Both plasmacytoid dendritic cells and monocytes stimulate natural killer cells early during human herpes simplex virus type 1 infections

Role of Innate Interferon Responses at the Ocular Surface in Herpes Simplex Virus-1-Induced Herpetic Stromal Keratitis

Herpes simplex virus type 1 (HSV-1) is a highly successful pathogen that primarily infects epithelial cells of the orofacial mucosa. After initial lytic replication, HSV-1 enters sensory neurons and undergoes lifelong latency in the trigeminal ganglion (TG). Reactivation from latency occurs throughout the host’s life and is more common in people with a compromised immune system. HSV-1 causes various diseases depending on the site of lytic HSV-1 replication. These include herpes labialis, herpetic stromal keratitis (HSK), meningitis, and herpes simplex encephalitis (HSE). HSK is an immunopathological condition and is usually the consequence of HSV-1 reactivation, anterograde transport to the corneal surface, lytic replication in the epithelial cells, and activation of the host’s innate and adaptive immune responses in the cornea. HSV-1 is recognized by cell surface, endosomal, and cytoplasmic pattern recognition receptors (PRRs) and activates innate immune responses that include interferons (IFNs), chemokine and cytokine production, as well as the recruitment of inflammatory cells to the site of replication. In the cornea, HSV-1 replication promotes type I (IFN-α/β) and type III (IFN-λ) IFN production. This review summarizes our current understanding of HSV-1 recognition by PRRs and innate IFN-mediated antiviral immunity during HSV-1 infection of the cornea. We also discuss the immunopathogenesis of HSK, current HSK therapeutics and challenges, proposed experimental approaches, and benefits of promoting local IFN-λ responses.

Diverse impact of a probiotic strain, Lacticaseibacillus paracasei Shirota, on peripheral mononuclear phagocytic cells in healthy Japanese office workers: a randomized, double-blind, controlled trial

Mononuclear phagocytic cells (MPCs) are classified into monocytes (Mos)/macrophages and dendritic cells (DCs) based on their functions. Cells of MPCs lineage act as immune modulators by affecting effector cells, such as NK cells, T cells, and B cells. This study aimed to investigate the effects of Lacticaseibacillus paracasei strain Shirota (LcS) ingestion on peripheral MPCs, particularly on their expression of functional cell-surface molecules enhanced in healthy adults. Thus, twelve healthy office workers consumed a fermented milk drink containing 1.0 × 10¹¹ cfu of LcS (LcS-FM) or a control unfermented milk drink (CM) once a day for 6 weeks. Peripheral blood mononuclear cells (PBMCs) were prepared from blood samples, and immune cells and functional cell-surface molecules were analyzed. We observed remarkable differences in the expression of HLAABC, MICA, CD40, and GPR43 in plasmacytoid DCs (pDCs) between the LcS-FM and CM groups, whereas no difference was found in CD86 or HLADR expression. The LcS-FM group exhibited higher CD40 expression in both conventional DCs (cDCs) and Mos, especially in type 2 conventional DCs (cDC2s) and classical monocytes (cMos); higher percentages of cMos, intermediate monocytes (iMos), and nonclassical monocytes; and higher numbers of cMos and iMos in PBMCs than the CM group. LcS ingestion increased the expression of HLAABC, MICA, CD40, and GPR43 in pDCs and CD40 in cDCs and Mos, particularly cDC2s and cMos. These results suggest that LcS modulates the function of MPCs that may lead to the regulation of immune effector functions in healthy adults.

Suppression of annexin A1 and its receptor reduces herpes simplex virus 1 lethality in mice

Herpes simplex virus 1 (HSV-1)-induced encephalitis is the most common cause of sporadic, fatal encephalitis in humans. HSV-1 has at least 10 different envelope glycoproteins, which can promote virus infection. The ligands for most of the envelope glycoproteins and the significance of these ligands in virus-induced encephalitis remain elusive. Here, we show that glycoprotein E (gE) binds to the cellular protein, annexin A1 (Anx-A1) to enhance infection. Anx-A1 can be detected on the surface of cells permissive for HSV-1 before infection and on virions. Suppression of Anx-A1 or its receptor, formyl peptide receptor 2 (FPR2), on the cell surface and gE or Anx-A1 on HSV-1 envelopes reduced virus binding to cells. Importantly, Anx-A1 knockout, Anx-A1 knockdown, or treatments with the FPR2 antagonist reduced the mortality and tissue viral loads of infected mice. Our results show that Anx-A1 is a novel enhancing factor of HSV-1 infection. Anx-A1-deficient mice displayed no evident physiology and behavior changes. Hence, targeting Anx-A1 and FPR2 could be a promising prophylaxis or adjuvant therapy to decrease HSV-1 lethality.

Herpes simplex virus 1 (HSV-1)-induced encephalitis is the most devastating consequence of HSV-1 infection, even in patients treated with anti-HSV-1 drugs. Moreover, encephalitis induced by drug-resistant HSV-1 has been reported in immunocompromised patients. Identifying the cellular factors in promoting HSV-1 replication, especially those increasing virus attachment and entry, could facilitate the development of alternative or adjuvant therapy. Here, we identified annexin A1 (Anx-A1) and its receptor, formyl peptide receptor 2 (FPR2), facilitating HSV-1 attachment to the cell surface. Suppression of Anx-A1 or blockage of FPR2 impaired HSV-1 attachment to cells, viral yields in cells, and HSV-1 lethality in mice. Moreover, blocking FPR2 decreased the replication of drug-resistant HSV-1 in BABL/c nude mice. Hence, targeting Anx-A1 and FPR2 could be alternative or adjuvant therapy for HSV-1 infection.

Th1 regulatory events by infectious pathogens, herpes zoster and herpes simplex viruses: prospects for therapeutic options for atopic eczema

Infections caused by viral and bacterial pathogens are typically perceived as harmful, such as in cases of herpes zoster and herpes simplex virus infections. However, clinical observation of an improvement in atopic skin lesions upon herpes virus infection has been noted, particularly at the site of varicella and Kaposi’s varicelliform eruption. Th1 immune cells and cytokines, mobilized and induced for protection against infectious pathogens, are expected to improve Th2 dominant atopic symptoms. This study focuses on Th1 immunoregulatory events mediated by infectious pathogens, particularly herpes viruses. Immunoregulatory events induced by herpes viruses may have a potential therapeutic value for treating atopic eczema.

Initial TK-deficient HSV-1 infection in the lip alters contralateral lip challenge immune dynamics

Primary infection with herpes simplex type 1 (HSV-1) occurring around the mouth and nose switches rapidly to lifelong latent infection in sensitive trigeminal ganglia (TG) neurons. Sporadic reactivation of these latent reservoirs later in life is the cause of acute infections of the corneal epithelium, which can cause potentially blinding herpes simplex keratitis (HSK). There is no effective vaccine to protect against HSK, and antiviral drugs provide only partial protection against recurrences. We previously engendered an acute disease-free, non-reactivating latent state in mice when challenged with virulent HSV-1 in orofacial mucosa, by priming with non-neurovirulent HSV-1 (TK_del) before the challenge. Herein, we define the local immune infiltration and inflammatory chemokine production changes after virulent HSV-1 challenge, which were elicited by TK_del prime. Heightened immunosurveillance before virulent challenge, and early enhanced lymphocyte-enriched infiltration of the challenged lip were induced, which corresponded to attenuation of inflammation in the TG and enhanced viral control. Furthermore, classical latent-phase T cell persistence around latent HSV-1 reservoirs were severely reduced. These findings identify the immune processes that are likely to be responsible for establishing non-reactivating latent HSV-1 reservoirs. Stopping reactivation is essential for development of efficient vaccine strategies against HSV-1.

Exhausted NK cells and cytokine storms in COVID-19: Whether NK cell therapy could be a therapeutic choice

The global outbreak of coronavirus-2019 (COVID-19) still claims more lives daily around the world due to the lack of a definitive treatment and the rapid tendency of virus to mutate, which even jeopardizes vaccination efficacy. At the forefront battle against SARS-CoV-2, an effective innate response to the infection has a pivotal role in the initial control and treatment of disease. However, SARS-CoV-2 subtly interrupts the equations of immune responses, disrupting the cytolytic antiviral effects of NK cells, while seriously activating infected macrophages and other immune cells to induce an unleashed "cytokine storm", a dangerous and uncontrollable inflammatory response causing life-threatening symptoms in patients. Notably, the NK cell exhaustion with ineffective cytolytic function against the sources of exaggerated cytokine release, acts as an Achilles' heel which exacerbates the severity of COVID-19. Given this, approaches that improve NK cell cytotoxicity may benefit treatment protocols. As a suggestion, adoptive transfer of NK or CAR-NK cells with proper cytotolytic potentials and the lowest capacity of cytokine-release (for example CD56^dim NK cells brightly express activating receptors), to severe COVID-19 patients may provide an effective cure especially in cases suffering from cytokine storms. More intriguingly, the ongoing evidence for persistent clonal expansion of NK memory cells characterized by an activating phenotype in response to viral infections, can benefit the future studies on vaccine development and adoptive NK cell therapy in COVID-19. Whether vaccinated volunteers or recovered patients can also be considered as suitable candidates for cell donation could be the subject of future research.

How dendritic cells sense and respond to viral infections

The ability of dendritic cells (DCs) to sense viral pathogens and orchestrate a proper immune response makes them one of the key players in antiviral immunity. Different DC subsets have complementing functions during viral infections, some specialize in antigen presentation and cross-presentation and others in the production of cytokines with antiviral activity, such as type I interferons. In this review, we summarize the latest updates concerning the role of DCs in viral infections, with particular focus on the complex interplay between DC subsets and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Despite being initiated by a vast array of immune receptors, DC-mediated antiviral responses often converge towards the same endpoint, that is the production of proinflammatory cytokines and the activation of an adaptive immune response. Nonetheless, the inherent migratory properties of DCs make them a double-edged sword and often viral recognition by DCs results in further viral dissemination. Here we illustrate these various aspects of the antiviral functions of DCs and also provide a brief overview of novel antiviral vaccination strategies based on DCs targeting.

In Situ Cancer Vaccination and Immunovirotherapy Using Oncolytic HSV

Herpes simplex virus (HSV) can be genetically altered to acquire oncolytic properties so that oncolytic HSV (oHSV) preferentially replicates in and kills cancer cells, while sparing normal cells, and inducing anti-tumor immune responses. Over the last three decades, a better understanding of HSV genes and functions, and improved genetic-engineering techniques led to the development of oHSV as a novel immunovirotherapy. The concept of in situ cancer vaccination (ISCV) was first introduced when oHSV was found to induce a specific systemic anti-tumor immune response with an abscopal effect on non-injected tumors, in the process of directly killing tumor cells. Thus, the use of oHSV for tumor vaccination in situ is antigen-agnostic. The research and development of oHSVs have moved rapidly, with the field of oncolytic viruses invigorated by the FDA/EMA approval of oHSV talimogene laherparepvec in 2015 for the treatment of advanced melanoma. Immunovirotherapy can be enhanced by arming oHSV with immunomodulatory transgenes and/or using them in combination with other chemotherapeutic and immunotherapeutic agents. This review offers an overview of the development of oHSV as an agent for ISCV against solid tumors, describing the multitude of different oHSVs and their efficacy in immunocompetent mouse models and in clinical trials.

Characterization of Resident Corneal Plasmacytoid Dendritic Cells and Their Pivotal Role in Herpes Simplex Keratitis

The presence and potential functions of resident plasmacytoid dendritic cells (pDCs) in peripheral tissues is unclear. We report that pDCs constitutively populate naïve corneas and are increased during sterile injuries or acute herpes simplex virus 1 (HSV-1) keratitis. Their local depletion leads to severe clinical disease, nerve loss, viral dissemination to the trigeminal ganglion and draining lymph nodes, and mortality, while their local adoptive transfer limits disease. pDCs are the main source of HSV-1-induced IFN-α in the corneal stroma through TLR9, and they prevent re-programming of regulatory T cells (Tregs) to effector ex-Tregs. Clinical signs of infection are observed in pDC-depleted corneas, but not in pDC-sufficient corneas, following low-dose HSV-1 inoculation, suggesting their critical role in corneal antiviral immunity. Our findings demonstrate a vital role for corneal pDCs in the control of local viral infections.

Jamali et al. show that the cornea, as an immune-privileged tissue, hosts resident pDCs, which mediate immunity against HSV-1 by secreting IFN-a via TLR9 and preserving Tregs. pDCs minimize the clinical severity of HSV-1 keratitis, infiltration of immune cells, nerve damage, and viral dissemination to TG and dLNs.

Prolonged high-intensity exercise induces fluctuating immune responses to herpes simplex virus infection via glucocorticoids

BACKGROUND

Epidemiologic studies have yielded conflicting results regarding the influence of a single bout of prolonged high-intensity exercise on viral infection.

OBJECTIVE

We sought to learn whether prolonged high-intensity exercise either exacerbates or ameliorates herpes simplex virus type 2 (HSV-2) infection according to the interval between virus exposure and exercise.

METHODS

Mice were intravaginally infected with HSV-2 and exposed to run on the treadmill.

RESULTS

Prolonged high-intensity exercise 17 hours after infection impaired the clearance of HSV-2, while exercise 8 hours after infection enhanced the clearance of HSV-2. These impaired or enhanced immune responses were related to a transient decrease or increase in the number of blood-circulating plasmacytoid dendritic cells. Exercise-induced glucocorticoids transiently decreased the number of circulating plasmacytoid dendritic cells by facilitating their homing to the bone marrow via the CXCL12-CXCR4 axis, which led to their subsequent increase in the blood.

CONCLUSION

A single bout of prolonged high-intensity exercise can be either deleterious or beneficial to antiviral immunity.

Natural Killer-Dendritic Cell Interactions in Liver Cancer: Implications for Immunotherapy

Simple Summary

The reciprocal crosstalk between dendritic cells (DCs) and natural killer (NK) cells plays a pivotal role in regulating immune defense against viruses and tumors. The Th-cell polarizing ability, cytokine-producing capacity, chemokine expression, and migration of DCs are regulated by activated NK cells. Conversely, the effector functions including lysis and cytokine production, proliferation, and migration of NK cells are influenced by close interactions with activated DCs. In this review, we explore the impact of DC–NK cell crosstalk and its therapeutic potential in immune control of liver malignances.

Abstract

Natural killer (NK) and dendritic cells (DCs) are innate immune cells that play a crucial role in anti-tumor immunity. NK cells kill tumor cells through direct cytotoxicity and cytokine secretion. DCs are needed for the activation of adaptive immune responses against tumor cells. Both NK cells and DCs are subdivided in several subsets endowed with specialized effector functions. Crosstalk between NK cells and DCs leads to the reciprocal control of their activation and polarization of immune responses. In this review, we describe the role of NK cells and DCs in liver cancer, focusing on the mechanisms involved in their reciprocal control and activation. In this context, intrahepatic NK cells and DCs present unique immunological features, due to the constant exposure to non-self-circulating antigens. These interactions might play a fundamental role in the pathology of primary liver cancer, namely hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC). Additionally, the implications of these immune changes are relevant from the perspective of improving the cancer immunotherapy strategies in HCC and ICC patients.

Macrophage polarization contributes to the efficacy of an oncolytic HSV-1 targeting human uveal melanoma in a murine xenograft model

Uveal melanoma (UM), the most common primary malignant tumor of the eye in adults, is difficult-to-treat. UM has a relatively high mortality secondary to distant metastasis and poor overall survival with existing therapies. The oncolytic virus herpes simplex virus type-1 (HSV-1) has been approved for clinical use in melanoma. This double-stranded DNA virus was suspected to directly activate lysis specifically in neoplastic cells. We tested the antitumor efficacy of recombinant oncolytic HSV-1-EGFP (oHSV-EGFP) in UM and characterized the local and systemic antitumor innate immune response in a murine xenograft model. We first determined the efficacy of the oncolytic virus in 92.1, MUM2B and MP41 cell lines. In murine xenograft models, oHSV-EGFP reduced intraocular tumors as well as systemic subcutaneous tumors. A significant change in cytokines was observed in viral infected cells, especially a rise in IFNγ. In vivo analyses showed increased anti-tumorigenic M1 macrophages and decreased pro-tumorigenic M2 macrophages in peripheral blood, and intraocular and distant tumors after intravitreal viral treatment. Increased infiltration of natural killer cells and mature dendritic cells was also detected after viral treatment. In addition, no virus was detected in major organs after the treatment. Our data support that oHSV-EGFP is effective, neoplasm specific, immune active and safe, providing possible clinical translatable options to treat ocular and metastatic UM.

Resident plasmacytoid dendritic cells patrol vessels in the naïve limbus and conjunctiva

Plasmacytoid dendritic cells (pDCs) constitute a unique population of bone marrow-derived cells that play a pivotal role in linking innate and adaptive immune responses. While peripheral tissues are typically devoid of pDCs during steady state, few tissues do host resident pDCs. In the current study, we aim to assess presence and distribution of pDCs in naïve murine limbus and bulbar conjunctiva. Immunofluorescence staining followed by confocal microscopy revealed that the naïve bulbar conjunctiva of wild-type mice hosts CD45⁺ CD11c^low PDCA-1⁺ pDCs. Flow cytometry confirmed the presence of resident pDCs in the bulbar conjunctiva through multiple additional markers, and showed that they express maturation markers, the T cell co-inhibitory molecules PD-L1 and B7-H3, and minor to negligible levels of T cell co-stimulatory molecules CD40, CD86, and ICAM-1. Epi-fluorescent microscopy of DPE-GFP×RAG1^-/- transgenic mice with GFP-tagged pDCs indicated lower density of pDCs in the bulbar conjunctiva compared to the limbus. Further, intravital multiphoton microscopy revealed that resident pDCs accompany the limbal vessels and patrol the intravascular space. In vitro multiphoton microscopy showed that pDCs are attracted to human umbilical vein endothelial cells and interact with them during tube formation. In conclusion, our study shows that the limbus and bulbar conjunctiva are endowed with resident pDCs during steady state, which express maturation and classic T cell co-inhibitory molecules, engulf limbal vessels, and patrol intravascular spaces.

Human NK Cells and Herpesviruses: Mechanisms of Recognition, Response and Adaptation

NK cells contribute to early defenses against viruses through their inborn abilities that include sensing of PAMPs and inflammatory signals such as cytokines or chemokines, recognition, and killing of infected cells through activating surface receptors engagement. Moreover, they support adaptive responses via Ab-dependent mechanisms, triggered by CD16, and DC editing. Their fundamental role in anti-viral responses has been unveiled in patients with NK cell deficiencies suffering from severe Herpesvirus infections. Notably, these infections, often occurring as primary infections early in life, can be efficiently cleared by NK, T, and B cells in healthy hosts. Herpesviruses however, generate a complicated balance with the host immune system through their latency cycle moving between immune control and viral reactivation. This lifelong challenge has contributed to the development of numerous evasion mechanisms by Herpesviruses, many of which devoted to elude NK cell surveillance from viral reactivations rather than primary infections. This delicate equilibrium can be altered in proportions of healthy individuals promoting virus reactivation and, more often, in immunocompromised subjects. However, the constant stimulus provided by virus-host interplay has also favored NK-cell adaptation to Herpesviruses. During anti-HCMV responses, NK cells can reshape their receptor repertoire and function, through epigenetic remodeling, and acquire adaptive traits such as longevity and clonal expansion abilities. The major mechanisms of recognition and effector responses employed by NK cells against Herpesviruses, related to their genomic organization will be addressed, including those allowing NK cells to generate memory-like responses. In addition, the mechanisms underlying virus reactivation or control will be discussed.

Prospect of Plasmacytoid Dendritic Cells in Enhancing Anti-Tumor Immunity of Oncolytic Herpes Viruses

The major type I interferon-producing plasmacytoid dendritic cells (pDC) surround and infiltrate certain tumors like malignant melanoma, head and neck cancer, and ovarian and breast cancer. The presence of pDC in these tumors is associated with an unfavorable prognosis for the patients as long as these cells are unstimulated. Upon activation by synthetic Toll-like receptor agonists or viruses, however, pDC develop cytotoxic activities. Viruses have the additional advantage to augment cytotoxic activities of pDC via lytic replication in malignant lesions. These effects turn cold tumors into hotspots, recruiting further immune cells to the site of inflammation. Activated pDC contribute to cross-presentation of tumor-associated antigens by classical dendritic cells, which induce cytotoxic T-cells in particular in the presence of checkpoint inhibitors. The modification of oncolytic herpes viruses via genetic engineering favorably affects this process through the enhanced production of pro-inflammatory cytokines, curbing of tumor blood supply, and removal of extracellular barriers for efficient viral spread. Importantly, viral vectors may contribute to stimulation of memory-type adaptive immune responses through presentation of tumor-related neo- and/or self-antigens. Eventually, both replication-competent and replication-deficient herpes simplex virus 1 (HSV-1) may serve as vaccine vectors, which contribute to tumor regression by the stimulation of pDC and other dendritic cells in adjuvant and neo-adjuvant situations.

Generation of an Oncolytic Herpes Simplex Virus 1 Expressing Human MelanA

Robust anti-tumor immunity requires innate as well as adaptive immune responses. We have shown that plasmacytoid dendritic cells develop killer cell-like activity in melanoma cell cocultures after exposure to the infectious but replication-deficient herpes simplex virus 1 (HSV-1) d106S. To combine this innate effect with an enhanced adaptive immune response, the gene encoding human MelanA/MART-1 was inserted into HSV-1 d106S via homologous recombination to increase direct expression of this tumor antigen. Infection of Vero cells using this recombinant virus confirmed MelanA expression by Western blotting, flow cytometry, and immunofluorescence. HSV-1 d106S-MelanA induced expression of the transgene in fibroblast and melanoma cell lines not naturally expressing MelanA. Infection of a melanoma cell line with CRISPR-Cas9-mediated knockout of MelanA confirmed de novo expression of the transgene in the viral context. Dependent on MelanA expression, infected fibroblast and melanoma cell lines induced degranulation of HLA-matched MelanA-specific CD8+ T cells, followed by killing of infected cells. To study infection of immune cells, we exposed peripheral blood mononuclear cells and in vitro-differentiated macrophages to the parental HSV-1 d106S, resulting in expression of the transgene GFP in CD11c+ cells and macrophages. These data provide evidence that the application of MelanA-encoding HSV-1 d106S could enhance adaptive immune responses and re-direct MelanA-specific CD8+ T cells to tumor lesions, which have escaped adaptive immune responses via downregulation of their tumor antigen. Hence, HSV-1 d106S-MelanA harbors the potential to induce innate immune responses in conjunction with adaptive anti-tumor responses by CD8+ T cells, which should be evaluated in further studies.

The yin-yang of the interaction between myelomonocytic cells and NK cells

NK cells are innate lymphoid cells, which play a key role in the immune response to cancer and pathogens and participate in the shaping of adaptive immunity. NK cells engage in a complex bidirectional interaction with myelomonocytic cells. In particular, macrophages, dendritic cells and neutrophils promote differentiation and effector function of NK cells and, on the other hand, myelomonocytic cells express triggers of checkpoint blockade (eg PD-L1) and other immunosuppressive molecules, which negatively regulate NK cell function. In addition, NK cells express high levels of IL-1R8, which acts as a checkpoint for IL-18 driven differentiation and activation of NK cells. Evidence suggests that targeting the myeloid cell-NK cell crosstalk unleashes effective anti-tumour and anti-viral resistance.

Kallikrein-Kinin System Suppresses Type I Interferon Responses: A Novel Pathway of Interferon Regulation

The Kallikrein–Kinin System (KKS), comprised of kallikreins (klks), bradykinins (BKs) angiotensin-converting enzyme (ACE), and many other molecules, regulates a number of physiological processes, including inflammation, coagulation, angiogenesis, and control of blood pressure. In this report, we show that KKS regulates Type I IFN responses, thought to be important in lupus pathogenesis. We used CpG (TLR9 ligand), R848 (TLR7 ligand), or recombinant IFN-α to induce interferon-stimulated genes (ISGs) and proteins, and observed that this response was markedly diminished by BKs, klk1 (tissue kallikrein), or captopril (an ACE inhibitor). BKs significantly decreased the ISGs induced by TLRs in vitro and in vivo (in normal and lupus-prone mice), and in human PBMCs, especially the induction of Irf7 gene (p < 0.05), the master regulator of Type I IFNs. ISGs induced by IFN-α were also suppressed by the KKS. MHC Class I upregulation, a classic response to Type I IFNs, was reduced by BKs in murine dendritic cells (DCs). BKs decreased phosphorylation of STAT2 molecules that mediate IFN signaling. Among the secreted pro-inflammatory cytokines/chemokines analyzed (IL-6, IL12p70, and CXCL10), the strongest suppressive effect was on CXCL10, a highly Type I IFN-dependent cytokine, upon CpG stimulation, both in normal and lupus-prone DCs. klks that break down into BKs, also suppressed CpG-induced ISGs in murine DCs. Captopril, a drug that inhibits ACE and increases BK, suppressed ISGs, both in mouse DCs and human PBMCs. The effects of BK were reversed with indomethacin (compound that inhibits production of PGE2), suggesting that BK suppression of IFN responses may be mediated via prostaglandins. These results highlight a novel regulatory mechanism in which members of the KKS control the Type I IFN response and suggest a role for modulators of IFNs in the pathogenesis of lupus and interferonopathies.

Immune response of T cells during herpes simplex virus type 1 (HSV-1) infection

Herpes simplex virus type 1 (HSV-1), a neurotropic member of the alphaherpes virus family, is among the most prevalent and successful human pathogens. HSV-1 can cause serious diseases at every stage of life including fatal disseminated disease in newborns, cold sores, eye disease, and fatal encephalitis in adults. HSV-1 infection can trigger rapid immune responses, and efficient inhibition and clearance of HSV-1 infection rely on both the innate and adaptive immune responses of the host. Multiple strategies have been used to restrict host innate immune responses by HSV-1 to facilitate its infection in host cells. The adaptive immunity of the host plays an important role in inhibiting HSV-1 infections. The activation and regulation of T cells are the important aspects of the adaptive immunity. They play a crucial role in host-mediated immunity and are important for clearing HSV-1. In this review, we examine the findings on T cell immune responses during HSV-1 infection, which hold promise in the design of new vaccine candidates for HSV-1.

The viral innate immune antagonism and an alternative vaccine design for PRRS virus

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PRRS virus has evolved to suppress the antiviral innate immunity during infection.

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Type I interferons are potent antiviral cytokines and function to stimulate the adaptive immune responses.

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Six viral proteins have been identified as interferon antagonists and characterized for their molecular actions.

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Interferon antagonism-negative viruses are attenuated and have been proven induce protective immunity.

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Interferon suppression-negative PRRS virus may serve as an alternative vaccine for PRRS.

Porcine reproductive and respiratory syndrome (PRRS) remains one of the most economically significant diseases in the swine industry worldwide. The current vaccines are less satisfactory to confer protections from heterologous infections and long-term persistence, and the need for better vaccines are urgent. The immunological hallmarks in PRRSV-infected pigs include the unusually poor production of type I interferons (IFNs-α/β) and the aberrant and delayed adaptive immune responses, indicating that PRRSV has the ability to suppress both innate and adaptive immune responses in the host. Type I IFNs are the potent antiviral cytokines and recent studies reveal their pleiotropic functions in the priming of expansion and maturation of adaptive immunity. Thus, IFN antagonism-negative PRRSV is hypothesized to be attenuated and to build effective and broad- spectrum innate and adaptive immune responses in pigs. Such vaccines are promising alternatives to traditional vaccines for PRRSV.

NK cells in host responses to viral infections

Natural killer (NK) cells are cytotoxic innate lymphocytes that play an important role in viral clearance. NK cell responses to viral infections were originally believed to be non-specific and lacked immune memory recall responses. It is now appreciated that NK cell responses to viral infections can be specific and in some cases memory recall responses are established. Increasing evidence also illuminates the complexity of NK cell interactions with both innate and adaptive immune cells. Here, we summarize the evidence for NK cell-specific memory responses to viral infections and the intricate reciprocal interactions between NK cells and other immune cells that dictate their activation and effector functions.

Insufficient natural killer cell responses against retroviruses: how to improve NK cell killing of retrovirus-infected cells

Natural killer (NK) cells belong to the innate immune system and protect against cancers and a variety of viruses including retroviruses by killing transformed or infected cells. They express activating and inhibitory receptors on their cell surface and often become activated after recognizing virus-infected cells. They have diverse antiviral effector functions like the release of cytotoxic granules, cytokine production and antibody dependent cellular cytotoxicity. The importance of NK cell activity in retroviral infections became evident due to the discovery of several viral strategies to escape recognition and elimination by NK cells. Mutational sequence polymorphisms as well as modulation of surface receptors and their ligands are mechanisms of the human immunodeficiency virus-1 to evade NK cell-mediated immune pressure. In Friend retrovirus infected mice the virus can manipulate molecular or cellular immune factors that in turn suppress the NK cell response. In this model NK cells lack cytokines for optimal activation and can be functionally suppressed by regulatory T cells. However, these inhibitory pathways can be overcome therapeutically to achieve full activation of NK cell responses and ultimately control dissemination of retroviral infection. One effective approach is to modulate the crosstalk between NK cells and dendritic cells, which produce NK cell-stimulating cytokines like type I interferons (IFN), IL-12, IL-15, and IL-18 upon retrovirus sensing or infection. Therapeutic administration of IFNα directly increases NK cell killing of retrovirus-infected cells. In addition, IL-2/anti-IL-2 complexes that direct IL-2 to NK cells have been shown to significantly improve control of retroviral infection by NK cells in vivo. In this review, we describe novel approaches to improve NK cell effector functions in retroviral infections. Immunotherapies that target NK cells of patients suffering from viral infections might be a promising treatment option for the future.

Oncolytic herpes simplex virus interactions with the host immune system

Oncolytic viruses (OVs), like oncolytic herpes simplex virus (oHSV), are genetically engineered to selectively replicate in and kill cancer cells, while sparing normal cells. Initial OV infection, cell death, and subsequent OV propagation within the tumor microenvironment leads to a cascade of host responses (innate and adaptive), reflective of natural anti-viral immune responses. These host-virus interactions are critical to the balance between OV activities, anti-viral immune responses limiting OV, and induction of anti-tumor immunity. The host response against oHSV is complex, multifaceted, and modulated by the tumor microenvironment and immunosuppression. As a successful pathogen, HSV has multiple mechanisms to evade such host responses. In this review, we will discuss these mechanisms and HSV evasion, and how they impact oHSV therapy.

Understanding natural herpes simplex virus immunity to inform next-generation vaccine design

Incremental advances in our knowledge of how natural immune control of herpes simplex virus (HSV) develops have yielded insight as to why previous vaccine attempts have only been partially successful, however, our understanding of these pathways, particularly in humans, is still incomplete. Further elucidation of the innate immune events that are responsible for stimulating these effector responses is required to accurately inform vaccine design. An enhanced understanding of the mechanism of action of novel adjuvants will also facilitate the rational choice of adjuvant to optimise such responses. Here we review the reasons for the hitherto partial HSV vaccine success and align these with our current knowledge of how natural HSV immunity develops. In particular, we focus on the innate immune response and the role of dendritic cells in inducing protective T-cell responses and how these pathways might be recapitulated in a vaccine setting.

Regulation and trafficking of the HLA-E molecules during monocyte-macrophage differentiation

HLA-E is a nonclassical HLA-class I molecule whose best known role is to protect from the natural killer cells. More recently, an additional function more similar to that of classical HLA-class I molecules, i.e., antigen presentation to T cells, is emerging. However, much remains to be explored about the intracellular trafficking of the HLA-E molecules. With the use of 3 different cellular contexts, 2 monocytic cell lines, U937 and THP1, and peripheral blood monocytes, we show here a remarkable increase of HLA-E during monocyte-macrophage differentiation. This goes independently from the classical HLA-class I, the main source of HLA-E-specific peptides, which is found strongly up-regulated upon differentiation of peripheral blood monocytes but not at all in the case of U937 and THP1 cell lines. Although in all cases, there was a moderate increase of HLA-E expressed in the cell surface, lysis by natural killer cells is comparably restored by an anti-NKG2A antibody in untreated as well as in PMA-differentiated U937 cells. Instead, the great majority of the HLA-E is retained in the vesicles of the autophagy-lysosome network, where they colocalize with the microtubule-associated protein light chain 3, as well as with the lysosomal-associated membrane protein 1. We conclude that differently from the classical HLA-class I molecules, the primary destination of the newly synthesized HLA-E molecules in macrophages is, rather than the cell membrane, the intracellular autophagy-lysosomal vesicles where they are stored and where they can encounter the exogenous antigens.

Combined cytotoxic activity of an infectious, but non-replicative herpes simplex virus type 1 and plasmacytoid dendritic cells against tumour cells

Malignant melanoma is an aggressive tumour of the skin with increasing incidence, frequent metastasis and poor prognosis. At the same time, it is an immunogenic type of cancer with spontaneous regressions. Most recently, the tumoricidal effect of plasmacytoid dendritic cells (pDC) and their capacity to overcome the immunosuppressive tumour microenvironment are being investigated. In this respect, we studied the effect of the infectious, but replication-deficient, herpes simplex virus 1 (HSV-1) d106S vaccine strain, which lacks essential immediate early genes, in pDC co-cultures with 11 melanoma cell lines. We observed a strong cytotoxic activity, inducing apoptotic and necrotic cell death in most melanoma cell lines. The cytotoxic activity of HSV-1 d106S plus pDC was comparable to the levels of cytotoxicity induced by natural killer cells, but required only a fraction of cells with effector : target ratios of 1 : 20 (P < 0·05). The suppressive activity of cell-free supernatants derived from virus-stimulated pDC was significantly neutralized using antibodies against the interferon-α receptor (P < 0·05). In addition to type I interferons, TRAIL and granzyme B contributed to the inhibitory effect of HSV-1 d106S plus pDC to a minor extent. UV-irradiated viral stocks were significantly less active than infectious particles, both in the absence and presence of pDC (P < 0·05), indicating that residual activity of HSV-1 d106S is a major component and sensitizes the tumour cells to interferon-producing pDC. Three leukaemic cell lines were also susceptible to this treatment, suggesting a general anti-tumour effect. In conclusion, the potential of HSV-1 d106S for therapeutic vaccination should be further evaluated in patients suffering from different malignancies.

A subset of human plasmacytoid dendritic cells expresses CD8α upon exposure to herpes simplex virus type 1

Classical and plasmacytoid dendritic cells (DC) play important roles in the defense against murine and human infections with herpes simplex virus (HSV). So far, CD8α expression has only been reported for murine DC. CD8α⁺ DC have prominent cross-presenting activities, which are enhanced by murine CD8α⁺ PDC. The human orthologue of murine CD8α⁺ DC, the CD141 (BDCA3)⁺ DC, mainly cross-present after TLR3 ligation. We report here the serendipitous finding that a subset of human PDC upregulates CD8α upon HSV-1 stimulation, as shown by gene array and flow cytometry analyses. CD8α, not CD8ß, was expressed upon exposure. Markers of activation, migration, and costimulation were upregulated on CD8α-expressing human PDC. In these cells, increased cytokine and chemokine levels were detected that enhance development and function of T, B, and NK cells, and recruit immature DC, monocytes, and Th1 cells, respectively. Altogether, human CD8α⁺ PDC exhibit a highly activated phenotype and appear to recruit other immune cells to the site of inflammation. Further studies will show whether CD8α-expressing PDC contribute to antigen cross-presentation, which may be important for immune defenses against HSV infections in vitro and in vivo.