Impairment of hepatic NK cell development in IFN-γ deficient mice

Intermediate monocytes induced by IFN-γ inhibit cancer metastasis by promoting NK cell activation through FOXO1 and interleukin-27

Background

Circulating monocytes are functionally heterogeneous and can be divided into classical (CMo), intermediate (IMo), and non-CMo/patrolling monocyte (PMo) subsets. CMo can differentiate into PMo through IMo. PMos have been shown to inhibit cancer metastasis but the role of IMo is unclear. To date, no strategy has been developed to inhibit cancer metastasis through enhancing PMo/IMo differentiation.

Methods

We screened multiple inflammatory cytokines/chemokines activity of modulating PMo/IMo associated cell markers expression using human monocyte in vitro culture system. We tested our candidate cytokine activity in vivo using multiple mice models. We identified critical key factors and cytokines for our candidate cytokine activity by using gene-knockout mice and neutralization antibodies.

Results

We identified IFN-γ as a candidate inflammatory cytokine in the regulation of human IMo/PMo marker expression. Our in vivo data demonstrated that IMo expansion was induced by short-term (3 days) IFN-γ treatment through increasing CMo-IMo differentiation and blocking IMo-PMo differentiation. The IMo induced by IFN-γ (IFN-IMo), but not IFN-γ activated CMo (IFN-CMo), inhibited cancer metastasis by 90%. Surprizing, the effect of IFN-γ is greater in PMo deficiency mice, indicating the effect of IFN-IMo is not mediated through further differentiation into PMo. We also found that IFN-IMos induced by short-term IFN-γ treatment robustly boosted NK cell expansion for threefold and promoted NK differentiation and function through IL-27 and CXCL9. Furthermore, we identified that FOXO1, a key molecule controlling cellular energy metabolism, mediated the effect of IFN-γ induced IL-27 expression, and that NR4A1, a key molecule controlling PMo differentiation and inhibiting cancer metastasis, inhibited the pro-NK cell and anti-metastasis activity of IFN-IMo by suppressing CXCL9 expression.

Conclusions

We have discovered the antimetastasis and pro-NK cell activity of IFN-IMo, identified FOXO1 as a key molecule for IFN-γ driven monocyte differentiation and function, and found NR4A1 as an inhibitory molecule for IFN-IMo activity. Our study has not only shown novel mechanisms for a classical antitumor cytokine but also provided potential target for developing superior monocytic cell therapy against cancer metastasis.

The Liver and the Hepatic Immune Response in Trypanosoma cruzi Infection, a Historical and Updated View

Chagas disease was described more than a century ago and, despite great efforts to understand the underlying mechanisms that lead to cardiac and digestive manifestations in chronic patients, much remains to be clarified. The disease is found beyond Latin America, including Japan, the USA, France, Spain, and Australia, and is caused by the protozoan Trypanosoma cruzi. Dr. Carlos Chagas described Chagas disease in 1909 in Brazil, and hepatomegaly was among the clinical signs observed. Currently, hepatomegaly is cited in most papers published which either study acutely infected patients or experimental models, and we know that the parasite can infect multiple cell types in the liver, especially Kupffer cells and dendritic cells. Moreover, liver damage is more pronounced in cases of oral infection, which is mainly found in the Amazon region. However, the importance of liver involvement, including the hepatic immune response, in disease progression does not receive much attention. In this review, we present the very first paper published approaching the liver's participation in the infection, as well as subsequent papers published in the last century, up to and including our recently published results. We propose that, after infection, activated peripheral T lymphocytes reach the liver and induce a shift to a pro-inflammatory ambient environment. Thus, there is an immunological integration and cooperation between peripheral and hepatic immunity, contributing to disease control.

Liver type 1 innate lymphoid cells develop locally via an interferon-γ-dependent loop

The pathways that lead to the development of tissue-resident lymphocytes, including liver type 1 innate lymphoid cells (ILC1s), remain unclear. We show here that the adult mouse liver contains Lin-Sca-1+Mac-1+ hematopoietic stem cells derived from the fetal liver. This population includes Lin-CD122+CD49a+ progenitors that can generate liver ILC1s but not conventional natural killer cells. Interferon-γ (IFN-γ) production by the liver ILC1s themselves promotes the development of these cells in situ, through effects on their IFN-γR+ liver progenitors. Thus, an IFN-γ-dependent loop drives liver ILC1 development in situ, highlighting the contribution of extramedullary hematopoiesis to regional immune composition within the liver.

The Tumor Microenvironment-A Metabolic Obstacle to NK Cells' Activity

NK cells have unique capabilities of recognition and destruction of tumor cells, without the requirement for prior immunization of the host. Maintaining tolerance to healthy cells makes them an attractive therapeutic tool for almost all types of cancer. Unfortunately, metabolic changes associated with malignant transformation and tumor progression lead to immunosuppression within the tumor microenvironment, which in turn limits the efficacy of various immunotherapies. In this review, we provide a brief description of the metabolic changes characteristic for the tumor microenvironment. Both tumor and tumor-associated cells produce and secrete factors that directly or indirectly prevent NK cell cytotoxicity. Here, we depict the molecular mechanisms responsible for the inhibition of immune effector cells by metabolic factors. Finally, we summarize the strategies to enhance NK cell function for the treatment of tumors.

STAT1 Isoforms Differentially Regulate NK Cell Maturation and Anti-tumor Activity

Natural killer (NK) cells are important components of the innate immune defense against infections and cancers. Signal transducer and activator of transcription 1 (STAT1) is a transcription factor that is essential for NK cell maturation and NK cell-dependent tumor surveillance. Two alternatively spliced isoforms of STAT1 exist: a full-length STAT1α and a C-terminally truncated STAT1β isoform. Aberrant splicing is frequently observed in cancer cells and several anti-cancer drugs interfere with the cellular splicing machinery. To investigate whether NK cell-mediated tumor surveillance is affected by a switch in STAT1 splicing, we made use of knock-in mice expressing either only the STAT1α (Stat1α/α) or the STAT1β (Stat1β/β ) isoform. NK cells from Stat1α/α mice matured normally and controlled transplanted tumor cells as efficiently as NK cells from wild-type mice. In contrast, NK cells from Stat1β/β mice showed impaired maturation and effector functions, albeit less severe than NK cells from mice that completely lack STAT1 (Stat1-/- ). Mechanistically, we show that NK cell maturation requires the presence of STAT1α in the niche rather than in NK cells themselves and that NK cell maturation depends on IFNγ signaling under homeostatic conditions. The impaired NK cell maturation in Stat1β/β mice was paralleled by decreased IL-15 receptor alpha (IL-15Rα) surface levels on dendritic cells, macrophages and monocytes. Treatment of Stat1β/β mice with exogenous IL-15/IL-15Rα complexes rescued NK cell maturation but not their effector functions. Collectively, our findings provide evidence that STAT1 isoforms are not functionally redundant in regulating NK cell activity and that the absence of STAT1α severely impairs, but does not abolish, NK cell-dependent tumor surveillance.

Tissue-resident NK cells and other innate lymphoid cells

Natural killer (NK) cells are important innate effectors for their defense against pathogens and tumors without the need of prior sensitization. Along with the growing understanding of basic NK cell biology, it has been widely accepted that NK cells are a heterogeneous population of innate lymphoid cell (ILC) family. Apart from the conventional NK cell (cNK) subset that circulates throughout the body, some non-lymphoid tissues contain tissue-resident NK (trNK) cell subsets, and the composition of NK cell subsets varies greatly with different locations. Except for cNK cells, other ILCs are known as tissue-resident cells. In this review, we summarize the unique properties of trNK cells, discuss their lineage relationship with other ILCs, and highlight recent advances in our understanding of the functions of trNK cells and other ILCs.

Differential expression of T helper cytokines in the liver during early pregnancy in sheep

Liver plays important roles in the innate and adaptive immunity, and contributes to the maternal immune adjustments during pregnancy in mice and rats. T helper 1 (Th1) and Th2 cytokines are related to immune response. However, expression of Th1 and Th2 cytokines in maternal livers is unclear during early pregnancy in sheep. In this study, livers were collected on day 16 of the estrous cycle and on days 13, 16 and 25 of pregnancy (n = 6 for each group) in ewes, and qRT-PCR, western blot and immunohistochemistry were used to analyze the expression of Th1 and Th2 cytokines in the livers. Our results showed that interferon-gamma (IFN-γ), interleukin (IL)-2, IL-4, IL-6 and IL-10 were downregulated, and IL-5 was upregulated in the livers during early pregnancy. Furthermore, there was no effect for early pregnancy on expression of TNF-β in the livers, and the IFN-γ protein was limited to the endothelial cells of the proper hepatic arteries and portal veins. In conclusion, early pregnancy exerted its effect on the liver to regulate the Th cytokines expression, but there was no evident shift from Th1 to Th2 cytokines, which may be necessary for the maternal hepatic immune adjustments during early pregnancy in sheep.

The Regulatory Role of IFN-γ on the Proliferation and Differentiation of Hematopoietic Stem and Progenitor Cells

The replenishment of all blood cell lineages is hierarchically organized by the process of hematopoiesis, which is based on the differentiation pathways of hematopoietic stem and progenitor cells (HSPCs). Due to the ability to balance between self-renewal and differentiation, hematopoietic stem cells (HSCs) can generate the appropriate cell type that is required by the immune system and peripheral blood in response to physiological or pathological conditions. Numerous studies have shown that some proinflammatory cytokines contribute to the regulation of the various hematopoietic compartments. Of these, IFN-γ is a type II interferon primarily produced by T cells and natural killer cells, and plays a major role in the defense against invading pathogens and transformed cancer cells; moreover, a growing amount of research indicates that it exerts negative or positive regulatory effect on hematopoiesis. Although IFN-γ is a widely regarded negative regulator of HSC proliferation, it also participates in some chronic infections or hematological malignancies that induce bone marrow failure. Recent studies have demonstrated unexpected effects of IFN-γ, including the promotion of HSC formation and the stimulation of myelopoiesis. Here, we review the direct and indirect effects of IFN-γ on hematopoiesis, as well as the underlying signaling mechanisms of how IFN-γ modulates the self-renewal, cell cycle entry, and proliferation of HSCs. Next, we describe how IFN-γ affects different stages of the lineage differentiation from HSCs. Finally, we discuss the relationship between IFN-γ and compensatory extramedullary hematopoiesis, as well as some related clinical diseases.

LDHA-Associated Lactic Acid Production Blunts Tumor Immunosurveillance by T and NK Cells

Elevated lactate dehydrogenase A (LDHA) expression is associated with poor outcome in tumor patients. Here we show that LDHA-associated lactic acid accumulation in melanomas inhibits tumor surveillance by T and NK cells. In immunocompetent C57BL/6 mice, tumors with reduced lactic acid production (Ldha^low) developed significantly slower than control tumors and showed increased infiltration with IFN-γ-producing T and NK cells. However, in Rag2^-/-γc^-/- mice, lacking lymphocytes and NK cells, and in Ifng^-/- mice, Ldha^low and control cells formed tumors at similar rates. Pathophysiological concentrations of lactic acid prevented upregulation of nuclear factor of activated T cells (NFAT) in T and NK cells, resulting in diminished IFN-γ production. Database analyses revealed negative correlations between LDHA expression and T cell activation markers in human melanoma patients. Our results demonstrate that lactic acid is a potent inhibitor of function and survival of T and NK cells leading to tumor immune escape.

The good and the bad faces of STAT1 in solid tumours

Signal transducer and activator of transcription (STAT) 1 is part of the Janus kinase (JAK)/STAT signalling cascade and is best known for its essential role in mediating responses to all types of interferons (IFN). STAT1 regulates a variety of cellular processes, such as antimicrobial activities, cell proliferation and cell death. It exerts important immune modulatory activities both in the innate and the adaptive arm of the immune system. Based on studies in mice and data from human patients, STAT1 is generally considered a tumour suppressor but there is growing evidence that it can also act as a tumour promoter. This review aims at contrasting the two faces of STAT1 in tumourigenesis and providing an overview on the current knowledge of the underlying mechanisms or pathways.

In vivo tumor surveillance by NK cells requires TYK2 but not TYK2 kinase activity

Tyrosine kinase 2 (TYK2) is a Janus kinase (JAK) that is crucially involved in inflammation, carcinogenesis and defense against infection. The cytotoxic activity of natural killer (NK) cells in TYK2-deficient (Tyk2^−/−) mice is severely reduced, although the underlying mechanisms are largely unknown. Using Tyk2^−/− mice and mice expressing a kinase-inactive version of TYK2 (Tyk2^K923E), we show that NK cell function is partly independent of the enzymatic activity of TYK2. Tyk2^−/− and Tyk2^K923E NK cells develop normally in the bone marrow, but the maturation of splenic Tyk2^−/− NK cells (and to a lesser extent of Tyk2^K923E NK cells) is impaired. In contrast, the production of interferon γ (IFNγ) in response to interleukin 12 (IL-12) or to stimulation through NK cell-activating receptors strictly depends on the presence of enzymatically active TYK2. The cytotoxic activity of Tyk2^K923E NK cells against a range of target cells in vitro is higher than that of Tyk2^−/− NK cells. Consistently, Tyk2^K923E mice control the growth of NK cell-targeted tumors significantly better than TYK2-deficient mice, showing the physiological relevance of the finding. Inhibitors of TYK2's kinase activity are being developed for the treatment of inflammatory diseases and cancers, but their effects on tumor immune surveillance have not been investigated. Our finding that TYK2 has kinase-independent functions in vivo suggests that such inhibitors will leave NK cell mediated tumor surveillance largely intact and that they will be suitable for use in cancer therapy.

IFN-γ production by CD27⁺ NK cells exacerbates Listeria monocytogenes infection in mice by inhibiting granulocyte mobilization

Natural killer (NK) cells are key components of the immune system involved in several immune reactions, including the clearance of intracellular pathogens. When activated, NK cells rapidly secrete particular cytokines that activate innate immunity and facilitate development of adaptive responses. Conflicting reports on the role of NK cells during infection by Listeria monocytogenes can be found in the literature. Here, we demonstrate that during lethal infection by L. monocytogenes, activation of NK cells via the costimulatory molecule CD27 leads to excessive IFN-γ production. This impairs innate anti-bacterial host defenses by inducing downregulation of CXCR2 on granulocytes and consequently inhibiting their recruitment to the sites of infection. The use of antibodies to block CD27 signaling or to deplete IFN-γ was sufficient to rescue mice from lethal challenge by L. monocytogenes. Our findings contribute to a better understanding of the importance of CD27 signaling in activation of NK cells and should provide new ways of interfering with infections.