Interaction between conventional dendritic cells and natural killer cells is integral to the activation of effective antiviral immunity

Mechanism of Qizhen decoction-mediated maturation of DC cells to activate the IL-12/JAK2/STAT4 pathway to sensitise PD-1 inhibitors in the treatment of colorectal cancer

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine has been utilized to treat colorectal cancer (CRC). Qizhen decoction (QZD), a potential compound prescription of traditional Chinese medicine, possesses multiple biological activities. It has been used to treat CRC in clinical practice and has been proven to be effective.

AIM OF THE STUDY

To investigate the impact of QZD supported by intestinal flora in combination with PD-1 inhibitor on colorectal cancer, and to elucidate the mechanism by which QZD enhances the sensitivity of PD-1 inhibitor against colorectal cancer.

MATERIALS AND METHODS

Observation of Intestinal Flora Mediating the Effect of QZD Combined with PD-1 Inhibitor in the Treatment of Colorectal Cancer. We used Flow cytometry and qPCR to detect the effect of QZD combined with PD-1 inhibitor on the activation of effector T cells in a wild mouse model of colorectal cancer. In wild and germ-free mouse models, the differences in inflammatory factors, pathological change, body mass, colorectal length, and tumour load were observed. In the study of the mechanism of QZD combined with PD-1 inhibitor in the treatment of colorectal cancer, the study evaluated the abundance of Akkermansia, the phenotypes of effector T cells and DC cells, as well as inflammatory factors in each group of mice to determine whether Akkermansia played a role in activating DC cells. Based on the JAK2/TYK2/STAT4 pathway, the mechanism of PD-1 inhibitor sensitisation by QZD in colorectal cancer was further investigated.

RESULTS

We found that QZD combined with PD-1 inhibitor could improve the therapeutic effect on colorectal cancer by inducing more critical immune functions. QZD promotes increased Akkermansia abundance in the gut. Akkermansia promotes maturation of DC cells, and mature DC cells activate the IL-12/JAK2/STAT4 pathway, which significantly activates effector T cells. Akkermansia is key to QZD combined with PD-1 inhibitor-mediated immunity exerting a therapeutic effect on colorectal cancer.

CONCLUSION

The mechanism of action of the QZD sensitizing PD-1 inhibitor is to promote the maturation of DC cells to release IL-12 and activate the JAK2/STAT4 pathway to induce effector T cell activation by increasing the abundance of Akkermansia.

Interferon-epsilon is a novel regulator of NK cell responses in the uterus

The uterus is a unique mucosal site where immune responses are balanced to be permissive of a fetus, yet protective against infections. Regulation of natural killer (NK) cell responses in the uterus during infection is critical, yet no studies have identified uterine-specific factors that control NK cell responses in this immune-privileged site. We show that the constitutive expression of IFNε in the uterus plays a crucial role in promoting the accumulation, activation, and IFNγ production of NK cells in uterine tissue during Chlamydia infection. Uterine epithelial IFNε primes NK cell responses indirectly by increasing IL-15 production by local immune cells and directly by promoting the accumulation of a pre-pro-like NK cell progenitor population and activation of NK cells in the uterus. These findings demonstrate the unique features of this uterine-specific type I IFN and the mechanisms that underpin its major role in orchestrating innate immune cell protection against uterine infection.

Crosstalk between Body Microbiota and the Regulation of Immunity

The microbiome corresponds to the genetic component of microorganisms (archaea, bacteria, phages, viruses, fungi, and protozoa) that coexist with an individual. During the last two decades, research on this topic has become massive demonstrating that in both homeostasis and disease, the microbiome plays an important role, and in some cases, a decisive one. To date, microbiota have been identified at different body locations, such as the eyes, lung, gastrointestinal and genitourinary tracts, and skin, and technological advances have permitted the taxonomic characterization of resident species and their metabolites, in addition to the cellular and molecular components of the host that maintain a crosstalk with local microorganisms. Here, we summarize recent studies regarding microbiota residing in different zones of the body and their relationship with the immune system. We emphasize the immune components underlying pathological conditions and how they interact with local (and distant) microbiota.

CCL22 mutations drive natural killer cell lymphoproliferative disease by deregulating microenvironmental crosstalk

Chronic lymphoproliferative disorder of natural killer cells (CLPD-NK) is characterized by clonal expansion of natural killer (NK) cells where the underlying genetic mechanisms are incompletely understood. In the present study, we report somatic mutations in the chemokine gene CCL22 as the hallmark of a distinct subset of CLPD-NK. CCL22 mutations were enriched at highly conserved residues, mutually exclusive of STAT3 mutations and associated with gene expression programs that resembled normal CD16^dim/CD56^bright NK cells. Mechanistically, the mutations resulted in ligand-biased chemokine receptor signaling, with decreased internalization of the G-protein-coupled receptor (GPCR) for CCL22, CCR4, via impaired β-arrestin recruitment. This resulted in increased cell chemotaxis in vitro, bidirectional crosstalk with the hematopoietic microenvironment and enhanced NK cell proliferation in vivo in transgenic human IL-15 mice. Somatic CCL22 mutations illustrate a unique mechanism of tumor formation in which gain-of-function chemokine mutations promote tumorigenesis by biased GPCR signaling and dysregulation of microenvironmental crosstalk.

Associations of Bitumen Fumes with Lymphocyte Subsets and Cytokines Expression in the Peripheral Blood of Exposed Workers

OBJECTIVES

The present study aimed to investigate the distribution of lymphocyte subsets and cytokines expression in the peripheral blood of bitumen fumes-exposed workers.

METHODS

In this study, 129 workers from molding and roasting workshops were recruited as the exposed group and 99 office and quality inspection staff were chosen as the control. The polycyclic aromatic hydrocarbons (PAHs) levels of bitumen fumes in individual and fixed-point air samples and the urinary levels of 1-hydroxypyrene (1-OH-P), 1-hydroxynaphthols (1-OH-N) and 2-hydroxynaphthols (2-OH-N) in workers were measured using High Performance Liquid Chromatography. The lymphocyte subsets and serum cytokines concentrations were analyzed by flow cytometry and cytometric bead array, respectively.

RESULTS

The median values of PAHs were 0.08 mg/m3 for permissible concentration-time weighted average and 0.12 mg/m3 for permissible concentration-short term exposure (PC-STEL) in molding and roasting workshops, which were higher than that in the control area (< 0.01 mg/m3). Multivariate linear regression models were used to adjust for influential covariates, including age, gender, work age, smoking status, and alcohol consumptions. After adjusting for these covariates, we compared levels of urinary PAHs metabolites, the percentages of lymphocyte subsets, and serum cytokines concentrations between the two groups. The 1-OH-P, 1-OH-N, and 2-OH-N levels in the urine of bitumen fumes exposed workers were significantly higher than that in the controls (P < 0.05). Compared with the control group, the percentage of the natural killer (NK) cell (CD56+ cell) was significantly increased in the exposed group (P < 0.001). There was a significant decrease in the percentages of CD3+ T cell, CD4+ T cell, and CD8+ T cell in the exposed group compared to the control (P < 0.001). The serum levels of interleukin-1β (IL-1β) and IL-6 in bitumen fumes exposed workers were significantly higher than that of the controls (P < 0.05). Moreover, positive correlations were observed between the serum levels of IL-1β, IL-6, and urinary 1-OH-P levels in bitumen fumes-exposed workers, respectively (P < 0.05). There were no significant differences in the serum levels of IL-8, tumor necrosis factor-α (TNF-α), macrophage inflammatory protein-1β (MIP-1β) and monocyte chemotactic protein-1 (MCP-1) between the exposed group and the control group (P > 0.05).

CONCLUSION

Our study suggested that low dose of bitumen fumes exposure could decrease the percentage of T cell, increase the percentage of NK cell and stimulate the release of serum IL-1β and IL-6 in the peripheral blood of exposed workers. The serum levels of IL-1β and IL-6 were positive correlated with the urinary 1-OH-P levels in bitumen fumes exposed workers. These results may inform the search for potential effective biomarkers and provide evidences for early health monitoring in workers occupationally exposed to bitumen fumes.

Intranasal Administration of Codium fragile Polysaccharide Elicits Anti-Cancer Immunity against Lewis Lung Carcinoma

Natural polysaccharides have shown promising effects on the regulation of immunity in animals. In this study, we examined the immune stimulatory effect of intranasally administered Codium fragile polysaccharides (CFPs) in mice. Intranasal administration of CFPs in C57BL/6 mice induced the upregulation of surface activation marker expression in macrophages and dendritic cells (DCs) in the mediastinal lymph node (mLN) and the production of interleukin-6 (IL-6), IL-12p70, and tumor necrosis factor-α in bronchoalveolar lavage fluid. Moreover, the number of conventional DCs (cDCs) was increased in the mLNs by the upregulation of C-C motif chemokine receptor 7 expression, and subsets of cDCs were also activated following the intranasal administration of CFP. In addition, the intranasal administration of CFPs promoted the activation of natural killer (NK) and T cells in the mLNs, which produce pro-inflammatory cytokines and cytotoxic mediators. Finally, daily administration of CFPs inhibited the infiltration of Lewis lung carcinoma cells into the lungs, and the preventive effect of CFPs on tumor growth required NK and CD8 T cells. Furthermore, CFPs combined with anti-programmed cell death-ligand 1 (PD-L1) antibody (Ab) improved the therapeutic effect of anti-PD-L1 Ab against lung cancer. Therefore, these data demonstrated that the intranasal administration of CFP induced mucosal immunity against lung cancer.

Natural killer cells contribute to enhanced respiratory disease after oil-in-water emulsion adjuvanted vaccination against respiratory syncytial virus and infection

Respiratory syncytial virus (RSV) infection caused severe acute respiratory disease in children and the elderly. There is no licensed vaccine. It has been a challenging problem to avoid vaccine enhanced respiratory disease in developing a safe and effective RSV vaccine. Here, we investigated the impact of MF59-like oil-in-water emulsion adjuvant Addavax on the vaccine efficacy of inactivated split RSV (sRSV) and the roles of natural killer (NK) cells in enhanced respiratory disease in sRSV vaccinated mice after RSV infection. Addavax-adjuvanted sRSV vaccination induced higher levels of IgG1 isotype antibodies and more effective lung viral clearance upon RSV infection but promoted enhanced respiratory disease of weight loss, pulmonary inflammation, and NK and NK T (NKT) cell infiltrations in the lungs. Antibody treatment depleting NK cells prior to RSV infection resulted in preventing severe weight loss and histopathology, as well as attenuating infiltration of dendritic cell subsets and TNF-α⁺ T cells in the lungs. This study demonstrated the impacts of oil-in-water emulsion adjuvant on sRSV vaccination and the potential roles of NK and NKT cells in protection and respiratory disease after adjuvanted RSV vaccination and infection in a mouse model.

Virus-specific NK cell memory

NK cells express a limited number of germline-encoded receptors that identify infected or transformed cells, eliciting cytotoxicity, effector cytokine production, and in some circumstances clonal proliferation and memory. To maximize the functional diversity of NK cells, the array and expression level of surface receptors vary between individual NK cell “clones” in mice and humans. Cytomegalovirus infection in both species can expand a population of NK cells expressing receptors critical to the clearance of infected cells and generate a long-lived memory pool capable of targeting future infection with greater efficacy. Here, we discuss the pathways and factors that regulate the generation and maintenance of effector and memory NK cells and propose how this understanding may be harnessed therapeutically.

Modulatory effects of gut microbiome in cancer immunotherapy: A novel paradigm for blockade of immune checkpoint inhibitors

The human gastrointestinal (GI) tract harbors gut microbiome, which plays a crucial role in preserving homeostasis at the intestinal host‐microbial interface. Conversely, specific gut microbiota may be altered during various pathological conditions and produce a number of toxic compounds and oncoproteins, in turn, to induce both inflammatory response and carcinogenesis. Recently, promising findings have been documented toward the implementation of certain intestinal microbiome in the next era of cancer biology and cancer immunotherapy. Notably, intestinal microbiota can cooperate with immune checkpoint inhibitors (ICIs) of its host, especially in enhancing the efficacy of programmed death 1 (PD‐1) protein and its ligand programmed death ligand 1 (PD‐L1) blockade therapy for cancer. Herein, we review the dual function of gut microbiota in triggering GI cancers, its association with host immunity and its beneficial functions in modulation of cancer immunotherapy responses. Furthermore, we consider the significance of gut microbiota as a potential biomarker for predicting the efficacy of cancer immunotherapy. Finally, we summarize the relevant limitations that affect the effectiveness and clinical applications of gut microbiome in response to immunotherapy.

A Testimony of the Surgent SARS-CoV-2 in the Immunological Panorama of the Human Host

The resurgence of SARS in the late December of 2019 due to a novel coronavirus, SARS-CoV-2, has shadowed the world with a pandemic. The physiopathology of this virus is very much in semblance with the previously known SARS-CoV and MERS-CoV. However, the unprecedented transmissibility of SARS-CoV-2 has been puzzling the scientific efforts. Though the virus harbors much of the genetic and architectural features of SARS-CoV, a few differences acquired during its evolutionary selective pressure is helping the SARS-CoV-2 to establish prodigious infection. Making entry into host the cell through already established ACE-2 receptor concerted with the action of TMPRSS2, is considered important for the virus. During the infection cycle of SARS-CoV-2, the innate immunity witnesses maximum dysregulations in its molecular network causing fatalities in aged, comorbid cases. The overt immunopathology manifested due to robust cytokine storm shows ARDS in severe cases of SARS-CoV-2. A delayed IFN activation gives appropriate time to the replicating virus to evade the host antiviral response and cause disruption of the adaptive response as well. We have compiled various aspects of SARS-CoV-2 in relation to its unique structural features and ability to modulate innate as well adaptive response in host, aiming at understanding the dynamism of infection.

Human immune cell mobilization during exercise: effect of IL-6 receptor blockade

NEW FINDINGS

What is the central question of this study? Does blockade of the IL-6 receptor by tocilizumab inhibit immune cell mobilization to the blood stream in humans during an acute bout of exercise? What is the main finding and its importance? Blockade of IL-6 receptor signalling by tocilizumab attenuates mobilization of NK cells and dendritic cells to the blood stream during exercise. This implies an inhibitory effect of tocilizumab on the innate immune response to physical stress, which could be considered in clinical settings.

ABSTRACT

Immune cells are recruited from their storage organs and the endothelial walls to the blood stream in response to physiological stress. This is essential for the recognition and clearing of infected, transformed or damaged cells. One of the most potent stimuli to recruit immune cells to the circulation is exercise. Accordingly, exercise has proven beneficial in disease settings, such as cancer and diabetes. Interleukin-6 (IL-6) is released from contracting skeletal muscle in response to exercise, and rodent studies have established a link between exercise-induced IL-6 and recruitment of natural killer (NK) cells. Whether exercise-induced IL-6 is involved in regulating NK cell mobilization in humans is unclear. This study explored the effect of IL-6 receptor blockade on immune cell mobilization during an acute bout of exercise in humans. In a randomized, placebo-controlled clinical study, abdominally obese humans receiving placebo infusions or tocilizumab infusions performed an acute bout of exercise before and after the intervention. Immune cell recruitment was measured by flow cytometry. IL-6 receptor blockade attenuated the increase of NK cells by 53% (mean difference -0.49 (95% CI: -0.89 to -0.08) × 10⁹ cells L^-1 , P < 0.001) and dendritic cells by 66% (mean difference -0.14 (95% CI: -0.28 to 0.010) × 10⁹ cells L^-1 , P < 0.001) induced by an acute bout of exercises. No changes were observed for T cells, monocytes and neutrophils. Treatments which interact with the exercise-mediated immune surveillance provide relevant clinical information in pursuing the 'exercise as medicine' concept.

Role of arachidonic acid-derived eicosanoids in intestinal innate immunity

Arachidonic acid (ARA), an n-6 essential fatty acid, plays an important role in human and animal growth and development. The ARA presents in the membrane phospholipids can be released by phospholipase A2. These free arachidonic acid molecules are then used to produce eicosanoids through three different pathways. Previous studies have demonstrated that eicosanoids have a wide range of physiological functions. Although they are generally considered to be pro-inflammatory molecules, recent advances have elucidated they have an effect on innate immunity via regulating the development, and differentiation of innate immune cells and the function of the intestinal epithelial barrier. Here, we review eicosanoids generation in intestine and their role in intestinal innate immunity, focusing on intestinal epithelial barrier, innate immune cell in lamina propria (LP) and their crosstalk.

Cytomegaloviruses and Macrophages-Friends and Foes From Early on?

Starting at birth, newborn infants are exposed to numerous microorganisms. Adaptation of the innate immune system to them is a delicate process, with potentially advantageous and harmful implications for health development. Cytomegaloviruses (CMVs) are highly adapted to their specific mammalian hosts, with which they share millions of years of co-evolution. Throughout the history of mankind, human CMV has infected most infants in the first months of life without overt implications for health. Thus, CMV infections are intertwined with normal immune development. Nonetheless, CMV has retained substantial pathogenicity following infection in utero or in situations of immunosuppression, leading to pathology in virtually any organ and particularly the central nervous system (CNS). CMVs enter the host through mucosal interfaces of the gastrointestinal and respiratory tract, where macrophages (MACs) are the most abundant immune cell type. Tissue MACs and their potential progenitors, monocytes, are established target cells of CMVs. Recently, several discoveries have revolutionized our understanding on the pre- and postnatal development and site-specific adaptation of tissue MACs. In this review, we explore experimental evidences and concepts on how CMV infections may impact on MAC development and activation as part of host-virus co-adaptation.

CD49a+CD49b+ NK cells induced by viral infection reflect an activated state of conventional NK cells

Natural killer (NK) cells are important innate effectors that play a pivotal role in the defense against tumors and infections and participate in regulating adaptive immunity. Recent studies have revealed phenotypic and functional heterogeneity of NK cells. Here, using murine models of acute and chronic lymphocytic choriomeningitis virus infection, we observed that a CD49a⁺ CD49b⁺ NK cell subset emerged in the liver and other tissues, and underwent vigorous expansion following viral infection, before progressively decreasing in cell number. These viral infection-induced CD49a⁺CD49b⁺ NK cells displayed an activated and mature phenotype. Moreover, compared with liver-resident NK cells and conventional NK (cNK) cells, CD49a⁺CD49b⁺ NK cells showed increased functional competence, as evidenced by higher amounts of IFN-γ production and stronger cytotoxic capabilities during viral infection. Generation of these CD49a⁺CD49b⁺ NK cells was shown to be independent of the T-bet transcription factor. Adoptive transfer experiments revealed that cNK cells could convert into CD49a⁺CD49b⁺ NK cells following viral infection. Collectively, these results suggest that viral infection-induced CD49a⁺CD49b⁺ NK cells represent a transiently activated state of cNK cells.

Broad and systemic immune-modulating capacity of plant-derived dsRNA

Double-stranded RNA (dsRNA) is well characterized as an inducer of anti-viral interferon responses. We previously reported that dsRNA extracted from a specific edible plant possesses an immune-modulating capacity to confer, in mice, resistance against respiratory viruses, including the H1N1 strain of the influenza A virus (IAV). We report here that the systemic immune-activating capacity of the plant-derived dsRNA protected mice from infection by a highly virulent H5N1 strain of the IAV. In addition, subcutaneous inoculation of the dsRNA together with the inactivated virion of the H5N1 strain of the IAV suppressed the lethality of the viral infection as compared with individual inoculation of either dsRNA or HA protein, suggesting its potential usage as a vaccination adjuvant. Moreover, intra-peritoneal inoculation of the dsRNA limited the growth of B16-F10 melanoma cells through the activation of NK cells in murine models. Taken together, this study demonstrated the systemic immune-modulating capacity of a plant-derived dsRNA and its potential for nucleic acid-based clinical applications.

Sesamolin promotes cytolysis and migration activity of natural killer cells via dendritic cells

The defense mechanism of the immune system is based on the interaction of many kinds of leukocytes. Among them, dendritic cells (DCs) control most immune responses. In our previous study, sesamolin was shown to create an optimal environment for natural killer (NK) cells to kill cancer cells. Here we attempted to demonstrate how sesamolin influences DCs to promote the killing and migration activity of NK cells. We co-cultured DCs and NK cells and analyzed the communication between them. NK cells co-cultured with 5 µg/ml sesamolin-treated mature dendritic cells (mDCs) had better cytolytic activity than did NK cells or mDCs co-cultured NK cells. Moreover, the migration of NK cells toward mDCs was enhanced compared to immature dendritic cells (iDCs). The migration of NK cells stimulated by mDCs was stronger after sesamolin activation of the mDCs. Altogether, this study demonstrated that sesamolin activated NK cells by modulating the differentiation and activation of DCs.

The epigenetic face of lupus: Focus on antigen-presenting cells

In recent years, epigenetic mechanisms became widely known due to their ability to regulate and maintain physiological processes such as cell growth, development, differentiation and genomic stability. When dysregulated, epigenetic mechanisms, may introduce gene expression changes and disturbance in immune homeostasis leading to autoimmune diseases. Systemic lupus erythematosus (SLE), the most extensively studied autoimmune disorder, has already been correlated with epigenetic modifications, especially in T cells. Since these cell rely on antigen presentation, it may be assumed that erroneous activity of antigen-presenting cells (APCs), culminates in T cell abnormalities. In this review we summarize and discuss the epigenetic modifications in SLE affected APCs, with the focus on dendritic cells (DCs), B cells and monocytes. Unravelling this aspect of SLE pathogenesis, might result in identification of new disease biomarkers and putative therapeutic approaches.

C-kit-derived CD11b+ cells are critical for cardiac allograft prolongation by autologous C-kit+ progenitor cells

Autologous C-kit⁺ cells robustly prolong cardiac allografts. As C-kit⁺ cells can transdifferentiate to hematopoietic cells as well as non-hematopoietic cells, we aimed to clarify the class(es) of C-kit-derived cell(s) required for cardiac allograft prolongation. Autologous C-kit⁺ cells were administered post-cardiac transplantation and allografts were evaluated for C-kit⁺ inoculum-derived cells. Results suggested that alloimmunity was a major signal for trafficking of C-kit-derived cells to the allograft and demonstrated that C-kit⁺ inoculum-derived cells expressed CD11b early after transfer. Allograft survival studies with CD11b-DTR C-kit⁺ cells demonstrated a requirement for C-kit⁺-derived CD11b⁺ cells. Co-therapy studies demonstrated near complete abrogation of acute rejection with concomitant CTLA4-Ig therapy and no loss of prolongation in combination with Cyclosporine A. These results strongly implicate a C-kit-derived myeloid population as critical for allograft preservation and demonstrate the potential therapeutic application of autologous C-kit⁺ progenitor cells as calcineurin inhibitor-sparing agents and possibly as co-therapeutics for durable graft survival.

Type I IFN Sensing by cDCs and CD4+ T Cell Help Are Both Requisite for Cross-Priming of AAV Capsid-Specific CD8+ T Cells

Adeno-associated virus (AAV) vectors are widely used in clinical gene therapy to correct genetic disease by in vivo gene transfer. Although the vectors are useful, in part because of their limited immunogenicity, immune responses directed at vector components have complicated applications in humans. These include, for instance, innate immune sensing of vector components by plasmacytoid dendritic cells (pDCs), which sense the vector DNA genome via Toll-like receptor 9. Adaptive immune responses employ antigen presentation by conventional dendritic cells (cDCs), which leads to cross-priming of capsid-specific CD8⁺ T cells. In this study, we sought to determine the mechanisms that promote licensing of cDCs, which is requisite for CD8⁺ T cell activation. Blockage of type 1 interferon (T1 IFN) signaling by monoclonal antibody therapy prevented cross-priming. Furthermore, experiments in cell-type-restricted knockout mice showed a specific requirement for the receptor for T1 IFN (IFNaR) in cDCs. In contrast, natural killer (NK) cells are not needed, indicating a direct rather than indirect effect of T1 IFN on cDCs. In addition, co-stimulation by CD4⁺ T cells via CD40-CD40L was required for cross-priming, and blockage of co-stimulation but not of T1 IFN additionally reduced antibody formation against capsid. These mechanistic insights inform the development of targeted immune interventions.

Post-translational Control of Innate Immune Signaling Pathways by Herpesviruses

Herpesviruses constitute a large family of disease-causing DNA viruses. Each herpesvirus strain is capable of infecting particular organisms with a specific cell tropism. Upon infection, pattern recognition receptors (PRRs) recognize conserved viral features to trigger signaling cascades that culminate in the production of interferons and pro-inflammatory cytokines. To invoke a proper immune response while avoiding collateral tissue damage, signaling proteins involved in these cascades are tightly regulated by post-translational modifications (PTMs). Herpesviruses have developed strategies to subvert innate immune signaling pathways in order to ensure efficient viral replication and achieve persistent infection. The ability of these viruses to control the proteins involved in these signaling cascades post-translationally, either directly via virus-encoded enzymes or indirectly through the deregulation of cellular enzymes, has been widely reported. This ability provides herpesviruses with a powerful tool to shut off or restrict host antiviral and inflammatory responses. In this review, we highlight recent findings on the herpesvirus-mediated post-translational control along PRR-mediated signaling pathways.

Modulation of innate and adaptive immunity by cytomegaloviruses

The coordinated activities of innate and adaptive immunity are critical for effective protection against viruses. To counter this, some viruses have evolved sophisticated strategies to circumvent immune cell recognition. In particular, cytomegaloviruses encode large arsenals of molecules that seek to subvert T cell and natural killer cell function via a remarkable array of mechanisms. Consequently, these 'immunoevasins' play a fundamental role in shaping the nature of the immune system by driving the evolution of new immune receptors and recognition mechanisms. Here, we review the diverse strategies adopted by cytomegaloviruses to target immune pathways and outline the host's response.

STING induces early IFN-β in the liver and constrains myeloid cell-mediated dissemination of murine cytomegalovirus

Cytomegalovirus is a DNA-encoded β-herpesvirus that induces STING-dependent type 1 interferon responses in macrophages and uses myeloid cells as a vehicle for dissemination. Here we report that STING knockout mice are as resistant to murine cytomegalovirus (MCMV) infection as wild-type controls, whereas mice with a combined Toll-like receptor/RIG-I-like receptor/STING signaling deficiency do not mount type 1 interferon responses and succumb to the infection. Although STING alone is dispensable for survival, early IFN-β induction in Kupffer cells is STING-dependent and controls early hepatic virus propagation. Infection experiments with an inducible reporter MCMV show that STING constrains MCMV replication in myeloid cells and limits viral dissemination via these cells. By contrast, restriction of viral dissemination from hepatocytes to other organs is independent of STING. Thus, during MCMV infection STING is involved in early IFN-β induction in Kupffer cells and the restriction of viral dissemination via myeloid cells, whereas it is dispensable for survival.

NKG2D Regulation of Lung Pathology and Dendritic Cell Function Following Respiratory Syncytial Virus Infection

Background

Respiratory syncytial virus (RSV) is a common cause of respiratory tract infection in vulnerable populations. Natural killer (NK) cells and dendritic cells (DC) are important for the effector functions of both cell types following infection.

Methods

Wild-type and NKG2D-deficient mice were infected with RSV. Lung pathology was assessed by histology. Dendritic cell function and phenotype were evaluated by enzyme-linked immunosorbent assay and flow cytometry. The expression of NKG2D ligands on lung and lymph node DCs was measured by immunostaining and flow cytometry. Adoptive transfer experiments were performed to assess the importance of NKG2D-dependent DC function in RSV infection.

Results

NKG2D-deficient mice exhibited greater lung pathology, marked by the accumulation of DCs following RSV infection. Dendritic cells isolated from NKG2D-deficient mice had impaired responses toward Toll-like receptor ligands. Dendritic cells expressed NKG2D ligands on their surface, which was further increased in NKG2D-deficient mice and during RSV infection. Adoptive transfer of DCs isolated from wild-type mice into the airways of NKG2D-deficient mice ameliorated the enhanced inflammation in NKG2D-deficient mice after RSV infection.

Conclusion

NKG2D-dependent interactions with DCs control the phenotype and function of DCs and play a critical role in pulmonary host defenses against RSV infection.

Interleukin-17D and Nrf2 mediate initial innate immune cell recruitment and restrict MCMV infection

Innate immune cells quickly infiltrate the site of pathogen entry and not only stave off infection but also initiate antigen presentation and promote adaptive immunity. The recruitment of innate leukocytes has been well studied in the context of extracellular bacterial and fungal infection but less during viral infections. We have recently shown that the understudied cytokine Interleukin (IL)-17D can mediate neutrophil, natural killer (NK) cell and monocyte infiltration in sterile inflammation and cancer. Herein, we show that early immune cell accumulation at the peritoneal site of infection by mouse cytomegalovirus (MCMV) is mediated by IL-17D. Mice deficient in IL-17D or the transcription factor Nuclear factor (erythroid-derived 2)-like 2 (Nrf2), an inducer of IL-17D, featured an early decreased number of innate immune cells at the point of viral entry and were more susceptible to MCMV infection. Interestingly, we were able to artificially induce innate leukocyte infiltration by applying the Nrf2 activator tert-butylhydroquinone (tBHQ), which rendered mice less susceptible to MCMV infection. Our results implicate the Nrf2/IL-17D axis as a sensor of viral infection and suggest therapeutic benefit in boosting this pathway to promote innate antiviral responses.

Cancer Cells Exploit Notch Signaling to Redefine a Supportive Cytokine Milieu

Notch signaling is a well-known key player in the communication between adjacent cells during organ development, when it controls several processes involved in cell differentiation. Notch-mediated communication may occur through the interaction of Notch receptors with ligands on adjacent cells or by a paracrine/endocrine fashion, through soluble molecules that can mediate the communication between cells at distant sites. Dysregulation of Notch pathway causes a number of disorders, including cancer. Notch hyperactivation may be caused by mutations of Notch-related genes, dysregulated upstream pathways, or microenvironment signals. Cancer cells may exploit this aberrant signaling to "educate" the surrounding microenvironment cells toward a pro-tumoral behavior. This may occur because of key cytokines secreted by tumor cells or it may involve the microenvironment through the activation of Notch signaling in stromal cells, an event mediated by a direct cell-to-cell contact and resulting in the increased secretion of several pro-tumorigenic cytokines. Up to now, review articles were mainly focused on Notch contribution in a specific tumor context or immune cell populations. Here, we provide a comprehensive overview on the outcomes of Notch-mediated pathological interactions in different tumor settings and on the molecular and cellular mediators involved in this process. We describe how Notch dysregulation in cancer may alter the cytokine network and its outcomes on tumor progression and antitumor immune response.

Suppression of autophagy and HCK signaling promotes PTGS2high FCGR3- NK cell differentiation triggered by ectopic endometrial stromal cells

Impaired NK cell cytotoxic activity contributes to the local dysfunctional immune environment in endometriosis (EMS), which is an estrogen-dependent gynecological disease that affects the function of ectopic endometrial tissue clearance. The reason for the impaired cytotoxic activity of NK cells in an ectopic lesion microenvironment (ELM) is largely unknown. In this study, we show that the macroautophagy/autophagy level of endometrial stromal cells (ESCs) from EMS decreased under negative regulation of estrogen. The ratio of peritoneal FCGR3^- NK to FCGR3⁺ NK cells increases as EMS progresses. Moreover, the autophagy suppression results in the downregulation of HCK (hematopoietic cellular kinase) by inactivating STAT3 (signal transducer and activator of transcription 3), as well as the increased secretion of the downstream molecules CXCL8/IL8 and IL23A by ESCs, and this increase induced the upregulation of FCGR3^- NK cells and decline of cytotoxic activity in ELM. This process is mediated through the depression of microRNA MIR1185-1-3p, which is associated with the activation of the target gene PTGS2 in NK cells. FCGR3^- NK with a phenotype of PTGS2/COX2^high IFNG^low PRF1^low GZMB^low induced by hck knockout (hck^-/-) or 3-methyladenine (3-MA, an autophagy inhibitor)-stimulated ESCs accelerates ESC's growth both in vitro and in vivo. These results suggest that the estrogen-autophagy-STAT3-HCK axis participates in the differentiation of PTGS2^high IFNG^low PRF1^low GZMB^low FCGR3^- NK cells in ELM and contributes to the development of EMS. This result provides a scientific basis for potential therapeutic strategies to treat diseases related to impaired NK cell cytotoxic activity.

ABBREVIATIONS

anti-FCGR3: anti-FCGR3 with neutralizing antibody; Ctrl-ESC: untreated ESCs; CXCL8: C-X-C motif chemokine ligand 8; ectoESC: ESCs from ectopic lesion; ELM: ectopic lesion microenvironment; EMS: endometriosis; ESCs: endometrial stromal cells; eutoESC:eutopic ESCs; HCK: hematopoietic cellular kinase; HCK(OE): overexpression of HCK; IFNG: interferon gamma; IL23A (OE): overexpression of IL23A; KLRK1: Killer cell lectin like receptor K1; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; 3 -MA: 3-methyladenine; 3-MA-ESC: 3-MA-treated ESCs; MIR1185-1-3p⁺: overexpression of HsMIR1185-1-3p; NK: natural killer; normESCs: normal ESCs; Rap-ESC:rapamycin-treated ESCs; PCNA: proliferating cell nuclear antigen; PF: peritoneal fluid; SFKs: SRC family of cytoplasmic tyrosine kinases; si-HCK: silencing of HCK; siIL23A: silencing of IL23A; USCs: uterus stromal cells.

The expanding role of murine class Ib MHC in the development and activation of Natural Killer cells

Major Histocompatibility Complex-I (MHC-I) molecules can be divided into class Ia and class Ib, with three distinct class Ib families found in the mouse. These families are designated as Q, T and M and are largely unexplored in terms of their immunological function. Among the class Ib MHC, H2-T23 (Qa-1b) has been a significant target for Natural Killer (NK) cell research, owing to its homology with the human class Ib human leukocyte antigen (HLA)-E. However, recent data has indicated that members of the Q and M family of class Ib MHC also play a critical role in the development and regulation NK cells. Here we discuss the recent advances in the control of NK cells by murine class Ib MHC as a means to stimulate further exploration of these molecules.

The NKG2D/NKG2DL Axis in the Crosstalk Between Lymphoid and Myeloid Cells in Health and Disease

Natural killer group 2, member D (NKG2D) receptor is a type II transmembrane protein expressed by both innate and adaptive immune cells, including natural killer (NK) cells, CD8+ T cells, invariant NKT cells, γδ T cells, and some CD4+ T cells under certain pathological conditions. NKG2D is an activating NK receptor that induces cytotoxicity and production of cytokines by effector cells and supports their proliferation and survival upon engagement with its ligands. In both innate and T cell populations, NKG2D can costimulate responses induced by other receptors, such as TCR in T cells or NKp46 in NK cells. NKG2D ligands (NKG2DLs) are remarkably diverse. Initially, NKG2DL expression was typically attributed to stressed, infected, or transformed cells, thus signaling “dysregulated-self.” However, many reports indicated their expression under homeostatic conditions, usually in the context of cell activation and/or proliferation. Myeloid cells, including macrophages and dendritic cells (DCs), are among the first cells sensing and responding to pathogens and tissue damage. By secreting a plethora of soluble mediators, by presenting antigens to T cells and by expressing costimulatory molecules, myeloid cells play vital roles in inducing and supporting responses of other immune cells in lymphoid organs and tissues. When activated, both macrophages and DCs upregulate NKG2DLs, thereby enabling them with additional mechanisms for regulating lymphocyte responses. In this review, we will focus on the expression of NKG2D by innate and adaptive lymphocytes, the regulation of NKG2DL expression on myeloid cells, and the contribution of the NKG2D/NKG2DL axis to the crosstalk of myeloid cells with NKG2D-expressing lymphocytes. In addition, we will highlight pathophysiological conditions associated with NKG2D/NKG2DL dysregulation and discuss the putative involvement of the NKG2D/NKG2DL axis in the lymphocyte/myeloid cell crosstalk in these diseases.

Conventional Dendritic Cells Confer Protection against Mouse Cytomegalovirus Infection via TLR9 and MyD88 Signaling

Cytomegalovirus (CMV) is an opportunistic virus severely infecting immunocompromised individuals. In mice, endosomal Toll-like receptor 9 (TLR9) and downstream myeloid differentiation factor 88 (MyD88) are central to activating innate immune responses against mouse CMV (MCMV). In this respect, the cell-specific contribution of these pathways in initiating anti-MCMV immunity remains unclear. Using transgenic mice, we demonstrate that TLR9/MyD88 signaling selectively in CD11c⁺ dendritic cells (DCs) strongly enhances MCMV clearance by boosting natural killer (NK) cell CD69 expression and IFN-γ production. In addition, we show that in the absence of plasmacytoid DCs (pDCs), conventional DCs (cDCs) promote robust NK cell effector function and MCMV clearance in a TLR9/MyD88-dependent manner. Simultaneously, cDC-derived IL-15 regulates NK cell degranulation by TLR9/MyD88-independent mechanisms. Overall, we compartmentalize the cellular contribution of TLR9 and MyD88 signaling in individual DC subsets and evaluate the mechanism by which cDCs control MCMV immunity.

Dose of Retroviral Infection Determines Induction of Antiviral NK Cell Responses

Natural killer (NK) cells are part of the innate immune system and recognize virus-infected cells as well as tumor cells. Conflicting data about the beneficial or even detrimental role of NK cells in different infectious diseases have been described previously. While the type of pathogen strongly influences NK cell functionality, less is known about how the infection dose influences the quality of a NK cell response against retroviruses. In this study, we used the well-established Friend retrovirus (FV) mouse model to investigate the impact of virus dose on the induction of antiviral NK cell functions. High-dose virus inoculation increased initial virus replication compared to that with medium- or low-dose viral challenge and significantly improved NK cell activation. Antiviral NK cell activity, including in vivo cytotoxicity toward infected target cells, was also enhanced by high-dose virus infection. NK cell activation following high-dose viral challenge was likely mediated by activated dendritic cells (DCs) and macrophages and the NK cell-stimulating cytokines interleukin 15 (IL-15) and IL-18. Neutralization of these cytokines decreased NK cell functions and increased viral loads, whereas IL-15 and IL-18 therapy improved NK cell activity. Here we demonstrate that virus dose positively correlates with antiviral NK cell activity and function, which are at least partly driven by IL-15 and IL-18. Our results suggest that NK cell activity may be therapeutically enhanced by administering IL-15 and IL-18 in virus infections that inadequately activate NK cells.

IMPORTANCE In infections with retroviruses, like HIV and FV infection of mice, NK cells clearly mediate antiviral activities, but they are usually not sufficient to prevent severe pathology. Here we show that the initial infection dose impacts the induction of an antiviral NK cell response during an acute retroviral infection, which had not investigated before. High-dose infection resulted in a strong NK cell functionality, whereas no antiviral activities were detected after low- or medium-dose infection. Interestingly, DCs and macrophages were highly activated after high-dose FV challenge, which corresponded with increased levels of NK cell-stimulating cytokines IL-15 and IL-18. IL-15 and IL-18 neutralization decreased NK cell functions, whereas IL-15 and IL-18 therapy improved NK cell activity. Here we show the importance of cytokines for NK cell activation in retroviral infections; our findings suggest that immunotherapy combining the well-tolerated cytokines IL-15 and IL-18 might be an interesting approach for antiretroviral treatment.

Chronic In Vivo Interaction of Dendritic Cells Expressing the Ligand Rae-1ε with NK Cells Impacts NKG2D Expression and Function

To investigate how dendritic cells (DCs) interact with NK cells in vivo, we developed a novel mouse model in which Rae-1ε, a ligand of the NKG2D receptor, is expressed in cells with high levels of CD11c. In these CD11c-Rae1 mice, expression of Rae-1 was confirmed on all subsets of DCs and a small subset of B and T cells, but not on NK cells. DC numbers and activation status were unchanged, and NK cells in these CD11c-Rae1 mice presented the same Ly49 repertoire and maturation levels as their littermate wildtype controls. Early NK cell activation after mouse CMV infection was slightly lower than in wildtype mice, but NK cell expansion and viral control were comparable. Notably, we demonstrate that chronic interaction of NK cells with NKG2D ligand-expressing DCs leads to a reversible NKG2D down-modulation, as well as impaired NKG2D-dependent NK cell functions, including tumor rejection. In addition to generating a useful mouse model, our studies reveal in vivo the functional importance of the NK cell and DC cross-talk.

Regulation of NK Cell Activation and Effector Functions by the IL-12 Family of Cytokines: The Case of IL-27

Natural killer (NK) cells are characterized by their ability to detect and induce apoptosis of susceptible target cells and by secretion of immunoregulatory cytokines such as IFN-γ. Activation of these effector functions is triggered upon recognition of tumor and pathogen (mostly virus)-infected cells and because of a bidirectional cross talk that NK cells establish with other cells of myeloid origin such as dendritic cells (DC) and macrophages. A common characteristic of these myeloid cells is their ability to secrete different members of the IL-12 family of cytokines such as IL-12, IL-23, and IL-27 and cytokines such as IL-15 and IL-18. Although the effect of IL-12, IL-15, and IL-18 has been characterized, the effect of IL-23 and IL-27 on NK cells (especially human) remains ill-defined. Particularly, IL-27 is a cytokine with dual functions as it has been described as pro- and as anti-inflammatory in different experimental settings. Recent evidence indicates that this cytokine indeed promotes human NK cell activation, IFN-γ secretion, NKp46-dependent NK cell-mediated cytotoxicity, and antibody (Ab)-dependent NK cell-mediated cytotoxicity (ADCC) against monoclonal Ab-coated tumor cells. Remarkably, IL-27 also primes NK cells for IL-18 responsiveness, enhancing these functional responses. Consequently, IL-27 acts as a pro-inflammatory cytokine that, in concert with other DC-derived cytokines, hierarchically contributes to NK cells activation and effector functions, which likely contributes to foster the adaptive immune response in different physiopathological conditions.

NK-DC Crosstalk in Immunity to Microbial Infection

The interaction between natural killer (NK) cell and dendritic cell (DC), two important cellular components of innate immunity, started to be elucidated in the last years. The crosstalk between NK cells and DC, which leads to NK cell activation, DC maturation, or apoptosis, involves cell-cell contacts and soluble factors. This interaction either in the periphery or in the secondary lymphoid organs acts as a key player linking innate and adaptive immune responses to microbial stimuli. This review focuses on the mechanisms of NK-DC interaction and their relevance in antimicrobial responses. We specifically aim to emphasize the ability of various microbial infections to differently influence NK-DC crosstalk thereby contributing to distinct adaptive immune response.

Soluble mediators produced by the crosstalk between microvascular endothelial cells and dengue-infected primary dermal fibroblasts inhibit dengue virus replication and increase leukocyte transmigration

When dengue virus (DENV)-infected mosquitoes use their proboscis to probe into human skin during blood feeding, both saliva and virus are released. During this process, cells from the epidermis and dermis layers of the skin, along with small blood vessels, may get exposed to or infected with DENV. In these microenvironments of the skin, the presence of DENV initiates a complex interplay among the DENV-infected and non-infected neighboring cells at the initial bite site. Previous studies suggested that DENV-infected human dermal fibroblasts (HDFs) participate in the immune response against DENV by secreting soluble mediators of innate immunity. In the present study, we investigated whether DENV-infected HDFs activate human dermal microvascular endothelial cells (HDMECs) in co-cultures. Our results suggest that co-cultures of DENV-infected HDFs and HDMECs elicit soluble mediators that are sufficient to reduce viral replication, activate HDMECs, and induce leukocyte migration through HDMEC monolayers. These effects were partly dependent on HDF donor and DENV serotype, which may provide novel insights into the natural variation in host susceptibility to DENV disease.

Activation of Innate and Adaptive Immunity by a Recombinant Human Cytomegalovirus Strain Expressing an NKG2D Ligand

Development of an effective vaccine against human cytomegalovirus (HCMV) is a need of utmost medical importance. Generally, it is believed that a live attenuated vaccine would best provide protective immunity against this tenacious pathogen. Here, we propose a strategy for an HCMV vaccine that aims at the simultaneous activation of innate and adaptive immune responses. An HCMV strain expressing the host ligand ULBP2 for the NKG2D receptor was found to be susceptible to control by natural killer (NK) cells, and preserved the ability to stimulate HCMV-specific T cells. Infection with the ULBP2-expressing HCMV strain caused diminished cell surface levels of MHC class I molecules. While expression of the NKG2D ligand increased the cytolytic activity of NK cells, NKG2D engagement in CD8+ T cells provided co-stimulation and compensated for lower MHC class I expression. Altogether, our data indicate that triggering of both arms of the immune system is a promising approach applicable to the generation of a live attenuated HCMV vaccine.

Human cytomegalovirus (CMV) is a major cause of morbidity and mortality in congenitally infected newborns and immunocompromised individuals, indicating an utmost need for a vaccine to protect these vulnerable groups. Recent experimental studies in animal models, including non-human primates, have shown that attenuated CMVs trigger a potent immune response and are attractive vaccine candidates. However, an effective CMV vaccine is still not available. Here, we demonstrate that rational engineering of a live attenuated human CMV vaccine candidate is feasible. We equipped a CMV strain with an immunostimulatory molecule that is a ligand for an activating receptor present on both Natural Killer cells and CD8+ T cells. Moreover, we deleted several immunoevasins involved in downregulation of MHC class I molecules and of a ligand for Natural Killer cells in order to elicit stronger immune responses. In vitro assays using human immune cells and a first assessment in a humanized mouse model in vivo suggest that the generated CMV strain is attenuated and has the ability to induce a virus-specific immune response. Our study proposes this novel approach for the development of a rationally engineered CMV vaccine.

Blocking Virus Replication during Acute Murine Cytomegalovirus Infection Paradoxically Prolongs Antigen Presentation and Increases the CD8+ T Cell Response by Preventing Type I IFN-Dependent Depletion of Dendritic Cells

Increasing amounts of pathogen replication usually lead to a proportionate increase in size and effector differentiation of the CD8⁺ T cell response, which is attributed to increased Ag and inflammation. Using a murine CMV that is highly sensitive to the antiviral drug famciclovir to modulate virus replication, we found that increased virus replication drove increased effector CD8⁺ T cell differentiation, as expected. Paradoxically, however, increased virus replication dramatically decreased the size of the CD8⁺ T cell response to two immunodominant epitopes. The decreased response was due to type I IFN-dependent depletion of conventional dendritic cells and could be reproduced by specific depletion of dendritic cells from day 2 postinfection or by sterile induction of type I IFN. Increased virus replication and type I IFN specifically inhibited the response to two immunodominant epitopes that are known to be dependent on Ag cross-presented by DCs, but they did not inhibit the response to "inflationary" epitopes whose responses can be sustained by infected nonhematopoietic cells. Our results show that type I IFN can suppress CD8⁺ T cell responses to cross-presented Ag by depleting cross-presenting conventional dendritic cells.

NK-CD11c+ Cell Crosstalk in Diabetes Enhances IL-6-Mediated Inflammation during Mycobacterium tuberculosis Infection

In this study, we developed a mouse model of type 2 diabetes mellitus (T2DM) using streptozotocin and nicotinamide and identified factors that increase susceptibility of T2DM mice to infection by Mycobacterium tuberculosis (Mtb). All Mtb-infected T2DM mice and 40% of uninfected T2DM mice died within 10 months, whereas all control mice survived. In Mtb-infected mice, T2DM increased the bacterial burden and pro- and anti-inflammatory cytokine and chemokine production in the lungs relative to those in uninfected T2DM mice and infected control mice. Levels of IL-6 also increased. Anti-IL-6 monoclonal antibody treatment of Mtb-infected acute- and chronic-T2DM mice increased survival (to 100%) and reduced pro- and anti-inflammatory cytokine expression. CD11c+ cells were the major source of IL-6 in Mtb-infected T2DM mice. Pulmonary natural killer (NK) cells in Mtb-infected T2DM mice further increased IL-6 production by autologous CD11c+ cells through their activating receptors. Anti-NK1.1 antibody treatment of Mtb-infected acute-T2DM mice increased survival and reduced pro- and anti-inflammatory cytokine expression. Furthermore, IL-6 increased inflammatory cytokine production by T lymphocytes in pulmonary tuberculosis patients with T2DM. Overall, the results suggest that NK-CD11c+ cell interactions increase IL-6 production, which in turn drives the pathological immune response and mortality associated with Mtb infection in diabetic mice.

Adipose Natural Killer Cells Regulate Adipose Tissue Macrophages to Promote Insulin Resistance in Obesity

Obesity-induced inflammation mediated by immune cells in adipose tissue appears to participate in the pathogenesis of insulin resistance. We show that natural killer (NK) cells in adipose tissue play an important role. High-fat diet (HFD) increases NK cell numbers and the production of proinflammatory cytokines, notably TNFα, in epididymal, but not subcutaneous, fat depots. When NK cells were depleted either with neutralizing antibodies or genetic ablation in E4bp4(+/-) mice, obesity-induced insulin resistance improved in parallel with decreases in both adipose tissue macrophage (ATM) numbers, and ATM and adipose tissue inflammation. Conversely, expansion of NK cells following IL-15 administration or reconstitution of NK cells into E4bp4(-/-) mice increased both ATM numbers and adipose tissue inflammation and exacerbated HFD-induced insulin resistance. These results indicate that adipose NK cells control ATMs as an upstream regulator potentially by producing proinflammatory mediators, including TNFα, and thereby contribute to the development of obesity-induced insulin resistance.

MCMV exploits the spleen as a transfer hub for systemic dissemination upon oronasal inoculation

Murine cytomegalovirus (MCMV) infection in mice is a commonly used animal model for studying human cytomegalovirus (HCMV) infections. In our previous studies, a mouse model based on an oronasal MCMV infection was set up for mimicking a natural infection, and the spleen was hypothesized to regulate viremia and virus dissemination to distal organs such as submandibular glands. Here, the role of the spleen during an MCMV infection was investigated by the comparison of intact and splenectomized Balb/c mice. Both highly passaged MCMV Smith and low passaged MCMV HaNa1 were used. Various samples were collected at 7, 14, and 21 days post inoculation (dpi) for analyses by virus isolation/titration, co-cultivation and qPCR. The results showed that for both virus strains, 1) cell-associated virus in PBMC (determined by co-cultivation) was detected in intact mice but not in splenectomized mice; 2) the mean viral DNA load in PBMC of splenectomized mice was 4.4-(HaNa1)/2.7-(Smith) fold lower at the peak viremia (7dpi) in contrast to that of intact mice; and 3) infectious virus in the submandibular glands was detected later in splenectomized mice (14dpi) than in intact mice (7dpi). Moreover, the average virus titers in submandibular glands of splenectomized mice were 10-(HaNa1)/7.9-(Smith) fold lower at 14dpi and 1.7-(HaNa1)/2.1-(Smith) fold lower at 21dpi compared with that of intact mice. Upon inoculation with MCMV Smith, infectious virus was found in the kidneys and liver of intact mice, but not in splenectomized mice. Taken together, all these data clearly demonstrate that virus dissemination to distant organs is reduced in splenectomized mice, further confirming the importance of the spleen as a viremia booming site for a natural MCMV infection.

Type I IFN promotes NK cell expansion during viral infection by protecting NK cells against fratricide

Madera et al. show that NK cells unable to receive type I IFN signals during MCMV infection have defective expansion and memory cell formation, possessing increased susceptibility to apoptosis due to NK cell–mediated fratricide.

Type I interferon (IFN) is crucial in host antiviral defense. Previous studies have described the pleiotropic role of type I IFNs on innate and adaptive immune cells during viral infection. Here, we demonstrate that natural killer (NK) cells from mice lacking the type I IFN-α receptor (Ifnar^−/−) or STAT1 (which signals downstream of IFNAR) are defective in expansion and memory cell formation after mouse cytomegalovirus (MCMV) infection. Despite comparable proliferation, Ifnar^−/− NK cells showed diminished protection against MCMV infection and exhibited more apoptosis compared with wild-type NK cells. Furthermore, we show that Ifnar^−/− NK cells express increased levels of NK group 2 member D (NKG2D) ligands during viral infection and are susceptible to NK cell–mediated fratricide in a perforin- and NKG2D-dependent manner. Adoptive transfer of Ifnar^−/− NK cells into NK cell–deficient mice reverses the defect in survival and expansion. Our study reveals a novel type I IFN–dependent mechanism by which NK cells evade mechanisms of cell death after viral infection.

Activation of Natural Killer Cells by Probiotics

During the last decade, probiotics have been established to be important mediators of host immunity. Their effects on both innate and adaptive immunity have been documented in the literature. Although several reports have correlated different strains of bacteria as probiotics, their effects on immunity vary. Clearly, there is a complex interplay between various constituents of probiotics and the immune response in humans. The role of probiotics on natural killer (NK) cells in the gut has been the subject of a few reports. In this review, we summarize the reported findings on the role of probiotics in the activation of gut-associated NK cells and the response of NK cells to stimuli elicited by probiotics and their microenvironment. The effects of probiotics on the activation of NK cells and their secretion of immune factors (e.g., interferon-γ, tumor necrosis factor-α, interleukin-2, etc.) are discussed in regard to their clinical significance in various diseases. Current investigations are being pursued, in particular, on the role of probiotics-activated NK cells in promoting the adaptive immune response against pathogens.

Dual Requirement of Cytokine and Activation Receptor Triggering for Cytotoxic Control of Murine Cytomegalovirus by NK Cells

Natural killer (NK) cells play a critical role in controlling murine cytomegalovirus (MCMV) and can mediate both cytokine production and direct cytotoxicity. The NK cell activation receptor, Ly49H, is responsible for genetic resistance to MCMV in C57BL/6 mice. Recognition of the viral m157 protein by Ly49H is sufficient for effective control of MCMV infection. Additionally, during the host response to infection, distinct immune and non-immune cells elaborate a variety of pleiotropic cytokines which have the potential to impact viral pathogenesis, NK cells, and other immune functions, both directly and indirectly. While the effects of various immune deficiencies have been examined for general antiviral phenotypes, their direct effects on Ly49H-dependent MCMV control are poorly understood. To specifically interrogate Ly49H-dependent functions, herein we employed an in vivo viral competition approach to show Ly49H-dependent MCMV control is specifically mediated through cytotoxicity but not IFNγ production. Whereas m157 induced Ly49H-dependent degranulation, efficient cytotoxicity also required either IL-12 or type I interferon (IFN-I) which acted directly on NK cells to produce granzyme B. These studies demonstrate that both of these distinct NK cell-intrinsic mechanisms are integrated for optimal viral control by NK cells.

Natural killer (NK) cells play a crucial role in the protection of the host against viruses and in particular herpesvirus infections. Through their activation receptors which recognize surface ligands on target cells, NK cells can mediate direct killing (cytotoxicity) of virus-infected cells and produce their signature cytokine IFNγ, but it is unclear to what extent these effector arms contribute to clearance of murine cytomegalovirus (MCMV) infections. Additionally, NK cells are activated through their cytokine receptors but the interplay between the activation and cytokine receptor pathways has not been elucidated. Herein we devised a viral competition assay that allowed direct evaluation of the requirements for NK cell mediated MCMV control. We found that cytotoxicity is the main effector mechanism by which NK cells control virus infection through activation receptors. Complemented by in vitro assays, we delineated the requirements for NK cell cytotoxicity and identified a 2-step mechanism for NK-mediated cytotoxicity. Firstly, NK cells require cytokine signals for the accumulation of cytotolytic proteins. Secondly, direct target cell recognition results in release of the cytolytic cargo and lysis of virus-infected cells. Our study demonstrates the integration of NK activation and cytokine receptor signals are required for effective viral control.

Dendritic Cells in Oncolytic Virus-Based Anti-Cancer Therapy

Dendritic cells (DCs) are specialized antigen-presenting cells that have a notable role in the initiation and regulation of innate and adaptive immune responses. In the context of cancer, appropriately activated DCs can induce anti-tumor immunity by activating innate immune cells and tumor-specific lymphocytes that target cancer cells. However, the tumor microenvironment (TME) imposes different mechanisms that facilitate the impairment of DC functions, such as inefficient antigen presentation or polarization into immunosuppressive DCs. These tumor-associated DCs thus fail to initiate tumor-specific immunity, and indirectly support tumor progression. Hence, there is increasing interest in identifying interventions that can overturn DC impairment within the TME. Many reports thus far have studied oncolytic viruses (OVs), viruses that preferentially target and kill cancer cells, for their capacity to enhance DC-mediated anti-tumor effects. Herein, we describe the general characteristics of DCs, focusing on their role in innate and adaptive immunity in the context of the TME. We also examine how DC-OV interaction affects DC recruitment, OV delivery, and anti-tumor immunity activation. Understanding these roles of DCs in the TME and OV infection is critical in devising strategies to further harness the anti-tumor effects of both DCs and OVs, ultimately enhancing the efficacy of OV-based oncotherapy.

Heparan sulfate mimetic PG545-mediated antilymphoma effects require TLR9-dependent NK cell activation

Heparan sulfate (HS) is an essential component of the extracellular matrix (ECM), which serves as a barrier to tumor invasion and metastasis. Heparanase promotes tumor growth by cleaving HS chains of proteoglycan and releasing HS-bound angiogenic growth factors and facilitates tumor invasion and metastasis by degrading the ECM. HS mimetics, such as PG545, have been developed as antitumor agents and are designed to suppress angiogenesis and metastasis by inhibiting heparanase and competing for the HS-binding domain of angiogenic growth factors. However, how PG545 exerts its antitumor effect remains incompletely defined. Here, using murine models of lymphoma, we determined that the antitumor effects of PG545 are critically dependent on NK cell activation and that NK cell activation by PG545 requires TLR9. We demonstrate that PG545 does not activate TLR9 directly but instead enhances TLR9 activation through the elevation of the TLR9 ligand CpG in DCs. Specifically, PG545 treatment resulted in CpG accumulation in the lysosomal compartment of DCs, leading to enhanced production of IL-12, which is essential for PG545-mediated NK cell activation. Overall, these results reveal that PG545 activates NK cells and that this activation is critical for the antitumor effect of PG545. Moreover, our findings may have important implications for improving NK cell-based antitumor therapies.

NKp46+ Innate Lymphoid Cells Dampen Vaginal CD8 T Cell Responses following Local Immunization with a Cholera Toxin-Based Vaccine

Innate and adaptive immune cells work in concert to generate efficient protection at mucosal surface. Vaginal mucosa is an epithelial tissue that contains innate and adaptive immune effector cells. Our previous studies demonstrated that vaginal administration of Cholera toxin -based vaccines generate antigen-specific CD8 T cells through the stimulation of local dendritic cells (DC). Innate lymphoid cells (ILC) are a group of lymphocytes localized in epithelial tissues that have important immune functions against pathogens and in tissue homeostasis. Their contribution to vaccine-induced mucosal T cell responses is an important issue for the design of protective vaccines. We report here that the vaginal mucosa contains a heterogeneous population of NKp46⁺ ILC that includes conventional NK cells and ILC1-like cells. We show that vaginal NKp46⁺ ILC dampen vaccine-induced CD8 T cell responses generated after local immunization. Indeed, in vivo depletion of NKp46⁺ ILC with anti-NK1.1 antibody or NKG2D blockade increases the magnitude of vaginal OVA-specific CD8 T cells. Furthermore, such treatments also increase the number of DC in the vagina. NKG2D ligands being expressed by vaginal DC but not by CD8 T cells, these results support that NKp46⁺ ILC limit mucosal CD8 T cell responses indirectly through the NKG2D-dependent elimination of vaginal DC. Our data reveal an unappreciated role of NKp46⁺ ILC in the regulation of mucosal CD8 T cell responses.

Adjuvant for vaccine immunotherapy of cancer--focusing on Toll-like receptor 2 and 3 agonists for safely enhancing antitumor immunity

Immune‐enhancing adjuvants usually targets antigen (Ag)‐presenting cells to tune up cellular and humoral immunity. CD141⁺ dendritic cells (DC) represent the professional Ag‐presenting cells in humans. In response to microbial pattern molecules, these DCs upgrade the maturation stage sufficient to improve cross‐presentation of exogenous Ag, and upregulation of MHC and costimulators, allowing CD4/CD8 T cells to proliferate and liberating cytokines/chemokines that support lymphocyte attraction and survival. These DCs also facilitate natural killer‐mediated cell damage. Toll‐like receptors (TLRs) and their signaling pathways in DCs play a pivotal role in DC maturation. Therefore, providing adjuvants in addition to Ag is indispensable for successful vaccine immunotherapy for cancer, which has been approved in comparison with antimicrobial vaccines. Mouse CD8α⁺DCs express TLR7 and TLR9 in addition to the TLR2 family (TLR1, 2, and 6) and TLR3, whereas human CD141⁺DCs exclusively express the TLR2 family and TLR3. Although human and mouse plasmacytoid DCs commonly express TLR7/9 to respond to their agonists, the results on mouse adjuvant studies using TLR7/9 agonists cannot be simply extrapolated to human adjuvant immunotherapy. In contrast, TLR2 and TLR3 are similarly expressed in both human and mouse Ag‐presenting DCs. Bacillus Calmette–Guerin peptidoglycan and polyinosinic–polycytidylic acid are representative agonists for TLR2 and TLR3, respectively, although they additionally stimulate cytoplasmic sensors: their functional specificities may not be limited to the relevant TLRs. These adjuvants have been posted up to a certain achievement in immunotherapy in some cancers. We herein summarize the history and perspectives of TLR2 and TLR3 agonists in vaccine‐adjuvant immunotherapy for cancer.