Serum amyloid A activates the NLRP3 inflammasome and promotes Th17 allergic asthma in mice

Stress-induced VIPergic activation mediates microbiota/Th17cell-dependent depressive-like behaviors

Chronic stress often has deleterious effects leading to the development of psychiatric diseases. The gut-brain axis represents a novel avenue for stress research. The negative effects of stress on the gut physiology have been well-described, whereas the pathways whereby stress controls microbial composition to modulate behaviors remains mainly unknown. We discovered that vasoactive intestinal peptide (VIP) activation promoted stress-induced microbial changes leading to increased infiltration of T helper (Th) 17 cells and microglial activation in the hippocampus and depressive-like behaviors, uncovering a close crosstalk between intestinal VIPergic release and the gut microbiota during stress and providing a new interaction between the nervous system and the gut microbiome after stress. Neutralization of the signature cytokine of Th17 cells, interleukin (IL)-17A, was sufficient to block depressive-like behaviors, reduce neuronal VIPergic activation and microglia activation induced by VIPergic activation after stress, opening new potential therapeutic targets for depression.

Serum amyloid A1 induced dysfunction of airway macrophages via CD36 pathway in allergic airway inflammation

Previous studies showed that serum amyloid A (SAA) and macrophages were associated with allergic airway inflammation. However, the interaction between SAA1 and macrophages in allergic airway inflammation remains to be further elucidated. In this study, the levels of SAA1 were measured in nasal tissues from patients with eosinophilic chronic rhinosinusitis with nasal polyps (CRSwNP), house dust mite (HDM)-treated BEAS-2B cells and the tissues of mice of HDM-induced allergic airway inflammation. Human monocytes-derived macrophages and mouse bone marrow-derived macrophages (BMDMs) were exposed to SAA1, and CCL17 and the other M1/M2-related factors were evaluated using RT-PCR and/or ELISA. To test the effects of SAA1-treated BMDMs on chemotaxis and differentiation of CD4+ T cells, number of migrated cells and the levels of Th1 and Th2 were measured using flow cytometry. SAA1 receptors were examined in BMDMs and lung macrophages of model mice. CD36 neutralizing antibody was applied to explore the mechanisms of SAA1 in regulating BMDMs using RT-PCR and/or ELISA. We found that SAA1 was expressed in epithelial cells, and was increased in the nasal tissues of patients with eosinophilic CRSwNP and HDM-treated BEAS-2B- cells as well as the bronchoalveolar lavage fluid and lung tissues of mice exposed to HDM. We also found that the level of CCL17 was increased in M2 macrophages, more CD4+ T cells were recruited and proportion of Th2 was increased after the treatment of SAA1. The treatment of CD36 neutralizing antibody decreased CCL17 level in SAA1-treated M2 BMDMs. In summary, our results showed that SAA1 was increased in allergic airway inflammation, and the administration of SAA1 upregulated the expression of CCL17 in M2 macrophages via CD36 and promoted the chemotaxis of CD4+ T cells and differentiation of Th2. It may provide a new therapeutic strategy that could mediate allergic airway inflammation via suppressing SAA1 to reduce recruitment of CD4+ T cells and activation of Th2.

The role of NLRP3 inflammasome in type 2 inflammation related diseases

Type 2 inflammation related diseases, such as atopic dermatitis, asthma, and allergic rhinitis, are diverse and affect multiple systems in the human body. It is common for individuals to have multiple co-existing type 2 inflammation related diseases, which can impose a significant financial and living burden on patients. However, the exact pathogenesis of these diseases is still unclear. The NLRP3 inflammasome is a protein complex composed of the NLRP3 protein, ASC, and Caspase-1, and is activated through various mechanisms, including the NF-κB pathway, ion channels, and lysosomal damage. The NLRP3 inflammasome plays a role in the immune response to pathogens and cellular damage. Recent studies have indicated a strong correlation between the abnormal activation of NLRP3 inflammasome and the onset of type 2 inflammation. Additionally, it has been demonstrated that suppressing NLRP3 expression effectively diminishes the inflammatory response, highlighting its promising therapeutic applications. Therefore, this article reviews the role of NLRP3 inflammasome in the development and therapy of multiple type 2 inflammation related diseases.

Serum amyloid A for predicting prognosis in patients with newly diagnosed Crohn's disease

OBJECTIVE

Serum amyloid A (SAA) was found to be positively correlated with the activity of Crohn's disease (CD); however, its prognostic value remains uncertain. Here, we examined its predictive ability in newly diagnosed CD and explored genetic association.

METHODS

This retrospective cohort study included patients newly diagnosed as CD at the First Affiliated Hospital of Sun Yat-sen University between June 2010 and March 2022. We employed receiver operating characteristic curve, Cox proportional hazard regression models and restricted cubic splines to investigate the prognostic performance of SAA for surgery and disease progression. To assess possible causality, a two-sample Mendelian randomisation (MR) of published genome-wide association study data was conducted.

RESULTS

During 2187.6 person-years (median age, 28 years, 72.4% male), 87 surgery and 153 disease progression events were documented. A 100-unit increment in SAA level generated 14% higher risk for surgery (adjusted HR (95% CI): 1.14 (1.05-1.23), p=0.001) and 12% for disease progression (1.12 (1.05-1.19), p<0.001). Baseline SAA level ≥89.2 mg/L led to significantly elevated risks for surgery (2.08 (1.31-3.28), p=0.002) and disease progression (1.72 (1.22-2.41), p=0.002). Such associations were assessed as linear. Adding SAA into a scheduled model significantly improved its predictive performances for surgery and disease progression (p for net reclassification indexes and integrated discrimination indexes <0.001). Unfortunately, no genetic causality between SAA and CD was observed in MR analysis. Sensitivity analyses showed robust results.

CONCLUSION

Although causality was not found, baseline SAA level was an independent predictor of surgery and disease progression in newly diagnosed CD, and had additive benefit to existing prediction models.

Hepatic Surf4 Deficiency Impairs Serum Amyloid A1 Secretion and Attenuates Liver Fibrosis in Mice

Liver fibrosis is a severe global health problem. However, no effective antifibrotic drugs have been approved. Surf4 is primarily located in the endoplasmic reticulum (ER) and mediates the transport of secreted proteins from the ER to the Golgi apparatus. Knockout of hepatic Surf4 (Surf4 LKO) in mice impairs very-low-density lipoprotein secretion without causing overt liver damage. Here, we found that collagen levels are significantly reduced in the liver of Surf4 LKO mice compared with control Surf4 flox mice, as demonstrated by proteomics, Western blot, and quantitative reverse transcription polymerase chain reaction. Therefore, this study aims to investigate whether and how hepatic Surf4 affects liver fibrosis. We observed that CCl4-induced liver fibrosis is significantly lower in Surf4 LKO mice than in Surf4 flox mice. Mechanistically, hepatic Surf4 deficiency reduces serum amyloid A1 (SAA1) secretion and hepatic stellate cell (HSC) activation. Surf4 coimmunoprecipitates and colocalizes with SAA1. Lack of hepatic Surf4 significantly reduces SAA1 secretion from hepatocytes, and SAA1 activates cultured human HSCs (LX-2 cells). Conditioned medium (CM) from Surf4-deficient primary hepatocytes activates LX-2 cells to a much lesser extent than CM from Surf4 flox primary hepatocytes, and this reduced effect is restored by the addition of recombinant SAA1 to CM from Surf4-deficient hepatocytes. Knockdown of SAA1 in primary hepatocytes or TLR2 in LX-2 cells significantly reduces LX-2 activation induced by CM from Surf4 flox hepatocytes but not from Surf4 LKO hepatocytes. Furthermore, knockdown of SAA1 significantly ameliorates liver fibrosis in Surf4 flox mice but does not further reduce liver fibrosis in Surf4 LKO mice. We also observe substantial expression of Surf4 and SAA1 in human fibrotic livers. Therefore, hepatic Surf4 facilitates SAA1 secretion, activates HSCs, and aggravates liver fibrosis, suggesting that hepatic Surf4 and SAA1 may serve as treatment targets for liver fibrosis.

High humidity and NO2 co-exposure exacerbates allergic asthma by increasing oxidative stress, inflammatory and TRP protein expressions in lung tissue

Allergic asthma is a chronic inflammatory airway disease with a high mortality rate and a rapidly increasing prevalence in recent decades that is closely linked to environmental change. Previous research found that high humidity (HH) and the traffic-related air pollutant NO2 both aggregated allergic asthma. Their combined effect and mechanisms on asthma exacerbation, however, are unknown. Our study aims to toxicologically clarify the role of HH (90%) and NO2 (5 ppm) on allergic asthma. Ninety male Balb/c mice were randomly assigned to one of six groups (n = 15 in each): saline control, ovalbumin (OVA)-sensitized, OVA + HH, OVA + NO2, OVA + HH + NO2, and OVA + HH + NO2+Capsazepine (CZP). After 38 days of treatment, the airway function, pathological changes in lung tissue, blood inflammatory cells, and oxidative stress and inflammatory biomarkers were comprehensively assessed. Co-exposure to HH and NO2 exacerbated histopathological changes and airway hyperresponsiveness, increased IgE, oxidative stress markers malonaldehyde (MDA) and allergic asthma-related inflammation markers (IL-1β, TNF-α and IL-17), and upregulated the expressions of the transient receptor potential (TRP) ion channels (TRPA1, TRPV1 and TRPV4). Our findings show that co-exposure to HH and NO2 disrupted the Th1/Th2 immune balance, promoting allergic airway inflammation and asthma susceptibility, and increasing TRPV1 expression, whereas CZP reduced TRPV1 expression and alleviated allergic asthma symptoms. Thus, therapeutic treatments that target the TRPV1 ion channel have the potential to effectively manage allergic asthma.

The potential role of serum amyloid A as biomarker of rheumatic diseases: a systematic review and meta-analysis

The identification of novel, robust biomarkers for the diagnosis of rheumatic diseases (RDs) and the presence of active disease might facilitate early treatment and the achievement of favourable long-term outcomes. We conducted a systematic review and meta-analysis of studies investigating the acute phase reactant, serum amyloid A (SAA), in RD patients and healthy controls to appraise its potential as diagnostic biomarker. We searched PubMed, Scopus, and Web of Science from inception to 10 April 2024 for relevant studies. We evaluated the risk of bias and the certainty of evidence using the JBI Critical Appraisal Checklist and GRADE, respectively (PROSPERO registration number: CRD42024537418). In 32 studies selected for analysis, SAA concentrations were significantly higher in RD patients compared to controls (SMD = 1.61, 95% CI 1.24-1.98, p < 0.001) and in RD patients with active disease compared to those in remission (SMD = 2.17, 95% CI 1.21-3.13, p < 0.001). Summary receiving characteristics curve analysis showed a good diagnostic accuracy of SAA for the presence of RDs (area under the curve = 0.81, 95% CI 0.78-0.84). The effect size of the differences in SAA concentrations between RD patients and controls was significantly associated with sex, body mass index, type of RD, and study country. Pending the conduct of prospective studies in different types of RDs, the results of this systematic review and meta-analysis suggest that SAA is a promising biomarker for the diagnosis of RDs and active disease.

Association Between Serum Amyloid A Expression and Disease Control after Endoscopic Sinus Surgery in Patients With Chronic Rhinosinusitis With Nasal Polyps

OBJECTIVE

Our previous study revealed that serum amyloid A (SAA) levels in polyp tissues could serve as a biomarker for the prediction of corticosteroid insensitivity in patients with chronic rhinosinusitis with nasal polyps (CRSwNP). However, their association with disease control status in the patients after endoscopic sinus surgery remains to be assessed.

METHODS

Polyp tissues and control uncinate process mucosa were collected from 48 patients with CRSwNP and 10 healthy control subjects. SAA expression was examined using immunohistochemistry and enzyme-linked immunosorbent assay. Receiver operating characteristic (ROC) curves were performed to determine the predictive value of SAA in nasal polyps. The clinical characteristics of 2 CRSwNP subtypes (SAAhigh and SAAlow) were evaluated.

RESULTS

The SAA expression levels in polyp tissues were significantly elevated both in non-eosinophilic and eosinophilic CRSwNP as compared to the healthy controls. In patients with CRSwNP, the tissue SAA level was significantly higher in the disease-controlled patients than those of the partly controlled and uncontrolled. ROC curve analysis revealed that a cut-off value of 114.9 ng/mL for the tissue SAA level predicted the patients with disease-controlled status with 93.33% sensitivity and 63.64% specificity (AUC = .8727, P < .001). Furthermore, The SAAhigh subgroup showed higher tissue eosinophil numbers and percentage of the disease-controlled patients compared to the SAAlow subgroup.

CONCLUSIONS

Our findings suggest that measurements of SAA in polyp tissues may provide useful information for evaluating CRSwNP conditions, especially identifying the CRSwNP patients with disease-controlled status after endoscopic sinus surgery.

Uncovering the molecular mechanism of Mume Fructus in treatment of Sjögren's syndrome

BACKGROUND

Modern medicine has no cure for the xerostomia caused by the early onset of Sjögren's syndrome. Mume Fructus is a common Chinese herbal medicine used to relieve xerostomia. However, the molecular mechanisms of the effects of Mume Fructus are unknown. In this study, network pharmacology and molecular docking were used to investigate the mechanisms of action of Mume Fructus on Sjögren's syndrome.

MATERIALS AND METHOD

The Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform database was used to identify the active components and targets of Mume Fructus, and the UniProt database was used to identify the genes encoding these targets. SS-related targets were also identified from the GeneCards and OMIM databases. By finding the intersection of the targets of the compounds and the targets of Sjögren's syndrome, the predicted targets of Mume Fructus in the treatment of Sjögren's syndrome were obtained. Further investigation of the active compounds and their targets was carried out by constructing a network of "medicine-candidate compound-target-disease" using Cytoscape 3.7.2, the Protein-Protein Interaction network using the STRING database and Cytoscape 3.7.2, and key targets were identified by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis on R software. Finally, molecular docking was used to verify the affinity of the candidate compounds to the key targets.

RESULTS

Quercetin, beta-sitosterol, and kaempferol in Mume Fructus interact with AKT1, IL-6, IL-1B, JUN, CASP3, and MAPK8. These results suggest that Mume Fructus exerts its therapeutic effects on the peripheral gland injury of Sjögren's syndrome and its secondary cardiovascular disease and tumorigenesis through anti-inflammatory, anti-oxidant, and anti-tumor pathways.

CONCLUSION

With network pharmacology, this study systematically identified the main active components, targets, and specific mechanisms of the therapeutic effects of Mume Fructus on Sjögren's syndrome, providing both a theoretical basis and research direction for further investigations on Mume Fructus.

Asthmatic patients with high serum amyloid A have proinflammatory HDL: Implications for augmented systemic and airway inflammation

RATIONALE

Serum amyloid A (SAA) is bound to high-density lipoproteins (HDL) in blood. Although SAA is increased in the blood of patients with asthma, it is not known whether this modifies asthma severity.

OBJECTIVE

We sought to define the clinical characteristics of patients with asthma who have high SAA levels and assess whether HDL from SAA-high patients with asthma is proinflammatory.

METHODS

SAA levels in serum from subjects with and without asthma were quantified by ELISA. HDLs isolated from subjects with asthma and high SAA levels were used to stimulate human monocytes and were intravenously administered to BALB/c mice.

RESULTS

An SAA level greater than or equal to 108.8 μg/mL was defined as the threshold to identify 11% of an asthmatic cohort (n = 146) as being SAA-high. SAA-high patients with asthma were characterized by increased serum C-reactive protein, IL-6, and TNF-α; older age; and an increased prevalence of obesity and severe asthma. HDL isolated from SAA-high patients with asthma (SAA-high HDL) had an increased content of SAA as compared with HDL from SAA-low patients with asthma and induced the secretion of IL-6, IL-1β, and TNF-α from human monocytes via a formyl peptide receptor 2/ATP/P2X purinoceptor 7 axis. Intravenous administration to mice of SAA-high HDL, but not normal HDL, induced systemic inflammation and amplified allergen-induced neutrophilic airway inflammation and goblet cell metaplasia.

CONCLUSIONS

SAA-high patients with asthma are characterized by systemic inflammation, older age, and an increased prevalence of obesity and severe asthma. HDL from SAA-high patients with asthma is proinflammatory and, when intravenously administered to mice, induces systemic inflammation, and amplifies allergen-induced neutrophilic airway inflammation. This suggests that systemic inflammation induced by SAA-high HDL may augment disease severity in asthma.

A Lipopolysaccharide-Enriched Cow's Milk Allergy Microbiome Promotes a TLR4-Dependent Proinflammatory Intestinal Immune Response

We have previously reported that the gut microbiota of healthy infants harbors allergy-protective bacteria taxa that are depleted in infants with cow's milk allergy (CMA). Few reports have investigated the role of the gut microbiota in promoting allergic responses. In this study we selected a CMA-associated microbiota with increased abundance of Gram-negative bacteria for analysis of its proinflammatory potential. LPS is the major component of the outer membrane of Gram-negative bacteria. Colonization of mice with a global or conditional mutation of the LPS receptor TLR4 with this CMA microbiota induced expression of serum amyloid A1 (Saa1) and other Th17-, B cell-, and Th2-associated genes in the ileal epithelium in a TLR4-dependent manner. In agreement with the gene expression data, mice colonized with the CMA microbiota have expanded populations of Th17 and regulatory T cells and elevated concentrations of fecal IgA. Importantly, we used both antibiotic-treated specific pathogen-free and germ-free rederived mice with a conditional mutation of TLR4 in the CD11c+ compartment to demonstrate that the induction of proinflammatory genes, fecal IgA, and Th17 cells is dependent on TLR4 signaling. Furthermore, metagenomic sequencing revealed that the CMA microbiota has an increased abundance of LPS biosynthesis genes. Taken together, our results show that a microbiota displaying a higher abundance of LPS genes is associated with TLR4-dependent proinflammatory gene expression and a mixed type 2/type 3 response in mice, which may be characteristic of a subset of infants with CMA.

Interorgan communication with the liver: novel mechanisms and therapeutic targets

The liver is a multifunctional organ that plays crucial roles in numerous physiological processes, such as production of bile and proteins for blood plasma, regulation of blood levels of amino acids, processing of hemoglobin, clearance of metabolic waste, maintenance of glucose, etc. Therefore, the liver is essential for the homeostasis of organisms. With the development of research on the liver, there is growing concern about its effect on immune cells of innate and adaptive immunity. For example, the liver regulates the proliferation, differentiation, and effector functions of immune cells through various secreted proteins (also known as "hepatokines"). As a result, the liver is identified as an important regulator of the immune system. Furthermore, many diseases resulting from immune disorders are thought to be related to the dysfunction of the liver, including systemic lupus erythematosus, multiple sclerosis, and heart failure. Thus, the liver plays a role in remote immune regulation and is intricately linked with systemic immunity. This review provides a comprehensive overview of the liver remote regulation of the body's innate and adaptive immunity regarding to main areas: immune-related molecules secreted by the liver and the liver-resident cells. Additionally, we assessed the influence of the liver on various facets of systemic immune-related diseases, offering insights into the clinical application of target therapies for liver immune regulation, as well as future developmental trends.

Discovering the deep evolutionary roots of serum amyloid A protein family

Deep evolutionary origin of the conserved animal serum amyloid A (SAA) apolipoprotein family leading to yet unknown highly similar SAA-like sequences occurring in certain bacterial genomes is demonstrated in this contribution. Horizontal gene transfer event of corresponding genes between gut bacteria and non-vertebrate animals was discovered in the reconstructed phylogenetic tree obtained with maximum likelihood and neighbor-joining methods, respectively. This detailed phylogeny based on totally 128 complete sequences comprised diverse serum amyloid A isoforms from various animal vertebrate and non-vertebrate phyla and also corresponding genes coding for highly similar proteins from animal gut bacteria. Typical largely conserved sequence motifs and a peculiar structural fold consisting mainly of four α-helices in a bundle within all reconstructed clades of the SAA protein family are discussed with respect to their supposed biological functions in various organisms that contain corresponding genes.

Inflammasomes cross-talk with lymphocytes to connect the innate and adaptive immune response

BACKGROUND

Innate and adaptive immunity are two different parts of the immune system that have different characteristics and work together to provide immune protection. Inflammasomes are a major part of the innate immune system that are expressed widely in myeloid cells and are responsible for inflammatory responses. Recent studies have shown that inflammasomes are also expressed and activated in lymphocytes, especially in T and B cells, to regulate the adaptive immune response. Activation of inflammasomes is also under the control of lymphocytes. Therefore, we propose that inflammasomes act as a bridge and they provide crosstalk between the innate and adaptive immune systems to obtain a fine balance in immune responses.

AIM OF REVIEW

This review systematially summarizes the interaction between inflammasomes and lymphocytes and describes the crosstalk between the innate and adaptive immune systems induced by inflammasomes, with the aim of providing new directions and important areas for further research.

KEY SCIENTIFIC CONCEPTS OF REVIEW

When considering the novel function of inflammasomes in various lymphocytes, attention should be given to the activity of specific inflammasomes in studies of lymphocyte function. Moreover, research on the function of various inflammasomes in lymphocytes will help advance knowledge on the mechanisms and treatment of various diseases, including autoimmune diseases and tumors. In addition, when studying inflammatory responses, inflammasomes in both lymphocytes and myeloid cells need to be considered.

Canonical and non-canonical functions of NLRP3

BACKGROUND

Since its discovery, NLRP3 is almost never separated from its major role in the protein complex it forms with ASC, NEK7 and Caspase-1, the inflammasome. This key component of the innate immune response mediates the secretion of proinflammatory cytokines IL-1β and IL-18 involved in immune response to microbial infection and cellular damage. However, NLRP3 has also other functions that do not involve the inflammasome assembly nor the innate immune response. These non-canonical functions have been poorly studied. Nevertheless, NLRP3 is associated with different kind of diseases probably through its inflammasome dependent function as through its inflammasome independent functions.

AIM OF THE REVIEW

The study and understanding of the canonical and non-canonical functions of NLRP3 can help to better understand its involvement in various pathologies. In parallel, the description of the mechanisms of action and regulation of its various functions, can allow the identification of new therapeutic strategies.

KEY SCIENTIFIC CONCEPTS OF THE REVIEW

NLRP3 functions have mainly been studied in the context of the inflammasome, in myeloid cells and in totally deficient transgenic mice. However, for several year, the work of different teams has proven that NLRP3 is also expressed in other cell types where it has functions that are independent of the inflammasome. If these studies suggest that NLRP3 could play different roles in the cytoplasm or the nucleus of the cells, the mechanisms underlying NLRP3 non-canonical functions remain unclear. This is why we propose in this review an inventory of the canonical and non-canonical functions of NLRP3 and their impact in different pathologies.

A two-decade journey in identifying high mobility group box 1 (HMGB1) and procathepsin L (pCTS-L) as potential therapeutic targets for sepsis

INTRODUCTION

Microbial infections and resultant sepsis are leading causes of death in hospitals, representing approximately 20% of total deaths worldwide. Despite the difficulties in translating experimental insights into effective therapies for often heterogenous patient populations, an improved understanding of the pathogenic mechanisms underlying experimental sepsis is still urgently needed. Sepsis is partly attributable to dysregulated innate immune responses manifested by hyperinflammation and immunosuppression at different stages of microbial infections.

AREAS COVERED

Here we review our recent progress in searching for late-acting mediators of experimental sepsis and propose high mobility group box 1 (HMGB1) and procathepsin-L (pCTS-L) as potential therapeutic targets for improving outcomes of lethal sepsis and other infectious diseases.

EXPERT OPINION

It will be important to evaluate the efficacy of HMGB1- or pCTS-L-targeting agents for the clinical management of human sepsis and other infectious diseases in future studies.

Serum amyloid protein A in inflammatory bowel disease: from bench to bedside

Inflammatory bowel diseases (IBD) is featured by gastrointestinal inflammation and a disease course with alternating recurrence and remission. The global burden caused by IBD has significantly boosted in recent years, necessitating treatment optimization. Serum amyloid A (SAA) is a class of 104 amino acid conservative acute-phase proteins, which is essential in immune-mediated inflammatory processes, like IBD. The SAA monomeric structure is composed of four α-helical regions and a C-terminal amorphous tail. Its disordered structure enables multiple bindings to different ligands and permits multiple functions. It has been proven that SAA has dual roles in the inflammatory process. SAA stimulates the pro-inflammatory cytokine expression and promotes the pathogenic differentiation of TH17 cells. In addition, SAA can remove toxic lipids produced during inflammatory responses and membrane debris from dead cells, redirect HDL, and recycle cholesterol for tissue repair. In IBD, SAA acts on gut epithelium barriers, induces T-cell differentiation, and promotes phagocytosis of Gram-negative bacteria. Owing to the tight connection between SAA and IBD, several clinical studies have taken SAA for a biomarker for diagnosis, assessing disease activity, and predicting prognosis in IBD. Furthermore, 5-MER peptide, a drug specifically targeting SAA, has shown anti-inflammatory effects in some SAA-dependent animal models, providing novel insights into the therapeutic targets of IBD.

Role of targeting TLR4 signaling axis in liver-related diseases

Toll-like receptor 4 (TLR4) plays an important role as a key signal-receiving transmembrane protein molecule in the liver, and substances that target the liver exert therapeutic effects via TLR4-related signaling pathways. This article provides a comprehensive review of targeting the TLR4 signaling axis to play an important role in the liver based on endogenous substances. Articles were divided into 5 major types of liver disease, acute liver injury, viral hepatitis, alcoholic and non-alcoholic liver disease, cirrhosis, and liver cancer, to elucidate how various endogenous substances affect the liver via the TLR4 pathway and the important role of the pathway itself in liver-related diseases to discover the potential therapeutic implications of the TLR4-related pathway in the liver. The results indicate that activation of the TLR4-related signaling axis primarily plays a role in promoting disease progression in liver-related diseases, and the TLR4/MyD88/NF-κB axis plays the most dominant role. Therefore, exploring the full effects of drugs targeting the TLR4-related signaling axis in the liver and the new use of old drugs may be a new research direction.

Invariant NKT cells metabolically adapt to the acute myeloid leukaemia environment

Acute myeloid leukaemia (AML) creates an immunosuppressive environment to conventional T cells through Arginase 2 (ARG2)-induced arginine depletion. We identify that AML blasts release the acute phase protein serum amyloid A (SAA), which acts in an autocrine manner to upregulate ARG2 expression and activity, and promote AML blast viability. Following in vitro cross-talk invariant natural killer T (iNKT) cells become activated, upregulate mitochondrial capacity, and release IFN-γ. iNKT retain their ability to proliferate and be activated despite the low arginine AML environment, due to the upregulation of Large Neutral Amino Acid Transporter-1 (LAT-1) and Argininosuccinate Synthetase 1 (ASS)-dependent amino acid pathways, resulting in AML cell death. T cell proliferation is restored in vitro and in vivo. The capacity of iNKT cells to restore antigen-specific T cell immunity was similarly demonstrated against myeloid-derived suppressor cells (MDSCs) in wild-type and Jα18^-/- syngeneic lymphoma-bearing models in vivo. Thus, stimulation of iNKT cell activity has the potential as an immunotherapy against AML or as an adjunct to boost antigen-specific T cell immunotherapies in haematological or solid cancers.

Serum Amyloid A in Stable Patients with Chronic Obstructive Pulmonary Disease Does Not Reflect the Clinical Course of the Disease

Serum amyloid A (SAA) is a good systemic marker of the exacerbations of chronic obstructive pulmonary disease (COPD), but the significance of SAA in stable patients with COPD has not been widely investigated. We aimed to evaluate the SAA level in peripheral blood from stable patients with COPD and to search for correlations between SAA and other inflammatory markers and clinical characteristics of the disease. Serum SAA, IL-6, IL-8, TNF-alpha, basic blood investigations, pulmonary function testing and a 6-min walk test were performed. The correlations between SAA and other inflammatory markers, functional performance and the number of disease exacerbations were evaluated. A total of 100 consecutive patients with COPD were analyzed. No correlations between SAA and inflammatory markers as well as pulmonary function were found. Hierarchical clustering identified two clusters incorporating SAA: one comprised SAA, PaO₂ and FEV₁ and the second was formed of SAA and nine other disease markers. The SAA level was higher in patients with blood eosinophils < 2% when compared to those with blood eosinophils ≥ 2% (41.8 (19.5-69.7) ng/mL vs. 18.9 (1.0-54.5) ng/mL, respectively, p = 0.04). We conclude that, in combination with other important disease features, SAA may be useful for patient evaluation in stable COPD.

NLRP3 activation in neutrophils induces lethal autoinflammation, liver inflammation, and fibrosis

Sterile inflammation is a central element in liver diseases. The immune response following injurious stimuli involves hepatic infiltration of neutrophils and monocytes. Neutrophils are major effectors of liver inflammation, rapidly recruited to sites of inflammation, and can augment the recruitment of other leukocytes. The NLRP3 inflammasome has been increasingly implicated in severe liver inflammation, fibrosis, and cell death. In this study, the role of NLRP3 activation in neutrophils during liver inflammation and fibrosis was investigated. Mouse models with neutrophil-specific expression of mutant NLRP3 were developed. Mutant mice develop severe liver inflammation and lethal autoinflammation phenocopying mice with a systemic expression of mutant NLRP3. NLRP3 activation in neutrophils leads to a pro-inflammatory cytokine and chemokine profile in the liver, infiltration by neutrophils and macrophages, and an increase in cell death. Furthermore, mutant mice develop liver fibrosis associated with increased expression of pro-fibrogenic genes. Taken together, the present work demonstrates how neutrophils, driven by the NLRP3 inflammasome, coordinate other inflammatory myeloid cells in the liver, and propagate the inflammatory response in the context of inflammation-driven fibrosis.

The deciphering of the immune cells and marker signature in COVID-19 pathogenesis: An update

The precise interaction between the immune system and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is critical in deciphering the pathogenesis of coronavirus disease 2019 (COVID-19) and is also vital for developing novel therapeutic tools, including monoclonal antibodies, antivirals drugs, and vaccines. Viral infections need innate and adaptive immune reactions since the various immune components, such as neutrophils, macrophages, CD4⁺ T, CD8⁺ T, and B lymphocytes, play different roles in various infections. Consequently, the characterization of innate and adaptive immune reactions toward SARS-CoV-2 is crucial for defining the pathogenicity of COVID-19. In this study, we explain what is currently understood concerning the conventional immune reactions to SARS-CoV-2 infection to shed light on the protective and pathogenic role of immune response in this case. Also, in particular, we investigate the in-depth roles of other immune mediators, including neutrophil elastase, serum amyloid A, and syndecan, in the immunopathogenesis of COVID-19.

Surviving the Storm: Cytokine Biosignature in SARS-CoV-2 Severity Prediction

Simple Summary

The world has been stricken mentally, physically, and economically by the COVID-19 virus. However, while SARS-CoV-2 viral infection results in mild flu-like symptoms in most patients, a number of those infected develop severe illness. These patients require hospitalization and intensive care. The severe disease can spiral downwards with eventual severe damage to the lungs and failure of multiple organs, leading to the individual’s demise. It is necessary to identify those who are developing a severe form of illness to provide early management. Therefore, it is crucial to learn about the mechanisms and chemical mediators that lead to critical conditions in SARS-CoV-2 infection. This paper reviews studies regarding the individual chemical mediators, pathways, and means that contribute to worsening health conditions in SARS-CoV-2 infection.

Abstract

A significant part of the world population has been affected by the devastating SARS-CoV-2 infection. It has deleterious effects on mental and physical health and global economic conditions. Evidence suggests that the pathogenesis of SARS-CoV-2 infection may result in immunopathology such as neutrophilia, lymphopenia, decreased response of type I interferon, monocyte, and macrophage dysregulation. Even though most individuals infected with the SARS-CoV-2 virus suffer mild symptoms similar to flu, severe illness develops in some cases, including dysfunction of multiple organs. Excessive production of different inflammatory cytokines leads to a cytokine storm in COVID-19 infection. The large quantities of inflammatory cytokines trigger several inflammation pathways through tissue cell and immune cell receptors. Such mechanisms eventually lead to complications such as acute respiratory distress syndrome, intravascular coagulation, capillary leak syndrome, failure of multiple organs, and, in severe cases, death. Thus, to devise an effective management plan for SARS-CoV-2 infection, it is necessary to comprehend the start and pathways of signaling for the SARS-CoV-2 infection-induced cytokine storm. This article discusses the current findings of SARS-CoV-2 related to immunopathology, the different paths of signaling and other cytokines that result in a cytokine storm, and biomarkers that can act as early signs of warning for severe illness. A detailed understanding of the cytokine storm may aid in the development of effective means for controlling the disease’s immunopathology. In addition, noting the biomarkers and pathophysiology of severe SARS-CoV-2 infection as early warning signs can help prevent severe complications.

The Immune Mechanisms of Severe Equine Asthma-Current Understanding and What Is Missing

Severe equine asthma is a chronic respiratory disease of adult horses, occurring when genetically susceptible individuals are exposed to environmental aeroallergens. This results in airway inflammation, mucus accumulation and bronchial constriction. Although several studies aimed at evaluating the genetic and immune pathways associated with the disease, the results reported are inconsistent. Furthermore, the complexity and heterogeneity of this disease bears great similarity to what is described for human asthma. Currently available studies identified two chromosome regions (ECA13 and ECA15) and several genes associated with the disease. The inflammatory response appears to be mediated by T helper cells (Th1, Th2, Th17) and neutrophilic inflammation significantly contributes to the persistence of airway inflammatory status. This review evaluates the reported findings pertaining to the genetical and immunological background of severe equine asthma and reflects on their implications in the pathophysiology of the disease whilst discussing further areas of research interest aiming at advancing treatment and prognosis of affected individuals.

Acute Inflammation Is a Predisposing Factor for Weight Gain and Insulin Resistance

In the course of infection and intense endotoxemia processes, induction of a catabolic state leading to weight loss is observed in mice and humans. However, the late effects of acute inflammation on energy homeostasis, regulation of body weight and glucose metabolism are yet to be elucidated. Here, we addressed whether serial intense endotoxemia, characterized by an acute phase response and weight loss, could be an aggravating or predisposing factor to weight gain and associated metabolic complications. Male Swiss Webster mice were submitted to 8 consecutive doses of lipopolysaccharide (10 mg/kg LPS), followed by 10 weeks on a high-fat diet (HFD). LPS-treated mice did not show changes in weight when fed standard chow. However, when challenged by a high-fat diet, LPS-treated mice showed greater weight gain, with larger fat depot areas, increased serum leptin and insulin levels and impaired insulin sensitivity when compared to mice on HFD only. Acute endotoxemia caused a long-lasting increase in mRNA expression of inflammatory markers such as TLR-4, CD14 and serum amyloid A (SAA) in the adipose tissue, which may represent the key factors connecting inflammation to increased susceptibility to weight gain and impaired glucose homeostasis. In an independent experimental model, and using publicly available microarray data from adipose tissue from mice infected with Gram-negative bacteria, we performed gene set enrichment analysis and confirmed upregulation of a set of genes responsible for cell proliferation and inflammation, including TLR-4 and SAA. Together, we showed that conditions leading to intense and recurring endotoxemia, such as common childhood bacterial infections, may resound for a long time and aggravate the effects of a western diet. If confirmed in humans, infections should be considered an additional factor contributing to obesity and type 2 diabetes epidemics.

Serum Amyloid A1 Exacerbates Hepatic Steatosis via TLR4 Mediated NF-κB Signaling Pathway

Objective

Chronic inflammatory response plays a prominent role in obesity-related nonalcoholic fatty liver disease (NAFLD). However, the intrahepatic triggering mechanism of inflammation remains obscure. This study aimed to elucidate the role of serum amyloid A1 (SAA1), an acute-phase response protein, in the obesity-induced hepatic inflammation and NAFLD.

Methods

Male mice were fed a high fat diet (HFD) for 16 weeks, and insulin resistance, hepatic steatosis, and inflammation in mice were monitored. Murine SAA1/2 was genetically manipulated to investigate the role of SAA1 in NAFLD.

Results

We found that SAA1 was increased in the NAFLD liver in both humans and mice. Knockout of SAA1/2 or knockdown of hepatic SAA1/2 promoted energy expenditure and alleviated HFD-induced metabolic disorder, hepatic steatosis, and inflammation. Endogenous overexpression of SAA1 in hepatocytes by adeno-associated virus 8 (AAV8) transfection aggravated overnutrition-associated gain of body weight, insulin resistance, hepatic lipid accumulation, and liver injury, which were markedly alleviated by knockout of murine toll-like receptor 4 (TLR4). Mechanistically, SAA1 directly bound with TLR4/myeloid differentiation 2 (MD2) to induce TLR4 internalization, leading to the activation of nuclear factor (NF)-κB signaling and production of both SAA1 and other inflammatory cytokines, including interleukin (IL)-6 and C–C chemokine ligand (CCL2) in hepatocytes. Administration of HFD mice with an AAV8-shRNA-SAA1/2 showed a therapeutic effect on hepatic inflammation and NAFLD progression.

Conclusions

These results demonstrate that SAA1 triggers hepatic steatosis and intrahepatic inflammatory response by forming a SAA1/TLR4/NF-κB/SAA1 feedforward regulatory circuit, which, in turn, leads to NAFLD progression. SAA1 may act as a potential target for the disease intervention.

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SAA1/2 deficiency alleviates HFD-induced hepatic steatosis and inflammation in mice.

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SAA1 aggravating overnutrition-associated hepatic steatosis and inflammation is dependent on TLR4.

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SAA1 directly binds to TLR4/MD2 to induce TLR4 internalization, leading to the activation of NF-κB signaling .

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SAA1/TLR4/NF-κB/SAA1 positive feedback in hepatocytes may be a potential target for obesity associated NAFLD.

Chemical Modulation of Gasdermin-Mediated Pyroptosis and Therapeutic Potential

Pyroptosis, a lytic form of programmed cell death, both stimulates effective immune responses and causes tissue damage. Gasdermin (GSDM) proteins are a family of pore-forming executors of pyroptosis. While the most-studied member, GSDMD, exerts critical functions in inflammasome biology, emerging evidence demonstrates potential broad relevance for GSDM-mediated pyroptosis across diverse pathologies. In this review, we describe GSDM biology, outline conditions where inflammasomes and GSDM-mediated pyroptosis represent rational therapeutic targets, and delineate strategies to manipulate these central immunologic processes for the treatment of human disease.

Inflammasome assembly is required for intracellular formation of β2-microglobulin amyloid fibrils, leading to IL-1β secretion

INTRODUCTION

Dialysis-related amyloidosis (DRA) caused by β2-microgloblin (B2M) fibrils is a serious complication for patients with kidney failure on long-term dialysis. Deposition of B2M amyloid fibrils is thought to be due not only to serum extracellular B2M but also to infiltrating inflammatory cells, which may have an important role in B2M amyloid deposition in osteoarticular tissues in patients with DRA. Here, we asked whether B2M amyloid fibrils activate the inflammasome and contribute to formation and deposition of amyloid fibrils in cells.

METHODS

Amyloid formation was confirmed by a thioflavin T (ThT) spectroscopic assay and scanning electron microscopy (SEM). Activation of inflammasomes was assessed by detecting interleukin (IL)-1β in culture supernatants from human embryonic kidney (HEK) 293T cells ectopically expressing inflammasome components. IL-1β secretion was measured by enzyme-linked immunosorbent assay. Expression and co-localization were analyzed by immunohistochemistry and dual immunofluorescence microscopy.

RESULTS

B2M amyloid fibrils interacted directly with NLRP3/Pyrin and to activate the NLRP3/Pyrin inflammasomes, resulting in IL-1β secretion. When HEK293T cells were transfected with inflammasome components NLRP3 or Pyrin, along with ASC, pro-caspase-1, pro-IL-1β, and B2M, ThT fluorescence intensity increased. This was accompanied by IL-1β secretion, which increased in line with the amount of transfected B2M. In this case, morphological glowing of amyloid fibrils was observed by SEM. In the absence of ASC, there was no increase in ThT fluorescence intensity or IL-1β secretion, or any morphological glowing of amyloid fibrils. NLRP3 or Pyrin and B2M were co-localized in a "speck" in HEK293T cells, and co-expressed in infiltrated monocytes/macrophages in the osteoarticular synovial tissues in a patient with DRA.

CONCLUSION

Taken together, these data suggest that inflammasome assembly is required for the subsequent triggering of intracellular formation of B2M amyloid fibrils, which may contribute to osteoarticular deposition of B2M amyloid fibrils and inflammation in patients with DRA.

Serum Amyloid A1: A Biomarker for Neutrophilic Airway Inflammation in Adult Asthmatic Patients

Purpose

We evaluated the role of serum amyloid A1 (SAA1) in the pathogenesis of airway inflammation according to the phenotype of asthma.

Methods

One hundred twenty-two asthmatic patients and 60 healthy control subjects (HCs) were enrolled to measure SAA1 levels. The production of SAA1 from airway epithelial cells (AECs) and its effects on macrophages and neutrophils were investigated in vitro and in vivo.

Results

The SAA1 levels were significantly higher in sera of asthmatic patients than in those of HCs (P = 0.014); among asthmatics, patients with neutrophilic asthma (NA) showed significantly higher SAA1 levels than those with non-NA (P < 0.001). In vitro, polyinosinic:polycytidylic acid (Poly I-C) treatment markedly enhanced the production of SAA1 from AECs, which was further augmented by neutrophils; SAA1 could induce the production of interleukin (IL)-6, IL-8, and S100 calcium-binding protein A9 from AECs. Additionally, SAA1 activated neutrophils and macrophages isolated from peripheral blood of asthmatics, releasing neutrophil extracellular traps (NETs) and secreting proinflammatory cytokines presenting M1 phenotype, respectively. In ovalbumin-induced asthma mice, Poly I-C treatment significantly increased SAA1 levels as well as IL-17A/interferon-gamma/IL-33 levels in bronchoalveolar lavage fluid (BALF), leading to airway hyperresponsiveness and inflammation. The highest levels of SAA1 and neutrophilia were noted in the BALF and sera of the NA mouse model, followed by the mixed granulocytic asthma (MA) model. Especially, SAA1 induced IL-17/retinoic acid receptor-related orphan receptor γt expression from activated CD4+ T lymphocytes in asthmatic mice.

Conclusions

The results show that SAA1 could induce neutrophilic airway inflammation by activating neutrophils along with NET formation, M1 macrophages, and Th2/Th17 predominant cells, contributing to the phenotype of NA or MA.

Role of Serum Amyloid A in Abdominal Aortic Aneurysm and Related Cardiovascular Diseases

Epidemiological data positively correlate plasma serum amyloid A (SAA) levels with cardiovascular disease severity and mortality. Studies by several investigators have indicated a causal role for SAA in the development of atherosclerosis in animal models. Suppression of SAA attenuates the development of angiotensin II (AngII)-induced abdominal aortic aneurysm (AAA) formation in mice. Thus, SAA is not just a marker for cardiovascular disease (CVD) development, but it is a key player. However, to consider SAA as a therapeutic target for these diseases, the pathway leading to its involvement needs to be understood. This review provides a brief description of the pathobiological significance of this enigmatic molecule. The purpose of this review is to summarize the data relevant to its role in the development of CVD, the pitfalls in SAA research, and unanswered questions in the field.

Serum amyloid A3 deficiency impairs in vitro and in vivo adipocyte differentiation

Obesity, caused by an excess adipose tissue, is one of the biggest health-threats of the 21^st century. Adipose tissue expansion occurs through two processes: (i) hypertrophy, and (ii) hyperplasia, the formation of new adipocytes, also termed adipogenesis. Recently, serum amyloid A3 (Saa3) has been implicated in adipogenesis. Therefore, the aim of this study was to investigate the effect of Saa3 on adipogenesis using both an in vitro and in vivo murine model. Saa3 gene silenced pre-adipocytes ha a lower expression of pro-adipogenic markers and less lipid accumulation, indicating impaired adipogenesis. Furthermore, male NUDE mice, injected with Saa3 gene silenced pre-adipocytes developed smaller fat pads with smaller adipocytes and lower expression of pro-adipogenic markers than their control counterparts. This confirms that Saa3 gene silencing indeed impairs adipogenesis, both in vitro and in vivo. These results indicate a clear role for Saa3 in adipogenesis and open new perspectives in the battle against obesity.

Ruxolitinib Ameliorates Airway Hyperresponsiveness and Lung Inflammation in a Corticosteroid-Resistant Murine Model of Severe Asthma

Asthma prevalence has increased considerably over the decades and it is now considered as one of the most common chronic disorders in the world. While the current anti-asthmatic therapies are effective for most asthma patients, there are 5-10% subjects whose disease is not controlled by such agents and they account for about 50% of the asthma-associated healthcare costs. Such patients develop severe asthma (SA), a condition characterized by a dominant Th1/Th17 cytokine response that is accompanied by Type 2 (T2)-low endotype. As JAK (Janus Kinase) signaling is very important for the activation of several cytokine pathways, we examined whether inhibition of JAKs might lessen the clinical and laboratory manifestations of SA. To that end, we employed a recently described murine model that recapitulates the complex immune response identified in the airways of human SA patients. To induce SA, mice were sensitized with house dust mite extract (HDME) and cyclic (c)-di-GMP and then subsequently challenged with HDME and a lower dose of c-di-GMP. In this model, treatment with the JAK inhibitor, Ruxolitinib, significantly ameliorated all the features of SA, including airway hyperresponsiveness and lung inflammation as well as total IgE antibody titers. Thus, these studies highlight JAKs as critical targets for mitigating the hyper-inflammation that occurs in SA and provide the framework for their incorporation into future clinical trials for patients that have severe or difficult-to manage asthma.

Nanomaterial- and shape-dependency of TLR2 and TLR4 mediated signaling following pulmonary exposure to carbonaceous nanomaterials in mice

Background

Pulmonary exposure to high doses of engineered carbonaceous nanomaterials (NMs) is known to trigger inflammation in the lungs paralleled by an acute phase response. Toll-like receptors (TLRs), particularly TLR2 and TLR4, have recently been discussed as potential NM-sensors, initiating inflammation. Using Tlr2 and Tlr4 knock out (KO) mice, we addressed this hypothesis and compared the pattern of inflammation in lung and acute phase response in lung and liver 24 h after intratracheal instillation of three differently shaped carbonaceous NMs, spherical carbon black (CB), multi-walled carbon nanotubes (CNT), graphene oxide (GO) plates and bacterial lipopolysaccharide (LPS) as positive control.

Results

The LPS control confirmed a distinct TLR4-dependency as well as a pronounced contribution of TLR2 by reducing the levels of pulmonary inflammation to 30 and 60% of levels in wild type (WT) mice. At the doses chosen, all NM caused comparable neutrophil influxes into the lungs of WT mice, and reduced levels were only detected for GO-exposed Tlr2 KO mice (35%) and for CNT-exposed Tlr4 KO mice (65%). LPS-induced gene expression was strongly TLR4-dependent. CB-induced gene expression was unaffected by TLR status. Both GO and MWCNT-induced Saa1 expression was TLR4-dependent. GO-induced expression of Cxcl2, Cxcl5, Saa1 and Saa3 were TLR2-dependent. NM-mediated hepatic acute phase response in terms of liver gene expression of Saa1 and Lcn2 was shown to depend on TLR2 for all three NMs. TLR4, in contrast, was only relevant for the acute phase response caused by CNTs, and as expected by LPS.

Conclusion

TLR2 and TLR4 signaling was not involved in the acute inflammatory response caused by CB exposure, but contributed considerably to that of GO and CNTs, respectively. The strong involvement of TLR2 in the hepatic acute phase response caused by pulmonary exposure to all three NMs deserves further investigations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00432-z.

Human lung cDC1 drive increased perforin-mediated NK cytotoxicity in Chronic Obstructive Pulmonary Disease

In chronic obstructive pulmonary disease (COPD), lung natural killer cells (NKs) lyse autologous lung epithelial cells in vitro, but underlying mechanisms and their relationship to epithelial cell apoptosis in vivo are undefined. Although this cytolytic capacity of lung NKs depends on priming by dendritic cells (DC), whether priming correlates with DC maturation or is limited to a specific DC subset are also unknown. We recruited ever-smokers (≥10 pack-years) (n=96) undergoing clinically-indicated lung resections. We analyzed lung NKs for cytotoxic molecule transcripts and for cytotoxicity, which we correlated with in situ detection of activated Caspase-3/7+ airway epithelial cells. To investigate DC priming, we measured lung DC expression of CCR2, CCR7, and CX3CR1, and co-cultured peripheral blood NKs with autologous lung DC, either matured using LPS (non-obstructed smokers) or separated into conventional DC type-1 (cDC1) versus cDC type-2 (cDC2) (COPD). Lung NKs in COPD expressed more perforin (p<0.02) and granzyme B (p<0.03) transcripts; inhibiting perforin blocked in vitro killing by lung NKs. Cytotoxicity in vitro correlated significantly (S_r=0.68, p=0.0043) with numbers of apoptotic epithelial cells per airway. In non-obstructed smokers, LPS-induced maturation enhanced DC-mediated priming of blood NKs, reflected by greater epithelial cell death. Although CCR7 expression was greater in COPD in both cDC1 (p<0.03) and cDC2 (p=0.009), only lung cDC1 primed NK killing. Thus, rather than being intrinsic to those with COPD, NK priming is a capacity of human lung DC that is inducible by recognition of bacterial (and possibly other) danger signals and restricted to the cDC1 subset.

Transcriptomic Analysis of Polyhexamethyleneguanidine-Induced Lung Injury in Mice after a Long-Term Recovery

Polyhexamethyleneguanidine phosphate (PHMG-P) is one of the causative agents of humidifier disinfectant-induced lung injury. Direct exposure of the lungs to PHMG-P causes interstitial pneumonia with fibrosis. Epidemiological studies showed that patients with humidifier disinfectant-associated lung injuries have suffered from restrictive lung function five years after the onset of the lung injuries. We investigated whether lung damage was sustained after repeated exposure to PHMG-P followed by a long-term recovery and evaluated the adverse effects of PHMG-P on mice lungs. Mice were intranasally instilled with 0.3 mg/kg PHMG-P six times at two weeks intervals, followed by a recovery period of 292 days. Histopathological examination of the lungs showed the infiltration of inflammatory cells, the accumulation of extracellular matrix in the lung parenchyma, proteinaceous substances in the alveoli and bronchiolar–alveolar hyperplasia. From RNA-seq, the gene expression levels associated with the inflammatory response, leukocyte chemotaxis and fibrosis were significantly upregulated, whereas genes associated with epithelial/endothelial cells development, angiogenesis and smooth muscle contraction were markedly decreased. These results imply that persistent inflammation and fibrotic changes caused by repeated exposure to PHMG-P led to the downregulation of muscle and vascular development and lung dysfunction. Most importantly, this pathological structural remodeling induced by PHMG-P was not reversed even after long-term recovery.

Endogenous Regulation and Pharmacological Modulation of Sepsis-Induced HMGB1 Release and Action: An Updated Review

Sepsis remains a common cause of death in intensive care units, accounting for approximately 20% of total deaths worldwide. Its pathogenesis is partly attributable to dysregulated inflammatory responses to bacterial endotoxins (such as lipopolysaccharide, LPS), which stimulate innate immune cells to sequentially release early cytokines (such as tumor necrosis factor (TNF) and interferons (IFNs)) and late mediators (such as high-mobility group box 1, HMGB1). Despite difficulties in translating mechanistic insights into effective therapies, an improved understanding of the complex mechanisms underlying the pathogenesis of sepsis is still urgently needed. Here, we review recent progress in elucidating the intricate mechanisms underlying the regulation of HMGB1 release and action, and propose a few potential therapeutic candidates for future clinical investigations.

Native and oxidised lipoproteins negatively regulate the serum amyloid A-induced NLRP3 inflammasome activation in human macrophages

Objectives

The NLRP3 inflammasome plays a key role in arterial wall inflammation. In this study, we elucidated the role of serum lipoproteins in the regulation of NLRP3 inflammasome activation by serum amyloid A (SAA) and other inflammasome activators.

Methods

The effect of lipoproteins on the NLRP3 inflammasome activation was studied in primary human macrophages and THP‐1 macrophages. The effect of oxidised low‐density lipoprotein (LDL) was examined in an in vivo mouse model of SAA‐induced peritoneal inflammation.

Results

Native and oxidised high‐density lipoproteins (HDL₃) and LDLs inhibited the interaction of SAA with TLR4. HDL₃ and LDL inhibited the secretion of interleukin (IL)‐1β and tumor necrosis factor by reducing their transcription. Oxidised forms of these lipoproteins reduced the secretion of mature IL‐1β also by inhibiting the activation of NLRP3 inflammasome induced by SAA, ATP, nigericin and monosodium urate crystals. Specifically, oxidised LDL was found to inhibit the inflammasome complex formation. No cellular uptake of lipoproteins was required, nor intact lipoprotein particles for the inhibitory effect, as the lipid fraction of oxidised LDL was sufficient. The inhibition of NLRP3 inflammasome activation by oxidised LDL was partially dependent on autophagy. Finally, oxidised LDL inhibited the SAA‐induced peritoneal inflammation and IL‐1β secretion in vivo.

Conclusions

These findings reveal that both HDL₃ and LDL inhibit the proinflammatory activity of SAA and this inhibition is further enhanced by lipoprotein oxidation. Thus, lipoproteins possess major anti‐inflammatory functions that hinder the NLRP3 inflammasome‐activating signals, particularly those exerted by SAA, which has important implications in the pathogenesis of cardiovascular diseases.

Accelerated atherosclerosis caused by serum amyloid A response in lungs of ApoE-/- mice

Airway exposure to eg particulate matter is associated with cardiovascular disease including atherosclerosis. Acute phase genes, especially Serum Amyloid A3 (Saa3), are highly expressed in the lung following pulmonary exposure to particles. We aimed to investigate whether the human acute phase protein SAA (a homolog to mouse SAA3) accelerated atherosclerotic plaque progression in Apolipoprotein E knockout (ApoE^-/- ) mice. Mice were intratracheally (i.t.) instilled with vehicle (phosphate buffered saline) or 2 µg human SAA once a week for 10 weeks. Plaque progression was assessed in the aorta using noninvasive ultrasound imaging of the aorta arch as well as by en face analysis. Additionally, lipid peroxidation, SAA3, and cholesterol were measured in plasma, inflammation was determined in lung, and mRNA levels of the acute phase genes Saa1 and Saa3 were measured in the liver and lung, respectively. Repeated i.t. instillation with SAA caused a significant progression in the atherosclerotic plaques in the aorta (1.5-fold). Concomitantly, SAA caused a statistically significant increase in neutrophils in bronchoalveolar lavage fluid (625-fold), in pulmonary Saa3 (196-fold), in systemic SAA3 (1.8-fold) and malondialdehyde levels (1.14-fold), indicating acute phase response (APR), inflammation and oxidative stress. Finally, pulmonary exposure to SAA significantly decreased the plasma levels of very low-density lipoproteins - low-density lipoproteins and total cholesterol, possibly due to lipids being sequestered in macrophages or foam cells in the arterial wall. Combined these results indicate the importance of the pulmonary APR and SAA3 for plaque progression.

The signal pathways and treatment of cytokine storm in COVID-19

The Coronavirus Disease 2019 (COVID-19) pandemic has become a global crisis and is more devastating than any other previous infectious disease. It has affected a significant proportion of the global population both physically and mentally, and destroyed businesses and societies. Current evidence suggested that immunopathology may be responsible for COVID-19 pathogenesis, including lymphopenia, neutrophilia, dysregulation of monocytes and macrophages, reduced or delayed type I interferon (IFN-I) response, antibody-dependent enhancement, and especially, cytokine storm (CS). The CS is characterized by hyperproduction of an array of pro-inflammatory cytokines and is closely associated with poor prognosis. These excessively secreted pro-inflammatory cytokines initiate different inflammatory signaling pathways via their receptors on immune and tissue cells, resulting in complicated medical symptoms including fever, capillary leak syndrome, disseminated intravascular coagulation, acute respiratory distress syndrome, and multiorgan failure, ultimately leading to death in the most severe cases. Therefore, it is clinically important to understand the initiation and signaling pathways of CS to develop more effective treatment strategies for COVID-19. Herein, we discuss the latest developments in the immunopathological characteristics of COVID-19 and focus on CS including the current research status of the different cytokines involved. We also discuss the induction, function, downstream signaling, and existing and potential interventions for targeting these cytokines or related signal pathways. We believe that a comprehensive understanding of CS in COVID-19 will help to develop better strategies to effectively control immunopathology in this disease and other infectious and inflammatory diseases.

Integrated Analysis of lncRNAs, mRNAs, and TFs to Identify Regulatory Networks Underlying MAP Infection in Cattle

Johne’s disease is a chronic infection of ruminants that burdens dairy herds with a significant economic loss. The pathogenesis of the disease has not been revealed clearly due to its complex nature. In order to achieve deeper biological insights into molecular mechanisms involved in MAP infection resulting in Johne’s disease, a system biology approach was used. As far as is known, this is the first study that considers lncRNAs, TFs, and mRNAs, simultaneously, to construct an integrated gene regulatory network involved in MAP infection. Weighted gene coexpression network analysis (WGCNA) and functional enrichment analysis were conducted to explore coexpression modules from which nonpreserved modules had altered connectivity patterns. After identification of hub and hub-hub genes as well as TFs and lncRNAs in the nonpreserved modules, integrated networks of lncRNA-mRNA-TF were constructed, and cis and trans targets of lncRNAs were identified. Both cis and trans targets of lncRNAs were found in eight nonpreserved modules. Twenty-one of 47 nonpreserved modules showed significant biological processes related to the immune system and MAP infection. Some of the MAP infection’s related pathways in the most important nonpreserved modules comprise “positive regulation of cytokine-mediated signaling pathway,” “negative regulation of leukocyte migration,” “T-cell differentiation,” “neutrophil activation,” and “defense response.” Furthermore, several genes were identified in these modules, including SLC11A1, MAPK8IP1, HMGCR, IFNGR1, CMPK2, CORO1A, IRF1, LDLR, BOLA-DMB, and BOLA-DMA, which are potentially associated with MAP pathogenesis. This study not only enhanced our knowledge of molecular mechanisms behind MAP infection but also highlighted several promising hub and hub-hub genes involved in macrophage-pathogen interaction.

IL-1β promotes immunoregulatory responses in human blood basophils

Human basophils are essential effector cells of chronic allergic inflammation. IL-1 family cytokines such as interleukin (IL)-33 and IL-1β are elevated in serum and bronchoalveolar lavage fluid of allergic asthmatics. IL-33 is known to be a critical regulator of basophil's T2 immune responses. However, the effect of IL-1β on the function of basophils has not been well investigated. Here, we elucidate whether IL-1β regulates the function of human basophils and compared the effects of IL-1β and IL-33 on basophils of healthy and allergic subjects. We found that IL-1β activates the p38 MAPK signaling pathway and promotes IL-8 release in basophils of healthy donors, while FcεRI-mediated LCT₄ and histamine secretion is not affected. Strikingly, in the presence of IL-3, IL-1β shows more potency than IL-33, as evidenced by the enhanced p38 phosphorylation and NF-κB activation, as well as the release of both IL-13 and IL-8. We found that the enhanced basophil responsiveness is achieved through IL-3-induced IL-1RI surface expression. Importantly, basophils of allergic donors release significantly higher amounts of IL-8 compared to those from healthy donors upon IL-33 and IL-1β stimulation. Consistently, we detected increased IL-1RI and decreased IL-3 receptor alpha-chain (CD123) and CCR3 expression on basophils of allergic subjects compared to healthy controls, suggesting an in vivo IL-3 priming in allergic donors. In summary, our results suggest enhanced sensitivity of basophils toward IL-33 and IL-1β in allergic subjects compared to those from healthy controls.

Serum Amyloid A1 Induces Classically Activated Macrophages: A Role for Enhanced Fibril Formation

AA amyloidosis belongs to the group of amyloid diseases which can follow chronic inflammatory conditions of various origin. The disease is characterized by the deposition of insoluble amyloid fibrils formed by serum amyloid A1 (SAA1) leading eventually to organ failure. Macrophages are intimately involved in the fibrillogenesis as well as in the clearance of amyloid fibrils. In vivo, macrophages may occur as classically (M1) or alternatively activated (M2) macrophages. We investigate here how SAA1 might affect the macrophage phenotype and function. Gene microarray analysis revealed upregulation of 64 M1-associated genes by SAA1. M1-like polarization was further confirmed by the expression of the M1-marker MARCO, activation of the NF-κB transcription factor, and secretion of the M1-cytokines TNF-α, IL-6, and MCP-1. Additionally, we demonstrate here that M1-polarized macrophages exhibit enhanced fibrillogenic activity towards SAA1. Based on our data, we propose reconsideration of the currently used cellular amyloidosis models towards an in vitro model employing M1-polarized macrophages. Furthermore, the data suggest macrophage repolarization as potential intervention strategy in AA amyloidosis.

The turning away of serum amyloid A biological activities and receptor usage

Serum amyloid A (SAA) is an acute-phase protein (APP) to which multiple immunological functions have been attributed. Regardless, the true biological role of SAA remains poorly understood. SAA is remarkably conserved in mammalian evolution, thereby suggesting an important biological function. Since its discovery in the 1970s, the majority of researchers have investigated SAA using recombinant forms made available through bacterial expression. Nevertheless, recent studies indicate that these recombinant forms of SAA are unreliable. Indeed, commercial SAA variants have been shown to be contaminated with bacterial products including lipopolysaccharides and lipoproteins. As such, biological activities and receptor usage (TLR2, TLR4) revealed through the use of commercial SAA variants may not reflect the inherent nature of this APP. Within this review, we discuss the biological effects of SAA that have been demonstrated through more solid experimental approaches. SAA takes part in the innate immune response via the recruitment of leucocytes and executes, through pathogen recognition, antimicrobial activity. Knockout animal models implicate SAA in a range of functions, such as regulation of T-cell-mediated responses and monopoiesis. Moreover, through its structural motifs, not only does SAA function as an extracellular matrix protein, but it also binds extracellular matrix proteins. Finally, we here also provide an overview of definite SAA receptor-mediated functions and highlight those that are yet to be validated. The role of FPR2 in SAA-mediated leucocyte recruitment has been confirmed; nevertheless, SAA has been linked to a range of other receptors including CD36, SR-BI/II, RAGE and P2RX7.

Sexually Dimorphic Relationships Among Saa3 (Serum Amyloid A3), Inflammation, and Cholesterol Metabolism Modulate Atherosclerosis in Mice

[Figure: see text].

Innate Immune Responses and Pulmonary Diseases

Innate immunity is the first defense line of the host against various infectious pathogens, environmental insults, and other stimuli causing cell damages. Upon stimulation, pattern recognition receptors (PRRs) act as sensors to activate innate immune responses, containing NF-κB signaling, IFN response, and inflammasome activation. Toll-like receptors (TLRs), retinoic acid-inducible gene I-like receptors (RLRs), NOD-like receptors (NLRs), and other nucleic acid sensors are involved in innate immune responses. The activation of innate immune responses can facilitate the host to eliminate pathogens and maintain tissue homeostasis. However, the activity of innate immune responses needs to be tightly controlled to ensure the optimal intensity and duration of activation under various contexts. Uncontrolled innate immune responses can lead to various disorders associated with aberrant inflammatory response, including pulmonary diseases such as COPD, asthma, and COVID-19. In this chapter, we will have a broad overview of how innate immune responses function and the regulation and activation of innate immune response at molecular levels as well as their contribution to various pulmonary diseases. A better understanding of such association between innate immune responses and pulmonary diseases may provide potential therapeutic strategies.

Leukotriene B4 Receptors Are Necessary for the Stimulation of NLRP3 Inflammasome and IL-1β Synthesis in Neutrophil-Dominant Asthmatic Airway Inflammation

The stimulation of the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome and IL-1β synthesis are associated with chronic respiratory diseases such as neutrophil-dominant severe asthma. Leukotriene B₄ (LTB₄) is a principal chemoattractant molecule for neutrophil recruitment, and its receptors BLT1 and BLT2 have been suggested to contribute to neutrophil-dominant asthmatic airway inflammation. However, the relationship between BLT1/2 and NLRP3 in neutrophil-dominant asthmatic airway inflammation has not been previously studied. In the present study, we investigated whether BLT1/2 play any roles in stimulating the NLRP3 inflammasome and IL-1βsynthesis. The blockade of BLT1 or BLT2 clearly suppressed the stimulation of the NLRP3 inflammasome and IL-1β synthesis in house dust mite (HDM)/lipopolysaccharide (LPS)-induced neutrophilic airway inflammation. The enzymes 5-lipoxygenase and 12-lipoxygenase, which catalyze the synthesis of BLT1/2 ligands [LTB₄, 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), and 12-hydroxyheptadecatreinoic acid (12-HHT)], were also critically associated with the stimulation of NLRP3 and IL-1β synthesis. Together, our results suggest that the 5-/12-LOX-BLT1/2-linked cascade are necessary for the simulation of the NLRP3 inflammasome and IL-1β synthesis, thus contributing to HDM/LPS-induced neutrophil-dominant airway inflammation.

Mycobacterium tuberculosis stimulates IL-1β production by macrophages in an ESAT-6 dependent manner with the involvement of serum amyloid A3

Despite its critical roles in immune responses against tuberculosis infection and immune pathology, the molecular details of interleukin (IL)-1β production in tuberculosis infection remain elusive. To explore IL-1β production in tuberculosis infection, we infected mouse bone marrow-derived macrophages (BMDM) with Mycobacterium tuberculosis (Mtb) H37Rv, its early secreted antigenic target protein of 6 kDa (ESAT-6) gene deletion (H37Rv:Δ3875) or complemented strain (H37Rv:Δ3875C) and evaluated IL-1β production. H37Rv induced significantly increased IL-1β production by BMDMs compared to non-infected BMDMs. In contrast, H37Rv:Δ3875 induced significantly less mature IL-1β production despite eliciting comparable levels of pro-IL-1β and IL-8 from BMDMs compared to H37Rv and H37Rv:Δ3875C. Blocking either NLRP3 or K⁺ efflux diminished H37Rv-induced IL-1β production by BMDMs. Infection of mice intranasally with H37Rv:Δ3875 induced less IL-1β production in the lungs compared with H37Rv. Intranasal delivery of ESAT-6 but not CFP10 induced production of IL-1β in mouse lungs and RNA-Seq analysis identified serum amyloid A (SAA) 3 as one of the highly expressed genes in mouse lungs. Infection of mice with H37Rv but not H37Rv:Δ3875 induced expression of lung SAA3 mRNA and protein, consistent with the effect of intranasal delivery of ESAT-6. Silencing SAA3 reduced Mtb-induced IL-1β production by BMDMs. We conclude that SAA3 plays critical role in ESAT-6 dependent IL-1β production by macrophages in tuberculosis infection.

Transcriptional analysis of cystic fibrosis airways at single-cell resolution reveals altered epithelial cell states and composition

Cystic fibrosis (CF) is a lethal autosomal recessive disorder that afflicts more than 70,000 people. People with CF experience multi-organ dysfunction resulting from aberrant electrolyte transport across polarized epithelia due to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CF-related lung disease is by far the most important determinant of morbidity and mortality. Here we report results from a multi-institute consortium in which single-cell transcriptomics were applied to define disease-related changes by comparing the proximal airway of CF donors (n = 19) undergoing transplantation for end-stage lung disease with that of previously healthy lung donors (n = 19). Disease-dependent differences observed include an overabundance of epithelial cells transitioning to specialized ciliated and secretory cell subsets coupled with an unexpected decrease in cycling basal cells. Our study yields a molecular atlas of the proximal airway epithelium that will provide insights for the development of new targeted therapies for CF airway disease.