Scavenger receptors: role in innate immunity and microbial pathogenesis

Role of CD163 in PRRSV infection

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly infectious agent that poses a significant economic threat to the global swine industry. Efficient viral entry relies on interactions with cellular receptors, with CD163-a cysteine-rich scavenger receptor found on porcine alveolar macrophages (PAMs)-playing a critical role. Extensive evidence supports CD163's essential function in PRRSV infection. This review synthesizes current knowledge about CD163's role, examining its structure-function relationship and identifying specific regions crucial for viral entry. We evaluate the established role of CD163 in PRRSV pathogenesis and highlight areas requiring further investigation, along with the potential for targeted therapeutic interventions. Understanding the molecular determinants of CD163's function is vital for developing effective strategies to control PRRSV infection and mitigate its economic impact on swine production. Further research into the PRRSV-CD163 interactions will be crucial for creating novel antiviral strategies.

The role of pattern recognition receptors in the innate immune system of Chinese mitten crab (Eriocheir sinensis)

Eriocheir sinensis (Chinese mitten crab) is one of the main economic species in China, which has evolved an extremely sophisticated innate immune system to fend off disease invasions. However, bacterial and viral infections have caused significant financial losses for the E. sinensis aquaculture in recent years. Making well-informed judgments for the control microbial infections would require a thorough understanding and clarification of the intricate innate immune system of E. sinensis. Innate immunity is essential for the host's defense against invasive pathogens. Pattern recognition receptors (PRRs) initially recognize pathogen-associated molecular patterns (PAMPs) and trigger an innate immune response, causing the generation of inflammatory cytokine and promoting the clearance and control of pathogens. In E. sinensis, Toll/Toll-like receptors, lipopolysaccharide and β-1,3-glucan binding proteins, C-type lectins, galactoside-binding lectins, L-type lectins, scavenger receptors, and down syndrome cell adhesion molecules have been identified to be PRRs that are involved in the recognition of bacteria, fungi, and viruses. In this review, we give a comprehensive overview of the literature regarding PRRs' roles in the immunological defenses of E. sinensis, with the aim of providing clues to the mechanisms of innate immunity.

Microglia in retinal diseases: From pathogenesis towards therapeutic strategies

Microglia, a widely dispersed cohort of immune cells in the retina, are intricately involved in a diverse range of pivotal biological processes, including inflammation, vascular development, complement activation, antigen presentation, and phagocytosis. Within the retinal milieu, microglia are crucial for the clearance of dead cells and cellular debris, release of anti-inflammatory agents, and orchestration of vascular network remodeling to maintain homeostasis. In addition, microglia are key mediators of neuroinflammation. Triggered by oxidative stress, elevated intraocular pressure, genetic anomalies, and immune dysregulation, microglia release numerous inflammatory cytokines, contributing to the pathogenesis of various retinal disorders. Recent studies on the ontogeny and broad functions of microglia in the retina have elucidated their characteristics during retinal development, homeostasis, and disease. Furthermore, therapeutic strategies that target microglia and their effector cytokines have been developed and shown positive results for some retinal diseases. Therefore, we systematically review the microglial ontogeny in the retina, elucidate their dual roles in retinal homeostasis and disease pathogenesis, and demonstrate microglia-based targeted therapeutic strategies for retinal diseases.

Genome-wide identification, characterization, molecular evolution and expression profiling analysis of scavenger receptors in black rockfish (Sebastes schlegelii)

The scavenger receptors (SRs) gene family is considered as the membrane-associated pattern recognition receptors that plays important roles in the immune responses of organisms. However, there is currently limited research on the systematic identification of the SRs gene family in teleost and their role in the innate immunity of S. schegelii. In this study, we identified and annotated 15 SRs genes in S. schegelii. Through phylogenetic analysis, analysis of conserved domains, gene structure, and motif composition, we found that SRs gene family within different classes were relatively conserved. Additionally, we used qRT-PCR to analyze the expression patterns of SRs genes in immune-related tissues from healthy and Acinetobacter johnsonii-infected S. schegelii. The results showed that SRs genes exhibited different tissue expression patterns and the expression of SRs genes significantly changed after A. johnsonii infection. These results provided a valuable basis for further understanding of the functions of SRs in the innate immune response of S. schegelii.

Genome and tissue-specific transcriptomes of the large-polyp coral, Fimbriaphyllia (Euphyllia) ancora: a recipe for a coral polyp

Coral polyps are composed of four tissues; however, their characteristics are largely unexplored. Here we report biological characteristics of tentacles (Te), mesenterial filaments (Me), body wall (Bo), and mouth with pharynx (MP), using comparative genomic, morpho-histological, and transcriptomic analyses of the large-polyp coral, Fimbriaphyllia ancora. A draft F. ancora genome assembly of 434 Mbp was created. Morpho-histological and transcriptomic characterization of the four tissues showed that they have distinct differences in structure, primary cellular composition, and transcriptional profiles. Tissue-specific, highly expressed genes (HEGs) of Te are related to biological defense, predation, and coral-algal symbiosis. Me expresses multiple digestive enzymes, whereas Bo expresses innate immunity and biomineralization-related molecules. Many receptors for neuropeptides and neurotransmitters are expressed in MP. This dataset and new insights into tissue functions will facilitate a deeper understanding of symbiotic biology, immunology, biomineralization, digestive biology, and neurobiology in corals.

Targeting Macrophage Polarization for Reinstating Homeostasis following Tissue Damage

Tissue regeneration and remodeling involve many complex stages. Macrophages are critical in maintaining micro-environmental homeostasis by regulating inflammation and orchestrating wound healing. They display high plasticity in response to various stimuli, showing a spectrum of functional phenotypes that vary from M1 (pro-inflammatory) to M2 (anti-inflammatory) macrophages. While transient inflammation is an essential trigger for tissue healing following an injury, sustained inflammation (e.g., in foreign body response to implants, diabetes or inflammatory diseases) can hinder tissue healing and cause tissue damage. Modulating macrophage polarization has emerged as an effective strategy for enhancing immune-mediated tissue regeneration and promoting better integration of implantable materials in the host. This article provides an overview of macrophages' functional properties followed by discussing different strategies for modulating macrophage polarization. Advances in the use of synthetic and natural biomaterials to fabricate immune-modulatory materials are highlighted. This reveals that the development and clinical application of more effective immunomodulatory systems targeting macrophage polarization under pathological conditions will be driven by a detailed understanding of the factors that regulate macrophage polarization and biological function in order to optimize existing methods and generate novel strategies to control cell phenotype.

Cholesterol nanoarchaeosomes for alendronate targeted delivery as an anti-endothelial dysfunction agent

Sodium alendronate (ALN) is a very hydrosoluble and poorly permeable molecule used as an antiresorptive agent and with vascular anticalcifying capacity. Loaded into targeted nanovesicles, its anti-inflammatory activity may be amplified towards extra-osseous and noncalcified target cells, such as severely irritated vascular endothelium. Here cytotoxicity, mitochondrial membrane potential, ATP content, and membrane fluidity of human endothelial venous cells (HUVECs) were determined after endocytosis of ALN-loaded nanoarchaeosomes (nanoARC-Chol(ALN), made of polar lipids from Halorubrum tebenquichense: cholesterol 7:3 w/w, 166 ± 5 nm, 0.16 ± 0.02 PDI, -40.8 ± 5.4 mV potential, 84.7 ± 21 µg/mg ALN/total lipids, TL). The effect of nanoARC-Chol(ALN) was further assessed on severely inflamed HUVECs. To that aim, HUVECs were grown on a porous barrier on top of a basal compartment seeded either with macrophages or human foam cells. One lighter and one more pronounced inflammatory context was modelled by adding lipopolysaccharide (LPS) to the apical or the apical and basal compartments. The endocytosis of nanoARC-Chol(ALN), was observed to partly reduce the endothelial-mesenchymal transition of HUVECs. Besides, while 10 mg/mL dexamethasone, 7.6 mM free ALN and ALN-loaded liposomes failed, 50 μg/mL TL + 2.5 μg/mL ALN (i.e., nanoARC-Chol(ALN)) reduced the IL-6 and IL-8 levels by, respectively, 75% and 65% in the mild and by, respectively, 60% and 40% in the pronounced inflammation model. This is the first report showing that the endocytosis of nanoARC-Chol(ALN) by HUVECs magnifies the anti-inflammatory activity of ALN even under conditions of intense irritation, not only surpassing that of free ALN but also that of dexamethasone.

Structure and function analyses of the SRC gene in Pacific white shrimp Litopenaeus vannamei

SRC gene encodes scavenger receptor class C, a member of the scavenger receptor family, and has only been identified and investigated in invertebrates. Our previous studies have revealed that SRC is a novel candidate gene associated with body weight in Pacific white shrimp (Litopenaeus vannamei). In order to comprehend the underlying mechanism by which LvSRC affects shrimp growth, we analyzed the structure, phylogeny, expression profiles and RNA interference (RNAi) of this gene in L. vannamei. We found that LvSRC contains two CCP domains and one MAM domain, with the highest expression level in the heart and relatively low expression level in other tissues. Notably, LvSRC exhibited significantly higher expression levels in the fast-growing group among groups with different growth rates, suggesting its potential involvement as a gene contributing to the growth of L. vannamei. RNAi of LvSRC inhibited body length and body weight gain compared to the control groups. Moreover, through RNA-seq analysis, we identified 598 differentially expressed genes (DEGs), including genes associated with growth, immunity, protein processing and modification, signal transduction, lipid synthesis and metabolism. Furthermore, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed significant changes in the signaling pathways related to growth, lipid metabolism and immune response, suggesting that LvSRC exhibits the potential to participate in diverse physiological processes and immune regulation. These findings deepen our understanding of the structure and function of the SRC in shrimp and lay the foundation for further research into the regulatory mechanism of LvSRC. Additionally, they provide potential applications in shrimp genetics and breeding.

Cellular localization and potential ligands of a novel scavenger receptor class B/CD36 protein homolog (Pt-SRB2) identified in the marine crab, Portunustrituberculatus

The scavenger receptor class B family proteins (SRB) are multiligand membrane receptor proteins. Herein, a novel SRB homolog (Pt-SRB2) was identified in Portunus trituberculatus. The open reading frame of Pt-SRB2 was predicted to encode 520 amino acid residues comprising a typical CD36 domain. Phylogenetic analysis showed that Pt-SRB2 distinctly clustered with the SRB homologs of most crustaceans and Drosophila but was separate from all vertebrate CD36/SRB. Semi-quantitative and Real-time quantitative PCR revealed that the abundance of Pt-SRB2 transcripts was the highest in hepatopancreas than in other tested tissues. Overexpressed Pt-SRB2 was distributed primarily in the cell membrane and cytoplasm of HEK293T or Drosophila Schneider 2 cells. In crab hemocytes, Pt-SRB2 was distributed primarily in the cell membrane by immunofluorescence staining. In addition, the immunofluorescence staining showed that green fluorescence signals were mainly located in the inner lumen membrane of the hepatopancreatic tubules. Moreover, solid-phase enzyme-linked immunosorbent assay revealed that rPt-SRB2-L exhibited relative high affinity with lipopolysaccharides, and relative moderate binding affinity with lipoteichoic acid or peptidoglycan. Of note, rPt-SRB2-L showed high binding affinity with eicosapentaenoic acid among a series of long-chain polyunsaturated fatty acids. Taken together, this study provided valuable data for understanding the functions of the crab CD36/SRB.

Identification of large yellow croakers (Larimichthys crocea) scavenger receptor genes: Involvement in immune response to Pseudomonas plecoglossicida infection and hypoxia-exposure experiments

Scavenger receptors (SRs) are pattern recognition receptors involved in the innate immune defense against pathogen infection in fish. However, there has not been much research done on teleosts. In this study, 18 members of the SR gene family were found in large yellow croaker. The identification of the SR gene family showed that the protein length of SR members in large yellow croaker were quite different, and most SR genes were distributed in nuclear and endoplasmic. The evolutionary relationship, exon/intron structure and motif analysis revealed that members of the SR gene family were highly conserved. The results of the expression profiles after Pseudomonas plecoglossicida infection and hypoxia-exposure demonstrated that SR members were involved in inflammatory reactions. Especially, COLEC12 and SCARF1 exhibited substantial changes in response to both P. plecoglossicida and hypoxia stress, indicating their possible immunological functions. The result of this study revealed that SR genes played a vital part in the innate immune response of large yellow croaker, and would give important details for a deeper comprehension of the SR gene family's regulation mechanism under various conditions in large yellow croaker.

Biomimetic Systems Involving Macrophages and Their Potential for Targeted Drug Delivery

The concept of targeted drug delivery can be described in terms of the drug systems' ability to mimic the biological objects' property to localize to target cells or tissues. For example, drug delivery systems based on red blood cells or mimicking some of their useful features, such as long circulation in stealth mode, have been known for decades. On the contrary, therapeutic strategies based on macrophages have gained very limited attention until recently. Here, we review two biomimetic strategies associated with macrophages that can be used to develop new therapeutic modalities: first, the mimicry of certain types of macrophages (i.e., the use of macrophages, including tumor-associated or macrophage-derived particles as a carrier for the targeted delivery of therapeutic agents); second, the mimicry of ligands, naturally absorbed by macrophages (i.e., the use of therapeutic agents specifically targeted at macrophages). We discuss the potential applications of biomimetic systems involving macrophages for new advancements in the treatment of infections, inflammatory diseases, and cancer.

Microglial crosstalk with astrocytes and immune cells in amyotrophic lateral sclerosis

In recent years, biomedical research efforts aimed to unravel the mechanisms involved in motor neuron death that occurs in amyotrophic lateral sclerosis (ALS). While the main causes of disease progression were first sought in the motor neurons, more recent studies highlight the gliocentric theory demonstrating the pivotal role of microglia and astrocyte, but also of infiltrating immune cells, in the pathological processes that take place in the central nervous system microenvironment. From this point of view, microglia-astrocytes-lymphocytes crosstalk is fundamental to shape the microenvironment toward a pro-inflammatory one, enhancing neuronal damage. In this review, we dissect the current state-of-the-art knowledge of the microglial dialogue with other cell populations as one of the principal hallmarks of ALS progression. Particularly, we deeply investigate the microglia crosstalk with astrocytes and immune cells reporting in vitro and in vivo studies related to ALS mouse models and human patients. At last, we highlight the current experimental therapeutic approaches that aim to modulate microglial phenotype to revert the microenvironment, thus counteracting ALS progression.

Comparative Characterization of Immune Response in Sheep with Caseous Lymphadenitis through Analysis of the Whole Blood Transcriptome

Caseous lymphadenitis (CL) is a chronic contagious disease that affects small ruminants and is characterized by the formation of pyogranulomas in lymph nodes and other organs. However, the pathogenesis of this disease and the response of the host genome to infection are not yet fully understood. This study aimed to investigate the whole blood transcriptome and evaluate differential gene expression during the later stages of CL in naturally infected ewes. The study included diseased, serologically positive (EP), exposed, serologically negative (EN) ewes from the same infected flock and healthy ewes (CN) from a different flock. RNA sequencing was performed using the Illumina NextSeq system, and differential gene expression was estimated using DESeq2 and Edge R approaches. The analysis identified 191 annotated differentially expressed genes (DEGs) in the EP group (102 upregulated and 89 downregulated) and 256 DEGs in the EN group (106 upregulated and 150 downregulated) compared to the CN group. Numerous immunoregulatory interactions between lymphoid and nonlymphoid cells were influenced in both EP and EN ewes. Immune DEGs were preferentially assigned to antigen presentation through the MHC complex, T lymphocyte-mediated immunity, and extracellular matrix interactions. Furthermore, the EP group showed altered regulation of cytokine and chemokine signaling and activation and recombination of B-cell receptors. Conversely, NF-kappa B signaling, apoptosis, and stress response were the main processes influenced in the EN group. In addition, statistically significant enrichment of the essential immune pathways of binding and uptake of ligands by scavenger receptors in EP and p53 signaling in the EN group was found. In conclusion, this study provides new insights into the disease course and host-pathogen interaction in naturally CL-infected sheep by investigating the blood transcriptome.

COPD Patients Exhibit Distinct Gene Expression, Accelerated Cellular Aging, and Bias to M2 Macrophages

COPD, one of world's leading contributors to morbidity and mortality, is characterized by airflow limitation and heterogeneous clinical features. Three main phenotypes are proposed: overlapping asthma/COPD (ACO), exacerbator, and emphysema. Disease severity can be classified as mild, moderate, severe, and very severe. The molecular basis of inflammatory amplification, cellular aging, and immune response are critical to COPD pathogenesis. Our aim was to investigate EP300 (histone acetylase, HAT), HDAC 2 (histone deacetylase), HDAC3, and HDAC4 gene expression, telomere length, and differentiation ability to M1/M2 macrophages. For this investigation, 105 COPD patients, 42 smokers, and 73 non-smoker controls were evaluated. We identified a reduced HDAC2 expression in patients with mild, moderate, and severe severity; a reduced HDAC3 expression in patients with moderate and severe severity; an increased HDAC4 expression in patients with mild severity; and a reduced EP300 expression in patients with severe severity. Additionally, HDAC2 expression was reduced in patients with emphysema and exacerbator, along with a reduced HDAC3 expression in patients with emphysema. Surprisingly, smokers and all COPD patients showed telomere shortening. COPD patients showed a higher tendency toward M2 markers. Our data implicate genetic changes in COPD phenotypes and severity, in addition to M2 prevalence, that might influence future treatments and personalized therapies.

Tim4, a macrophage receptor for apoptotic cells, binds polystyrene microplastics via aromatic-aromatic interactions

Understanding the interface between microplastics and biological systems will provide new insights into the impacts of microplastics on living organisms. When microplastics enter the body, they are engulfed preferentially by phagocytes such as macrophages. However, it is not fully understood how phagocytes recognize microplastics and how microplastics impact phagocyte functions. In this study, we demonstrate that T cell immunoglobulin mucin 4 (Tim4), a macrophage receptor for phosphatidylserine (PtdSer) on apoptotic cells, binds polystyrene (PS) microparticles as well as multi-walled carbon nanotubes (MWCNTs) through the extracellular aromatic cluster, revealing a novel interface between microplastics and biological systems via aromatic-aromatic interactions. Genetic deletion of Tim4 demonstrated that Tim4 is involved in macrophage engulfment of PS microplastics as well as of MWCNTs. While Tim4-mediated engulfment of MWCNTs causes NLRP3-dependent IL-1β secretion, that of PS microparticles does not. PS microparticles neither induce TNF-α, reactive oxygen species, nor nitric oxide production. These data indicate that PS microparticles are not inflammatory. The PtdSer-binding site of Tim4 contains an aromatic cluster that binds PS, and Tim4-mediated macrophage engulfment of apoptotic cells, a process called efferocytosis, was competitively blocked by PS microparticles. These data suggest that PS microplastics do not directly cause acute inflammation but perturb efferocytosis, raising concerns that chronic exposure to large amounts of PS microplastics may cause chronic inflammation leading to autoimmune diseases.

Identification and function analysis of a scavenger receptor B gene in red swamp crayfish Procambarus clarkii

Scavenger receptor (SRs) are pattern recognition receptors that play important roles in innate immunity. However, studies on SR in Procambarus clarkii are still lacking. In the present study, a novel scavenger receptor B on P. clarkii (PcSRB) was identified. The ORF of PcSRB was 548 bp and encoded 505 amino acid residues. It was a transmembrane protein with two transmembrane domains. The molecular weight was about 57.1 kDa. The tissue analysis by real-time PCR showed that the highest expression level was found in hepatopancreas, while the lowest expression level was found in heart, muscle, nerve and gill. After P. clarkii were infected with Aeromonas hydrophila, the expression of SRB in hemocytes increased rapidly at 12 h, and SRB in hepatopancreas and intestine also increased rapidly at 48 h after infection. The recombinant protein was obtained by prokaryotic expression. The recombinant protein (rPcSRB) could bind to bacteria and different molecular pattern recognition substances. The present study confirmed that SRB may be involved in the immune regulation process and play a certain role in the immune defense of P. clarkii, especially in the recognition and binding of pathogens. Therefore, this study provides theoretical support for further improving and enriching the immune system of P. clarkii.

Requirement of scavenger receptors for activation of the IRF-3/IFN-β/STAT-1 pathway in TLR4-mediated production of NO by LPS-activated macrophages

Production of nitric oxide (NO) by LPS-activated macrophages is due to a complex cellular signaling initiated by TLR4 that leads to the transcription of IFN-β, which activates IRF-1 and STAT-1, as well as to the activation of NF-κB, required for iNOS transcription. High concentrations of LPS can also be uptaken by scavenger receptors (SRs), which, in concert with TLR4, leads to inflammatory responses. The mechanisms by which TLR4 and SRs interact, and the pathways activated by this interaction in macrophages are not elucidated. Therefore, our main goal was to evaluate the role of SRs, particularly SR-A, in LPS-stimulated macrophages for NO production. We first showed that, surprisingly, LPS can induce the expression of iNOS and the production of NO in TLR4^-/- mice, provided exogenous IFN-β is supplied. These results indicate that LPS stimulate receptors other than TLR4. The inhibition of SR-A using DSS or neutralizing antibody to SR-AI showed that SR-A is essential for the expression of iNOS and NO production in stimulation of TLR4 by LPS. The restoration of the ability to express iNOS and produce NO by addition of rIFN-β to inhibited SR-A cells indicated that the role of SR-AI in LPS-induced NO production is to provide IFN-β, probably by mediating the internalization of LPS/TLR4, and the differential inhibition by DSS and neutralizing antibody to SR-AI suggested that other SRs are also involved. Our results reinforce that TLR4 and SR-A act in concert in LPS activation and demonstrated that, for the production of NO, it does mainly by synthesizing IRF-3 and also by activating the TRIF/IRF-3 pathway for IFN-β production, essential for LPS-mediated transcription of iNOS. Consequently STAT-1 is activated, and IRF-1 is expressed, which together with NF-κB from TLR4/MyD88/TIRAP, induce iNOS synthesis and NO production. SUMMARY SENTENCE: TLR4 and SRs act in concert activating IRF-3 to transcribe IFN-β and activate STAT-1 to produce NO by LPS-activated macrophages.

Innate immune responses in pneumonia

The lungs are an immunologically unique environment; they are exposed to innumerable pathogens and particulate matter daily. Appropriate clearance of pathogens and response to pollutants is required to prevent overwhelming infection, while preventing tissue damage and maintaining efficient gas exchange. Broadly, the innate immune system is the collection of immediate, intrinsic immune responses to pathogen or tissue injury. In this review, we will examine the innate immune responses of the lung, with a particular focus on their role in pneumonia. We will discuss the anatomic barriers and antimicrobial proteins of the lung, pathogen and injury recognition, and the role of leukocytes (macrophages, neutrophils, and innate lymphocytes) and lung stromal cells in innate immunity. Throughout the review, we will focus on new findings in innate immunity as well as features that are unique to the lung.

Microglial Activation in Metal Neurotoxicity: Impact in Neurodegenerative Diseases

Neurodegenerative processes encompass a large variety of diseases with different pathological patterns and clinical features, such as Alzheimer's and Parkinson's diseases. Exposure to metals has been hypothesized to increase oxidative stress in brain cells leading to cell death and neurodegeneration. Neurotoxicity of metals has been demonstrated by several in vitro and in vivo experimental studies, and most probably, each metal has its specific pathway to trigger cell death. As a result, exposure to essential metals, such as manganese, iron, copper, zinc, and cobalt, and nonessential metals, including lead, aluminum, and cadmium, perturbs metal homeostasis at the cellular and organism levels leading to neurodegeneration. In this contribution, a comprehensive review of the molecular mechanisms by which metals affect microglia physiology and signaling properties is presented. Furthermore, studies that validate the disruption of microglia activation pathways as an essential mechanism of metal toxicity that can contribute to neurodegenerative disease are also presented and discussed.

Stage-specific and cell type-specific requirements of ikzf1 during haematopoietic differentiation in zebrafish

The zinc finger transcription factor Ikaros1 (Ikzf1) is required for lymphoid development in mammals. Four zinc fingers constitute its DNA binding domain and two zinc fingers are present in the C-terminal protein interaction module. We describe the phenotypes of zebrafish homozygous for two distinct mutant ikzf1 alleles. The IT325 variant lacks the C-terminal two zinc fingers, whereas the fr105 variant retains only the first zinc finger of the DNA binding domain. An intact ikzf1 gene is required for larval T cell development, whereas low levels of adult lymphoid development recover in the mutants. By contrast, the mutants exhibit a signature of increased myelopoiesis at larval and adult stages. Both mutations stimulate erythroid differentiation in larvae, indicating that the C-terminal zinc fingers negatively regulate the extent of red blood cell production. An unexpected differential effect of the two mutants on adult erythropoiesis suggests a direct requirement of an intact DNA binding domain for entry of progenitors into the red blood cell lineage. Collectively, our results reinforce the biological differences between larval and adult haematopoiesis, indicate a stage-specific function of ikzf1 in regulating the hierarchical bifurcations of differentiation, and assign distinct functions to the DNA binding domain and the C-terminal zinc fingers.

PRRS virus receptors and an alternative pathway for viral invasion

Porcine reproductive and respiratory syndrome virus (PRRSV) has a highly restricted cell tropism, which is closely related to the specific receptors associated with PRRSV infection. At least nine cellular molecules have been identified as putative receptors for PRRSV, including CD163, a cysteine-rich scavenger receptor. With the participation of the CD163 receptor and other cofactors, PRRSV invades cells via low pH-dependent clathrin-mediated endocytosis. In addition, PRRSV utilizes viral apoptotic mimicry to infect cells though macropinocytosis as an alternative pathway. In this review, we discuss recent advances in the studies on receptors and pathways that play an important role in PRRSV invasion, and simultaneously explore the use of specific antibodies, small molecules, and blockers targeting receptor-ligand interactions, as a potential strategy for controlling PRRSV infection. Novel antiviral strategies against PRRSV could be developed by identifying the interaction between receptors and ligands.

Emerging Evidence on Tenebrio molitor Immunity: A Focus on Gene Expression Involved in Microbial Infection for Host-Pathogen Interaction Studies

In recent years, the scientific community's interest in T. molitor as an insect model to investigate immunity and host-pathogen interactions has considerably increased. The reasons for this growing interest could be explained by the peculiar features of this beetle, which offers various advantages compared to other invertebrates models commonly used in laboratory studies. Thus, this review aimed at providing a broad view of the T. molitor immune system in light of the new scientific evidence on the developmental/tissue-specific gene expression studies related to microbial infection. In addition to the well-known cellular component and humoral response process, several studies investigating the factors associated with T. molitor immune response or deepening of those already known have been reported. However, various aspects remain still less understood, namely the possible crosstalk between the immune deficiency protein and Toll pathways and the role exerted by T. molitor apolipoprotein III in the expression of the antimicrobial peptides. Therefore, further research is required for T. molitor to be recommended as an alternative insect model for pathogen-host interaction and immunity studies.

Sequence and functional features of a novel scavenger receptor homolog, SCARA5 from Yellow drum (Nibea albiflora)

As an important member in SR-As, member 5 (SCARA5) can swallow apoptotic cells and foreign bodies, and participate multiple signaling pathways to inhibit tumor occurrence, development growth and metastasis. To explore its immune function, SCARA5 was identified from the yellow drum (Nibea albiflora) according to its transcriptome data, and its full-length cDNA was 6968 bp (named as NaSCARA5, GenBank accession no: MW070211) encoding 497 amino acids with a calculated molecular weight of 55.12 kDa, which had the typical motifs of SR family, such as transmembrane helix region, coil region, Pfam collagens region and SR region. BLASTp and the phylogenetic relationship analysis illustrated that the sequences shared high similarity with known SCARA5 of teleosts. Quantitative real time RT-PCR analysis showed that NaSCARA5 was expressed in intestine, stomach, liver, kidney, gill, heart and spleen, with the highest in the spleen (24.42-fold compared with that in heart). After being infected with Polyinosinic:polycytidylic acid (PolyI:C), Vibrio alginolyticus and Vibrio parahaemolyticus, NaSCARA5 mRNA were up-regulated with time dependent mode in spleen, which suggested that NaSCARA5 might play an important role in the immune process of fish. The extracellular domain of NaSCARA5 was successfully expressed in BL21 (DE3), and yielded the target protein of the expected size with many active sites for their conferring protein-protein interaction functions. After being purified by Ni-NAT Superflow resin and renatured, it was found to bind all the tested bacteria (V.parahaemolyticus,V.alginolyticus and Vibrio harveyi). The eukaryotic expression vector of the NaSCARA5-EGFP fusion protein was constructed and transferred into epithelioma papulosum cyprini (EPC) cells, and it was mainly expressed on the cell membrane indicating that NaSCARA5 was a typical transmembrane protein. The aforementioned results indicated that NaSCARA5 played a significant role in the defense against pathogenic bacteria infection as PRRs, which may provide some further understandings of the regulatory mechanisms in the fish innate immune system for SR family.

Genome-wide identification and analysis of scavenger receptors and their expression profiling in response to Edwardsiella tarda infection in Japanese flounder (Paralichthys olivaceus)

The scavenger receptors (SRs) gene family, as one of pattern recognition receptors, participates in the innate immune response in diverse lineages. However, the systematic identification, characteristics and functions of SRs family are lacking in teleost. Here, we identified all 19 SRs family members in Japanese flounder (Paralichthys olivaceus) based on the genome and transcriptome data. Phylogenetic and Ka/Ks analysis demonstrated that these SRs genes were divided into five classes and all exhibited pronounced purified selection pressures. Whole genome duplication event was found in colec12, scarb2, and lamp1. Gene structure, functional domain and motif distribution analyses indicated that SRs within the different subfamilies are severely conservative. SRs genes showed diverse expression patterns in the embryogenesis and unchanged tissues. The regulations of 14 SRs genes in blood, gill and kidney after E. tarda infection suggested their roles in innate immune response. Meanwhile, ten SRs genes were differentially expressed after E. tarda stimulation in macrophages in vitro. Then we proved that PoSCARA3 could suppress the activity of NF-κB and AP-1 in HEK 293T cells by dual-luciferase assays. In summary, this study provided valuable basis for further functional characterization and immune functions of SRs genes in P. olivaceus.

High-density lipoproteins negatively regulate innate immunity and facilitate red-spotted grouper nervous necrosis virus entry via scavenger receptor B type 1

Lipid metabolism plays an important role in viral infections, and it can directly or indirectly affect various stages of viral infection in cells. As an important component of lipid metabolism, high-density lipoprotein (HDL) plays crucial roles in inflammation, immunity, and viral infections. Scavenger receptor B type 1 (SR-B1), a receptor of HDL, cannot be ignored in the regulation of lipid metabolism. Here, we investigate, for the first time, the role of Epinephelus coioides SR-B1 (Ec-SR-B1) in red-spotted grouper nervous necrosis virus (RGNNV) infection. Our results indicate that Ec-SR-B1 could promote RGNNV infection. We also demonstrate that Ec-SR-B1 could facilitate viral entry and interact with capsid protein (CP) of RGNNV. As the natural ligand of SR-B1, HDL significantly increased RGNNV entry in a dose-dependent manner. However, we observed no effect of HDL on Ec-SR-B1 expression. The results of the micro-scale thermophoresis assay did not reveal an association between HDL and CP, suggesting that RGNNV does not enter target cells by using HDL as a ligand to bind to its receptor. In addition, block lipid transport-1, a compound that inhibits HDL-mediated cholesterol transfer, reduced the HDL-induced enhancement of RGNNV infection, indicating a role for lipid transfer in facilitating RGNNV entry. Furthermore, HDL inhibited the expression of pro-inflammatory factors and antiviral genes in a dose-dependent manner. These findings suggest that the HDL-induced enhancement of RGNNV entry involves the complex interplay between Ec-SR-B1, HDL, and RGNNV, as well as the regulation of innate antiviral responses by HDL. In summary, we highlight the crucial role of HDL in RGNNV entry, identify a possible molecular connection between RGNNV and lipoprotein metabolism, and indicate the role of Ec-SR-B1 in RGNNV infection.

Comparison of the immune activation capacities of fucoidan and laminarin extracted from Laminaria japonica

Laminaria japonica is a brown alga and is composed primarily of polysaccharides. Fucoidan and laminarin are the major polysaccharides of L. japonica and exhibit biological activities, including immune modulation and anti-coagulant and antioxidant effects in animals and humans. In this study, we evaluated the ability of fucoidan and laminarin from L. japonica to induce immune cell activation and anti-cancer immunity, which has not yet been studied. The injection of fucoidan to mice promoted the upregulation of major histocompatibility complex and surface activation molecules in splenic dendritic cell subsets, whereas laminarin showed a weaker immune activation ability. In addition, fucoidan treatment elicited inflammatory cytokine production; however, laminarin did not induce the production of these cytokines. Regarding cytotoxic cell activities, fucoidan induced the activation of lymphocytes, including natural killer and T cells, whereas laminarin did not induce cell activation. Finally, fucoidan enhanced the anticancer efficacy of anti-programmed Death-Ligand 1 (PD-L1) antibody against Lewis lung carcinoma, whereas laminarin did not promote the cancer inhibition effect of anti-PD-L1 antibody. Thus, these data suggest that fucoidan from L. japonica can be used as an immune stimulatory molecule to enhance the anticancer activities of immune checkpoint inhibitors.

Host F-Box Protein 22 Enhances the Uptake of Brucella by Macrophages and Drives a Sustained Release of Proinflammatory Cytokines through Degradation of the Anti-Inflammatory Effector Proteins of Brucella

Brucella species are intracellular bacterial pathogens, causing the worldwide zoonotic disease brucellosis. Brucella invades professional and nonprofessional phagocytic cells, followed by resisting intracellular killing and establishing a replication permissive niche. Brucella also modulates the innate and adaptive immune responses of the host for its chronic persistence. The complex intracellular cycle of Brucella depends in a major way on multiple host factors, but limited information is available on host and bacterial proteins that play an essential role in the invasion, intracellular replication, and modulation of host immune responses. By employing a small interfering RNA (siRNA) screening, we identified a role for the host protein FBXO22 in the Brucella-macrophage interaction. FBXO22 is the key element in the SCF E3 ubiquitination complex, where it determines the substrate specificity for ubiquitination and degradation of various host proteins. Downregulation of FBXO22 by siRNA or the CRISPR-Cas9 system resulted in diminished uptake of Brucella into macrophages, which was dependent on NF-κB-mediated regulation of phagocytic receptors. FBXO22 expression was upregulated in Brucella-infected macrophages, which resulted in induction of phagocytic receptors and enhanced production of proinflammatory cytokines through NF-κB. Furthermore, we found that FBXO22 recruits the effector proteins of Brucella, including the anti-inflammatory proteins TcpB and OMP25, for degradation through the SCF complex. We did not observe any role for another F-box-containing protein of the SCF complex, β-TrCP, in the Brucella-macrophage interaction. Our findings unravel novel functions of FBXO22 in host-pathogen interaction and its contribution to pathogenesis of infectious diseases.

Macropinocytosis in Phagocyte Function and Immunity

Phagocytes play critical roles in the maintenance of organismal homeostasis and immunity. Central to their role is their ability to take up and process exogenous material via the related processes of phagocytosis and macropinocytosis. The mechanisms and functions underlying macropinocytosis have remained severely understudied relative to phagocytosis. In recent years, however, there has been a renaissance in macropinocytosis research. Phagocytes can engage in various forms of macropinocytosis including an "induced" form and a "constitutive" form. This chapter, however, will focus on constitutive macropinocytosis and its role in the maintenance of immunity. Functions previously attributed to macropinocytosis, including antigen presentation and immune surveillance, will be revisited in light of recent revelations and emerging concepts will be highlighted.

Positive Selection and Enhancer Evolution Shaped Lifespan and Body Mass in Great Apes

Within primates, the great apes are outliers both in terms of body size and lifespan, since they include the largest and longest-lived species in the order. Yet, the molecular bases underlying such features are poorly understood. Here, we leveraged an integrated approach to investigate multiple sources of molecular variation across primates, focusing on over 10,000 genes, including approximately 1,500 previously associated with lifespan, and additional approximately 9,000 for which an association with longevity has never been suggested. We analyzed dN/dS rates, positive selection, gene expression (RNA-seq), and gene regulation (ChIP-seq). By analyzing the correlation between dN/dS, maximum lifespan, and body mass, we identified 276 genes whose rate of evolution positively correlates with maximum lifespan in primates. Further, we identified five genes, important for tumor suppression, adaptive immunity, metastasis, and inflammation, under positive selection exclusively in the great ape lineage. RNA-seq data, generated from the liver of six species representing all the primate lineages, revealed that 8% of approximately 1,500 genes previously associated with longevity are differentially expressed in apes relative to other primates. Importantly, by integrating RNA-seq with ChIP-seq for H3K27ac (which marks active enhancers), we show that the differentially expressed longevity genes are significantly more likely than expected to be located near a novel "ape-specific" enhancer. Moreover, these particular ape-specific enhancers are enriched for young transposable elements, and specifically SINE-Vntr-Alus. In summary, we demonstrate that multiple evolutionary forces have contributed to the evolution of lifespan and body size in primates.

Scavenger receptors in host defense: from functional aspects to mode of action

Scavenger receptors belong to a superfamily of proteins that are structurally heterogeneous and encompass the miscellaneous group of transmembrane proteins and soluble secretory extracellular domain. They are functionally diverse as they are involved in various disorders and biological pathways and their major function in innate immunity and homeostasis. Numerous scavenger receptors have been discovered so far and are apportioned in various classes (A-L). Scavenger receptors are documented as pattern recognition receptors and known to act in coordination with other co-receptors such as Toll-like receptors in generating the immune responses against a repertoire of ligands such as microbial pathogens, non-self, intracellular and modified self-molecules through various diverse mechanisms like adhesion, endocytosis and phagocytosis etc. Unlike, most of the scavenger receptors discussed below have both membrane and soluble forms that participate in scavenging; the role of a potential scavenging receptor Angiotensin-Converting Enzyme-2 has also been discussed whereby only its soluble form might participate in preventing the pathogen entry and replication, unlike its membrane-bound form. This review majorly gives an insight on the functional aspect of scavenger receptors in host defence and describes their mode of action extensively in various immune pathways involved with each receptor type. Video abstract.

Lipid scavenging macrophages and inflammation

Macrophages are professional phagocytes, indispensable for maintenance of tissue homeostasis and integrity. Depending on their resident tissue, macrophages are exposed to highly diverse metabolic environments. Adapted to their niche, they can contribute to local metabolic turnover through metabolite uptake, conversion, storage and release. Disturbances in tissue homeostasis caused by infection, inflammation or damage dramatically alter the local milieu, impacting macrophage activation status and metabolism. In the case of persisting stimuli, defective macrophage responses ensue, which can promote tissue damage and disease. Especially relevant herein are disbalances in lipid rich environments, where macrophages are crucially involved in lipid uptake and turnover, preventing lipotoxicity. Lipid uptake is to a large extent facilitated by macrophage expressed scavenger receptors that are dynamically regulated and important in many metabolic diseases. Here, we review the receptors mediating lipid uptake and summarize recent findings on their role in health and disease. We further highlight the underlying pathways driving macrophage lipid acquisition and their impact on myeloid metabolic remodelling.

Scavenger receptor C regulates antimicrobial peptide expression by activating toll signaling in silkworm, Bombyx mori

Scavenger receptor is pattern-recognition receptor (PRR) that plays a crucial function in host defense against pathogens. Scavenger receptor C (SR-C) is present only in invertebrates and its function has not been studied in detail. In this study, an SR-C homologous gene from the silkworm, Bombyx mori, was identified and characterized. SR-C was largely expressed in hemocytes and Malpighian tubules, with continuous expression in hemocytes. The peak expression was observed in hemocytes during molting and wandering stages both at mRNA and protein levels. Furthermore, immunofluorescence demonstrated it to be mainly distributed in the cell membranes of hemocytes, including oenocytoids and granulocytes. The recombinant SR-C protein (rSR-C) could bind to different types of bacteria and pathogen-associated molecular patterns (PAMPs), with strong binding to gram-positive bacteria and Lys-type peptidoglycans. The overexpression of SR-C induced the expression of genes related to the Toll pathway and antibacterial peptides. While the knockdown of SR-C reduced the expression of AMPs and inhibited the Toll pathway, it impaired the bacterial clearance ability of silkworm larvae, thus decreasing silkworm larvae's survival rate. Altogether, SR-C is a PRR that protect silkworms against bacterial pathogens by enhancing the expression of AMPs expression via the Toll pathway in hemocytes.

Microglial Potassium Channels: From Homeostasis to Neurodegeneration

The growing interest in the role of microglia in the progression of many neurodegenerative diseases is developing in an ever-expedited manner, in part thanks to emergent new tools for studying the morphological and functional features of the CNS. The discovery of specific biomarkers of the microglia phenotype could find application in a wide range of human diseases, and creates opportunities for the discovery and development of tailored therapeutic interventions. Among these, recent studies highlight the pivotal role of the potassium channels in regulating microglial functions in physiological and pathological conditions such as Alzheimer's Disease, Parkinson's Disease, and Amyotrophic Lateral Sclerosis. In this review, we summarize the current knowledge of the involvement of the microglial potassium channels in several neurodegenerative diseases and their role as modulators of microglial homeostasis and dysfunction in CNS disorders.

Leishmania Parasites Differently Regulate Antioxidant Genes in Macrophages Derived From Resistant and Susceptible Mice

Macrophage-Leishmania interactions are central to parasite growth and disease outcome. Macrophages have developed various strategies to fight invaders, including oxidative burst. While some microorganisms seem to survive and even thrive in an oxidative environment, others are susceptible and get killed. To counter oxidative stress, macrophages switch the expressions of cytoprotective and detoxifying enzymes, which are downstream targets of the nuclear factor erythroid 2-related factor 2 (Nrf2), to enhance cell survival. We have explored the transcription of NRF2 and of its target genes and compared the effect of the parasite on their transcription in bone marrow-derived macrophages (BMdMs) from Leishmania-resistant and Leishmania-susceptible mice. While heme oxygenase 1 (HO-1) transcription is independent of the genetic background, the transcription of glutathione reductase (Gsr) and of cysteine/glutamate exchange transporter (Slc7a11), involved in glutathione accumulation, was differentially regulated in BMdMs from both mouse strains. We also show that, except for HO-1, known to favor the survival of the parasite, the transcription of the selected genes, including Gsr, CD36, and catalase (CAT), was actively repressed, if not at all time points at least at the later ones, by the parasite, especially in Balb/c BMdMs. Consistent with these results, we found that the silencing of NRF2 in this study increases the survival and multiplication of the parasite.

Microglia Regulate Neuronal Circuits in Homeostatic and High-Fat Diet-Induced Inflammatory Conditions

Microglia are brain resident macrophages, which actively survey the surrounding microenvironment and promote tissue homeostasis under physiological conditions. During this process, microglia participate in synaptic remodeling, neurogenesis, elimination of unwanted neurons and cellular debris. The complex interplay between microglia and neurons drives the formation of functional neuronal connections and maintains an optimal neural network. However, activation of microglia induced by chronic inflammation increases synaptic phagocytosis and leads to neuronal impairment or death. Microglial dysfunction is implicated in almost all brain diseases and leads to long-lasting functional deficiency, such as hippocampus-related cognitive decline and hypothalamus-associated energy imbalance (i.e., obesity). High-fat diet (HFD) consumption triggers mediobasal hypothalamic microglial activation and inflammation. Moreover, HFD-induced inflammation results in cognitive deficits by triggering hippocampal microglial activation. Here, we have summarized the current knowledge of microglial characteristics and biological functions and also reviewed the molecular mechanism of microglia in shaping neural circuitries mainly related to cognition and energy balance in homeostatic and diet-induced inflammatory conditions.

Scavenger receptors

Scavenger receptors (SRs) are a large family of cell-surface receptors that are diverse in their structure and biological function and are divided into different classes. SRs can bind to a range of ligands and enhance the elimination of altered-self or non-self targets. The functional mechanisms that lead to their clearance of harmful substances involve phagocytosis, endocytosis, adhesion, and signaling.

Stabilin-1 plays a protective role against Listeria monocytogenes infection through the regulation of cytokine and chemokine production and immune cell recruitment

Scavenger receptors are part of a complex surveillance system expressed by host cells to efficiently orchestrate innate immune response against bacterial infections. Stabilin-1 (STAB-1) is a scavenger receptor involved in cell trafficking, inflammation, and cancer; however, its role in infection remains to be elucidated. Listeria monocytogenes (Lm) is a major intracellular human food-borne pathogen causing severe infections in susceptible hosts. Using a mouse model of infection, we demonstrate here that STAB-1 controls Lm-induced cytokine and chemokine production and immune cell accumulation in Lm-infected organs. We show that STAB-1 also regulates the recruitment of myeloid cells in response to Lm infection and contributes to clear circulating bacteria. In addition, whereas STAB-1 appears to promote bacterial uptake by macrophages, infection by pathogenic Listeria induces the down regulation of STAB-1 expression and its delocalization from the host cell membrane.

We propose STAB-1 as a new SR involved in the control of Lm infection through the regulation of host defense mechanisms, a process that would be targeted by bacterial virulence factors to promote infection.

Understanding microglial diversity and implications for neuronal function in health and disease

Genetic data implicate microglia as central players in brain health and disease, urging the need to better understand what microglia do in the brain. Microglia are critical partners in neuronal wiring and function during development and disease. Emerging literature suggests that microglia have diverse functional roles, raising the intriguing question of which functions of microglia become impaired in disease to undermine proper neuronal function. It is also becoming increasingly clear that microglia exist in heterogeneous cell states. Microglial cell states appear context-dependent, that is, age, sex, location, and health of their microenvironment; these are further influenced by external signaling factors including gut microbiota and lipid metabolites. These data altogether suggest that microglia exist in functional clusters that impact, and are impacted by, surrounding neuronal microenvironment. However, we still lack understanding of how we can translate microglia cell states into function. Here, we summarize the state-of-the-art on the diverse functions of microglia in relation to neuronal health. Then, we discuss heterogeneity during developing, healthy adult and diseased brains, and whether this may be predetermined by origin and/or regulated by local milieu. Finally, we propose that it is critical to gain high-resolution functional discernment into microglia-neuron interactions while preserving the spatial architecture of the tissue. Such insight will reveal specific targets for biomarker and therapeutic development toward microglia-neuron crosstalk in disease.

Molecular Characterisation of Uterine Endometrial Proteins during Early Stages of Pregnancy in Pigs by MALDI TOF/TOF

The molecular mechanism underlying embryonic implantation is vital to understand the correct communications between endometrium and developing conceptus during early stages of pregnancy. This study’s objective was to determine molecular changes in the uterine endometrial proteome during the preimplantation and peri-implantation between 9 days (9D), 12 days (12D), and 16 days (16D) of pregnant Polish Large White (PLW) gilts. 2DE-MALDI-TOF/TOF and ClueGO^TM approaches were employed to analyse the biological networks and molecular changes in porcine endometrial proteome during maternal recognition of pregnancy. A total of sixteen differentially expressed proteins (DEPs) were identified using 2-DE gels and MALDI-TOF/TOF mass spectrometry. Comparison between 9D and 12D of pregnancy identified APOA1, CAPZB, LDHB, CCT5, ANXA4, CFB, TTR upregulated DEPs, and ANXA5, SMS downregulated DEPs. Comparison between 9D and 16D of pregnancy identified HP, APOA1, ACTB, CCT5, ANXA4, CFB upregulated DEPs and ANXA5, SMS, LDHB, ACTR3, HP, ENO3, OAT downregulated DEPs. However, a comparison between 12D and 16D of pregnancy identified HP, ACTB upregulated DEPs, and CRYM, ANXA4, ANXA5, CAPZB, LDHB, ACTR3, CCT5, ENO3, OAT, TTR down-regulated DEPs. Outcomes of this study revealed key proteins and their interactions with metabolic pathways involved in the recognition and establishment of early pregnancy in PLW gilts.

The role of macrophage scavenger receptor 1 (Msr1) in prion pathogenesis

The progression of prion diseases is accompanied by the accumulation of prions in the brain. Ablation of microglia enhances prion accumulation and accelerates disease progression, suggesting that microglia play a neuroprotective role by clearing prions. However, the mechanisms underlying the phagocytosis and clearance of prion are largely unknown. The macrophage scavenger receptor 1 (Msr1) is an important phagocytic receptor expressed by microglia in the brain and is involved in the uptake and clearance of soluble amyloid-β. We therefore asked whether Msr1 might play a role in prion clearance and assessed the scavenger function of Msr1 in prion pathogenesis. We found that Msr1 expression was upregulated in prion-infected mouse brains. However, Msr1 deficiency did not change prion disease progression or lesion patterns. Prion deposition in Msr1 deficient mice was similar to their wild-type littermates. In addition, prion-induced neuroinflammation was not affected by Msr1 ablation. We conclude that Msr1 does not play a major role in prion pathogenesis. KEY MESSAGES: Msr1 expression is upregulated in prion-infected mouse brains at the terminal stage Msr1 deficiency does not affect prion disease progression Msr1 does not play a major role in prion clearance or prion pathogenesis Microglia-mediated phagocytosis and clearance of Aβ and prion may adopt distinct molecular pathways.

Epidermal SR-A Complexes Are Lipid Raft Based and Promote Nucleic Acid Nanoparticle Uptake

Scavenger receptors clear pathogens, transport lipid, and mediate polyanionic ligand uptake in macrophages, but their expression and role in the skin are poorly understood. Although the epidermal barrier typically excludes nucleic acid entry, topically applied, spherically arranged oligonucleotide nanoconjugates (spherical nucleic acids [SNAs]) penetrate mouse skin, three-dimensional (3D) skin equivalents, and human skin. We explored the mechanism of SNA uptake in normal human epidermal keratinocytes and 3D skin equivalents. Normal human epidermal keratinocytes and 3D raft treatment with SR-A inhibitors reduced SNA uptake by >80%. The human epidermis expresses SR-As SCARA3 and, to a lesser extent, MARCO. Simultaneous lentiviral knockdown of SCARA3 and MARCO reduced SNA uptake in normal human epidermal keratinocytes and 3D rafts after topical application, affirming a role for SR-As in SNA uptake and 3D raft penetration. Incubation of normal human epidermal keratinocytes at 4oC or with sodium azide prevented SNA uptake, suggesting active endocytosis. Endocytosis inhibitors, immunofluorescence, immunoprecipitation, and knockdown studies localized functional SR-As to FLOT-1-containing lipid rafts throughout the epidermis and CAV-1-containing rafts only in the upper epidermis. These studies suggest a central role for SR-A complexes in epidermal lipid rafts in mediating the uptake of nucleic acid‒laden nanoparticles.

Scavenger receptor A1 participates in uptake of Leptospira interrogans serovar Autumnalis strain 56606v and inflammation in mouse macrophages

Leptospirosis, caused by pathogenic Leptospira species, has emerged as a widespread zoonotic disease worldwide. Macrophages mediate the elimination of pathogens through phagocytosis and cytokine production. Scavenger receptor A1 (SR-A1), one of the critical receptors mediating this process, plays a complicated role in innate immunity. However, the role of SR-A1 in the immune response against pathogenic Leptospira invasion is unknown. In the present study, we found that SR-A1 is an important nonopsonic phagocytic receptor on murine macrophages for Leptospira. However, intraperitoneal injection of leptospires into WT mice presented with more apparent jaundice, subcutaneous hemorrhaging, and higher bacteria burdens in blood and tissues than that of SR-A1^-/- mice. Exacerbated cytokine and inflammatory mediator levels were also observed in WT mice and higher recruited macrophages in the liver than those of SR-A1^-/- mice. Our findings collectively reveal that although beneficial in the uptake of Leptospira by macrophage, SR-A1 might be exploited by Leptospira to modulate inflammatory activation and increase the susceptibility of infection in the host. These results provide our new insights into the innate immune response during early infection by L. interrogans.

Human monocyte-derived type 1 and 2 macrophages recognize Ara h 1, a major peanut allergen, by different mechanisms

Evidence has suggested that major peanut allergen Ara h 1 activates dendritic cells (DCs) via interaction with DC-SIGN (dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin), a C-type lectin receptor, and contributes to development of peanut allergy. Since macrophages, as well as DCs, play a crucial role in innate immunity, we investigated whether natural Ara h 1 (nAra h 1) activates two different subsets of macrophages, human monocyte derived macrophage type 1 (hMDM1: pro-inflammatory model) and type 2 (hMDM2: anti-inflammatory model). hMDM1 and hMDM2 predominantly produced pro-inflammatory cytokines (IL-6 and TNF-α) and an anti-inflammatory cytokine (IL-10) in response to nAra h 1, respectively. hMDM2 took up nAra h 1 and expressed DC-SIGN at higher levels than hMDM1. However, small interfering RNA knockdown of DC-SIGN did not suppress nAra h 1 uptake and nAra h 1-mediated cytokine production in hMDM2. Inhibitors of scavenger receptor class A type I (SR-AI) suppressed the response of hMDM2, but not of hMDM1, suggesting that SR-AI is a major receptor in hMDM2 for nAra h 1 recognition and internalization. nAra h 1 appears to exert stimulatory capacity on DC and macrophages via different receptors. This study advances our understanding how a major peanut allergen interacts with innate immunity.

Recent Advances in PRRS Virus Receptors and the Targeting of Receptor-Ligand for Control

Cellular receptors play a critical role in viral infection. At least seven cellular molecules have been identified as putative viral entry mediators for porcine reproductive and respiratory syndrome virus (PRRSV). Accumulating data indicate that among these candidates, CD163, a cysteine-rich scavenger receptor on macrophages, is the major receptor for PRRSV. This review discusses the recent advances and understanding of the entry of PRRSV into cells, viral pathogenesis in CD163 gene-edited swine, and CD163 as a potential target of receptor–ligand for the control of PRRS.

Scavenger receptor B8 improves survivability by mediating innate immunity in silkworm, Bombyx mori

Scavenger receptor class B (SR-B) is an extracellular transmembrane glycoprotein that plays a vital role in innate immunity. Although SR-Bs have been widely studied in vertebrates, their functions remained to elucidate in insects. Here, we identified and characterized a scavenger receptor class B member from the silkworm, Bombyx mori (designated as BmSCRB8). BmSCRB8 is broadly expressed in various immune tissues/organs, including fat body, gut, and hemocyte. Its expression is dramatically enhanced after challenge with different types of bacteria or pathogen-associated molecular patterns (PAMPs). The recombinant BmSCRB8 protein can detect different types of bacteria by directly binding to PAMPs and significantly improve the bacterial clearance in vivo. After knockdown of BmSCRB8, the pathogenic bacterial clearance was strongly impaired, and several AMP genes were down-regulated following E. coli challenge. Moreover, pathogenic bacteria's treatment following the depletion of BmSCRB8 remarkably decreased silkworm larvae's survival rate. Taken together, these results demonstrate that BmSCRB8 acts as a pattern recognition protein and plays an essential role in silkworm innate immunity by enhancing bacterial clearance and contributing to the production of AMPs in vivo.

SCARA5 suppresses the proliferation and migration, and promotes the apoptosis of human retinoblastoma cells by inhibiting the PI3K/AKT pathway

Retinoblastoma (RB) is the most common ocular malignancy that occurs during childhood. Scavenger receptor class A member 5 (SCARA5) is considered to function as an anti-oncogene in several types of malignant tumor. The present study investigated the functional role and underlying mechanism of SCARA5 in human RB cells. Reverse transcription-quantitative PCR and western blotting were used to detect the relative expression levels of SCARA5 in four human RB cell lines. In addition, transfection was performed to either knockdown or induce overexpression of SCARA5 in human RB Y79 cells. The proliferation, migration and apoptosis of RB cells was then measured by Cell Counting Kit 8 assay, 5-ethynyl-2′-deoxyuridine assay, clone formation assay, Transwell assay, Hoechst staining and TUNEL staining, respectively. Western blotting was performed to detect changes in the expression levels of key proteins involved in the PI3K/AKT and apoptotic pathways. The present study revealed that SCARA5 was expressed at lower levels in four tumorigenic human RB cell lines compared with in a human retinal pigment non-tumorigenic cell line. Functional analysis demonstrated that overexpression of SCARA5 decreased the proliferation and migration, and promoted the apoptosis of human RB cells in vitro, whereas in vivo experiments revealed a decrease in RB progression following SCARA5 overexpression. In addition, overexpression of SCARA5 inhibited phosphorylated (p)-PI3K and p-AKT expression, and knockdown of SCARA5 increased p-PI3K and p-AKT expression; however, no changes in total PI3K and AKT expression were observed. Bcl-2 exhibited similar changes in expression to those displayed by p-PI3K and p-AKT, whereas Bax and cleaved caspase-3 exhibited trends in expression that were the opposite to those shown by p-PI3K and p-AKT. In conclusion, the present results demonstrated that SCARA5 could inhibit the proliferation and promote the apoptosis of RB cell lines by suppressing the PI3K/AKT signaling pathway, thus suggesting a novel strategy for treating RB.

Scavenger receptor MARCO contributes to cellular internalization of exosomes by dynamin-dependent endocytosis and macropinocytosis

Macrophage receptor with collagenous structure (MARCO) is a scavenger receptor class-A protein that is expressed on the cell surface of macrophages. MARCO mediates binding and ingestion of unopsonized environmental particles, including nano-sized materials. Exosomes are cell-derived, nano-sized vesicles (40–150 nm) that can contain lipids, RNA, DNA, and various proteins. Exosomes play an essential role in cell-to-cell communication via body fluids. However, mechanisms for the recognition and internalization of exosomes by recipient cells remain poorly characterized. In this study, cellular association of serum-derived fluorescent exosomes and 20-nm fluorescent nanoparticles (positive control) was compared between MARCO-expressing (CHO-MARCO) and control (CHO-CT) CHO-K1 cells to examine whether MARCO expression by recipient cells mediates the cellular uptake of exosomes and environmental nanoparticles. Fluorescence microscopic studies and quantitative analyses revealed that the cellular associations of both exosomes and 20-nm nanoparticles were greater in CHO-MARCO cells than in CHO-CT cells. Exosomes and nanoparticles colocalized with green fluorescent protein (GFP)-MARCO in cells transfected with GFP-MARCO-encoding constructs . Furthermore, inhibitory studies showed that actin reorganization and dynamin are involved in the MARCO-mediated cellular internalization of exosomes. These results indicated that MARCO plays a role in the uptake of exosomes.

Organic dust-induced lung injury and repair: Bi-directional regulation by TNFα and IL-10

Exposure to organic dust increases chronic airway inflammatory disorders. Effective treatment strategies are lacking. It has been reported that hog barn dust extracts (HDE) induce TNFα through protein kinase C (PKC) activation and that lung inflammation is enhanced in scavenger receptor A (SRA/CD204) knockout (KO) mice following HDE. Because interleukin (IL)-10 production can limit excessive inflammation, it was hypothesized here that HDE-induced IL-10 would require CD204 to effect inflammatory responses. C57BL/6 wild-type (WT), SRA KO, and IL-10 KO mice were intranasally challenged daily for 8 days with HDE and subsequently rested for 3 days with/without recombinant IL-10 (rIL-10) treatment. Primary peritoneal macrophages (PM) and murine alveolar macrophages (MH-S cells) were treated in vitro with HDE, SRA ligand (fucoidan), rIL-10, and/or PKC isoform inhibitors. HDE induced in vivo lung IL-10 in WT, but not SRA KO mice, and similar trends were demonstrated in isolated PM from same treated mice. Lung lymphocyte aggregates and neutrophils were elevated in in vivo HDE-treated SRA and IL-10 KO mice after a 3-d recovery, and treatment during recovery with rIL-10 abrogated these responses. In vitro rIL-10 treatment reduced HDE-stimulated TNFα release in MH-S and WT PM. In SRA KO macrophages, there was reduced IL-10 and PKC zeta (ζ) activity and increased TNFα following in vitro HDE stimulation. Similarly, blocking SRA (24 hr fucoidan pre-treatment) resulted in enhanced HDE-stimulated macrophage TNFα and decreased IL-10 and PKCζ activation. PKCζ inhibitors blocked HDE-stimulated IL-10, but not TNFα. Collectively, HDE stimulates IL-10 by an SRA- and PKCζ-dependent mechanism to regulate TNFα. Enhancing resolution of dust-mediated lung inflammation through targeting IL-10 and/or SRA may represent new approaches to therapeutic interventions.