The absence of CCR7 results in dysregulated monocyte migration and immunosuppression facilitating chronic cutaneous leishmaniasis

Comprehensive analysis of human monocyte subsets using full-spectrum flow cytometry and hierarchical marker clustering

Introduction

Exploring monocytes' roles within the tumor microenvironment is crucial for crafting targeted cancer treatments.

Methods

This study unveils a novel methodology utilizing four 20-color flow cytometry panels for comprehensive peripheral immune system phenotyping, specifically targeting classical, intermediate, and non-classical monocyte subsets.

Results

By applying advanced dimensionality reduction techniques like t-distributed stochastic neighbor embedding (tSNE) and FlowSom analysis, we performed an extensive profiling of monocytes, assessing 50 unique cell surface markers related to a wide range of immunological functions, including activation, differentiation, and immune checkpoint regulation.

Discussion

This in-depth approach significantly refines the identification of monocyte subsets, directly supporting the development of personalized immunotherapies and enhancing diagnostic precision. Our pioneering panel for monocyte phenotyping marks a substantial leap in understanding monocyte biology, with profound implications for the accuracy of disease diagnostics and the success of checkpoint-inhibitor therapies. Key findings include revealing distinct marker expression patterns linked to tumor progression and providing new avenues for targeted therapeutic interventions.

C-C motif chemokine receptor 2 and 7 synergistically control inflammatory monocyte recruitment but the infecting virus dictates monocyte function in the brain

Inflammatory monocytes (iMO) are recruited from the bone marrow to the brain during viral encephalitis. C-C motif chemokine receptor (CCR) 2 deficiency substantially reduces iMO recruitment for most, but not all encephalitic viruses. Here we show CCR7 acts synergistically with CCR2 to control this process. Following Herpes simplex virus type-1 (HSV-1), or La Crosse virus (LACV) infection, we find iMO proportions are reduced by approximately half in either Ccr2 or Ccr7 knockout mice compared to control mice. However, Ccr2/Ccr7 double knockouts eliminate iMO recruitment following infection with either virus, indicating these receptors together control iMO recruitment. We also find that LACV induces a more robust iMO recruitment than HSV-1. However, unlike iMOs in HSV-1 infection, LACV-recruited iMOs do not influence neurological disease development. LACV-induced iMOs have higher expression of proinflammatory and proapoptotic but reduced mitotic, phagocytic and phagolysosomal transcripts compared to HSV-1-induced iMOs. Thus, virus-specific activation of iMOs affects their recruitment, activation, and function.

Monocyte-endothelial cell interactions in vascular and tissue remodeling

Monocytes are circulating leukocytes of innate immunity derived from the bone marrow that interact with endothelial cells under physiological or pathophysiological conditions to orchestrate inflammation, angiogenesis, or tissue remodeling. Monocytes are attracted by chemokines and specific receptors to precise areas in vessels or tissues and transdifferentiate into macrophages with tissue damage or infection. Adherent monocytes and infiltrated monocyte-derived macrophages locally release a myriad of cytokines, vasoactive agents, matrix metalloproteinases, and growth factors to induce vascular and tissue remodeling or for propagation of inflammatory responses. Infiltrated macrophages cooperate with tissue-resident macrophages during all the phases of tissue injury, repair, and regeneration. Substances released by infiltrated and resident macrophages serve not only to coordinate vessel and tissue growth but cellular interactions as well by attracting more circulating monocytes (e.g. MCP-1) and stimulating nearby endothelial cells (e.g. TNF-α) to expose monocyte adhesion molecules. Prolonged tissue accumulation and activation of infiltrated monocytes may result in alterations in extracellular matrix turnover, tissue functions, and vascular leakage. In this review, we highlight the link between interactions of infiltrating monocytes and endothelial cells to regulate vascular and tissue remodeling with a special focus on how these interactions contribute to pathophysiological conditions such as cardiovascular and chronic liver diseases.

Pathological roles of macrophages in Leishmania infections

Macrophages are the major host cells for Leishmania parasites, and determine the fate of infection by either limiting or allowing growth of the parasites, resulting in development or control of leishmaniasis, respectively. They also play important roles in causing pathological outcomes during Leishmania infection. The pathophysiology is complex and include a wide variety of molecular and cellular responses including enhancement of inflammatory responses by releasing cytokines, causing damages to surrounding cells by reactive oxygen species, or disordered phagocytosis of other cells. It is of note that disease severity in leishmaniasis sometimes does not correlate with parasite burdens, indicating that pathological roles of macrophages are not necessarily linked to their parasite-killing activities that are often defined by M1/M2 status. Here, we review the roles of macrophages in leishmaniasis with a focus on their pathological mechanisms in disease development.

Role of host genetics and cytokines in Leishmania infection

Cytokines and chemokines are important regulators of innate and specific responses in leishmaniasis, a disease that currently affects 12 million people. We overviewed the current information about influences of genetically engineered mouse models of cytokine and chemokine on leishmaniasis. We found that genetic background of the host, parasite species and sub-strain, as well as experimental design often modify effects of genetically engineered cytokine genes. Next we analyzed genes and QTLs (quantitative trait loci) that control response to Leishmania species in mouse in order to establish relationship between genetic control of cytokine expression and organ pathology. These studies revealed a network-like complexity of the combined effects of the multiple functionally diverse QTLs and their individual specificity. Genetic control of organ pathology and systemic immune response overlap only partially. Some QTLs control both organ pathology and systemic immune response, but the effects of genes and loci with the strongest impact on disease are cytokine-independent, whereas several loci modify cytokines levels in serum without influencing organ pathology. Understanding this genetic control might be important in development of vaccines designed to stimulate certain cytokine spectrum.

Monocyte-Derived Dendritic Cell Differentiation in Inflammatory Arthritis Is Regulated by the JAK/STAT Axis via NADPH Oxidase Regulation

Monocyte-derived Dendritic cells (Mo-DC) are a distinct DC subset, involved in inflammation and infection, they originate from monocytes upon stimulation in the circulation and their activation and function may vary in autoimmune diseases. In this study we investigate the differences in Mo-DC differentiation and function in patients with Rheumatoid (RA) compared to Psoriatic arthritis (PsA). A significant increase in the Mo-DC differentiation marker CD209, paralleled by a corresponding decrease in the monocytic marker CD14, was demonstrated in RA compared to PsA, as early as 1 day post Mo-DC differentiation. RA monocytes ex-vivo were phenotypically different to PsA, displaying a more mature phenotype associated with altered cellular-morphology, early dendrite formation, and a significant increase in the CD40 marker. In addition, SPICE algorithm flow cytometric analysis showed distinct differences in chemokine receptors distribution in HC compared to PsA and RA CD14+ cells in the blood, with increased expression of the chemokine receptors CCR7 and CXCR4 observed in PsA and RA. In addition CD14+ cells at the site of inflammation showed a different chemokine receptor pattern between PsA and RA patients, with higher expression of CXCR3 and CXCR5 in RA when compared to PsA. The early priming observed in RA resulted in monocyte-endocytosis and antigen-uptake mechanisms to be impaired, effects that were not observed in PsA where phagocytosis capacity remained highly functional. Tofacitinib inhibited early Mo-DC differentiation, decreasing both CD209 and CD40 activation markers in RA. Inhibition of Mo-DC differentiation in response to Tofacitinib was mediated via an imbalance in the activation of NADPH-oxidases NOX5 and NOX2. This effect was reversed by NOX5 inhibition, but not NOX2, resulting in suppression of NOX5-dependent ROS production. In conclusion, RA monocytes are already primed ex vivo to become DC, evident by increased expression of activation markers, morphological appearance and impaired endocytosis capacity. Furthermore, we demonstrated for the first time that NOX5 mediates Mo-DC differentiation and function in response to Tofacitinib, which may alter DC functions.

Hemodynamic loads distinctively impact the secretory profile of biomaterial-activated macrophages - implications for in situ vascular tissue engineering

Biomaterials are increasingly used for in situ vascular tissue engineering, wherein resorbable fibrous scaffolds are implanted as temporary carriers to locally initiate vascular regeneration. Upon implantation, macrophages infiltrate and start degrading the scaffold, while simultaneously driving a healing cascade via the secretion of paracrine factors that direct the behavior of tissue-producing cells. This balance between neotissue formation and scaffold degradation must be maintained at all times to ensure graft functionality. However, the grafts are continuously exposed to hemodynamic loads, which can influence macrophage response in a hitherto unknown manner and thereby tilt this delicate balance. Here we aimed to unravel the effects of physiological levels of shear stress and cyclic stretch on biomaterial-activated macrophages, in terms of polarization, scaffold degradation and paracrine signaling to tissue-producing cells (i.e. (myo)fibroblasts). Human THP-1-derived macrophages were seeded in electrospun polycaprolactone bis-urea scaffolds and exposed to shear stress (∼1 Pa), cyclic stretch (∼1.04), or a combination thereof for 8 days. The results showed that macrophage polarization distinctly depended on the specific loading regime applied. In particular, hemodynamic loading decreased macrophage degradative activity, especially in conditions of cyclic stretch. Macrophage activation was enhanced upon exposure to shear stress, as evidenced from the upregulation of both pro- and anti-inflammatory cytokines. Exposure to the supernatant of these dynamically cultured macrophages was found to amplify the expression of tissue formation- and remodeling-related genes in (myo)fibroblasts statically cultured in comparable electrospun scaffolds. These results emphasize the importance of macrophage mechano-responsiveness in biomaterial-driven vascular regeneration.

Role of CCR7 on dendritic cell‑mediated immune tolerance in the airways of allergy‑induced asthmatic rats

Dendritic cells (DCs) have an important role in initiating and maintaining the immune inflammatory response in allergic asthma, and CC chemokine receptor 7 (CCR7) is directly involved in the pathogenesis of DC- and T cell-mediated allergic asthma. The present study aimed to investigate the effects of CCR7 on DC-mediated immune tolerance in allergic asthma. In the present study, bone marrow-derived DCs were transfected with an adenovirus encoding the rat CCR7 gene or a short hairpin RNA targeting CCR7 (sh-CCR7). Rats injected with DCs overexpressing CCR7 or presenting CCR7 knockdown were examined. After the rats were injected with DCs via the tail vein, bronchoalveolar lavage fluid was collected to assess its cellular composition. The protein expression levels of CCR7 in DCs were determined using immunohistochemistry and western blot analysis. The protein expression levels of interferon-γ (IFN-γ), interleukin-4 (IL-4), IL-10, IL-12, transforming growth factor-β (TGF-β) and immunoglobulin E (IgE) were determined by ELISA. Compared with the control group, the protein expression level of CCR7 was significantly higher in the CCR7 overexpression group and significantly lower in sh-CCR7 group. Similarly, the number of DCs was higher in the CCR7 overexpression group and lower in the sh-CCR7 group. The protein expression levels of IL-10 and TGF-β were significantly lower in the CCR7 overexpression group and higher in the sh-CCR7 group. In addition, the expression levels of IL-4, IL-12, IFN-γ and IgE were higher in the CCR7 overexpression group and lower in the sh-CCR7 group. The present results suggested that the role of cytokines and IgE in immune inflammation and immune tolerance in allergic asthma may be associated with the expression level of CCR7 in DCs, suggesting that CCR7 may serve a role in DC-mediated immune tolerance in allergic asthma.

Peripheral Blood Monocytes With an Antiinflammatory Phenotype Display Limited Phagocytosis and Oxidative Burst in Patients With Visceral Leishmaniasis

Background

Monocytes are important effector cells during Leishmania infection, and changes in their functions may impact development of immunity. However, functional characteristics of monocytes in patients with visceral leishmaniasis (VL) remains poorly understood.

Methods

Peripheral blood monocytes from patients with VL and healthy endemic controls from Muzaffarpur, India, were isolated and compared in an ex vivo setting, using cell-culture techniques, flow cytometry, and reverse transcription quantitative polymerase chain reaction analysis.

Results

A blood monocyte population with a gene signature comprising upregulated expression of TGM2, CTLRs, VDR, PKM, SOCS1, and CAMP1 and downregulated expression of NOS2 and HIF1A was observed in patients with VL but not in controls. Monocytes from patients with VL also had impaired expression of chemokine receptors and adhesion molecules and decreased frequencies of interleukin 1β- and interleukin 6-producing cells. Importantly, monocytes from patients with VL had a markedly reduced capacity for phagocytosis of amastigotes, p47phox and p67phox expression, and reactive oxygen species production.

Conclusions

Monocytes from patients with VL express antiinflammatory molecules and lack a classically activated phenotype. They have reduced expression of molecules related to activation and antiparasitic effector functions, indicating that monocytes are skewed toward an antiinflammatory phenotype. These findings provide insights into the functional status of monocytes during VL and advise that therapeutic manipulation of this important cell population may result in favorable patient outcomes.

The effects of CCR7 and related signaling pathways on Leishmania major -infected human dendritic cells

OBJECTIVES

In our research, we aimed to investigate the roles of CC-chemokine receptor 7 (CCR7) and relevant signaling pathways in Leishmania major-infected human dendritic cells (DCs).

METHODS

Differentially expressed genes (DEGs) in L. major-infected human DCs were selected out and visualized using R program. Kyoto Encyclopedia of Genes and Genomes pathway analysis was conducted for investigation of significantly enriched signaling pathways and Gene Ontology enrichment analysis was carried out for the unveiling of enriched Molecular Functions and Biological Processes in L. major-infected human DCs. Besides, Hub gene was screened out using weighted gene coexpression network analysis and Cytoscape. In addition, enzyme-linked immunosorbent assay and real-time quantitative polymerase chain reaction were used for detection of relative expression of CCR7, interleukin-12 (IL-12), and interferon-γ (IFN-γ) in L. major-infected human DCs and western blot analysis was used for detection of relative expression of CCR7 and other proteins in JAK-STAT signaling pathway in L. major-infected human DCs.

RESULTS

CCR7 was upregulated and both chemokine and JAK-STAT signaling pathway were activated in L. major-infected human DCs. During the L. major infection, total number of L. major-infected human DCs were increased, as well as the relative expression levels of CCR7, IL-12, and IFN-γ and proteins in the JAK-STAT signaling pathway. Overexpression of CCR7 not only increased expression levels of IL-12 and IFN-γ but also activated the JAK-STAT signaling pathway to affect the leishmaniasis progression.

CONCLUSION

L. major infection-induced activation of CCR7, as well as JAK2 and STAT1, might well upregulate the expression of BAX yet suppress the expression of both Bcl2 and c-Jun to affect leishmaniasis progression.

Absence of Tumor Necrosis Factor Supports Alternative Activation of Macrophages in the Liver after Infection with Leishmania major

The absence of tumor necrosis factor (TNF) causes lethal infection by Leishmania major in normally resistant C57BL/6J (B6.WT) mice. The underlying pathogenic mechanism of this fatal disease has so far remained elusive. We found that B6.WT mice deficient for the tnf gene (B6.TNF^−/−) displayed not only a non-healing cutaneous lesion but also a serious infection of the liver upon L. major inoculation. Infected B6.TNF^−/− mice developed an enlarged liver that showed increased inflammation. Furthermore, we detected an accumulating monocyte-derived macrophage population (CD45⁺F4/80⁺CD11b^hiLy6C^low) that displayed a M2 macrophage phenotype with high expression of CD206, arginase-1, and IL-6, supporting the notion that IL-6 could be involved in M2 differentiation. In in vitro experiments, we demonstrated that IL-6 upregulated M-CSF receptor expression and skewed monocyte differentiation from dendritic cells to macrophages. This was countered by the addition of TNF. Furthermore, TNF interfered with the activation of IL-6-induced gp130-signal transducer and activator of transcription (STAT) 3 and IL-4-STAT6 signaling, thereby abrogating IL-6-facilitated M2 macrophage polarization. Therefore, our results support the notion of a general role of TNF in the inflammatory activation of macrophages and define a new role of IL-6 signaling in macrophage polarization downstream of TNF.

Impact of CCR7 on T-Cell Response and Susceptibility to Yersinia pseudotuberculosis Infection

Background

To successfully limit pathogen dissemination, an immunological link between the entry tissue of the pathogen and the underlying secondary lymphoid organs (SLOs) needs to be established to prime adaptive immune responses. Here, the prerequisite of CCR7 to mount host immune responses within SLOs during gastrointestinal Yersinia pseudotuberculosis infection to limit pathogen spread was investigated.

Methods

Survival, bacterial dissemination, and intestinal and systemic pathology of wild-type and CCR7-/- mice were assessed and correlated to the presence of immune cell subsets and cytokine responses throughout the course of infection.

Results

The CCR7-/- mice show a significantly higher morbidity and are more prone to pathogen dissemination and intestinal and systemic inflammation during the oral route of infection. Significant impact of CCR7 deficiency over the course of infection on several immunological parameters were observed (ie, elevated neutrophil-dominated innate immune response in Peyer's patches, limited dendritic cell migration to mesenteric lymph nodes [mLNs] causing reduced T cell-mediated adaptive immune responses (in particular Th17-like responses) in mLNs).

Conclusions

Our work indicates that CCR7 is required to mount a robust immune response against enteropathogenic Y. pseudotuberculosis by promoting Th17-like responses in mLNs.

Human hantavirus infection elicits pronounced redistribution of mononuclear phagocytes in peripheral blood and airways

Hantaviruses infect humans via inhalation of virus-contaminated rodent excreta. Infection can cause severe disease with up to 40% mortality depending on the viral strain. The virus primarily targets the vascular endothelium without direct cytopathic effects. Instead, exaggerated immune responses may inadvertently contribute to disease development. Mononuclear phagocytes (MNPs), including monocytes and dendritic cells (DCs), orchestrate the adaptive immune responses. Since hantaviruses are transmitted via inhalation, studying immunological events in the airways is of importance to understand the processes leading to immunopathogenesis. Here, we studied 17 patients infected with Puumala virus that causes a mild form of hemorrhagic fever with renal syndrome (HFRS). Bronchial biopsies as well as longitudinal blood draws were obtained from the patients. During the acute stage of disease, a significant influx of MNPs expressing HLA-DR, CD11c or CD123 was detected in the patients’ bronchial tissue. In parallel, absolute numbers of MNPs were dramatically reduced in peripheral blood, coinciding with viremia. Expression of CCR7 on the remaining MNPs in blood suggested migration to peripheral and/or lymphoid tissues. Numbers of MNPs in blood subsequently normalized during the convalescent phase of the disease when viral RNA was no longer detectable in plasma. Finally, we exposed blood MNPs in vitro to Puumala virus, and demonstrated an induction of CCR7 expression on MNPs. In conclusion, the present study shows a marked redistribution of blood MNPs to the airways during acute hantavirus disease, a process that may underlie the local immune activation and contribute to immunopathogenesis in hantavirus-infected patients.

Inhalation of hantavirus-infected rodent droppings can cause a wide range of disease ranging from mild symptoms to deaths in humans. Central to hantavirus disease is vascular leakage that can manifest in different organs, including the lungs. Although the virus can infect endothelial cells lining the blood vessels, it does not cause cell death. Instead, activation of the immune system in response to viral infection has been implicated in causing vascular leakage. In this study, we investigated how monocytes and dendritic cells (DCs) are involved in hantavirus disease, given their capacity to activate other immune cells. We obtained unique clinical material from 17 Puumala virus-infected patients including mucosal biopsies from the airways as well as multiple blood draws over the course of disease. In the airways of these patients, we observed an infiltration of monocytes and DCs. In parallel, there was a dramatic depletion in peripheral blood—more than ten-fold—of monocytes and DCs that was sustained throughout the first two weeks of disease. Taken together, this study provides novel insights into immune mediated processes underlying human hantavirus pathogenesis.