Mesenchymal Stromal/Stem Cells Know Best: The Remarkable Complexities of Its Interactions With Polymorphonuclear Neutrophils.

Polymorphonuclear neutrophils (PMNs), the predominant immune cell type in humans, have long been known as first-line effector cells against bacterial infections mainly through phagocytosis and production of reactive oxygen species (ROS). However, recent research has unveiled novel and pivotal roles of these abundant but short-lived granulocytes in health and disease. Human mesenchymal stromal/stem cells (MSCs), renowned for their regenerative properties and modulation of T lymphocytes from effector to regulatory phenotypes, exhibit complex and context-dependent interactions with PMNs. Regardless of species or source, MSCs strongly abrogate PMN apoptosis, a critical determinant of PMN function, except if PMNs are highly stimulated. MSCs also have the capacity to fine-tune PMN activation, particularly in terms of CD11b expression and phagocytosis. Moreover, MSCs can modulate numerous other PMN functions, spanning migration, ROS production, and neutrophil extracellular trap (NET) formation/NETosis, but directionality is remarkably dependent on the underlying context: in normal nondiseased conditions, MSCs enhance PMN migration and ROS production, whereas in inflammatory conditions, MSCs reduce both these functions and NETosis. Furthermore, the state of the MSCs themselves, whether isolated from diseased or healthy donors, and the specific secreted products and molecules, can impact interactions with PMNs; while healthy MSCs prevent PMN infiltration and NETosis, MSCs isolated from patients with cancer promote these functions. This comprehensive analysis highlights the intricate interplay between PMNs and MSCs and its profound relevance in healthy and pathological conditions, shedding light on how to best strategize the use of MSCs in the expanding list of diseases with PMN involvement.

Clinical implications of hepatitis B virus core antigen-mediated immunopathologic T cell responses in chronic hepatitis B.

Hepatitis B virus (HBV) infection significantly impacts Asian populations. The influences of continuous HBV antigen and inflammatory stimulation to T cells in chronic hepatitis B (CHB) remain unclear. In this study, we first conducted bioinformatics analysis to assess T-cell signaling pathways in CHB patients. In a Taiwanese cohort, we examined the phenotypic features of HBVcore -specific T cells and their correlation with clinical parameters. We used core protein overlapping peptides from the Taiwan prevalent genotype B HBV to investigate the antiviral response and the functional implication of HBV-specific T cells. In line with Taiwanese dominant HLA-alleles, we also evaluated ex vivo HBVcore -specific T cells by pMHC-tetramers targeting epitopes within HBV core protein. Compared to healthy subjects, we disclosed CD8 T cells from CHB patients had higher activation marker CD38 levels but showed an upregulation in the inhibitory receptor PD-1. Our parallel study showed HBV-specific CD8 T cells were more activated with greater PD-1 expression than CMV-specific subset and bulk CD8 T cells. Moreover, our longitudinal study demonstrated a correlation between the PD-1 fluctuation pattern of HBVcore -specific CD8 T cells and liver inflammation in CHB patients. Our research reveals the HBV core antigen-mediated immunopathologic profile of CD8 T cells in chronic HBV infection. Our findings suggest the PD-1 levels of HBVcore -specific CD8 T cells can be used as a valuable indicator of personal immune response for clinical application in hepatitis management.

Excess glucose alone depress young mesenchymal stromal/stem cell osteogenesis and mitochondria activity within hours/days via NAD+/SIRT1 axis.

BACKGROUND: The impact of global overconsumption of simple sugars on bone health, which peaks in adolescence/early adulthood and correlates with osteoporosis (OP) and fracture risk decades, is unclear. Mesenchymal stromal/stem cells (MSCs) are the progenitors of osteoblasts/bone-forming cells, and known to decrease their osteogenic differentiation capacity with age. Alarmingly, while there is correlative evidence that adolescents consuming greatest amounts of simple sugars have the lowest bone mass, there is no mechanistic understanding on the causality of this correlation. METHODS: Bioinformatics analyses for energetics pathways involved during MSC differentiation using human cell information was performed. In vitro dissection of normal versus high glucose (HG) conditions on osteo-/adipo-lineage commitment and mitochondrial function was assessed using multi-sources of non-senescent human and murine MSCs; for in vivo validation, young mice was fed normal or HG-added water with subsequent analyses of bone marrow CD45- MSCs. RESULTS: Bioinformatics analyses revealed mitochondrial and glucose-related metabolic pathways as integral to MSC osteo-/adipo-lineage commitment. Functionally, in vitro HG alone without differentiation induction decreased both MSC mitochondrial activity and osteogenesis while enhancing adipogenesis by 8 h' time due to depletion of nicotinamide adenine dinucleotide (NAD+), a vital mitochondrial co-enzyme and co-factor to Sirtuin (SIRT) 1, a longevity gene also involved in osteogenesis. In vivo, HG intake in young mice depleted MSC NAD+, with oral NAD+ precursor supplementation rapidly reversing both mitochondrial decline and osteo-/adipo-commitment in a SIRT1-dependent fashion within 1 ~ 5 days. CONCLUSIONS: We found a surprisingly rapid impact of excessive glucose, a single dietary factor, on MSC SIRT1 function and osteogenesis in youthful settings, and the crucial role of NAD+-a single molecule-on both MSC mitochondrial function and lineage commitment. These findings have strong implications on future global OP and disability risks in light of current worldwide overconsumption of simple sugars.

Endometriosis and Sjögren's syndrome: Bidirectional associations in population-based 15-year retrospective cohorts.

INTRODUCTION: Primary Sjögren's syndrome (pSS) is a chronic autoimmune disorder affecting salivary and lacrimal glands, while endometriosis involves uterine-like tissue growth outside the uterus, causing pelvic pain and infertility. Investigating their intricate relationship using real-world data is crucial due to limited research on their connection. MATERIAL AND METHODS: This population-based cohort study included patients with endometriosis and controls without endometriosis. Propensity score matching was used to balance baseline differences in demographic and clinic characteristics between the two groups. Cox proportional hazards model were used to estimate the effect of endometriosis on the risk of new-onset pSS over time. A symmetrical cohort study, including patients with pSS and propensity score-matched controls without pSS, was conducted to investigate the effect of pSS on the risk of endometriosis over time. To elaborate on the mechanisms linking endometriosis and pSS, Ingenuity Pathway Analysis was performed to identify activated pathways in eutopic endometrium from patients with endometriosis and parotid tissues from patients with pSS. RESULTS: A total of 15 947 patients with endometriosis and 15 947 propensity score-matched controls without endometriosis were included. Patients with endometriosis presented a significantly greater risk of pSS compared to non-endometriosis controls (adjusted hazard ratio, aHR = 1.57, 95% CI = 1.29-1.91, p < 0.001). In the symmetrical cohort study, which included 4906 pSS patients and 4,906 propensity score-matched controls without pSS, patients with pSS were found to be at a significantly higher risk of endometriosis compared to non-pSS controls (aHR = 1.51, 95% CI = 1.12-2.04, p = 0.012). Ingenuity Pathway Analysis showed that the underlying cellular mechanisms involved autoimmune-related pathways, including activation of dendritic cell maturation, and chronic inflammatory pathways, including the fibrosis signaling pathway. CONCLUSIONS: These findings support a bidirectional association between endometriosis and pSS, which may be driven by dendritic cell maturation and fibrosis signaling pathways.

Placental mesenchymal stem cells boost M2 alveolar over M1 bone marrow macrophages via IL-1ß in Klebsiella-mediated acute respiratory distress syndrome.

RATIONALE: Acute respiratory distress syndrome (ARDS) is a lethal complication of severe bacterial pneumonia due to the inability to dampen overexuberant immune responses without compromising pathogen clearance. Both of these processes involve tissue-resident and bone marrow (BM)-recruited macrophage (MΦ) populations which can be polarised to have divergent functions. Surprisingly, despite the known immunomodulatory properties of mesenchymal stem cells (MSCs), simultaneous interactions with tissue-resident and recruited BMMΦ populations are largely unexplored. OBJECTIVES: We assessed the therapeutic use of human placental MSCs (PMSCs) in severe bacterial pneumonia with elucidation of the roles of resident alveolar MΦs (AMΦs) and BMMΦs. METHODS: We developed a lethal, murine pneumonia model using intratracheal infection of a clinically relevant Klebsiella pneumoniae (KP) strain with subsequent intravenous human PMSC treatment. Pulmonary AMΦ and recruited BMMΦ analyses, histological evaluation, bacterial clearance and mice survival were assessed. To elucidate the role of resident AMΦs in improving outcome, we performed AMΦ depletion in the KP-pneumonia model with intratracheal clodronate pretreatment. MEASUREMENTS AND MAIN RESULTS: Human PMSC treatment decreased tissue injury and improved survival of severe KP-pneumonia mice by decreasing the presence and function of recruited M1 BMMΦ while preserving M2 AMΦs and enhancing their antibacterial functions. Interestingly, PMSC therapy failed to rescue AMΦ-depleted mice with KP pneumonia, and PMSC-secreted IL-1ß was identified as critical in increasing AMΦ antibacterial activities to significantly improve pathogen clearance-especially bacteraemia-and survival. CONCLUSIONS: Human PMSC treatment preferentially rescued resident M2 AMΦs over recruited M1 BMMΦs with overall M2 polarisation to improve KP-related ARDS survival.

Migraine and subsequent head and neck cancer: A nationwide population-based cohort study.

OBJECTIVES: The association of migraine with the risk of certain cancer has been reported. The aim of this pilot study was to examine the associations between migraine and the onset of head and neck cancers (HNC). MATERIALS AND METHODS: A total of 1755 individuals were identified through a nationwide population-based cohort registry in Taiwan between 2000 and 2013. The primary end point variable was new-onset head and neck cancers in patients with migraine versus non-migraine controls. Cox proportional hazard regression was used to derive the risk of HNC. Subgroup analyses were performed to determine subpopulations at risk of migraine-associated HNC. Sub-outcome analyses were carried out to provide the subtypes of migraine-associated HNC. Propensity score matching was utilized to validate the findings. RESULTS: A total of four patients out of 351 patients with migraine and seven out of 1404 non-migraine controls developed HNC. The incidence of HNC was higher in patients with migraine than that in non-migraine controls (108.93 vs. 48.77 per 100,000 person-years) (adjusted hazard ratio, aHR = 2.908, 95% CI = 0.808-10.469; p = 0.102). The risk of HNC in patients with migraine with aura (aHR = 5.454, 95% CI = 0.948-26.875; p = 0.264) and without aura (aHR = 2.777, 95% CI = 0.755-8.473; p = 0.118) was revealed. The incidence of non-nasopharyngeal HNC secondary to migraine (112.79 per 100,000 person-years) was higher than that of nasopharyngeal cancer secondary to migraine (105.33 per 100,000 person-years). CONCLUSION: A higher incidence of HNC was observed in a small sample of patients with migraine, especially in those with migraine with aura. Migraine-associated HNC included non-nasopharyngeal HNC. Studies with a larger sample are needed to confirm the finding of the high risk of HNC in people with migraine.

Patients with juvenile idiopathic arthritis are at increased risk for obstructive sleep apnoea: a population-based cohort study.

BACKGROUND AND OBJECTIVES: Juvenile idiopathic arthritis (JIA), an autoimmune disease, has been proposed to be comorbid with obstructive sleep apnoea (OSA). We aimed at testing the hypothesis that patients with JIA may presented with high risk of OSA in a cohort study. SUBJECTS AND METHODS: This is a cohort study including patients with JIA from 1999 to 2013 identified from a longitudinal health registry. A matched non-JIA control group was also included. The primary outcome variable was presence of OSA. A Cox proportional hazard model was developed to estimate the risk of OSA in patients with JIA. A cumulative probability model was adopted to assess the time-dependent effect of JIA on OSA development, implying a causal link of the association. RESULTS: A total of 2791 patients with JIA were included, and 11 164 individuals without JIA were selected as matched controls. A total of 95 included subjects had OSA: 31 in the JIA group and 64 in the control group. Patients with JIA were more likely to have OSA compared with controls (adjusted hazard ratio, aHR = 1.922, 95% confidence interval [CI] = 1.244-2.970). The incidence of developing OSA was particularly high among patients with JIA-associated deformity that presented at age 18-30 years (aHR = 1.993, 95% CI = 1.277-3.113) and males (aHR = 1.786, 95% CI = 1.097-2.906). The risk of developing OSA increased over 60 months (aHR = 2.523, 95% CI = 1.322-4.815) of follow-up after the JIA diagnosis. CONCLUSIONS: Patients with JIA have a significantly increased risk of developing OSA compared with matched individuals without JIA.

HLA-G Expression in Human Mesenchymal Stem Cells (MSCs) Is Related to Unique Methylation Pattern in the Proximal Promoter as well as Gene Body DNA.

Multipotent human mesenchymal stem cells (MSCs) harbor clinically relevant immunomodulation, and HLA-G, a non-classical MHC class I molecule with highly restricted tissue expression, is one important molecule involved in these processes. Understanding of the natural regulatory mechanisms involved in expression of this elusive molecule has been difficult, with near exclusive reliance on cancer cell lines. We therefore studied the transcriptional control of HLA-G in primary isolated human bone marrow- (BM), human embryonic stem cell-derived (hE-), as well as placenta-derived MSCs (P-MSCs), and found that all 3 types of MSCs express 3 of the 7 HLA-G isoforms at the gene level; however, fibroblasts did not express HLA-G. Protein validation using BM- and P-MSCs demonstrated expression of 2 isoforms including a larger HLA-G-like protein. Interferon-γ (IFN-γ) stimulation upregulated both gene and protein expression in MSCs but not the constitutively expressing JEG-3 cell line. Most interestingly in human MSCs and placental tissue, hypomethylation of CpG islands not only occurs on the HLA-G proximal promoter but also on the gene body as well, a pattern not seen in either of the 2 commonly used choriocarcinoma cell lines which may contribute to the unique HLA-G expression patterns and IFN-γ-responsiveness in MSCs. Our study implicates the importance of using normal cells and tissues for physiologic understanding of tissue-specific transcriptional regulation, and highlight the utility of human MSCs in unraveling the transcriptional regulation of HLA-G for better therapeutic application.

Differentiation of Mesenchymal Stem Cells from Human Induced Pluripotent Stem Cells Results in Downregulation of c-Myc and DNA Replication Pathways with Immunomodulation Toward CD4 and CD8 Cells.

Multilineage tissue-source mesenchymal stem cells (MSCs) possess strong immunomodulatory properties and are excellent therapeutic agents, but require constant isolation from donors to combat replicative senescence. The differentiation of human induced pluripotent stem cells (iPSCs) into MSCs offers a renewable source of MSCs; however, reports on their immunomodulatory capacity have been discrepant. Using MSCs differentiated from iPSCs reprogrammed using diverse cell types and protocols, and in comparison to human embryonic stem cell (ESC)-MSCs and bone marrow (BM)-MSCs, we performed transcriptome analyses and assessed for functional immunomodulatory properties. Differentiation of MSCs from iPSCs results in decreased c-Myc expression and its downstream pathway along with a concomitant downregulation in the DNA replication pathway. All four lines of iPSC-MSCs can significantly suppress in vitro activated human peripheral blood mononuclear cell (PBMC) proliferation to a similar degree as ESC-MSCs and BM-MSCs, and modulate CD4 T lymphocyte fate from a type 1 helper T cell (Th1) and IL-17A-expressing (Th17) cell fate to a regulatory T cell (Treg) phenotype. Moreover, iPSC-MSCs significantly suppress cytotoxic CD8 T proliferation, activation, and differentiation into type 1 cytotoxic T (Tc1) and IL-17-expressing CD8 T (Tc17) cells. Coculture of activated PBMCs with human iPSC-MSCs results in an overall shift of secreted cytokine profile from a pro-inflammatory environment to a more immunotolerant milieu. iPSC-MSC immunomodulation was also validated in vivo in a mouse model of induced inflammation. These findings support that iPSC-MSCs possess low oncogenicity and strong immunomodulatory properties regardless of cell-of-origin or reprogramming method and are good potential candidates for therapeutic use. Stem Cells 2018;36:903-914.

Human mesenchymal stem cells (MSCs) for treatment towards immune- and inflammation-mediated diseases: review of current clinical trials.

Human mesenchymal stem cells (MSCs) are multilineage somatic progenitor/stem cells that have been shown to possess immunomodulatory properties in recent years. Initially met with much skepticism, MSC immunomodulation has now been well reproduced across tissue sources and species to be clinically relevant. This has opened up the use of these versatile cells for application as 3rd party/allogeneic use in cell replacement/tissue regeneration, as well as for immune- and inflammation-mediated disease entities. Most surprisingly, use of MSCs for in immune-/inflammation-mediated diseases appears to yield more efficacy than for regenerative medicine, since engraftment of the exogenous cell does not appear necessary. In this review, we focus on this non-traditional clinical use of a tissue-specific stem cell, and highlight important findings and trends in this exciting area of stem cell therapy.

Mesenchymal stem cells tune the development of monocyte-derived dendritic cells toward a myeloid-derived suppressive phenotype through growth-regulated oncogene chemokines.

Mesenchymal stem/stromal cells (MSCs) are promising potential candidates for the treatment of immunological diseases because of their immunosuppressive functions. However, the molecular mechanisms that mediate MSCs' immunosuppressive activity remain elusive. In this article, we report for the first time, to our knowledge, that secreted growth-regulated oncogene (GRO) chemokines, specifically GRO-γ, in human MSC-conditioned media have an effect on the differentiation and the function of human monocyte-derived dendritic cells. The monocyte-derived dendritic cells were driven toward a myeloid-derived suppressor cell (MDSC)-like phenotype by the GRO chemokines. GRO-γ-treated MDSCs had a tolerogenic phenotype that was characterized by an increase in the secretion of IL-10 and IL-4, and a reduction in the production of IL-12 and IFN-γ. We have also shown that the mRNA expression levels of the arginase-1 and inducible NO synthase genes, which characterize MDSCs, were upregulated by GRO-γ-primed mouse bone marrow cells. In addition, the ability of GRO-γ-treated bone marrow-derived dendritic cells to stimulate the OVA-specific CD8(+) T (OT-1) cell proliferation and the cytokine production of IFN-γ and TNF-α were significantly decreased in vivo. Our findings allow a greater understanding of how MDSCs can be generated and offer new perspectives to exploit the potential of MDSCs for alternative approaches to treat chronic inflammation and autoimmunity, as well as for the prevention of transplant rejection.

Efficacy of adhesive strategies for restorative dentistry: A systematic review and network meta-analysis of double-blind randomized controlled trials over 12 months of follow-up.

PURPOSE: The efficacy of etch-and-rinse, selective enamel-etching, and self-etching protocols for universal adhesives in follow-ups of over 12 months was compared in a network meta-analysis. STUDY SELECTION: Randomized controlled trials (RCTs) published from 1998 to 2022 that compared marginal staining, marginal adaptation, retention and fractures, post-operative sensitivity, or recurrence of caries that took place over 12-months post-restoration were selected. A network meta-analysis determined the performance of each adhesive protocol. RESULTS: After screening 981 articles, 16 RCTs were subjected to data extraction. Of which, 674 patients with 2816 restorations, were included in the network meta-analysis. The pooled risk of marginal discoloration following self-etching was significantly higher than that following etch-and-rinse at over 12, 24, and 36 months, which was time-dependent. The pooled risks of unfavorable marginal adaptation and unfavorable retention and fractures following self-etching were also significantly higher than that following etch-and-rinse, with the rates of unfavorable retention and fractures in non-carious cervical lesions increasing in a time-dependent manner. The pooled risks of marginal discoloration, unfavorable marginal adaptation, retention and fractures were similar between etch-and-rinse and selective enamel-etching protocols. Post-operative hypersensitivity and recurrence of caries were not significantly different among etch-and-rinse, selective enamel-etching, and self-etching protocols. CONCLUSIONS: In follow-ups over 12 months, esthetic and functional outcomes of restorations completed with an etch-and-rinse adhesive protocol were superior to the ones achieved with a self-etching strategy without selective enamel-etching. Selective enamel etching is recommended for self-etching systems. Biological responses were similar for all three adhesive strategies.

Targeting Conserved Pathways in 3D Spheroid Formation of Diverse Cell Types for Translational Application: Enhanced Functional and Antioxidant Capacity.

Three-dimensional (3D) in vitro spheroid/organoid culture increasingly appears to better mimic physiological states than standard 2D systems. The biological consequence of 3D spheroids, however, differs for different cell types: for pluripotent embryonic stem cells (ESCs), differentiation and loss of stemness occur, while the converse is true for somatic and cancer cells. Despite such diverse consequences, there are likely conserved mechanisms governing 3D spheroid formation across cell types that are unknown but could be efficiently targeted for translational application. To elucidate such processes, we performed transcriptome analysis with functional validation on 2D- and 3D-cultured mouse ESCs, mesenchymal stromal/stem cells (MSCs), and cancer cells. At both the transcriptomic and functional levels, 3D spheroid formation resulted in commitment towards known cell-specific functional outcomes. Surprisingly in all cell types, downregulation of the cholesterol synthesis pathway was found during 3D spheroid formation, with modulation concomitantly affecting 3D spheroid formation and cell-specific consequences; similar results were seen with human cell types. Furthermore, improved antioxidant capacity after 3D spheroid formation across cell types was further enhanced with modulation of the pathway. These findings demonstrate the profound cell-specific consequences and the translational value of understanding conserved mechanisms across diverse cell types after 3D spheroid formation.

The Risk of Endometrial Cancer and Uterine Sarcoma Following Endometriosis or Pelvic Inflammatory Disease.

The relationship between uterine corpus cancer and endometriosis was conflicting. We aimed to determine the risk of uterine cancer in patients with endometriosis or pelvic inflammatory disease (PID). In this population-based cohort study, a total of 135,236 females with endometriosis (n = 20,510) or PID (n = 114,726), as well as 135,236 age-matched controls, were included. Cox regression models estimated the risk of uterine cancer in each group. Sub-outcomes of risk for uterine corpus cancer included endometrial cancer and uterine sarcoma were analyzed. An age subgroup analysis was performed to determine the moderator effect of age. A landmark analysis depicted the time varying effect of endometriosis and PID. A propensity score matching analysis was conducted to validate the findings. Patients with endometriosis had significantly higher risk of endometrial cancer (adjusted hazard ratio, aHR = 2.92; 95% CI = 2.12-4.03) and uterine sarcoma (aHR = 5.83; 95% CI = 2.02-16.89), while PID was not associated with the risk of uterine cancer. The increased risk of uterine cancer in patients with endometriosis persisted after propensity score matching (aHR = 2.83, 95%CI = 1.70-4.71). The greatest risk of endometrial cancer occurred in patients who had endometriosis for 37 to 60 months (adjusted relative risk, aRR = 9.15, 95% CI = 4.40-19.02). Females aged 12 to 35 years were at the greatest risk of endometriosis-associated uterine cancer (RR = 6.97, 95% CI = 3.41-14.26). In conclusion, patients with endometriosis were at great risk of uterine cancer, including endometrial cancer and uterine sarcoma, compared with propensity score-matched populations and compared with patients of PID. Younger females with endometriosis and patients who had endometriosis for three to five years were at the greatest risk of endometriosis-associated uterine cancer.

Three-Dimensional Spheroid Culture of Human Mesenchymal Stem Cells: Offering Therapeutic Advantages and In Vitro Glimpses of the In Vivo State.

As invaluable as the standard 2-dimensional (2D) monolayer in vitro cell culture system has been, there is increasing evidence that 3-dimensional (3D) non-adherent conditions are more relevant to the in vivo condition. While one of the criteria for human mesenchymal stem cells (MSCs) has been in vitro plastic adherence, such 2D culture conditions are not representative of in vivo cell-cell and cell-extracellular matrix (ECM) interactions, which may be especially important for this progenitor/stem cell of skeletal and connective tissues. The 3D spheroid, a multicellular aggregate formed under non-adherent 3D in vitro conditions, may be particularly suited as an in vitro method to better understand MSC physiological processes, since expression of ECM and other adhesion proteins are upregulated in such a cell culture system. First used in embryonic stem cell in vitro culture to recapitulate in vivo developmental processes, 3D spheroid culture has grown in popularity as an in vitro method to mimic the 3-dimensionality of the native niche for MSCs within tissues/organs. In this review, we discuss the relevance of the 3D spheroid culture for understanding MSC biology, summarize the biological outcomes reported in the literature based on such this culture condition, as well as contemplate limitations and future considerations in this rapidly evolving and exciting area.

Exposure to environmental air pollutants as a risk factor for primary Sjögren's syndrome.

Background: Environmental etiology of primary Sjögren's syndrome (pSS), an autoimmune disease, has been proposed. This study determined whether the exposure to air pollutants was an independent risk factor for pSS. Methods: Participants were enrolled from a population-based cohort registry. Daily average concentrations of air pollutants from 2000 to 2011 were divided into 4 quartiles. Adjusted hazard ratios (aHRs) of pSS for exposure to air pollutants were estimated in a Cox proportional regression model adjusting for age, sex, socioeconomic status, and residential areas. A subgroup analysis stratified by sex was conducted to validate the findings. Windows of susceptibility indicated years of exposure which contributed the most to the observed association. Ingenuity Pathway Analysis was used to identify underlying pathways of air pollutant-associated pSS pathogenesis, using Z-score visualization. Results: Two hundred patients among 177,307 participants developed pSS, with a mean age of 53.1 years at acumulative incidence of 0.11% from 2000 to 2011. Exposure to carbon monoxide (CO), nitric oxide (NO), and methane (CH4) was associated with a higher risk of pSS. Compared to those exposed to the lowest concentration level, the aHRs for pSS were 2.04 (95%CI=1.29-3.25), 1.86 (95%CI=1.22-2.85), and 2.21 (95%CI=1.47-3.31) for those exposed to high levels of CO, NO, and CH4, respectively. The findings persisted in the subgroup analysis, in which females exposed to high levels of CO, NO, and CH4 and males exposed to high levels of CO were associated with significantly great risk of pSS. The cumulative effect of air pollution on pSS was time-dependent. The underlying cellular mechanisms involved chronic inflammatory pathways including the interleukin-6 signaling pathway. Conclusion: Exposure to CO, NO, and CH4 was associated with a high risk of pSS, which was biologically plausible.