Human and Mouse Mononuclear Phagocyte Networks: A Tale of Two Species?

Macrophages - Controlling the Bifurcation Between Tumor Existence or Regression

Macrophages are multifunctional cells that are employed by the tumor to further its growth and adaptation. While tumor-associated macrophages (TAMs) have widely diverse phenotypes, tumors coevolve with the ones that can promote tumorigenesis. Functionally, TAMs/myeloid cells constitute the largest negative influence on the tumor microenvironment and need to be reprogrammed in order to enable successful anti-tumor response in most tumors. It is predicted that successful TAM repolarization has the potential to become a staple of immuno-oncology across most indications.

Leukocyte-Specific Morrbid Promotes Leukocyte Differentiation and Atherogenesis

Monocyte-to-M0/M1 macrophage differentiation with unclear molecular mechanisms is a pivotal cellular event in many cardiovascular diseases including atherosclerosis. Long non-coding RNAs (lncRNAs) are a group of protein expression regulators; however, the roles of monocyte-lncRNAs in macrophage differentiation and its related vascular diseases are still unclear. The study aims to investigate whether the novel leukocyte-specific lncRNA Morrbid could regulate macrophage differentiation and atherogenesis. We identified that Morrbid was increased in monocytes and arterial walls from atherosclerotic mouse and from patients with atherosclerosis. In cultured monocytes, Morrbid expression was markedly increased during monocyte to M0 macrophage differentiation with an additional increase during M0 macrophage-to-M1 macrophage differentiation. The differentiation stimuli-induced monocyte-macrophage differentiation and the macrophage activity were inhibited by Morrbid knockdown. Moreover, overexpression of Morrbid alone was sufficient to elicit the monocyte-macrophage differentiation. The role of Morrbid in monocyte-macrophage differentiation was also identified in vivo in atherosclerotic mice and was verified in Morrbid knockout mice. We identified that PI3-kinase/Akt was involved in the up-regulation of Morrbid expression, whereas s100a10 was involved in Morrbid-mediated effect on macrophage differentiation. To provide a proof of concept of Morrbid in pathogenesis of monocyte/macrophage-related vascular disease, we applied an acute atherosclerosis model in mice. The results revealed that overexpression of Morrbid enhanced but monocyte/macrophage-specific Morrbid knockout inhibited the monocytes/macrophages recruitment and atherosclerotic lesion formation in mice. The results suggest that Morrbid is a novel biomarker and a modulator of monocyte-macrophage phenotypes, which is involved in atherogenesis.

Gestational Development of the Human Immune System

Building an immune system is a monumental task critical to the survival of the fetus and newborn. A functional fetal immune system must complement the maternal immune system in handling in utero infection; abstain from damaging non-self-reactions that would compromise the materno-fetal interface; mobilize in response to infection and equip mucosal tissues for pathogen exposure at birth. There is growing appreciation that immune cells also have noncanonical roles in development and specifically may contribute to tissue morphogenesis. In this review we detail how hematopoietic and lymphoid organs jointly establish cellular constituents of the immune system; how these constituents are organized in 2 mucosal sites-gut and lung-where early life immune function has long-term consequences for health; and how exemplar diseases of prematurity and inborn errors of immunity reveal dominant pathways in prenatal immunity.

Macrophage response mediated by extracellular matrix: recent progress

Biomaterials are one of efficient treatment options for tissue defects in regenerative medicine. Compared to synthetic materials which tend to induce chronic inflammatory response and fibrous capsule, extracellular matrix (ECM) scaffold materials composed of biopolymers are thought to be capable of inducing a pro-regenerative immune microenvironment and facilitate wound healing. Immune cells are the first line of response to implanted biomaterials. In particular, macrophages greatly affect cell behavior and the ultimate treatment outcome based on multiple cell phenotypes with various functions. The macrophage polarization status is considered as a general reflection of the characteristics of the immune microenvironment. Since numerous reports has emphasized the limitation of classical M1/M2 nomenclature, high-resolution techniques such as single-cell sequencing has been applied to recognize distinct macrophage phenotypes involved in host responses to biomaterials. After reviewing latest literatures that explored the immune microenvironment mediated by ECM scaffolds, this paper describe the behaviors of highly heterogeneous and plastic macrophages subpopulations which affect the tissue regeneration. The mechanisms by which ECM scaffolds interact with macrophages are also discussed from the perspectives of the ECM ultrastructure along with the nucleic acid, protein, and proteoglycan compositions, in order to provide targets for potential therapeutic modulation in regenerative medicine.

MNPmApp: An image analysis tool to quantify mononuclear phagocyte distribution in mucosal tissues

Mononuclear phagocytes (MNPs) such as dendritic cells and macrophages perform key sentinel functions in mucosal tissues and are responsible for inducing and maintaining adaptive immune responses to mucosal pathogens. Positioning of MNPs at the epithelial interface facilitates their access to luminally-derived antigens and regulates MNP function through soluble mediators or surface receptor interactions. Therefore, accurately quantifying the distribution of MNPs within mucosal tissues as well as their spatial relationship with other cells is important to infer functional cellular interactions in health and disease. In this study, we developed and validated a MATLAB-based tissue cytometry platform, termed "MNP mapping application" (MNPmApp), that performs high throughput analyses of MNP density and distribution in the gastrointestinal mucosa based on digital multicolor fluorescence microscopy images and that integrates a Monte Carlo modeling feature to assess randomness of MNP distribution. MNPmApp identified MNPs in tissue sections of the human gastric mucosa with 98 ± 2% specificity and 76 ± 15% sensitivity for HLA-DR+ MNPs and 98 ± 1% specificity and 85 ± 12% sensitivity for CD11c+ MNPs. Monte Carlo modeling revealed that mean MNP-MNP distances for both HLA-DR+ and CD11c+ MNPs were significantly lower than anticipated based on random cell placement, whereas MNP-epithelial distances were similar to randomly placed cells. Surprisingly, H. pylori infection had no significant impact on the number of HLA-DR and CD11c MNPs or their distribution within the gastric lamina propria. However, our study demonstrated that MNPmApp is a reliable and user-friendly tool for unbiased quantitation of MNPs and their distribution at mucosal sites.

High Macrophage Densities in Native Kidney Biopsies Correlate With Renal Dysfunction and Promote ESRD

Introduction

Macrophages and monocytes are main players in innate immunity. The relevance of mononuclear phagocyte infiltrates on clinical outcomes remains to be determined in native kidney diseases.

Methods

Our cross-sectional study included 324 patients with diagnostic renal biopsies comprising 17 disease entities and normal renal tissues for comparison. All samples were stained for CD68⁺ macrophages. Selected groups were further subtyped for CD14⁺ monocytes and CD163⁺ alternatively activated macrophages. Using precise pixel-based digital measurements, we quantified cell densities as positively stained areas in renal cortex and medulla as well as whole renal tissue. Laboratory and clinical data of all cases at the time of biopsy and additional follow-up data in 158 cases were accessible.

Results

Biopsies with renal disease consistently revealed higher CD68⁺-macrophage densities and CD163⁺-macrophage densities in cortex and medulla compared to controls. High macrophage densities correlated with impaired renal function at biopsy and at follow-up in all diseases and in diseases analyzed separately. High cortical CD68⁺-macrophage densities preceded shorter renal survival, defined as requirement of permanent dialysis. CD14⁺ monocyte densities showed no difference compared to controls and did not correlate with renal function.

Conclusion

Precise quantification of macrophage densities in renal biopsies may contribute to risk stratification to identify patients with high risk for end-stage renal disease (ESRD) and might be a promising therapeutic target in renal disease.

An In Vivo Model of Human Macrophages in Metastatic Melanoma

Despite recent therapeutic progress, advanced melanoma remains lethal for many patients. The composition of the immune tumor microenvironment (TME) has decisive impacts on therapy response and disease outcome, and high-dimensional analyses of patient samples reveal the heterogeneity of the immune TME. Macrophages infiltrate TMEs and generally associate with tumor progression, but the underlying mechanisms are incompletely understood. Because experimental systems are needed to elucidate the functional properties of these cells, we developed a humanized mouse model reconstituted with human immune cells and human melanoma. We used two strains of recipient mice, supporting or not supporting the development of human myeloid cells. We found that human myeloid cells favored metastatic spread of the primary tumor, thereby recapitulating the cancer-supportive role of macrophages. We next analyzed the transcriptome of human immune cells infiltrating tumors versus other tissues. This analysis identified a cluster of myeloid cells present in the TME, but not in other tissues, which do not correspond to canonical M2 cells. The transcriptome of these cells is characterized by high expression of glycolytic enzymes and multiple chemokines and by low expression of gene sets associated with inflammation and adaptive immunity. Compared with humanized mouse results, we found transcriptionally similar myeloid cells in patient-derived samples of melanoma and other cancer types. The humanized mouse model described here thus complements patient sample analyses, enabling further elucidation of fundamental principles in melanoma biology beyond M1/M2 macrophage polarization. The model can also support the development and evaluation of candidate antitumor therapies.

Inhibition of Notch Signaling Stimulates Osteoclastogenesis From the Common Trilineage Progenitor Under Inflammatory Conditions

Osteoclasts, macrophages and dendritic cells (DCs) can be derived from a common trilineage myeloid progenitor of hematopoietic origin. Progenitor commitment is susceptible to regulation through Notch signaling. Our aim was to determine the effects of Notch modulation on trilineage progenitor commitment and functional properties of differentiated cells under inflammatory conditions. We used the conditional inducible CX3CR1CreERT2 mouse strain to achieve overexpression of the Notch 1 intracellular domain (NICD1) or to inhibit Notch signaling via deletion of the transcription factor RBP-J in a bone marrow population, used as a source of the trilineage progenitor (CD45+Ly6G−CD3−B220−NK1.1−CD11b–/loCD115+). Cre-recombinase, under the control of the CX3CR1 promoter, expressed in the monocyte/macrophage lineage, was induced in vitro by 4-hydroxytamoxifen. Differentiation of osteoclasts was induced by M-CSF/RANKL; macrophages by M-CSF; DCs by IL-4/GM-CSF, and inflammation by LPS. Functionally, DCs were tested for the ability to process and present antigen, macrophages to phagocytose E. coli particles, and osteoclasts to resorb bone and express tartrate-resistant acid phosphatase (TRAP). We found that Notch 1 signal activation suppressed osteoclast formation, whereas disruption of the Notch canonical pathway enhanced osteoclastogenesis, resulting in a higher number and size of osteoclasts. RANK protein and Ctsk gene expression were upregulated in osteoclastogenic cultures from RBP-J+ mice, with the opposing results in NICD1+ mice. Notch modulation did not affect the number of in vitro differentiated macrophages and DCs. However, RBP-J deletion stimulated Il12b and Cd86 expression in macrophages and DCs, respectively. Functional assays under inflammatory conditions confirmed that Notch silencing amplifies TRAP expression by osteoclasts, whereas the enhanced phagocytosis by macrophages was observed in both NICD1+ and RBP-J+ strains. Finally, antigen presentation by LPS-stimulated DCs was significantly downregulated with NICD1 overexpression. This experimental setting allowed us to define a cell-autonomous response to Notch signaling at the trilineage progenitor stage. Although Notch signaling modulation affected the activity of all three lineages, the major effect was observed in osteoclasts, resulting in enhanced differentiation and function with inhibition of canonical Notch signaling. Our results indicate that Notch signaling participates as the negative regulator of osteoclast activity during inflammation, which may be relevant in immune and bone diseases.

Tissue-Resident Innate Immune Cell-Based Therapy: A Cornerstone of Immunotherapy Strategies for Cancer Treatment

Cancer immunotherapy has led to impressive advances in cancer treatment. Unfortunately, in a high percentage of patients is difficult to consistently restore immune responses to eradicate established tumors. It is well accepted that adaptive immune cells, such as B lymphocytes, CD4⁺ helper T lymphocytes, and CD8⁺ cytotoxic T-lymphocytes (CTLs), are the most effective cells able to eliminate tumors. However, it has been recently reported that innate immune cells, including natural killer cells (NK), dendritic cells (DC), macrophages, myeloid-derived suppressor cells (MDSCs), and innate lymphoid cells (ILCs), represent important contributors to modulating the tumor microenvironment and shaping the adaptive tumor response. In fact, their role as a bridge to adaptive immunity, make them an attractive therapeutic target for cancer treatment. Here, we provide a comprehensive overview of the pleiotropic role of tissue-resident innate immune cells in different tumor contexts. In addition, we discuss how current and future therapeutic approaches targeting innate immune cells sustain the adaptive immune system in order to improve the efficacy of current tumor immunotherapies.

Macrophage: A Cell With Many Faces and Functions in Tuberculosis

Mycobacterium tuberculosis (Mtb) is the causative agent of human tuberculosis (TB) which primarily infects the macrophages. Nearly a quarter of the world's population is infected latently by Mtb. Only around 5%-10% of those infected develop active TB disease, particularly during suppressed host immune conditions or comorbidity such as HIV, hinting toward the heterogeneity of Mtb infection. The aerosolized Mtb first reaches the lungs, and the resident alveolar macrophages (AMs) are among the first cells to encounter the Mtb infection. Evidence suggests that early clearance of Mtb infection is associated with robust innate immune responses in resident macrophages. In addition to lung-resident macrophage subsets, the recruited monocytes and monocyte-derived macrophages (MDMs) have been suggested to have a protective role during Mtb infection. Mtb, by virtue of its unique cell surface lipids and secreted protein effectors, can evade killing by the innate immune cells and preferentially establish a niche within the AMs. Continuous efforts to delineate the determinants of host defense mechanisms have brought to the center stage the crucial role of macrophage phenotypical variations for functional adaptations in TB. The morphological and functional heterogeneity and plasticity of the macrophages aid in confining the dissemination of Mtb. However, during a suppressed or hyperactivated immune state, the Mtb virulence factors can affect macrophage homeostasis which may skew to favor pathogen growth, causing active TB. This mini-review is aimed at summarizing the interplay of Mtb pathomechanisms in the macrophages and the implications of macrophage heterogeneity and plasticity during Mtb infection.

A Selective β-Catenin-Metadherin/CEACAM1-CCL3 Axis Mediates Metastatic Heterogeneity upon Tumor-Macrophage Interaction

Tumor heterogeneity plays a key role in cancer relapse and metastasis, however, the distinct cellular behaviors and kinetics of interactions among different cancer cell subclones and the tumor microenvironment are poorly understood. By profiling an isogenic model that resembles spontaneous human ovarian cancer metastasis with an highly metastatic (HM) and non-metastatic (NM) tumor cell pair, one finds an upregulation of Wnt/β-catenin signaling uniquely in HM. Using humanized immunocompetent mice, one shows for the first time that activated β-catenin acts nonautonomously to modulate the immune microenvironment by enhancing infiltrating tumor-associated macrophages (TAM) at the metastatic site. Single-cell time-lapse microscopy further reveals that upon contact with macrophages, a significant subset of HM, but not NM, becomes polyploid, a phenotype pivotal for tumor aggressiveness and therapy resistance. Moreover, HM, but not NM, polarizes macrophages to a TAM phenotype. Mechanistically, β-catenin upregulates cancer cell surface metadherin, which communicates through CEACAM1 expressed on macrophages to produce CCL3. Tumor xenografts in humanized mice and clinical patient samples both corroborate the relevance of enhanced metastasis, TAM activation, and polyploidy in vivo. The results thus suggest that targeting the β-catenin-metadherin/CEACAM1-CCL3 positive feedback cascade holds great therapeutic potential to disrupt polyploidization of the cancer subclones that drive metastasis.

An Experimental Model of Neuro-Immune Interactions in the Eye: Corneal Sensory Nerves and Resident Dendritic Cells

The cornea is an avascular connective tissue that is crucial, not only as the primary barrier of the eye but also as a proper transparent refractive structure. Corneal transparency is necessary for vision and is the result of several factors, including its highly organized structure, the physiology of its few cellular components, the lack of myelinated nerves (although it is extremely innervated), the tightly controlled hydration state, and the absence of blood and lymphatic vessels in healthy conditions, among others. The avascular, immune-privileged tissue of the cornea is an ideal model to study the interactions between its well-characterized and dense sensory nerves (easily accessible for both focal electrophysiological recording and morphological studies) and the low number of resident immune cell types, distinguished from those cells migrating from blood vessels. This paper presents an overview of the corneal structure and innervation, the resident dendritic cell (DC) subpopulations present in the cornea, their distribution in relation to corneal nerves, and their role in ocular inflammatory diseases. A mouse model in which sensory axons are constitutively labeled with tdTomato and DCs with green fluorescent protein (GFP) allows further analysis of the neuro-immune crosstalk under inflammatory and steady-state conditions of the eye.

Complexity of immune responses in COVID-19

The global COVID-19 pandemic has caused substantial morbidity and mortality to humanity. Remarkable progress has been made in understanding both the innate and adaptive mechanisms involved in the host response to the causative SARS-CoV-2 virus, but much remains to be discovered. Robust upper airway defenses are critical in restricting SARS-CoV-2 replication and propagation. Further, the nasal abundance of viral uptake receptor, ACE2, and the host epithelial transcriptional landscape, are associated with differential disease outcomes across different patient cohorts. The adaptive host response to systemic COVID-19 is heterogeneous and complex. Blunted responses to interferon and robust cytokine generation are hallmarks of the disease, particularly at the advanced stages. Excessive immune cell influx into tissues can lead to substantial collateral damage to the host akin to sepsis.

This review offers a contemporary summary of these mechanisms of disease and highlights potential avenues for diagnostic and therapeutic development. These include improved disease stratification, targeting effectors of immune-mediated tissue damage, and blunting of immune cell-mediated tissue damage.

Prophylactic Knockdown of the miR-183/96/182 Cluster Ameliorates Pseudomonas aeruginosa-Induced Keratitis

Purpose

Previously, we demonstrated that miR-183/96/182 cluster (miR-183C) knockout mice exhibit decreased severity of Pseudomonas aeruginosa (PA)-induced keratitis. This study tests the hypothesis that prophylactic knockdown of miR-183C ameliorates PA keratitis indicative of a therapeutic potential.

Methods

Eight-week-old miR-183C wild-type and C57BL/6J inbred mice were used. Locked nucleic acid-modified anti-miR-183C or negative control oligoribonucleotides with scrambled sequences (NC ORNs) were injected subconjunctivally 1 day before and then topically applied once daily for 5 days post-infection (dpi) (strain 19660). Corneal disease was graded at 1, 3, and 5 dpi. Corneas were harvested for RT-PCR, ELISA, immunofluorescence (IF), myeloperoxidase and plate count assays, and flow cytometry. Corneal nerve density was evaluated in flatmounted corneas by IF staining with anti-β-III tubulin antibody.

Results

Anti-miR-183C downregulated miR-183C in the cornea. It resulted in an increase in IL-1β at 1 dpi, which was decreased at 5 dpi; fewer polymorphonuclear leukocytes (PMNs) at 5 dpi; lower viable bacterial plate count at both 1 and 5 dpi; increased percentages of MHCII+ macrophages (Mϕ) and dendritic cells (DCs), consistent with enhanced activation/maturation; and decreased severity of PA keratitis. Anti-miR-183C treatment in the cornea of naïve mice resulted in a transient reduction of corneal nerve density, which was fully recovered one week after the last anti-miR application. miR-183C targets repulsive axon-guidance receptor molecule Neuropilin 1, which may mediate the effect of anti-miR-183C on corneal nerve regression.

Conclusions

Prophylactic miR-183C knockdown is protective against PA keratitis through its regulation of innate immunity, corneal innervation, and neuroimmune interactions.

NogoA-expressing astrocytes limit peripheral macrophage infiltration after ischemic brain injury in primates

Astrocytes play critical roles after brain injury, but their precise function is poorly defined. Utilizing single-nuclei transcriptomics to characterize astrocytes after ischemic stroke in the visual cortex of the marmoset monkey, we observed nearly complete segregation between stroke and control astrocyte clusters. Screening for the top 30 differentially expressed genes that might limit stroke recovery, we discovered that a majority of astrocytes expressed RTN4A/ NogoA, a neurite-outgrowth inhibitory protein previously only associated with oligodendrocytes. NogoA upregulation on reactive astrocytes post-stroke was significant in both the marmoset and human brain, whereas only a marginal change was observed in mice. We determined that NogoA mediated an anti-inflammatory response which likely contributes to limiting the infiltration of peripheral macrophages into the surviving parenchyma.

Nicotine causes alternative polarization of macrophages via Src-mediated STAT3 activation: Potential pathobiological implications

Nicotine is an addictive ingredient of tobacco products and other noncigarette substitutes, including those being used for smoking cessation to relieve withdrawal symptoms. Earlier research, however, has associated nicotine with the risk and poorer outcome of several diseases, including cancer. Macrophages are an important component of the innate immune system and can have both pro-and anti-inflammatory functions depending upon their polarization state. Here, we investigated the effect of nicotine on macrophage polarization, growth, and invasion to understand its role in human physiology. We observed that nicotine induced M2 polarization of RAW264.7 and THP-1-derived macrophages in a dose-dependent manner. Cytokine profiling suggested a mixed M2a/d phenotype of nicotine-polarized macrophages associated with tissue repair and pro-angiogenic functions. Moreover, nicotine treatment also enhanced the growth, motility, and invasion of macrophages. Mechanistic studies revealed increased phosphorylation of STAT3 in nicotine-treated macrophages that was mediated through Src activation. Importantly, pretreatment of macrophages with either Src or STAT3 inhibitor abrogated nicotine-induced macrophage polarization, growth, and motility, suggesting a functional role of the Src-STAT3 signaling axis. Together, our findings reveal a novel role of nicotine in immunosuppression via causing M2 polarization of macrophages that could be implicated in the pathogenesis of various diseases.

The mannose receptor (CD206) identifies a population of colonic macrophages in health and inflammatory bowel disease

To understand the contribution of mononuclear phagocytes (MNP), which include monocyte-derived intestinal macrophages, to the pathogenesis of inflammatory bowel disease (IBD), it is necessary to identify functionally-different MNP populations. We aimed to characterise intestinal macrophage populations in patients with IBD. We developed 12-parameter flow cytometry protocols to identify and human intestinal MNPs. We used these protocols to purify and characterize colonic macrophages from colonic tissue from patients with Crohn’s disease (CD), ulcerative colitis (UC), or non-inflamed controls, in a cross-sectional study. We identify macrophage populations (CD45⁺CD64⁺ HLA-DR⁺) and describe two distinct subsets, differentiated by their expression of the mannose receptor, CD206. CD206⁺ macrophages expressed markers consistent with a mature phenotype: high levels of CD68 and CD163, higher transcription of IL-10 and lower expression of TREM1. CD206⁻ macrophages appear to be less mature, with features more similar to their monocytic precursors. We identified and purified macrophage populations from human colon. These appear to be derived from a monocytic precursor with high CCR2 and low CD206 expression. As these cells mature, they acquire expression of IL-10, CD206, CD63, and CD168. Targeting the newly recruited monocyte-derived cells may represent a fruitful avenue to ameliorate chronic inflammation in IBD.

Macrophage phenotypes in tissue repair and the foreign body response: Implications for biomaterial-based regenerative medicine strategies

Macrophages are a highly heterogeneous and plastic population of cells that are crucial for tissue repair and regeneration. This has made macrophages a particularly attractive target for biomaterial-directed regenerative medicine strategies. However, macrophages also contribute to adverse inflammatory and fibrotic responses to implanted biomaterials, typically related to the foreign body response (FBR). The traditional model in the field asserts that the M2 macrophage phenotype is pro-regenerative and associated with positive wound healing outcomes, whereas the M1 phenotype is pro-inflammatory and associated with pathogenesis. However, recent studies indicate that both M1 and M2 macrophages play different, but equally vital, roles in promoting tissue repair. Furthermore, recent technological developments such as single-cell RNA sequencing have allowed for unprecedented insights into the heterogeneity within the myeloid compartment, related to activation state, niche, and ontogenetic origin. A better understanding of the phenotypic and functional characteristics of macrophages critical to tissue repair and FBR processes will allow for rational design of biomaterials to promote biomaterial-tissue integration and regeneration. In this review, we discuss the role of temporal and ontogenetic macrophage heterogeneity on tissue repair processes and the FBR and the potential implications for biomaterial-directed regenerative medicine applications. STATEMENT OF SIGNIFICANCE: This review outlines the contributions of different macrophage phenotypes to different phases of wound healing and angiogenesis. Pathological outcomes, such as chronic inflammation, fibrosis, and the foreign body response, related to disruption of the macrophage inflammation-resolution process are also discussed. We summarize recent insights into the vast heterogeneity of myeloid cells related to their niche, especially the biomaterial microenvironment, and ontogenetic origin. Additionally, we present a discussion on novel tools that allow for resolution of cellular heterogeneity at the single-cell level and how these can be used to build a better understanding of macrophage heterogeneity in the biomaterial immune microenvironment to better inform immunomodulatory biomaterial design.

Different Phenotypes in Asthma: Clinical Findings and Experimental Animal Models

Asthma is a respiratory allergic disease presenting a high prevalence worldwide, and it is responsible for several complications throughout life, including death. Fortunately, asthma is no longer recognized as a unique manifestation but as a very heterogenic manifestation. Its phenotypes and endotypes are known, respectively, as pathologic and molecular features that might not be directly associated with each other. The increasing number of studies covering this issue has brought significant insights and knowledge that are constantly expanding. In this review, we intended to summarize this new information obtained from clinical studies, which not only allowed for the creation of patient clusters by means of personalized medicine and a deeper molecular evaluation, but also created a connection with data obtained from experimental models, especially murine models. We gathered information regarding sensitization and trigger and emphasizing the most relevant phenotypes and endotypes, such as Th2-^high asthma and Th2-^low asthma, which included smoking and obesity-related asthma and mixed and paucigranulocytic asthma, not only in physiopathology and the clinic but also in how these phenotypes can be determined with relative similarity using murine models. We also further investigated how clinical studies have been treating patients using newly developed drugs focusing on specific biomarkers that are more relevant according to the patient's clinical manifestation of the disease.

Pattern recognition receptor expression and maturation profile of dendritic cell subtypes in human tonsils and lymph nodes

Dendritic cells (DCs) with capacity of antigen cross-presentation are of key interest for immunotherapy against cancer as they can induce antigen-specific cytotoxic T lymphocyte (CTL) responses. This study describes frequencies of DC subtypes in human tonsils and lymph nodes, and phenotypic aspects that may be targeted by adjuvant measures. From human tonsils and neck lymph nodes, DCs were identified through flow cytometry, and subsets of plasmacytoid DCs (pDCs) and myeloid DCs (mDCs) were investigated. Maturity status was assessed and surface receptors with CTL-promoting potentials were studied. CD123⁺ pDCs as well as CD1c⁺, CD141⁺, and CD1c^-CD141^- mDCs were detected in tonsils and lymph nodes. Both sites featured a similar presence of DC subsets, with CD123⁺ pDC being dominant and CD141⁺ mDCs least frequent. Based on CD80/CD86 expression, all DC subtypes featured a low degree of maturation. Expression of pattern recognition receptors (PRRs) CD206, CD207, DC-SIGN, TLR2, and TLR4, as well as the chemokine receptor XCR1, indicated DC subset-specific receptor profiles. We conclude that tonsils and lymph nodes share common features in terms of DC subset frequency and maturation as well as PRR and XCR1 expression pattern. Our work suggests that both sites may be considered for vaccine deposition in DC-mediated immunotherapy.

An Nphp1 knockout mouse model targeting exon 2-20 demonstrates characteristic phenotypes of human Nephronophthisis

Nephronophthisis (NPH) is the most prevalent monogenetic disorder leading to end-stage renal failure (ESRD) in childhood. Mutations in Nphp1, encoding a cilia-localized protein, account for the majority of NPH cases. Despite its identification many years ago, Nphp1 deletions targeting exon 4 or exon 20 have not reproduced the histological features of human NPH in murine models. In this study, we deleted exon 2-20 of Nphp1 by CRISPR/Cas9 gene editing to create a near-total knockout (KO) mouse model (Nphp1del2-20/del2-20). Nphp1del2-20/del2-20 mice faithfully reproduced the renal and extrarenal phenotypes associated with human NPH, including renal cyst development, tubular basement membrane thickening, retinal degeneration and abnormal spermatogenesis. Importantly, Nphp1 re-expression using an adenoviral-associated-virus-9 (AAV9) vector could partially rescue both renal and retinal phenotypes in Nphp1del2-20/del2-20 mice. Our results reported the first relevant Nphp1 mouse model with renal phenotypes for human disease. It will be a valuable model for future studies of Nphp1 function and to develop novel treatments for this common childhood disease.

Monocytes and Macrophages in Kidney Transplantation and Insights from Single Cell RNA-Seq Studies

Single-cell RNA sequencing (scRNA-seq) is a powerful technology that allows for the identification of minority cell types in complex tissues, such as immune cells in the kidney. Previously, gene expression from infrequent cell types was missed using bulk RNA-sequencing methods due to an averaging effect. Additionally, scRNA-seq facilitates assignment of cell origin in a sample, a shortcoming of previous bulk sequencing technologies. Thus, scRNA-seq is ideal to study the immune cell landscape and the alloimmune response in the human kidney transplant. However, there are few studies published to date. Macrophages are known to play an important role in health and disease in the kidney. Furthermore, it is known that macrophages play key roles in rejection of the kidney transplant. The definition, ontogeny, and function of these cells is complex and nomenclature has evolved as new technologies have become available. In this review, an overview is provided of monocyte and macrophage nomenclature, ontogeny, and function, with a specific focus on kidney transplantation, and including novel scRNA-seq findings. scRNA-seq offers an unbiased transcriptional approach to defining macrophages and provides insights into macrophage ontogeny and function not possible with contemporary methods.

Review of Dendritic Cells, Their Role in Clinical Immunology, and Distribution in Various Animal Species

Dendritic cells (DCs) are cells derived from the hematopoietic stem cells (HSCs) of the bone marrow and form a widely distributed cellular system throughout the body. They are the most efficient, potent, and professional antigen-presenting cells (APCs) of the immune system, inducing and dispersing a primary immune response by the activation of naïve T-cells, and playing an important role in the induction and maintenance of immune tolerance under homeostatic conditions. Thus, this review has elucidated the general aspects of DCs as well as the current dynamic perspectives and distribution of DCs in humans and in various species of animals that includes mouse, rat, birds, dog, cat, horse, cattle, sheep, pig, and non-human primates. Besides the role that DCs play in immune response, they also play a pathogenic role in many diseases, thus becoming a target in disease prevention and treatment. In addition, its roles in clinical immunology have also been addressed, which include its involvement in transplantation, autoimmune disease, viral infections, cancer, and as a vaccine target. Therefore, based on the current knowledge and understanding of the important roles they play, DCs can be used in the future as a powerful tool for manipulating the immune system.

Role of Macrophages and Related Cytokines in Kidney Disease

Inflammation is a key characteristic of kidney disease, but this immune response is two-faced. In the acute phase of kidney injury, there is an activation of the immune cells to fight against the insult, contributing to kidney repair and regeneration. However, in chronic kidney diseases (CKD), immune cells that infiltrate the kidney play a deleterious role, actively participating in disease progression, and contributing to nephron loss and fibrosis. Importantly, CKD is a chronic inflammatory disease. In early CKD stages, patients present sub-clinical inflammation, activation of immune circulating cells and therefore, anti-inflammatory strategies have been proposed as a common therapeutic target for renal diseases. Recent studies have highlighted the plasticity of immune cells and the complexity of their functions. Among immune cells, monocytes/macrophages play an important role in all steps of kidney injury. However, the phenotype characterization between human and mice immune cells showed different markers; therefore the extrapolation of experimental studies in mice could not reflect human renal diseases. Here we will review the current information about the characteristics of different macrophage phenotypes, mainly focused on macrophage-related cytokines, with special attention to the chemokine CCL18, and its murine functional homolog CCL8, and the macrophage marker CD163, and their role in kidney pathology.

Insights Into Dendritic Cells in Cancer Immunotherapy: From Bench to Clinical Applications

Dendritic cells (DCs) are efficient antigen-presenting cells (APCs) and potent activators of naïve T cells. Therefore, they act as a connective ring between innate and adaptive immunity. DC subsets are heterogeneous in their ontogeny and functions. They have proven to potentially take up and process tumor-associated antigens (TAAs). In this regard, researchers have developed strategies such as genetically engineered or TAA-pulsed DC vaccines; these manipulated DCs have shown significant outcomes in clinical and preclinical models. Here, we review DC classification and address how DCs are skewed into an immunosuppressive phenotype in cancer patients. Additionally, we present the advancements in DCs as a platform for cancer immunotherapy, emphasizing the technologies used for in vivo targeting of endogenous DCs, ex vivo generated vaccines from peripheral blood monocytes, and induced pluripotent stem cell-derived DCs (iPSC-DCs) to boost antitumoral immunity.

Acute stress increases monocyte levels and modulates receptor expression in healthy females

There has been a growing recognition of the involvement of the immune system in stress-related disorders. Acute stress leads to the activation of neuroendocrine systems, which in turn orchestrate a large-scale redistribution of innate immune cells, such as monocytes. Even though acute stress/monocyte interactions have been well-characterized in mice, this is not the case for humans. As such, this study aimed to investigate whether acute stress modulates blood monocyte levels in a subtype-dependent manner and whether the receptor expression of stress-related receptors is affected in humans. Blood was collected from healthy female volunteers at baseline and 1 h after the socially evaluated cold pressor test, after which blood monocyte levels and receptor expression were assessed by flow cytometry. Our results reveal a stress-induced increase in blood monocyte levels, which was independent of monocyte subtypes. Furthermore, colony stimulating factor 1 receptor (CSF-1R) and CD29 receptor expression was increased, while CD62L showed a trend towards increased expression. These results provide novel insights into how acute stress affects the innate immune system.

Different Sensitivity of Macrophages to Phospholipidosis Induction by Amphiphilic Cationic Drugs

Phospholipidosis (PLD), the intracellular accumulation of phospholipids, is an adaptive response to toxic stimuli and serves as an important parameter in the biological assessment of compounds. Cationic amphiphilic drugs are the main inducers of PLD and may impair the function of alveolar macrophages. In vivo and in vitro models are used for PLD screening but the choice of the cellular model may be important because PLD develops in a cell- and species-specific manner. In this study, a panel of different staining (LysoSensor, Acridine Orange, Nile Red, HCS LipidTOX, LysoID) was evaluated in murine (DMBM-2, J774, RAW264.7) and human (THP-1, monocyte-derived macrophages from peripheral blood) cells to identify the most sensitive and easy to analyze staining method and to detect species-specific differences in the reaction pattern. Amiodarone and chloroquine served as inducers of PLD. High content screening was used to compare number, area, and intensity of the staining. Due to the fast staining protocol and the sensitivity of the detection, LysoID proved to be the most suitable dye of the testing. The lower induction of PLD by chloroquine reported in vivo was also seen in this study. THP-1 macrophages, followed by DMBM-2 cells, produced the most similar reaction pattern to human monocyte-derived macrophages.

Human and Mouse Transcriptome Profiling Identifies Cross-Species Homology in Pulmonary and Lymph Node Mononuclear Phagocytes

The mononuclear phagocyte (MP) system consists of macrophages, monocytes, and dendritic cells (DCs). MP subtypes play distinct functional roles in steady-state and inflammatory conditions. Although murine MPs are well characterized, their pulmonary and lymph node (LN) human homologs remain poorly understood. To address this gap, we have created a gene expression compendium across 24 distinct human and murine lung and LN MPs, along with human blood and murine spleen MPs, to serve as validation datasets. In-depth RNA sequencing identifies corresponding human-mouse MP subtypes and determines marker genes shared and divergent across species. Unexpectedly, only 13%-23% of the top 1,000 marker genes (i.e., genes not shared across species-specific MP subtypes) overlap in corresponding human-mouse MP counterparts. Lastly, CD88 in both species helps distinguish monocytes/macrophages from DCs. Our cross-species expression compendium serves as a resource for future translational studies to investigate beforehand whether pursuing specific MP subtypes or genes will prove fruitful.

Harmful and beneficial effects of inflammatory response on reproduction: sterile and pathogen-associated inflammation

In reproduction, inflammatory processes play important roles in the development of many pregnancy complications such as preterm labor/birth, recurrent pregnancy loss, recurrent implantation failure, and preeclampsia. Inflammation can be initiated by both microbial and non-microbial causes. Bacterial infection in the feto-maternal interface and uterus can provoke preterm labor/birth, miscarriage, and chronic endometritis. By contrast, inflammation without infection, or 'sterile inflammation,' can also lead to many kinds of complications, such as preterm labor/birth, miscarriage, or preeclampsia. Aberrant inflammation is facilitated by immune cells such as macrophages, dendritic cells, natural killer cells, and invariant natural killer T cells. In addition, cytokines, chemokines, and several kinds of inflammatory mediators are involved. On the other hand, appropriate inflammation is required for a successful offspring during the progression of the entire pregnancy. Herein, we discuss the relation between pregnancy and inflammation with immunological alterations. Understanding the role of inflammation in complications during pregnancy may establish new perspectives of the progress of normal pregnancy as well as treatments during pregnancy complications.

IL-34 Actions on FOXP3+ Tregs and CD14+ Monocytes Control Human Graft Rejection

Cytokines are major players regulating immune responses toward inflammatory and tolerogenic results. In organ and bone marrow transplantation, new reagents are needed to inhibit tissue destructive mechanisms and eventually induce immune tolerance without overall immunosuppression. IL-34 is a cytokine with no significant homology with any other cytokine but that acts preferentially through CSF-1R, as CSF-1 does, and through PTPζ and CD138. Although IL-34 and CSF-1 share actions, a detailed analysis of their effects on immune cells needs further research. We previously showed that both CD4⁺ and CD8⁺ FOXP3⁺ Tregs suppress effector T cells through the production of IL-34, but not CSF-1, and that this action was mediated through antigen-presenting cells. We showed here by single-cell RNAseq and cytofluorimetry that different subsets of human monocytes expressed different levels of CSF-1R, CD138, and PTPζ and that both CD4⁺ and CD8⁺ FOXP3⁺ Tregs expressed higher levels of CSF-1R than conventional T cells. The effects of IL-34 differed in the survival of these different subpopulations of monocytes and RNAseq analysis showed several genes differentially expressed between IL-34, CSF-1, M0, M1, and also M2 macrophages. Acute graft-vs.-host disease (aGVHD) in immunodeficient NSG mice injected with human PBMCs was decreased when treated with IL-34 in combination with an anti-CD45RC mAb that depleted conventional T cells. When IL-34-differentiated monocytes were used to expand Tregs in vitro, both CD4⁺ and CD8⁺ FOXP3⁺ Tregs were highly enriched and this effect was superior to the one obtained with CSF-1. Human CD8⁺ Tregs expanded in vitro with IL-34-differentiated allogeneic monocytes suppressed human immune responses in an NSG mouse aGVHD model humanized with hPBMCs. Overall, we showed that IL-34 induced the differentiation of human monocytes with a particular transcriptional profile and these cells favored the development of potent suppressor FOXP3⁺ Tregs.

Novel multiparameter correlates of Coxiella burnetii infection and vaccination identified by longitudinal deep immune profiling

Q-fever is a flu-like illness caused by Coxiella burnetii (Cb), a highly infectious intracellular bacterium. There is an unmet need for a safe and effective vaccine for Q-fever. Correlates of immune protection to Cb infection are limited. We proposed that analysis by longitudinal high dimensional immune (HDI) profiling using mass cytometry combined with other measures of vaccination and protection could be used to identify novel correlates of effective vaccination and control of Cb infection. Using a vaccine-challenge model in HLA-DR transgenic mice, we demonstrated significant alterations in circulating T-cell and innate immune populations that distinguished vaccinated from naïve mice within 10 days, and persisted until at least 35 days post-vaccination. Following challenge, vaccinated mice exhibited reduced bacterial burden and splenomegaly, along with distinct effector T-cell and monocyte profiles. Correlation of HDI data to serological and pathological measurements was performed. Our data indicate a Th1-biased response to Cb, consistent with previous reports, and identify Ly6C, CD73, and T-bet expression in T-cell, NK-cell, and monocytic populations as distinguishing features between vaccinated and naïve mice. This study refines the understanding of the integrated immune response to Cb vaccine and challenge, which can inform the assessment of candidate vaccines for Cb.

Molecular mechanisms of dendritic cell migration in immunity and cancer

Dendritic cells (DCs) are a heterogeneous population of antigen-presenting cells that act to bridge innate and adaptive immunity. DCs are critical in mounting effective immune responses to tissue damage, pathogens and cancer. Immature DCs continuously sample tissues and engulf antigens via endocytic pathways such as phagocytosis or macropinocytosis, which result in DC activation. Activated DCs undergo a maturation process by downregulating endocytosis and upregulating surface proteins controlling migration to lymphoid tissues where DC-mediated antigen presentation initiates adaptive immune responses. To traffic to lymphoid tissues, DCs must adapt their motility mechanisms to migrate within a wide variety of tissue types and cross barriers to enter lymphatics. All steps of DC migration involve cell-cell or cell-substrate interactions. This review discusses DC migration mechanisms in immunity and cancer with a focus on the role of cytoskeletal processes and cell surface proteins, including integrins, lectins and tetraspanins. Understanding the adapting molecular mechanisms controlling DC migration in immunity provides the basis for therapeutic interventions to dampen immune activation in autoimmunity, or to improve anti-tumour immune responses.

Targeting of CD163+ Macrophages in Inflammatory and Malignant Diseases

The macrophage is a key cell in the pro- and anti-inflammatory response including that of the inflammatory microenvironment of malignant tumors. Much current drug development in chronic inflammatory diseases and cancer therefore focuses on the macrophage as a target for immunotherapy. However, this strategy is complicated by the pleiotropic phenotype of the macrophage that is highly responsive to its microenvironment. The plasticity leads to numerous types of macrophages with rather different and, to some extent, opposing functionalities, as evident by the existence of macrophages with either stimulating or down-regulating effect on inflammation and tumor growth. The phenotypes are characterized by different surface markers and the present review describes recent progress in drug-targeting of the surface marker CD163 expressed in a subpopulation of macrophages. CD163 is an abundant endocytic receptor for multiple ligands, quantitatively important being the haptoglobin-hemoglobin complex. The microenvironment of inflammation and tumorigenesis is particular rich in CD163⁺ macrophages. The use of antibodies for directing anti-inflammatory (e.g., glucocorticoids) or tumoricidal (e.g., doxorubicin) drugs to CD163⁺ macrophages in animal models of inflammation and cancer has demonstrated a high efficacy of the conjugate drugs. This macrophage-targeting approach has a low toxicity profile that may highly improve the therapeutic window of many current drugs and drug candidates.

Macrophages Derived From Human Induced Pluripotent Stem Cells Are Low-Activated "Naïve-Like" Cells Capable of Restricting Mycobacteria Growth

In peripheral tissues, immune protection critically depends on the activity of tissue resident macrophages, which makes our understanding of the biology of these cells of great significance. Until recently, human macrophage studies were largely based on the analysis of monocyte-derived macrophages that differ from tissue resident macrophages by many characteristics. To model tissue resident macrophages, methods of generating macrophages from pluripotent stem cells have been developed. However, the immunological properties of macrophages derived from pluripotent stem cells remain under-investigated. In this study, we aimed to perform the multifarious immunological characteristics of macrophages generated from human induced pluripotent stem cells (iMϕs), including an analysis of their phenotype, secretory and antibacterial activities, as well as their comparison with macrophages derived from blood monocytes and infected lung tissue. We report that iMϕs displayed the morphology and the CD11b⁺CD45⁺CD14⁺ phenotype typical for mononuclear phagocytes. The cells co-expressed markers known to be associated with classically (CD80, CD86, CCR5) and alternatively (CD163 and CD206) activated macrophages, with a bias toward a higher expression of the latter. iMϕs secreted pro-inflammatory (IL-6, CXCL8, CCL2, CCL4, CXCL1, CXCL10) and anti-inflammatory (IL-10, IL-1RA, CCL22) cytokines with a high IL-10/IL-12p70 index (>20). iMϕs were phagocytic and restricted Mycobacterium tuberculosis growth in vitro by >75%. iMϕs differed from blood monocytes/macrophages by a lower expression level of HLA-DR and the CD14⁺CD16^int phenotype and shared several phenotypic characteristics with lung macrophages. In response to LPS, iMϕs up-regulated HLA-DR and produced TNF-α. IFN-γ increased iMϕ reactivity to LPS, but did not increase iMϕ mycobactericidal capacity. The results characterize iMϕs as differentiated but low-activated/low-polarized “naïve-like” macrophages that are capable of mounting inflammatory and antibacterial responses when exposed to inflammatory stimuli or pathogens. iMϕs represent a valuable model for studying antibacterial responses of tissue resident macrophages and for developing approaches to modulating macrophage activity.

Secretory Functions of Macrophages in the Human Pancreatic Islet Are Regulated by Endogenous Purinergic Signaling

Endocrine cells of the pancreatic islet interact with their microenvironment to maintain tissue homeostasis. Communication with local macrophages is particularly important in this context, but the homeostatic functions of human islet macrophages are not known. In this study, we show that the human islet contains macrophages in perivascular regions that are the main local source of the anti-inflammatory cytokine interleukin-10 (IL-10) and the metalloproteinase MMP9. Macrophage production and secretion of these homeostatic factors are controlled by endogenous purinergic signals. In obese and diabetic states, macrophage expression of purinergic receptors MMP9 and IL-10 is reduced. We propose that in those states, exacerbated β-cell activity due to increased insulin demand and increased cell death produce high levels of ATP that downregulate purinergic receptor expression. Loss of ATP sensing in macrophages may reduce their secretory capacity.

Tumor associated macrophages and 'NO'

Nitric oxide (NO) and its pro and anti-tumor activities are dual roles that continue to be debated in cancer biology. The cell situations in the tumor and within the tumor microenvironment also have roles involving NO. In early tumorigenic events, macrophages in the tumor microenvironment promote tumor cell death, and later are reprogramed to support the growth of tumor, through regulatory events involving NO and several stimulatory signals. These two opposing and active phenotypes of tumor associated macrophages known as the M1 or anti-tumorigenic state and M2 or pro-tumorigenic state show differences in metabolic pathways such as glycolysis and arginine utilization, signaling pathways and cytokine induction including iNOS expression, therefore contributing to their function. Polarization of M2 to M1 macrophages, inhibition of M2 state, or reprogramming via NO in combination with other signals may determine or alter tumor kinetics. These strategies and an overview are presented.

The quest for faithful in vitro models of human dendritic cells types

Dendritic cells (DCs) are mononuclear phagocytes that are specialized in the induction and functional polarization of effector lymphocytes, thus orchestrating immune defenses against infections and cancer. The population of DC encompasses distinct cell types that vary in their efficacy for complementary functions and are thus likely involved in defending the body against different threats. Plasmacytoid DCs specialize in the production of high levels of the antiviral cytokines type I interferons. Type 1 conventional DCs (cDC1s) excel in the activation of cytotoxic CD8⁺ T cells (CTLs) which are critical for defense against cancer and infections by intracellular pathogens. Type 2 conventional DCs (cDC2s) prime helper CD4⁺ T cells for the production of type 2 cytokines underpinning immune defenses against worms or of IL-17 promoting control of infections by extracellular bacteria or fungi. Hence, clinically manipulating the development and functions of DC types could have a major impact for improving treatments against many diseases. However, the rarity and fragility of human DC types is impeding advancement towards this goal. To overcome this roadblock, major efforts are ongoing to generate in vitro large numbers of distinct human DC types. We review here the current state of this research field, emphasizing recent breakthrough and proposing future priorities. We also pinpoint the necessity to develop a consensus nomenclature and rigorous methodologies to ensure proper identification and characterization of human DC types. Finally, we elaborate on how faithful in vitro models of human DC types can accelerate our understanding of the biology of these cells and the engineering of next generation vaccines or immunotherapies against viral infections or cancer.

Reconstructing human DC, monocyte and macrophage development in utero using single cell technologies

The repertoire of dendritic cells (DCs), monocytes and macrophages in adult humans is diverse and we are appreciating this to a greater extent as high throughput methods, such a single-cell RNA sequencing, become widely adopted and scalable. This powerful lens of analysis is also beginning to shed light on prenatal immunology, allowing us to chart the emergence, tissue distribution and developmental regulation of DCs, monocytes and macrophages during early human life. In this review, we will integrate recent insights from studies of the developing immune system into our understanding of adult DC, monocyte and macrophage organization, illustrating where insights from early life both affirm and challenge current understanding.

Structure and function of the immune system in the spleen

The spleen is the largest secondary lymphoid organ in the body and, as such, hosts a wide range of immunologic functions alongside its roles in hematopoiesis and red blood cell clearance. The physical organization of the spleen allows it to filter blood of pathogens and abnormal cells and facilitate low-probability interactions between antigen-presenting cells (APCs) and cognate lymphocytes. APCs specific to the spleen regulate the T and B cell response to these antigenic targets in the blood. This review will focus on cell types, cell organization, and immunologic functions specific to the spleen and how these affect initiation of adaptive immunity to systemic blood-borne antigens. Potential differences in structure and function between mouse and human spleen will also be discussed.

Cripto shapes macrophage plasticity and restricts EndMT in injured and diseased skeletal muscle

Macrophages are characterized by a high plasticity in response to changes in tissue microenvironment, which allows them to acquire different phenotypes and to exert essential functions in complex processes, such as tissue regeneration. Here, we report that the membrane protein Cripto plays a key role in shaping macrophage plasticity in skeletal muscle during regeneration and disease. Conditional deletion of Cripto in the myeloid lineage (Cripto^My‐LOF) perturbs MP plasticity in acutely injured muscle and in mouse models of Duchenne muscular dystrophy (mdx). Specifically, Cripto^My‐LOF macrophages infiltrate the muscle, but fail to properly expand as anti‐inflammatory CD206⁺ macrophages, which is due, at least in part, to aberrant activation of TGFβ/Smad signaling. This reduction in macrophage plasticity disturbs vascular remodeling by increasing Endothelial‐to‐Mesenchymal Transition (EndMT), reduces muscle regenerative potential, and leads to an exacerbation of the dystrophic phenotype. Thus, in muscle‐infiltrating macrophages, Cripto is required to promote the expansion of the CD206⁺ anti‐inflammatory macrophage type and to restrict the EndMT process, providing a direct functional link between this macrophage population and endothelial cells.

Immunophenotyping monocytes, macrophages and granulocytes in the Pteropodid bat Eonycteris spelaea

Bats are asymptomatic reservoir hosts for several highly pathogenic viruses. Understanding this enigmatic relationship between bats and emerging zoonotic viruses requires tools and approaches which enable the comparative study of bat immune cell populations and their functions. We show that bat genomes have a conservation of immune marker genes which delineate phagocyte populations in humans, while lacking key mouse surface markers such as Ly6C and Ly6G. Cross-reactive antibodies against CD44, CD11b, CD14, MHC II, and CD206 were multiplexed to characterize circulating monocytes, granulocytes, bone-marrow derived macrophages (BMDMs) and lung alveolar macrophages (AMs) in the cave nectar bat Eonycteris spelaea. Transcriptional profiling of bat monocytes and BMDMs identified additional markers – including MARCO, CD68, CD163, CD172α, and CD88 – which can be used to further characterize bat myeloid populations. Bat cells often resembled their human counterparts when comparing immune parameters that are divergent between humans and mice, such as the expression patterns of certain immune cell markers. A genome-wide comparison of immune-related genes also revealed a much closer phylogenetic relationship between bats and humans compared to rodents. Taken together, this study provides a set of tools and a comparative framework which will be important for unravelling viral disease tolerance mechanisms in bats.

Dendritic cell subsets in T cell programming: location dictates function

Dendritic cells (DCs) can be viewed as translators between innate and adaptive immunity. They integrate signals derived from tissue infection or damage and present processed antigen from these sites to naive T cells in secondary lymphoid organs while also providing multiple soluble and surface-bound signals that help to guide T cell differentiation. DC-mediated tailoring of the appropriate T cell programme ensures a proper cascade of immune responses that adequately targets the insult. Recent advances in our understanding of the different types of DC subsets along with the cellular organization and orchestration of DC and lymphocyte positioning in secondary lymphoid organs over time has led to a clearer understanding of how the nature of the T cell response is shaped. This Review discusses how geographical organization and ordered sequences of cellular interactions in lymph nodes and the spleen regulate immunity.

Interplay Between Macrophages and Angiogenesis: A Double-Edged Sword in Liver Disease

During chronic liver disease, macrophages support angiogenesis, not only by secreting proangiogenic growth factors and matrix-remodeling proteases, but also by physically interacting with the sprouting vasculature to assist the formation of complex vascular networks. In the liver, macrophages acquire specific characteristics becoming Kupffer cells and working to ensure protection and immunotolerance. Angiogenesis is another double-edged sword in health and disease and it is the biggest ally of macrophages allowing its dissemination. Angiogenesis and fibrosis may occur in parallel in several tissues as macrophages co-localize with newly formed vessels and secrete cytokines, interleukins, and growth factors that will activate other cell types in the liver such as hepatic stellate cells and liver sinusoidal endothelial cells, promoting extracellular matrix accumulation and fibrogenesis. Vascular endothelial growth factor, placental growth factor, and platelet-derived growth factor are the leading secreted factors driving pathological angiogenesis and consequently increasing macrophage infiltration. Tumor development in the liver has been widely linked to macrophage-mediated chronic inflammation in which epidermal growth factors, STAT3 and NF-kβ are some of the most relevant signaling molecules involved. In this article, we review the link between macrophages and angiogenesis at molecular and cellular levels in chronic liver disease.

Endocytosis mechanism in physiologically-based pharmacokinetic modeling of nanoparticles

BACKGROUND

The physiologically based pharmacokinetic (PBPK) model is a useful tool to predict the pharmacokinetics of various types of nanoparticles (NPs). The endocytosis mechanism plays a key role in pharmacokinetics of NPs. However, the effect of endocytosis mechanism both in the blood and tissue are seldom considered in PBPK model.

OBJECTIVES

To investigate the biodistribution of intravenously injected pegylated AuNPs in mice and human using PBPK model considering the endocytosis mechanism both in the blood and tissue.

METHODS

Taking polyethylene glycol-coated gold nanoparticles (AuNPs) as an example, we developed a PBPK model to explore biodistribution of different size AuNPs. In the model, we considered the role of endocytosis mechanism both in the blood and tissue. In addition, the size-dependent permeability coefficient, excretion rate constant, phagocytic capacity, uptake rate, and release rate were derived from literatures. The mice PBPK model was extrapolated to the human by changing physiology parameters and the number of phagocytic cell (PCs).

RESULTS

AuNPs were primarily distributed in the blood, liver, and spleen regardless of particle size, and almost all captured by the PCs in the liver and spleen, while few was captured in the blood. There are more organ distribution and longer circulation for smaller NPs. The 24-h accumulation of AuNPs decreased with increasing size in the most organ, while the accumulation of AuNPs showed an inverted U-shaped curve in the liver and slight U-shaped curve in the blood. The human results of model-predicted displayed a similar tendency with those in mice. Size, partition coefficients, and body weight were the key factors influencing the organ distribution of AuNPs.

CONCLUSIONS

The size played an important role on the distribution and accumulation of AuNPs in various tissues. Our PBPK model was well predicted the NPs distribution in mice and human. A better understanding of these mechanisms could provide effective guides for nanomedine delivery.

Myeloid and Plasmacytoid Dendritic Cells and Cancer - New Insights

Dendritic cells (DCs) use effective mechanisms to combat antigens and to bring about adaptive immune responses through their ability to stimulate näive T cells. At present, four major cell types are categorised as DCs: Classical or conventional (cDCs), Plasmacytoid (pDCs), Langerhans cells (LCs), and monocyte-derived DCs (Mo-DCs). It was suggested that pDCs, CD1c+ DCs and CD141+ DCs in humans are equivalent to mouse pDCs, CD11b+ DCs and CD8α+ DCs, respectively. Human CD141+ DCs compared to mouse CD8α+ DCs have remarkable functional and transcriptomic similarities. Characteristic markers, transcription factors, toll-like receptors, T helpers (Th) polarisation, cytokines, etc. of DCs are discussed in this review. Major histocompatibility complex (MHC) I and II antigen presentation, cross-presentation and Th polarisation are defined, and the dual role of DCs in the tumour is discussed. Human DCs are the main immune cells that orchestrate the immune response in the tumour microenvironment.

The Role of Innate Leukocytes during Influenza Virus Infection

Influenza virus infection is a serious threat to humans and animals, with the potential to cause severe pneumonia and death. Annual vaccination strategies are a mainstay to prevent complications related to influenza. However, protection from the emerging subtypes of influenza A viruses (IAV) even in vaccinated individuals is challenging. Innate immune cells are the first cells to respond to IAV infection in the respiratory tract. Virus replication-induced production of cytokines from airway epithelium recruits innate immune cells to the site of infection. These leukocytes, namely, neutrophils, monocytes, macrophages, dendritic cells, eosinophils, natural killer cells, innate lymphoid cells, and γδ T cells, become activated in response to IAV, to contain the virus and protect the airway epithelium while triggering the adaptive arm of the immune system. This review addresses different anti-influenza virus schemes of innate immune cells and how these cells fine-tune the balance between immunoprotection and immunopathology during IAV infection. Detailed understanding on how these innate responders execute anti-influenza activity will help to identify novel therapeutic targets to halt IAV replication and associated immunopathology.

Innate immune cell-epithelial crosstalk during wound repair

Skin and intestinal epithelial barriers play a pivotal role in protecting underlying tissues from harsh external environments. The protective role of these epithelia is, in part, dependent on a remarkable capacity to restore barrier function and tissue homeostasis after injury. In response to damage, epithelial wounds repair by a series of events that integrate epithelial responses with those of resident and infiltrating immune cells including neutrophils and monocytes/macrophages. Compromise of this complex interplay predisposes to development of chronic nonhealing wounds, contributing to morbidity and mortality of many diseases. Improved understanding of crosstalk between epithelial and immune cells during wound repair is necessary for development of better pro-resolving strategies to treat debilitating complications of disorders ranging from inflammatory bowel disease to diabetes. In this Review we focus on epithelial and innate immune cell interactions that mediate wound healing and restoration of tissue homeostasis in the skin and intestine.

Dendritic Cell-Mediated Th2 Immunity and Immune Disorders

Dendritic cells (DCs) are the professional antigen-presenting cells that recognize and present antigens to naïve T cells to induce antigen-specific adaptive immunity. Among the T-cell subsets, T helper type 2 (Th2) cells produce the humoral immune responses required for protection against helminthic disease by activating B cells. DCs induce a Th2 immune response at a certain immune environment. Basophil, eosinophil, mast cells, and type 2 innate lymphoid cells also induce Th2 immunity. However, in the case of DCs, controversy remains regarding which subsets of DCs induce Th2 immunity, which genes in DCs are directly or indirectly involved in inducing Th2 immunity, and the detailed mechanisms underlying induction, regulation, or maintenance of the DC-mediated Th2 immunity against allergic environments and parasite infection. A recent study has shown that a genetic defect in DCs causes an enhanced Th2 immunity leading to severe atopic dermatitis. We summarize the Th2 immune-inducing DC subsets, the genetic and environmental factors involved in DC-mediated Th2 immunity, and current therapeutic approaches for Th2-mediated immune disorders. This review is to provide an improved understanding of DC-mediated Th2 immunity and Th1/Th2 immune balancing, leading to control over their adverse consequences.

Lipopolysaccharide inhalation recruits monocytes and dendritic cell subsets to the alveolar airspace

Mononuclear phagocytes (MPs) including monocytes, macrophages and dendritic cells (DCs) are critical innate immune effectors and initiators of the adaptive immune response. MPs are present in the alveolar airspace at steady state, however little is known about DC recruitment in acute pulmonary inflammation. Here we use lipopolysaccharide inhalation to induce acute inflammation in healthy volunteers and examine the impact on bronchoalveolar lavage fluid and blood MP repertoire. Classical monocytes and two DC subsets (DC2/3 and DC5) are expanded in bronchoalveolar lavage fluid 8 h after lipopolysaccharide inhalation. Surface phenotyping, gene expression profiling and parallel analysis of blood indicate recruited DCs are blood-derived. Recruited monocytes and DCs rapidly adopt typical airspace-resident MP gene expression profiles. Following lipopolysaccharide inhalation, alveolar macrophages strongly up-regulate cytokines for MP recruitment. Our study defines the characteristics of human DCs and monocytes recruited into bronchoalveolar space immediately following localised acute inflammatory stimulus in vivo.

The diversity of human mononuclear phagocyte subsets remains to be characterized in many tissue-specific and functional contexts, including pulmonary inflammation. Here the authors characterize dendritic cell and monocyte subset recruitment to the bronchoalveolar space in a human LPS inhalation model.