Lipopolysaccharide Downregulates CD163 Expression to Inhibit PRRSV Infection via TLR4-NF-κB Pathway

Porcine reproductive and respiratory syndrome virus infection activates ADAM17 to induce inflammatory responses

Porcine reproductive and respiratory syndrome (PRRS), which has posed substantial threats to the swine industry worldwide, is primarily characterized by interstitial pneumonia. A disintegrin and metalloproteinase 17 (ADAM17) is a multifunctional sheddase involved in various inflammatory diseases. Herein, our study showed that PRRS virus (PRRSV) infection elevated ADAM17 activity, as demonstrated in primary porcine alveolar macrophages (PAMs), an immortalized PAM cell line (IPAM cells), and the lung tissues of PRRSV-infected piglets. We found that PRRSV infection promoted ADAM17 translocation from the endoplasmic reticulum to the Golgi by enhancing its interaction with inactive rhomboid protein 2 (iRhom2), a newly identified ADAM17 regulator, which in turn elevated ADAM17 activity. By screening for PRRSV-encoded structural proteins, viral envelope (E) and nucleocapsid (N) proteins were identified as the predominant ADAM17 activators. E and N proteins bind with both ADAM17 and iRhom2 to form ternary protein complexes, ultimately strengthening their interactions. Additionally, we demonstrated, using an ADAM17-knockout cell line, that ADAM17 augmented the shedding of soluble TNF-α, a pivotal inflammatory mediator. We also discovered that ADAM17-mediated cleavage of porcine TNF-α occurred between Arg-78 and Ser-79. By constructing a precision mutant cell line with Arg-78-Glu/Ser-79-Glu substitution mutations in TNF-α, we further revealed that the ADAM17-mediated production of soluble TNF-α contributed to the induction of inflammatory responses by PRRSV and its E and N proteins. Taken together, our results elucidate the mechanism by which PRRSV infection activates the iRhom2/ADAM17/TNF-α axis to enhance inflammatory responses, providing valuable insights into the elucidation of PRRSV pathogenesis.

Discovery of galectin-8 as an LILRB4 ligand driving M-MDSCs defines a class of antibodies to fight solid tumors

LILRB4 is an immunosuppressive receptor, and its targeting drugs are undergoing multiple preclinical and clinical trials. Currently, the absence of a functional LILRB4 ligand in solid tumors not only limits the strategy of early antibody screening but also leads to the lack of companion diagnostic (CDx) criteria, which is critical to the objective response rate in early-stage clinical trials. Here, we show that galectin-8 (Gal-8) is a high-affinity functional ligand of LILRB4, and its ligation induces M-MDSC by activating STAT3 and inhibiting NF-κB. Significantly, Gal-8, but not APOE, can induce MDSC, and both ligands bind LILRB4 noncompetitively. Gal-8 expression promotes in vivo tumor growth in mice, and the knockout of LILRB4 attenuates tumor growth in this context. Antibodies capable of functionally blocking Gal-8 are able to suppress tumor growth in vivo. These results identify Gal-8 as an MDSC-driving ligand of LILRB4, and they redefine a class of antibodies for solid tumors.

Carbohydrate supplementation retains intestinal barrier and ameliorates bacterial translocation in an antibiotic-induced mouse model

Bacterial translocation (BT), with antibiotic use as an inducer, is associated with increased risk of developing multiple inflammatory disorders, and is closely associated with intestinal barrier integrity. Deacetylated konjac glucomannan (DKGM) and konjac oligo-glucomannan (KOGM) are two of the most widely used derivatives in the food industry. They are structurally and physiologically distinct from konjac glucomannan (KGM), and previous studies have confirmed their prebiotic effects. But whether they play a role in antibiotic-induced BT is unknown. Here, we applied an antibiotic cocktail (Abx) to a mouse model and investigated whether and how KGM and its derivatives function in BT and inflammation response amelioration during and after antibiotics, and which intervention plan is more effective. The results showed that KGM and its derivatives all inhibited BT. The colon tissue lesions caused by BT were largely alleviated, and short-chain fatty acid (SCFA) production was highly improved with the supplementation of carbohydrates. The prolonged intervention plan using KGM and its derivatives was more efficient than intervention only during the Abx administration period. Among the three dietary fibers, KGM behaved best, while DKGM and KOGM behaved equivalently. Additionally, KGM and its derivatives all reduced the inflammatory response accompanying BT, but DKGM may have a direct inhibitory efficacy in inflammation other than that through IL-10, unlike KGM or KOGM.

Targeting Pseudomonas aeruginosa quorum sensing with sodium salicylate modulates immune responses in vitro and in vivo

Introduction

Chronic infections are a major clinical challenge in hard-to-heal wounds and implanted devices. Pseudomonas aeruginosa is a common causative pathogen that produces numerous virulence factors. Due to the increasing problem of antibiotic resistance, new alternative treatment strategies are needed. Quorum sensing (QS) is a bacterial communication system that regulates virulence and dampens inflammation, promoting bacterial survival. QS inhibition is a potent strategy to reduce bacterial virulence and alleviate the negative impact on host immune response.

Aim

This study investigates how secreted factors from P. aeruginosa PAO1, cultured in the presence or absence of the QS inhibitor sodium salicylate (NaSa), influence host immune response.

Material and methods

In vitro, THP-1 macrophages and neutrophil-like HL-60 cells were used. In vivo, discs of titanium were implanted in a subcutaneous rat model with local administration of P. aeruginosa culture supernatants. The host immune response to virulence factors contained in culture supernatants (+/-NaSa) was characterized through cell viability, migration, phagocytosis, gene expression, cytokine secretion, and histology.

Results

In vitro, P. aeruginosa supernatants from NaSa-containing cultures significantly increased THP-1 phagocytosis and HL-60 cell migration compared with untreated supernatants (-NaSa). Stimulation with NaSa-treated supernatants in vivo resulted in: (i) significantly increased immune cell infiltration and cell attachment to titanium discs; (ii) increased gene expression of IL-8, IL-10, ARG1, and iNOS, and (iii) increased GRO-α protein secretion and decreased IL-1β, IL-6, and IL-1α secretion, as compared with untreated supernatants.

Conclusion

In conclusion, treating P. aeruginosa with NaSa reduces the production of virulence factors and modulates major immune events, such as promoting phagocytosis and cell migration, and decreasing the secretion of several pro-inflammatory cytokines.

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.

Recent advances in inhibition of porcine reproductive and respiratory syndrome virus through targeting CD163

Porcine reproductive and respiratory syndrome virus (PRRSV) has plagued the pig industry for more than 30 years and causes great economic losses. At present different commercial vaccines are available but limited tools. Until now at least six potential host factors are identified as the key receptors for PRRSV infection. Among them, CD163 molecule is the most important and critical in PRRSV life cycle responsible for mediating virus uncoating and genome release. It determines the susceptibility of target cells to the virus. Several PRRSV non-permissive cells (such as PK-15, 3D4/21, and BHK-21) are demonstrated to become completely susceptible to PRRSV infection in the presence of expression of porcine CD163 protein. Therefore, CD163 has become the target for the design of novel antiviral molecules disrupting the interaction between CD163 and viral glycoproteins, or the breeding of gene-modified animals against PRRSV infection. In this review, we comprehensively summarize the recent progress in inhibition of PRRSV replication via targeting CD163 receptor. In addition, whether there are other potential molecules interacting with CD163 in the process of uncoating of virus life cycle is also discussed.

Grossamide attenuates inflammation by balancing macrophage polarization through metabolic reprogramming of macrophages in mice

Macrophages exhibited different phenotypes in response to environmental cues. To meet the needs of rapid response to stimuli, M1-activated macrophages preferred glycolysis to oxidative phosphorylation (OXPHOS) in mitochondria to quickly produce energy and obtain ample raw materials to support cell activation at the same time. Activated macrophages produced free radicals and cytokines to eradicate pathogens but also induced oxidative damage and enhanced inflammation. Grossamide (GSE), a lignanamide from Polygonum multiflorum Thunb., exhibited notable anti-inflammatory effects. In this study, the potential of GSE on macrophage polarization was explored. GSE significantly down-regulated the levels of M1 macrophage biomarkers (Cd32a, Cd80 and Cd86) while increased the levels of M2 indicators (Cd163, Mrc1 and Socs1), showing its potential to inhibit LPS-induced M1 polarization of macrophages. This ability has close a link to its effect on metabolic reprogramming of macrophage. GSE shunted nitric oxide (NO) production from arginine by up-regulation of arginase and down-regulation of inducible nitric oxide synthase, thus attenuated the inhibition of NO on OXPHOS. LPS created three breakpoints in the tricarboxylic acid cycle (TCA) cycle of macrophage as evidenced by down-regulated isocitrate dehydrogenase, accumulation of succinate and the inhibited SDH activity, significantly decreased level of oxoglutarate dehydrogenase expression and its substrate α-ketoglutarate. Thus GSE reduced oxidative stress and amended fragmented TCA cycle. As a result, GSE maintained redox (NAD⁺/NADH) and energy (ATP/ADP) state, reduced extracellular acidification rate and enhanced the oxygen consumption rate. In addition, GSE decreased the release of inflammatory cytokines by inhibiting the activation of the LPS/TLR4/NF-κB pathway. These findings highlighted the central role of immunometabolism of macrophages in its functional plasticity, which invited future study of mode of action of anti-inflammatory drugs from viewpoint of metabolic reprogramming.

Porcine Reproductive and Respiratory Syndrome Virus Adapts Antiviral Innate Immunity via Manipulating MALT1

To fulfill virus replication and persistent infection in hosts, viruses have to find ways to compromise innate immunity, including timely impedance on antiviral RNases and inflammatory responses. Porcine reproductive and respiratory syndrome virus (PRRSV) is a major swine pathogen causing immune suppression. MALT1 is a central immune regulator in both innate and adaptive immunity. In this study, MALT1 was confirmed to be induced rapidly upon PRRSV infection and mediate the degradation of two anti-PRRSV RNases, MCPIP1 and N4BP1, relying on its proteolytic activity, consequently facilitating PRRSV replication. Multiple PRRSV nsps, including nsp11, nsp7β, and nsp4, contributed to MALT1 elicitation. Interestingly, the elevated expression of MALT1 began to decrease once intracellular viral expression reached a high enough level. Higher infection dose brought earlier MALT1 inflection. Further, PRRSV nsp6 mediated significant MALT1 degradation via ubiquitination-proteasome pathway. Downregulation of MALT1 suppressed NF-κB signals, leading to the decrease in proinflammatory cytokine expression. In conclusion, MALT1 expression was manipulated by PRRSV in an elaborate manner to antagonize precisely the antiviral effects of host RNases without excessive and continuous activation of inflammatory responses. These findings throw light on the machinery of PRRSV to build homeostasis in infected immune system for viral settlement.

TLR4 is required for macrophage efferocytosis during resolution of ventilator-induced lung injury

Mechanical ventilation is a life-sustaining therapy for patients with respiratory failure but can cause further lung damage known as ventilator-induced lung injury (VILI). However, the intrinsic molecular mechanisms underlying recovery of VILI remain unknown. Phagocytosis of apoptotic cells (also known as efferocytosis) is a key mechanism orchestrating successful resolution of inflammation. Here we show the positive regulation of macrophage Toll-like receptor (TLR) 4 in efferocytosis and resolution of VILI. Mice were depleted of alveolar macrophages and then subjected to injurious ventilation (tidal volume, 20 mL/kg) for 4 h. On day 1 after mechanical ventilation, Tlr4^+/+ or Tlr4^-/- bone marrow-derived macrophages (BMDMs) were intratracheally administered to alveolar macrophage-depleted mice. We observed that mice depleted of alveolar macrophages exhibited defective resolution of neutrophilic inflammation, exuded protein, lung edema, and lung tissue injury after ventilation, whereas these delayed responses were reversed by administration of Tlr4^+/+ BMDMs. Importantly, these proresolving effects by Tlr4^+/+ BMDMs were abolished in mice receiving Tlr4^-/- BMDMs. The number of macrophages containing apoptotic cells or bodies in bronchoalveolar lavage fluid was much less in mice receiving Tlr4^-/- BMDMs than that in those receiving Tlr4^+/+ BMDMs. Macrophage TLR4 deletion facilitated a disintegrin and metalloprotease 17 maturation and enhanced Mer cleavage in response to mechanical ventilation. Heat shock protein 70 dramatically increased Mer tyrosine kinase surface expression, phagocytosis of apoptotic neutrophils, and rescued the inflammatory phenotype in alveolar macrophage-depleted mice receiving Tlr4^+/+ BMDMs, but not Tlr4^-/- BMDMs. Our results suggest that macrophage TLR4 promotes resolution of VILI via modulation of Mer-mediated efferocytosis.

Recombinant Antigen of Type 2 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV-2) Promotes M1 Repolarization of Porcine Alveolar Macrophages and Th1 Type Response

The polarization status of porcine alveolar macrophages (PAMs) determines the infectivity of porcine reproductive and respiratory syndrome virus (PRRSV). PRRSV infection skews macrophage polarization toward an M2 phenotype, followed by T-cells inactivation. CD163, one of the scavenger receptors of M2 macrophages, has been described as a putative receptor for PRRSV. In this study, we examined two types of PRRSV-2-derived recombinant antigens, A1 (g6Ld10T) and A2 (lipo-M5Nt), for their ability to mediate PAM polarization and T helper (Th1) response. A1 and A2 were composed of different combination of ORF5, ORF6, and ORF7 in full or partial length. To enhance the adaptive immunity, they were conjugated with T cells epitopes or lipidated elements, respectively. Our results showed that CD163⁺ expression on PAMs significantly decreased after being challenged with A1 but not A2, followed by a significant increase in pro-inflammatory genes (TNF-α, IL-6, and IL-12). In addition, next generation sequencing (NGS) data show an increase in T-cell receptor signaling in PAMs challenged with A1. Using a co-culture system, PAMs challenged with A1 can induce Th1 activation by boosting IFN-γ and IL-12 secretion and TNF-α expression. In terms of innate and T-cell-mediated immunity, we conclude that A1 is regarded as a potential vaccine for immunization against PRRSV infection due to its ability to reverse the polarization status of PAMs toward pro-inflammatory phenotypes, which in turn reduces CD163 expression for viral entry and increases immunomodulation for Th1-type response.

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.

Analyzing the Carotenoid Composition of Melilot (Melilotus officinalis (L.) Pall.) Extracts and the Effects of Isolated (All-E)-lutein-5,6-epoxide on Primary Sensory Neurons and Macrophages

Melilotus officinalis is known to contain several types of secondary metabolites. In contrast, the carotenoid composition of this medicinal plant has not been investigated, although it may also contribute to the biological activities of the drug, such as anti-inflammatory effects. Therefore, this study focuses on the isolation and identification of carotenoids from Meliloti herba and on the effect of isolated (all-E)-lutein 5,6-epoxide on primary sensory neurons and macrophages involved in nociception, as well as neurogenic and non-neurogenic inflammatory processes. The composition of the plant extracts was analyzed by high performance liquid chromatography (HPLC). The main carotenoid was isolated by column liquid chromatography (CLC) and identified by MS and NMR. The effect of water-soluble lutein 5,6-epoxide-RAMEB (randomly methylated-β-cyclodextrin) was investigated on Ca²⁺-influx in rat primary sensory neurons induced by the activation of the transient receptor potential ankyrin 1 receptor agonist to mustard-oil and on endotoxin-induced IL-1β release from isolated mouse peritoneal macrophages. (all-E)-Lutein 5,6-epoxide significantly decreased the percent of responsive primary sensory neurons compared to the vehicle-treated stimulated control. Furthermore, endotoxin-evoked IL-1β release from macrophages was significantly decreased by 100 µM lutein 5,6-epoxide compared to the vehicle-treated control. The water-soluble form of lutein 5,6-epoxide-RAMEB decreases the activation of primary sensory neurons and macrophages, which opens perspectives for its analgesic and anti-inflammatory applications.

CD163 Antibodies Inhibit PRRSV Infection via Receptor Blocking and Transcription Suppression

CD163 has been identified as the essential receptor for Porcine reproductive and respiratory syndrome (PRRSV), a major etiologic agent of pigs. Scavenger receptor cysteine-rich domain 5–9 (SRCR5–9) in CD163 was shown to be responsible for the virus interaction. In this study, monoclonal antibodies (mAbs) 6E8 and 9A10 against SRCR5–9 were selected based on the significant activity to inhibit PRRSV infection in Porcine Alveolar Macrophage (PAMs) and Marc-145. Both mAbs are capable of blocking variable PRRSV strains in a dose-dependent manner. Meanwhile, as candidates for both prevention and therapeutics, the antibodies successfully inhibit PRRSV infection and the related NF-κB pathway either before or after virus attachment. Besides, the antibody treatment with either mAb leads to a remarkable decrease of CD163 transcription in PAMs and Marc-145. It is potentially caused by the excessive accumulation of membrane associated CD163 due to the failure in CD163 cleavage with the antibody binding. Further, conformational epitopes targeted by 6E8 and 9A10 are identified to be spanning residues ⁵⁷⁰SXDVGXV⁵⁷⁶ in SRCR5 and Q⁷⁹⁷ in SRCR7, respectively. CD163 with mutated epitopes expressed in 3D4 cells fails to support PRRSV infection while wild type CD163 recovers PRRSV infection, indicating the critical role of these residues in PRRSV invasion. These findings promote the understanding in the interaction between PRRSV and the receptor and provide novel broad antiviral strategies for PRRSV prevention and treatment via alternative mechanisms.