed recruitment of myeloid and T cells to the infected epidermis in Peli1‒/‒ mice. This was associated with decreased expression of the cytokine mRNAs Il1a, Il36b and 2610528A11Rik; the latter also known as Gpr15l. In conclusion, Pellino1 plays important roles in restricting viral dissemination, and the involved pathways may represent novel therapeutic targets in patients with frequent or chronic HSV infections.

Mouse Mx1 Inhibits Herpes Simplex Virus Type 1 Genomic Replication and Late Gene Expression In Vitro and Prevents Lesion Formation in the Mouse Zosteriform Model

Myxovirus resistance (Mx) proteins are dynamin-like GTPases that are inducible by interferons (IFNs) following virus infections. Most studies investigating Mx proteins have focused on their activity against influenza A viruses (IAV), although emerging evidence suggests that some Mx proteins may exhibit broader antiviral activity. Herein, we demonstrate that in addition to IAV, overexpression of mouse Mx1 (mMx1), but not mMx2, resulted in potent inhibition of growth of the human alphaherpesviruses herpes simplex virus 1 (HSV-1) and HSV-2, whereas neither inhibited the mouse betaherpesvirus murine cytomegalovirus (MCMV) in vitro. IFN induction of a functional endogenous mMx1 in primary mouse fibroblasts ex vivo was also associated with inhibition of HSV-1 growth. Using an in vitro overexpression approach, we demonstrate that mutations that result in redistribution of mMx1 from the nucleus to the cytoplasm or in loss of its combined GTP binding and GTPase activity also abrogated its ability to inhibit HSV-1 growth. Overexpressed mMx1 did not inhibit early HSV-1 gene expression but was shown to inhibit both replication of the HSV-1 genome as well as subsequent late gene expression. In a mouse model of cutaneous HSV-1 infection, mice expressing a functional endogenous mMx1 showed significant reductions in the severity of skin lesions as well as reduced HSV-1 titers in both the skin and dorsal root ganglia (DRG). Together, these data demonstrate that mMx1 mediates potent antiviral activity against human alphaherpesviruses by blocking replication of the viral genome and subsequent steps in virus replication. Moreover, endogenous mMx1 potently inhibited pathogenesis in the zosteriform mouse model of HSV-1 infection. IMPORTANCE While a number of studies have demonstrated that human Mx proteins can inhibit particular herpesviruses in vitro, we are the first to report the antiviral activity of mouse Mx1 (mMx1) against alphaherpesviruses both in vitro and in vivo. We demonstrate that both overexpressed mMx1 and endogenous mMx1 potently restrict HSV-1 growth in vitro. mMx1-mediated inhibition of HSV-1 was not associated with inhibition of virus entry and/or import of the viral genome into the nucleus, but rather with inhibition of HSV-1 genomic replication as well as subsequent late gene expression. Therefore, inhibition of human alphaherpesviruses by mMx1 occurs by a mechanism that is distinct from that reported for human Mx proteins against herpesviruses. Importantly, we also provide evidence that expression of a functional endogenous mMx1 can limit HSV-1 pathogenesis in a mouse model of infection.

Treatment of glioblastoma with current oHSV variants reveals differences in efficacy and immune cell recruitment

Oncolytic herpes simplex viruses (oHSVs) have demonstrated efficient lytic replication in human glioblastoma tumors using immunodeficient mouse models, but early-phase clinical trials have reported few complete responses. Potential reasons for the lack of efficacy are limited vector potency and the suppressive glioma tumor microenvironment (TME). Here we compare the oncolytic activity of two HSV-1 vectors, a KOS-strain derivative KG4:T124 and an F-strain derivative rQNestin34.5v.1, in the CT2A and GL261N4 murine syngeneic glioma models. rQNestin34.5v1 generally demonstrated a greater in vivo viral burden compared to KG4:T124. However, both vectors were rapidly cleared from CT2A tumors, while virus remained ensconced in GL261N4 tumors. Immunological evaluation revealed that the two vectors induced similar changes in immune cell recruitment to either tumor type at 2 days after infection. However, at 7 days after infection, the CT2A microenvironment displayed the phenotype of an untreated tumor, while GL261N4 tumors exhibited macrophage and CD4+/CD8+ T cell accumulation. Furthermore, the CT2A model was completely resistant to virus therapy, while in the GL261N4 model rQNestin34.5v1 treatment resulted in enhanced macrophage recruitment, impaired tumor progression, and long-term survival of a few animals. We conclude that prolonged intratumoral viral presence correlates with immune cell recruitment, and both are needed to enhance anti-tumor immunity.

Peptide Inhibitor of Complement C1, RLS-0071, Reduces Zosteriform Spread of Herpes Simplex Virus Type 1 Skin Infection and Promotes Survival in Infected Mice

Herpes simplex virus type 1 (HSV-1) is a prevalent human pathogen primarily transmitted through skin-to-skin contact, especially on and around mucosal surfaces where there is contact with contaminated saliva during periods of viral shedding. It is estimated that 90% of adults worldwide have HSV-1 antibodies. Cutaneous HSV-1 infections are characterized by a sensation of tingling or numbness at the initial infection site followed by an eruption of vesicles and then painful ulcers with crusting. These symptoms can take ten days to several weeks to heal, leading to significant morbidity. Histologically, infections cause ballooning degeneration of keratinocytes and formation of multinucleated giant cells, ultimately resulting in a localized immune response. Commonly prescribed treatments against HSV-1 infections are nucleoside analogs, such as acyclovir (ACV). However, the emergence of ACV-resistant HSV (ACV^R-HSV) clinical isolates has created an urgent need for the development of compounds to control symptoms of cutaneous infections. RLS-0071, also known as peptide inhibitor of complement C1 (PIC1), is a 15-amino-acid anti-inflammatory peptide that inhibits classical complement pathway activation and modulates neutrophil activation. It has been previously shown to aid in the healing of chronic diabetic wounds by inhibiting the excessive activation of complement component C1 and infiltration of leukocytes. Here, we report that treatment of cutaneous infections of HSV-1 and ACV^R-HSV-1 in BALB/cJ mice with RLS-0071 significantly reduced the rate of mortality, decreased zosteriform spread, and enhanced the healing of the infection-associated lesions compared to control-treated animals. Therefore, RLS-0071 may work synergistically with other antiviral drugs to aid in wound healing of HSV-1 cutaneous infection and may potentially aid in rapid wound healing of other pathology not limited to HSV-1.

Crosstalk Between Epithelial Cells, Neurons and Immune Mediators in HSV-1 Skin Infection

Herpes simplex virus type 1 (HSV-1) infection is highly prevalent in humans, with approximately two-thirds of the world population living with this virus. However, only a fraction of those carrying HSV-1, which elicits lifelong infections, are symptomatic. HSV-1 mainly causes lesions in the skin and mucosae but reaches the termini of sensory neurons innervating these tissues and travels in a retrograde manner to the neuron cell body where it establishes persistent infection and remains in a latent state until reactivated by different stimuli. When productive reactivations occur, the virus travels back along axons to the primary infection site, where new rounds of replication are initiated in the skin, in recurrent or secondary infections. During this process, new neuron infections occur. Noteworthy, the mechanisms underlying viral reactivations and the exit of latency are somewhat poorly understood and may be regulated by a crosstalk between the infected neurons and components of the immune system. Here, we review and discuss the immune responses that occur at the skin during primary and recurrent infections by HSV-1, as well as at the interphase of latently-infected neurons. Moreover, we discuss the implications of neuronal signals over the priming and migration of immune cells in the context of HSV-1 infection.

Mouse Models and Tools for the in vivo Study of Neutrophils

Neutrophils are the most abundant leukocytes in human blood and critical actors of the immune system. Many neutrophil functions and facets of their activity in vivo were revealed by studying genetically modified mice or by tracking fluorescent neutrophils in animals using imaging approaches. Assessing the roles of neutrophils can be challenging, especially when exact molecular pathways are questioned or disease states are interrogated that alter normal neutrophil homeostasis. This review discusses the main in vivo models for the study of neutrophils, their advantages and limitations. The side-by-side comparison underlines the necessity to carefully choose the right model(s) to answer a given scientific question, and exhibit caveats that need to be taken into account when designing experimental procedures. Collectively, this review suggests that at least two models should be employed to legitimately conclude on neutrophil functions.

IL-36 promotes anti-viral immunity by boosting sensitivity to IFN-α/β in IRF1 dependent and independent manners

The functions of the IL-36 cytokines remain poorly understood. We report a previously unrecognized mechanism whereby IL-36 promotes innate antiviral immunity in mouse and human models of herpes simplex virus-1 (HSV-1) infections. HSV-1 actively suppresses production of type I interferon (IFN); our data reveal that IL-36 overcomes this immune evasion strategy by increasing cellular sensitivity to IFN. IL-36β deficient mice display impaired IFN responses and poorly restrict viral replication in skin keratinocytes. In mouse and human keratinocytes IL-36 elicits an antiviral state driven by STAT1 and STAT2 via enhanced expression of IFNAR1 and IFNAR2 subunits of the type I IFN receptor. The degree of IFN regulatory factor 1 (IRF1) involvement is species dependent, with IRF1 playing a more prominent role in human cells. Similar mechanisms are activated by IL-1. Overall, IL-36 acts as an antiviral cytokine by potentiating type I IFN signaling and thereby upholds immune responses to viruses that limit the production of IFNs.

The Role of Neonatal Gr-1+ Myeloid Cells in a Murine Model of Rhesus-Rotavirus-Induced Biliary Atresia

Activation of innate immunity together with cholangiocyte damage occurs in biliary atresia (BA). However, detailed information on the inflammatory cells involved is lacking. This study investigates both the pathophysiology of CD11b⁺Gr-1⁺ cells in a mouse model of BA and their presence in BA patients. CD11b⁺Gr-1⁺ cells were targeted by an anti-Ly6G antibody in murine BA induced by inoculation with rhesus rotavirus. Expression of the Ly6G homolog CD177⁺ was examined in biopsies from BA patients. The symptoms of BA were ameliorated, and survival was prolonged in those mice receiving 5 to 10 μg of antibody per mouse every 3 days for four times compared with the mice treated with virus alone. However, the mice later developed chronic BA with persistent low body weight and jaundice. Hepatic inflammatory cells were reduced compared with acute BA. Blockade of extrahepatic bile ducts occurred, whereas intrahepatic ductules were partially preserved, and a progressive increase in liver fibrosis was observed. High levels of CD11b⁺Gr-1⁺ cells were present in these mice. The administration of an anti-Ly6G antibody again in those chronic BA mice reduced jaundice and restored body weight. In BA patients CD177⁺ cells were highly expressed in the liver. Our data suggest that the chronic mouse BA model shares key characteristics with clinical BA and indicates the importance of CD11b⁺Gr-1⁺ cells in the initiation and progression of BA.

PD-L1/B7-H1 Inhibits Viral Clearance by Macrophages in HSV-1-Infected Corneas

Immune privilege helps protect the cornea from damaging inflammation but can also impair pathogen clearance from this mucosal surface. Programmed death-ligand 1 (PD-L1 or B7-H1) contributes to corneal immune privilege by inhibiting the function of a variety of immune cells. We asked whether programmed death-1 (PD-1)/PD-L1 interaction regulates HSV-1 clearance from infected corneas. We show that PD-L1 is constitutively expressed in the corneal epithelium and is upregulated upon HSV-1 corneal infection, with peak expression on CD45⁺ cells NK cells, dendritic cells, neutrophils, and macrophages and CD45^- corneal epithelial cells at 4 d postinfection (dpi). As early as 1 dpi, HSV-1-infected corneas of B7-H1^-/- mice as compared with wild-type mice showed increased chemokine expression and this correlated with increased migration of inflammatory cells into the viral lesions and decreased HSV-1 corneal titers. Local PD-L1 blockade caused a similar increase in viral clearance, suggesting a local effect of PD-1/PD-L1 in the cornea. The enhanced HSV-1 clearance at 2 dpi resulting from PD-1/PD-L1 blockade is mediated primarily by a monocyte/macrophage population. Studies in bone marrow chimeras demonstrated enhanced viral clearance when PD-L1 was absent only from nonhematopoietic cells. We conclude that PD-L1 expression on corneal cells negatively impacts the ability of the innate immune system to clear HSV-1 from infected corneas.

Interleukin-36β provides protection against HSV-1 infection, but does not modulate initiation of adaptive immune responses

Interleukin-36 (IL-36) represents three cytokines, IL-36α, IL-36β and IL-36γ, which bind to the same receptor, IL-1RL2; however, their physiological function(s) remain poorly understood. Here, the role of IL-36 in immunity against HSV-1 was examined using the flank skin infection mouse model. Expression analyses revealed increased levels of IL-36α and IL-36β mRNA in infected skin, while constitutive IL-36γ levels remained largely unchanged. In human keratinocytes, IL-36α mRNA was induced by HSV-1, while IL-1β and TNFα increased all three IL-36 mRNAs. The dominant alternative splice variant of human IL-36β mRNA was isoform 2, which is the ortholog of the known mouse IL-36β mRNA. Mice deficient in IL-36β, but not IL-36α or IL-36γ, succumbed more frequently to HSV-1 infection than wild type mice. Furthermore, IL-36β^−/− mice developed larger zosteriform skin lesions along infected neurons. Levels of HSV-1 specific antibodies, CD8⁺ cells and IFNγ-producing CD4⁺ cells were statistically equal in wild type and IL-36β^−/− mice, suggesting similar initiation of adaptive immunity in the two strains. This correlated with the time at which HSV-1 genome and mRNA levels in primary skin lesions started to decline in both wild type and IL-36β^−/− mice. Our data indicate that IL-36β has previously unrecognized functions protective against HSV-1 infection.

Neutrophils are dispensable in the modulation of T cell immunity against cutaneous HSV-1 infection

Neutrophils rapidly infiltrate sites of inflammation during peripheral infection or tissue injury. In addition to their well described roles as pro-inflammatory phagocytes responsible for pathogen clearance, recent studies have demonstrated a broader functional repertoire including mediating crosstalk between innate and adaptive arms of the immune system. Specifically, neutrophils have been proposed to mediate antigen transport to lymph nodes (LN) to modulate T cell priming and to influence T cell migration to infected tissues. Using a mouse model of cutaneous herpes simplex virus type 1 (HSV-1) infection we explored potential contributions of neutrophils toward anti-viral immunity. While a transient, early influx of neutrophils was triggered by dermal scarification, we did not detect migration of neutrophils from the skin to LN. Furthermore, despite recruitment of neutrophils into LN from the blood, priming and expansion of CD4⁺ and CD8⁺ T cells was unaffected following neutrophil depletion. Finally, we found that neutrophils were dispensable for the migration of effector T cells into infected skin. Our study suggests that the immunomodulatory roles of neutrophils toward adaptive immunity may be context-dependent, and are likely determined by the type of pathogen and anatomical site of infection.

The Role of Myeloid-Derived Suppressor Cells in Viral Infection

Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature myeloid cells that are well described as potent immune regulatory cells during human cancer and murine tumor models. Reports of MDSCs during viral infections remain limited, and their association with immunomodulation of viral diseases is still being defined. Here, we provide an overview of MDSCs or MDSC-like cells identified during viral infections, including murine viral models and human viral diseases. Understanding the similarities and/or differences of virally induced versus tumor-derived MDSCs will be important for designing future immunotherapeutic approaches.

Signal transducer and activator of transcription 3 (Stat3) regulates host defense and protects mice against herpes simplex virus-1 (HSV-1) infection

Signal transducer and activator of transcription 3 (STAT3) mediates cellular responses to multiple cytokines, governs gene expression, and regulates the development and activation of immune cells. STAT3 also modulates reactivation of latent herpes simplex virus-1 (HSV-1) in ganglia. However, it is unclear how STAT3 regulates the innate immune response during the early phase of HSV-1 lytic infection. Many cell types critical for the innate immunity are derived from the myeloid lineage. Therefore, in this study, we used myeloid-specific Stat3 knockout mice to investigate the role of STAT3 in the innate immune response against HSV-1. Our results demonstrate that Stat3 knockout bone marrow-derived macrophages (BMMs) expressed decreased levels of interferon-α (IFN-α) and interferon-stimulated genes (ISGs) upon HSV-1 infection. In vivo, knockout mice were more susceptible to HSV-1, as marked by higher viral loads and more significant weight loss. Splenic expression of IFN-α and ISGs was reduced in the absence of STAT3, indicating that STAT3 is required for optimal type I interferon response to HSV-1. Expression of TNF-α and IL-12, cytokines that have been shown to limit HSV-1 replication and pathogenesis, was also significantly lower in knockout mice. Interestingly, Stat3 knockout mice failed to expand the CD8⁺ conventional DC (cDC) population upon HSV-1 infection, and this was accompanied by impaired NK and CD8 T cell activation. Collectively, our data demonstrate that myeloid-specific Stat3 deletion causes defects in multiple aspects of the immune system and that STAT3 has a protective role at the early stage of systemic HSV-1 infection.

IL-2 complex treatment amplifies CD8+ T cell mediated immunity following herpes simplex virus-1 infection

CD8⁺ T cells play an important role in controlling numerous virus infections and some tumors and therefore several strategies have been adopted to modulate CD8⁺ T cell responses. One such approach includes treatment with IL-2 bound to a monoclonal antibody against IL-2 (IL-2 complex) which was shown to enhance CD8⁺ T cell responses and provide protection against some cancers and pathogens. This report analyses the value of IL-2 complex therapy to protect against a cutaneous virus infection as occurs with herpes simplex virus-1 (HSV-1) infection. Treatment with IL-2 complex after infection reduced virus levels and lesion severity in a zosteriform model of HSV infection in mice. Furthermore, IL-2 complex treatment expanded HSV-1-gB epitope-specific CD8⁺ T cells, IFN-γ and TNF-α producing CD8⁺ T cells as well as cells that produced more than one cytokine. In addition, IL-2 complex therapy recipients showed enhanced cytolytic activity of CD8⁺ T cells as shown by increased granzyme B expression and lytic granule release. Taken, together, these studies demonstrate that IL-2 complex therapy can be useful to boost protection against a cutaneous virus infection.

Granulocytes in Ocular HSV-1 Infection: Opposing Roles of Mast Cells and Neutrophils

PURPOSE

The contributions of mast cells (MCs) to immunologic defense against pathogens in the eye are unknown. We have characterized pericorneal MCs as tissue-resident innate sentinels and determined their impact on the immune response to herpes simplex virus type-1 (HSV-1), a common ocular pathogen.

METHODS

The impact of mast cells on the immune response to HSV-1 infection was investigated using MC-deficient Kit(W-sh) mice. Virus titers, inflammatory cytokine production, eicosanoid profiles, cellular immune responses, and ocular pathology were evaluated and compared with C57BL/6J mice during an acute corneal HSV-1 infection.

RESULTS

Corneas of Kit(W-sh) mice have higher viral titers, increased edema, and greater leukocyte infiltration following HSV-1 infection. Following infection, cytokine profiles were slightly elevated overall in Kit(W-sh) mice. Eicosanoid profiles were remarkably different only when comparing uninfected corneas from both groups. Neutrophils within infected corneas expressed HSV-1 antigen, lytic genes, and served as a disease-causing vector when adoptively transferred into immunocompromised animals. Myeloid-derived suppressor cells did not infiltrate into the cornea or suppress the expansion, recruitment, or cytokine production by CD8+ T cells following acute HSV-1 infection.

CONCLUSIONS

Collectively, these findings provide new insight into host defense in the cornea and the pathogenesis of HSV-1 infection by identifying previously unacknowledged MCs as protective innate sentinels for infection of the ocular surface and reinforcing that neutrophils are detrimental to corneal infection.

Redundant Function of Plasmacytoid and Conventional Dendritic Cells Is Required To Survive a Natural Virus Infection

Viruses that spread systemically from a peripheral site of infection cause morbidity and mortality in the human population. Innate myeloid cells, including monocytes, macrophages, monocyte-derived dendritic cells (mo-DC), and dendritic cells (DC), respond early during viral infection to control viral replication, reducing virus spread from the peripheral site. Ectromelia virus (ECTV), an orthopoxvirus that naturally infects the mouse, spreads systemically from the peripheral site of infection and results in death of susceptible mice. While phagocytic cells have a requisite role in the response to ECTV, the requirement for individual myeloid cell populations during acute immune responses to peripheral viral infection is unclear. In this study, a variety of myeloid-specific depletion methods were used to dissect the roles of individual myeloid cell subsets in the survival of ECTV infection. We showed that DC are the primary producers of type I interferons (T1-IFN), requisite cytokines for survival, following ECTV infection. DC, but not macrophages, monocytes, or granulocytes, were required for control of the virus and survival of mice following ECTV infection. Depletion of either plasmacytoid DC (pDC) alone or the lymphoid-resident DC subset (CD8α(+) DC) alone did not confer lethal susceptibility to ECTV. However, the function of at least one of the pDC or CD8α(+) DC subsets is required for survival of ECTV infection, as mice depleted of both populations were susceptible to ECTV challenge. The presence of at least one of these DC subsets is sufficient for cytokine production that reduces ECTV replication and virus spread, facilitating survival following infection.

IMPORTANCE

Prior to the eradication of variola virus, the orthopoxvirus that causes smallpox, one-third of infected people succumbed to the disease. Following successful eradication of smallpox, vaccination rates with the smallpox vaccine have significantly dropped. There is now an increasing incidence of zoonotic orthopoxvirus infections for which there are no effective treatments. Moreover, the safety of the smallpox vaccine is of great concern, as complications may arise, resulting in morbidity. Like many viruses that cause significant human diseases, orthopoxviruses spread from a peripheral site of infection to become systemic. This study elucidates the early requirement for innate immune cells in controlling a peripheral infection with ECTV, the causative agent of mousepox. We report that there is redundancy in the function of two innate immune cell subsets in controlling virus spread early during infection. The viral control mediated by these cell subsets presents a potential target for therapies and rational vaccine design.

Immunological aspects of acute and recurrent herpes simplex keratitis

Herpes simplex keratitis (HSK) belongs to the major causes of visual morbidity worldwide and available methods of treatment remain unsatisfactory. Primary infection occurs usually early in life and is often asymptomatic. Chronic visual impairment and visual loss are caused by corneal scaring, thinning, and vascularization connected with recurrent HSV infections. The pathogenesis of herpetic keratitis is complex and is still not fully understood. According to the current knowledge, corneal scarring and vascularization are the result of chronic inflammatory reaction against HSV antigens. In this review we discuss the role of innate and adaptive immunities in acute and recurrent HSV ocular infection and present the potential future targets for novel therapeutical options based on immune interventions.

Ontogeny of myeloid cells

Granulocytes, monocytes, macrophages, and dendritic cells (DCs) represent a subgroup of leukocytes, collectively called myeloid cells. During the embryonic development of mammalians, myelopoiesis occurs in a stepwise fashion that begins in the yolk sac and ends up in the bone marrow (BM). During this process, these early monocyte progenitors colonize various organs such as the brain, liver, skin, and lungs and differentiate into resident macrophages that will self-maintain throughout life. DCs are constantly replenished from BM precursors but can also arise from monocytes in inflammatory conditions. In this review, we summarize the different types of myeloid cells and discuss new insights into their early origin and development in mice and humans from fetal to adult life. We specifically focus on the function of monocytes, macrophages, and DCs at these different developmental stages and on the intrinsic and environmental influences that may drive these adaptations.

Role for Gr-1+ cells in the control of high-dose Mycobacterium bovis recombinant BCG

Mycobacterium bovis bacillus Calmette-Guérin (BCG) is an attractive target for development as a live vaccine vector delivering transgenic antigens from HIV and other pathogens. Most studies aimed at defining the clearance of BCG have been performed at doses between 10(2) and 10(4) CFU. Interestingly, however, recombinant BCG (rBCG) administered at doses of >10(6) CFU effectively generates antigen-specific T-cell responses and primes for heterologous boost responses. Thus, defining clearance at high doses might aid in the optimization of rBCG as a vector. In this study, we used bioluminescence imaging to examine the kinetics of rBCG transgene expression and clearance in mice immunized with 5 × 10(7) CFU rBCG expressing luciferase. Similar to studies using low-dose rBCG, our results demonstrate that the adaptive immune response is necessary for long-term control of rBCG beginning 9 days after immunizing mice. However, in contrast to these reports, we observed that the majority of mycobacterial antigen was eliminated prior to day 9. By examining knockout and antibody-mediated depletion mouse models, we demonstrate that the rapid clearance of rBCG occurs in the first 24 h and is mediated by Gr-1(+) cells. As Gr-1(+) granulocytes have been described as having no impact on BCG clearance at low doses, our results reveal an unappreciated role for Gr-1(+) neutrophils and inflammatory monocytes in the clearance of high-dose rBCG. This work demonstrates the potential of applying bioluminescence imaging to rBCG in order to gain an understanding of the immune response and increase the efficacy of rBCG as a vaccine vector.

Treg depletion attenuates the severity of skin disease from ganglionic spread after HSV-2 flank infection

Regulatory T cells (Tregs) attenuate lesion severity and disease after HSV ocular or genital infection, but their role in cutaneous infection remains unclear. Treg depletion (anti-CD25 mAb in C57BL/6 mice or diphtheria toxin (DT) in DEREG mice) prior to tk-deficient HSV-2 flank infection significantly decreased skin lesion severity, granulocyte receptor-1(Gr-1(+)) cell number, and chemokine (KC) expression in the secondary skin, but significantly increased immune effectors and chemokine expression (MCP-1, KC, VEGF-A) in the draining LN, and activated, interferon-γ producing CD8(+)T cells in the ganglia. Treg depletion also significantly reduced HSV-2 DNA in the ganglia. Thus, Tregs increase the severity of recurrent skin lesions, and differentially alter chemokine expression and immune effector homing in the skin and LN after cutaneous infection, and limit CD8(+) T cell responses in the ganglia. Our data suggests that effects of Treg manipulation on recurrent herpes lesions should be considered when developing Treg mediated therapeutics.

Characterization of chikungunya virus infection of a human keratinocyte cell line: role of mosquito salivary gland protein in suppressing the host immune response

The chikungunya virus (CHIKV) is a mosquito-borne virus that has recently re-emerged in several countries. On infection, the first vertebrate cells to come into contact with CHIKV are skin cells; mosquitoes inoculate the virus together with salivary gland protein into host skin while probing and feeding on blood. However, there is little known about the susceptibility of human skin cells to CHIKV infection. To clarify this, we investigated the kinetics of CHIKV in the human keratinocyte cell line, HaCaT. CHIKV actively replicated in HaCaT cells, with virus titers in the supernatant increasing to 2.8 × 10(4) plaque-forming units (PFU) ml(-1) 24h post infection. CHIKV infection suppressed production of interleukin-8 (IL-8) in HaCaT cells. The function of IL-8 is to recruit immune cells to virus-infected sites, a process known as chemotaxis. Furthermore, we assessed the role of mosquito salivary gland protein in CHIKV infections by comparing the levels of CHIKV gene expression and chemokine production in HaCaT cells with and without salivary gland extract (SGE). SGE enhanced both the expression of the CHIKV gene and the suppression effect of CHIKV on IL-8 production. Our data suggest that the HaCaT cell line represents an effective tool for investigating the mechanism of CHIKV transmission and spread in skin cells. At the mosquito bite site, CHIKV works together with SGE to ensure the virus replicates in skin cells and escapes the host immune system by suppression of IL-8 production.

CXCL1-deficient mice are highly sensitive to pseudomonas aeruginosa but not herpes simplex virus type 1 corneal infection

PURPOSE

To determine the role of the chemokine CXCL1 on leukocyte recruitment, cytokine production and host resistance during HSV-1 and Pseudomonas aeruginosa infection.

METHODS

Viral titer and bacterial load were compared following infection of wild-type (WT) and CXCL1(-/-) mice. Corneal leukocyte recruitment was determined using flow cytometry. Cytokine levels were assessed by luminex-based suspension arrays. Hematoxylin and eosin (H&E) staining, confocal microscopy, and optical coherence tomography (OCT) were used to visualize leukocyte recruitment and corneal thickening.

RESULTS

HSV-1-infected WT and CXCL1(-/-) mice possessed similar viral titers in the cornea during late acute infection. Flow cytometry analysis detected similar leukocyte levels in the cornea following infection as well. By comparison, there was a significant increase in P. aeruginosa recovered from CXCL1(-/-) corneas as compared with WT mice. Imaging analysis and histochemical staining revealed impaired leukocyte recruitment to the central cornea and earlier corneal thickening in CXCL1(-/-) mice. IFN-γ, CCL2, and CCL5 protein levels were similar between WT and CXCL1(-/-) corneas following HSV-1 or P. aeruginosa infection. However, CXCL2 levels were significantly reduced in the CXCL1(-/-) corneas following either infection.

CONCLUSIONS

The absence of CXCL1 and CXCL2 expression significantly impairs the ability of the host to control P. aeruginosa replication through the recruitment of leukocytes to the central cornea. In contrast, CXCL1, CXCL2, and the cells they recruit, are not required for HSV-1 clearance during acute infection.

Early responding dendritic cells direct the local NK response to control herpes simplex virus 1 infection within the cornea

Dendritic cells (DCs) regulate both innate and adaptive immune responses. In this article, we exploit the unique avascularity of the cornea to examine a role for local or very early infiltrating DCs in regulating the migration of blood-derived innate immune cells toward HSV-1 lesions. A single systemic diphtheria toxin treatment 2 d before HSV-1 corneal infection transiently depleted CD11c(+) DCs from both the cornea and lymphoid organs of CD11c-DTR bone marrow chimeric mice for up to 24 h postinfection. Transient DC depletion significantly delayed HSV-1 clearance from the cornea through 6 d postinfection. No further compromise of viral clearance was observed when DCs were continuously depleted throughout the first week of infection. DC depletion did not influence extravasation of NK cells, inflammatory monocytes, or neutrophils into the peripheral cornea, but it did significantly reduce migration of NK cells and inflammatory monocytes, but not neutrophils, toward the HSV-1 lesion in the central cornea. Depletion of NK cells resulted in similar loss of viral control to transient DC ablation. Our findings demonstrate that resident corneal DCs and/or those that infiltrate the cornea during the first 24 h after HSV-1 infection contribute to the migration of NK cells and inflammatory monocytes into the central cornea, and are consistent with a role for NK cells and possibly inflammatory monocytes, but not polymorphonuclear neutrophils, in clearing HSV-1 from the infected cornea.

Neutrophils in tuberculosis: friend or foe?

Neutrophils are rapidly recruited to sites of mycobacterial infection, where they phagocytose bacilli. Whether neutrophils can kill mycobacteria in vivo probably depends on the tissue microenvironment, stage of infection, individual host, and infecting organism. The interaction of neutrophils with macrophages, as well as the downstream effects on T cell activity, could result in a range of outcomes from early clearance of infection to dissemination of viable bacteria together with an attenuated acquired immune response. In established disease, neutrophils accumulate in situations of high pathogen load or immunological dysfunction, and are likely to contribute to pathology. These activities may have clinical importance in terms of new treatments, targeted interventions and vaccine strategies.

CD11b⁺, Ly6G⁺ cells produce type I interferon and exhibit tissue protective properties following peripheral virus infection

The goal of the innate immune system is containment of a pathogen at the site of infection prior to the initiation of an effective adaptive immune response. However, effector mechanisms must be kept in check to combat the pathogen while simultaneously limiting undesirable destruction of tissue resulting from these actions. Here we demonstrate that innate immune effector cells contain a peripheral poxvirus infection, preventing systemic spread of the virus. These innate immune effector cells are comprised primarily of CD11b⁺Ly6C⁺Ly6G^- monocytes that accumulate initially at the site of infection, and are then supplemented and eventually replaced by CD11b⁺Ly6C⁺Ly6G⁺ cells. The phenotype of the CD11b⁺Ly6C⁺Ly6G⁺ cells resembles neutrophils, but the infiltration of neutrophils typically occurs prior to, rather than following, accumulation of monocytes. Indeed, it appears that the CD11b⁺Ly6C⁺Ly6G⁺ cells that infiltrated the site of VACV infection in the ear are phenotypically distinct from the classical description of both neutrophils and monocyte/macrophages. We found that CD11b⁺Ly6C⁺Ly6G⁺ cells produce Type I interferons and large quantities of reactive oxygen species. We also observed that depletion of Ly6G⁺ cells results in a dramatic increase in tissue damage at the site of infection. Tissue damage is also increased in the absence of reactive oxygen species, although reactive oxygen species are typically thought to be damaging to tissue rather than protective. These data indicate the existence of a specialized population of CD11b⁺Ly6C⁺Ly6G⁺ cells that infiltrates a site of virus infection late and protects the infected tissue from immune-mediated damage via production of reactive oxygen species. Regulation of the action of this population of cells may provide an intervention to prevent innate immune-mediated tissue destruction.

During a natural virus infection, small doses of infectious virus are deposited at a peripheral infection site, and then a “race” ensues, in which the replicating virus attempts to “outpace” the responding immune system of the host. In the early phases of infection, the innate immune system must contain the infection prior to the development of an effective adaptive response. Here we have characterized the cells of the innate immune system that move to a site of peripheral virus infection, and we find that a subset of these cells display atypical expression of cell surface molecules, timing of infiltration, and function. These cells protect the infected tissue from damage by producing reactive oxygen molecules, which are widely accepted to increase tissue damage. Therefore our findings indicate that during a peripheral virus infection, the typical rules governing the function of the innate immune system are altered to prevent tissue damage.

Neutrophils sustain effective CD8(+) T-cell responses in the respiratory tract following influenza infection

Neutrophils have an important role in early host protection during influenza A virus infection. Their ability to modulate the virus-specific adaptive immune response is less clear. Here, we have used a mouse model to examine the impact of neutrophils on CD8(+) T-cell responses during influenza virus infection. CD8(+) T-cell priming, expansion, migration, cytokine secretion and cytotoxic capacity were investigated in the virus-infected airways and secondary lymphoid organs. To do this, we utilised a Ly6G-specific monoclonal antibody (mAb; 1A8) that specifically depletes neutrophils in vivo. Neutrophil depletion early after infection with influenza virus strain HKx31 (H3N2) did not alter influenza virus-derived antigen presentation or naïve CD8(+) T-cell expansion in the secondary lymphoid organs. Trafficking of virus-specific CD8(+) T cells into the infected pulmonary airways was also unaltered. Instead, early neutropenia reduced both the overall magnitude of influenza virus-specific CD8(+) T cells, together with impaired cytokine production and cytotoxic effector function. Therefore, neutrophils are important participants in anti-viral mechanisms that sustain effective CD8(+) T-cell responses in the respiratory tract of influenza virus-infected mice.