Genomic study of the Type IVC secretion system in Clostridium difficile: understanding C. difficile evolution via horizontal gene transfer.

Clostridium difficile, the etiological agent of Clostridium difficile infection (CDI), is a gram-positive, spore-forming bacillus that is responsible for ∼20% of antibiotic-related cases of diarrhea and nearly all cases of pseudomembranous colitis. Previous data have shown that a substantial proportion (11%) of the C. difficile genome consists of mobile genetic elements, including seven conjugative transposons. However, the mechanism underlying the formation of a mosaic genome in C. difficile is unknown. The type-IV secretion system (T4SS) is the only secretion system known to transfer DNA segments among bacteria. We searched genome databases to identify a candidate T4SS in C. difficile that could transfer DNA among different C. difficile strains. All T4SS gene clusters in C. difficile are located within genomic islands (GIs), which have variable lengths and structures and are all conjugative transposons. During the horizontal-transfer process of T4SS GIs within the C. difficile population, the excision sites were altered, resulting in different short-tandem repeat sequences among the T4SS GIs, as well as different chromosomal insertion sites and additional regions in the GIs.

MST1 coordinately regulates autophagy and apoptosis in diabetic cardiomyopathy in mice.

AIMS/HYPOTHESIS: Diabetic cardiomyopathy (DCM) is associated with suppressed autophagy and augmented apoptosis in the heart although the interplay between the two remains elusive. The ability of mammalian sterile 20-like kinase 1 to regulate both autophagy and apoptosis prompted us to investigate it as a possible candidate in the progression of DCM. METHODS: Wild-type, Mst1 (also known as Stk4) transgenic and Mst1-knockout mice were challenged with streptozotocin to induce experimental diabetes. In addition, cultured neonatal mouse cardiomyocytes were subjected to simulated diabetes to probe mechanisms. RESULTS: Mst1 knockout alleviated while Mst1 overexpression aggravated cardiac dysfunction in diabetes. Diabetic Mst1 transgenic mice exhibited decreased LC3 expression and enhanced protein aggregation. In contrast, typical autophagosomes were observed in diabetic Mst1-knockout mice with increased LC3 expression and reduced protein aggregation. Mst1 downregulation promoted autophagic flux as demonstrated by increased LC3-II and decreased p62 expression in the presence of bafilomycin A1. Furthermore, Mst1 overexpression increased, while Mst1 knockout decreased, cardiomyocyte apoptosis both in vivo and in vitro. Co-immunoprecipitation assays showed that Mst1 overexpression promoted Beclin1 binding to B cell lymphoma 2 (Bcl-2) and induced dissociation of Bcl-2 from Bax in diabetic mice. Conversely, Mst1 knockout disrupted the Beclin1-Bcl-2 complex and enhanced the interaction between Bcl-2 and Bax. CONCLUSIONS/INTERPRETATION: Mst1 knockout restores autophagy and protects against apoptosis in cardiomyocytes, en route to the rescue against DCM.

Nosocomial transmission of Clostridium difficile ribotype 027 in a Chinese hospital, 2012-2014, traced by whole genome sequencing.

BACKGROUND: The rapid spread of Clostridium difficile NAP1/BI/027 (C. difficile 027) has become one of the leading threats of healthcare-associated infections worldwide. However, C. difficile 027 infections have been rarely reported in Asia, particularly in China. RESULTS: In this study, we identified a rare C. difficile bloodstream infection (BSI) from three isolates of a patient during repeated hospital admission. This finding triggered a retrospective epidemiological study to scan all cases and strains emerged from this ward during the past three years. Using medical personnel interviews, medical record reviews and the genomic epidemiology, two outbreaks in 2012 and 2013-2014 were identified. Through using whole genome sequencing, we succeeded to trace the origin of the BSI strain. Surprisingly, we found the genome sequences were similar to C. difficile 027 strain R20291, indicating the occurrence of a rare C. difficile 027 strain in China. Integrated epidemiological investigation and whole genome sequencing of all strains, we constructed a nosocomial transmission map of these two C. difficile 027 outbreaks and traced the origin of the infection. CONCLUSIONS: By genome sequencing, spatio-temporal analysis and field epidemiology investigation, we can estimate their complex transform network and reveal the possible modes of transmission in this ward. Based on their genetic diversity, we can assume that the toilets, bathroom, and janitor's equipment room may be contaminated area, which may be suggested to improve infection control measures in the following health care.

Sequence variation in tcdA and tcdB of Clostridium difficile: ST37 with truncated tcdA is a potential epidemic strain in China.

Clostridium difficile is a well-known nosocomial infectious pathogen. Research on C. difficile infection has primarily focused on strains such as the hypervirulent PCR ribotype 027 (sequence type 1 [ST1]) emerging in Europe and North America. However, other new emerging ribotypes in some countries have attracted attention, such as PCR ribotype 17 (ST37) in Asia and Latin America. We collected 70 strains and sequenced their toxin genes, tcdA and tcdB. Multilocus sequence typing (MLST) was used to study their population structure. In addition, tcdA and/or tcdB sequences of 25 other isolates were obtained from GenBank. Single nucleotide polymorphisms (SNPs) were identified and analyzed. Phylogenetic analyses were performed to study toxin gene evolution. All tcdA and tcdB sequences were divided into 1 of 16 types (denoted A01 to -16 and B01 to -16, respectively). Hypervirulent strain RT027 is A13B12, and RT078 is A14B10, whereas the newly epidemic strain RT017 is A15B13. SNP analysis suggests the possibility of recombination in tcdB, perhaps through horizontal gene transfer. SNPs were also found in the sequences corresponding to the PCR primers widely used for toxin detection. Our study shows that ST037 shares a few genotypic features in its tcdA and tcdB genes with some known hypervirulent strains, indicating that they fall into a unique clade. Our findings can be used to map the relationships among C. difficile strains more finely than can be done with less sensitive methods, such as toxinotyping or even MLST, to reveal their inherent epidemiological characteristics.

[Construction, expression, and identification of the gene of human anti-prostate specific membrane antigen single-chain antibody].

OBJECTIVE: To construct, express and purify human fusion proteins composed of a single-chain antibody fragment scFv that recognizes the prostate specific membrane antigen (PSMA) protein, Fdt, HA2 and tp, and to analyze the binding activity of the expressed fusion proteins. METHODS: The fusion protein genes scFv, scFv-tp, and scFv-Fdt-HA2-tp were amplified by PCR, and the genes obtained were then cloned into the expression vector pET28 and expressed in E. coli BL21. The expressed products were identified by SDS-PAGE and Western blot and purified with Ni(2+)-NTA chelating agarose. The antigen-binding activity of the fusion proteins was determined by ELISA. RESULTS: The human anti-PSMA fusion gene was successfully constructed and expressed in M15 as the inclusion body after induced with IPTG. All the target proteins expressed could bind the PSMA antigen. CONCLUSION: Fusion proteins can specifically bind the PSMA antigen. This finding contributes to the study of the targeted delivery of siRNA.

Rosuvastatin enhances the therapeutic efficacy of adipose-derived mesenchymal stem cells for myocardial infarction via PI3K/Akt and MEK/ERK pathways.

The poor viability of transplanted stem cells hampers their therapeutic efficacy for treatment of myocardial infarction. The aim of this study was to investigate whether rosuvastatin improved survival of adipose-derived mesenchymal stem cells (AD-MSCs) after transplantation into infarcted hearts. AD-MSCs isolated from Tg(Fluc-egfp) mice which constitutively express both firefly luciferase (Fluc) and enhanced green fluorescent protein were transplanted into infarcted hearts with or without rosuvastatin administration. Longitudinal in vivo bioluminescence imaging and histological staining revealed that rosuvastatin enhanced the survival of engrafted AD-MSCs. Furthermore, combined therapy of AD-MSC and rosuvastatin reduced fibrosis, decreased cardiomyocyte apoptosis, and preserved heart function. AD-MSCs were then subjected to hypoxia and serum deprivation injury in vitro to mimic the ischemic environment. Rosuvastatin (10(-6) mmol/L) enhanced the viability and paracrine effect of AD-MSCs, and decreased their apoptotic rate. Western blotting revealed that rosuvastatin supplementation increased Akt and ERK phosphorylation, which resulted in FoxO3a phosphorylation and nuclear export. In addition, rosuvastatin administration decreased the pro-apoptotic proteins Bim and Bax, and increased the anti-apoptotic proteins Bcl-xL and Bcl-2. Furthermore, these effects were abolished by PI3K inhibitor LY294002 and MEK1/2 inhibitor U0126. This study demonstrates that rosuvastatin may improve the survival of engrafted AD-MSCs at least in part through the PI3K/Akt and MEK/ERK1/2 signaling pathways. Combination therapy with rosuvastatin and AD-MSCs has a synergetic effect on improving myocardial function after infarction.

Aramid Nanofiber/XNBR Nanocomposite with High Mechanical, Thermal, and Electrical Performance.

Aramid nanofibers (ANFs) were successfully produced by deprotonation of Kevlar fiber followed by grafting epichlorohydrin in dimethyl sulfoxide solution. The ANFs were then incorporated into carboxylated acrylonitrile butadiene rubber (XNBR) by means of latex blending, followed by vulcanization. The interaction between ANFs and XNBR, and the effects of ANFs on the mechanical strength, dielectric properties, and thermal stability of ANF/XNBR nanocomposites were investigated. The results revealed that hydrogen bonding and covalent bonding interactions existed between ANFs and the XNBR matrix and played a critical role in the reinforcement of ANFs to XNBR nanocomposites. After adding 5 phr (parts per hundred rubber) of ANFs, the XNBR nanocomposite exhibited a significant improvement in mechanical properties, namely a 182% increase in tensile strength and a 101% increase in tear strength. In addition, the dielectric constant and thermal properties of ANF/XNBR also increased dramatically. ANFs may thus make an ideal candidate for high-performance rubber materials.

The Effects of Carbon-Silica Dual-Phase Filler on the Crosslink Structure of Natural Rubber.

Carbon-silica dual-phase filler (CSDPF)/natural rubber (NR) vulcanizate was prepared by mechanical blending, followed by a hot-press vulcanization. The dispersion of CSDPF in the NR matrix and the effects of CSDPF on the filler-rubber interaction and structure of the rubber network were studied. Scanning electron microscope results showed that CSDPF dispersed uniformly; however, there were some aggregates of CSDPF when loading too many fillers. With an increase in CSDPF, the interaction between CSDPF and NR chains increases, which was detected by bound rubber in the CSDPF/NR compound. The spectra of solid-state nuclear magnetic resonance revealed that CSDPF could promote the formation of poly-sulfidic crosslink in the rubber vulcanization network. Further, the molecular chain movement ability of vulcanizates decreases according to the spin-spin relaxation of 1H nuclei in CSDPF/NR compounds. The crosslink density of vulcanizate increases, while the chemical crosslink and physical crosslink in the vulcanization network also increase according to the tube model.

Rv1258c acts as a drug efflux pump and growth controlling factor in Mycobacterium tuberculosis.

The possible role of efflux pump as a survival mechanism in Mycobacterium tuberculosis (M. tb) is gaining an increasing attention. Previously, Rv1258c (Tap) and its certain mutations confer the clinically relevant drug resistance. In this study, we found new mutations of Rv1258c in G195C, T297P and I328T. Effect of modulating T297P and I328T on the drug resistance by knockout and complement in M. tb H37Rv showed that M. tb ΔRv1258c showed a slightly lower MIC for rifampin, ethambutol, ofloxacin, amikacin, capreomycin and streptomycin than M. tb H37Rv WT and the complement. Rv1258c T297P and Rv1258c I328T showed an increased drug resistance to ethambutol and capreomycin than the complement of Rv1258c WT. Most importantly, M. tb ΔRv1258c exhibited a slow growth in the normal culture medium. TMT-based quantitative proteomics analysis of M. tb ΔRv1258c and WT showed that the knockout of Rv1258c greatly down-regulated the expression of the ribosome system and one of the special five type VII secretion systems, ESX-3, which impaired the bacterial growth. These results indicate that the newly found T297P and I328T mutations of Rv1258c contributed to an increased resistance to ethambutol and capreomycin, and Rv1258c as growth controlling factor influencing the growth of M. tb.

Adhesive and high-sensitivity modified Ti3C2TX (MXene)-based organohydrogels with wide work temperature range for wearable sensors.

Hydrogel-based wearable sensors have gained great interest on account of their huge application in human-machine interfaces, electronic skin, and healthcare monitoring. However, there are still challenges in designing hydrogel-based sensors with high stability in a wide temperature range, superior adhesion, and excellent sensitivity. Herein, sensors based on oxidized sodium alginate (OSA)/polyacrylamide (PAm)/polydopamine-Ti3C2TX (PMXene) /glycerol/water (Gly/H2O) organohydrogels were designed. The organohydrogels exhibited excellent mechanical properties (elongation at break of 1037%, tensile strength of 0.17 MPa), predominant self-healing ability (self-healing efficiency of 91%), as well as high sensing stability in a wide temperature range (from -20 to 60°C). The introduction of PDA (polydopamine) and viscous glycerin (Gly) provide organohydrogels with superior adhesion. Organohydrogels sensors demonstrated high sensitivity (Gauge Factor, GF = 2.2) due to the combination of ionic and electron conduction. Sensors could stably detect human movement under different strain levels at high and low temperatures, providing a new solution for wearable sensors in extreme conditions.

Aramid Nanofibers/Reduced Graphene Oxide Composite Electrodes with High Mechanical Properties.

In this work, aramid nanofibers (ANFs)/reduced graphene oxide (ANFs/RGO) film electrodes were prepared by vacuum-assisted filtration, followed by hydroiodic acid reduction. Compared with thermal reduced ANFs/RGO, these as-prepared film electrodes exhibit a combination of mechanical and electrochemical properties with a tensile strength of 184.5 MPa and a volumetric specific capacitance of 134.4 F/cm3 at a current density of 0.125 mA/cm2, respectively. In addition, the film electrodes also show a superior cycle life with 94.6% capacitance retention after 5000 cycles. This kind of free-standing film electrode may have huge potential for flexible energy-storage devices.

A chromosome-encoded T4SS independently contributes to horizontal gene transfer in Enterococcus faecalis.

Bacterial type IV secretion systems (T4SSs) are the specific devices that mediate the dissemination of antibiotic resistant genes via horizontal gene transfer (HGT). Multi-drug-resistant Enterococcus faecalis (E. faecalis) represents a clinical public health threat because of its transferable plasmid with a functional plasmid-encoded (PE)-T4SS. Here, we report a chromosome-encoded (CE)-T4SS that exists in 40% of E. faecalis isolates. Compared with the PE-T4SS, CE-T4SS displays distinct characteristics in protein architecture and is capable of mediating large and genome-wide gene transfer in an imprecise manner. Reciprocal exchange of CE-T4SS- or PE-T4SS-associated origin of transfer (oriT) could disrupt HGT function, indicating that CE-T4SS is an independent system compared with PE-T4SS. Taken together, the CE-T4SS sheds light on the knowledge of HGT in gram-positive bacteria and triggers us to explore more evolutionary mechanisms in E. faecalis.

Analysis on Drug-Resistance-Associated Mutations among Multidrug-Resistant Mycobacterium tuberculosis Isolates in China.

As the causative bacteria of tuberculosis, Mycobacteriumtuberculosis (M. tb) is aggravated by the emergence of its multidrug-resistant isolates in China. Mutations of six of the most frequently reported resistant genes (rpoB, katG, inhA, embB, gyrA, and rpsL) were detected for rifampicin (RIF), isoniazid (INH), ethambutol (EMB), ofloxacin (OFX), and streptomycin (STR) in this study. The amino acid missense mutations (MMs) and their corresponding single nucleotide polymorphism mutations for all drug-resistant (DR) isolates are described in detail. All isolates were divided into non-extensively drug-resistant (Non-XDR) and preXDR/XDR groups. No statistical differences were detected among MMs and linked MMs (LMs) between the two groups, except for rpsL 88 (p = 0.037). In the preXDR/XDR group, the occurrence of MMs in rpoB, katG, and inhA developed phenotypic resistance and MMs of rpoB 531, katG 315, rpsL 43, and rpsL 88 could develop high levels of DR. It is necessary to carry out epidemiological investigations of DR gene mutations in the local region, and thus provide necessary data to support the design of new technologies for rapid detection of resistant M. tb and the optimization of detection targets.

A Conjugative MDR pMG1-Like Plasmid Carrying the lsa(E) Gene of Enterococcus faecium With Potential Transmission to Staphylococcus aureus.

lsa(E) is a pleuromutilin, lincosamide, and streptogramin A (PLSA phenotype) resistance gene that was first described in S. aureus and was thought to have been transferred from Enterococcus sp. This study aimed to elucidate the prevalence of the lsa(E) gene among E. faecium isolates at a tertiary teaching hospital and to evaluate the transferability of the lsa(E) gene from E. faecium to S. aureus in vitro. A total of 96 E. faecium strains isolated from one hospital in Beijing in 2013 were analysed for quinupristin-dalfopristin (QDA) resistance genes, and multilocus sequence typing (MLST) was performed. The transferability of QDA resistance between ten E. faecium strains and four S. aureus strains was determined by filter mating. Genome sequencing of the transconjugant was performed. A total of 46 E. faecium isolates (46/96, 47.92%) tested positive for lsa(E), while two isolates (2/96, 2.08%) tested positive for lsa(A). Thirty-six lsa(E)-positive strains (36/46, 78.3%) belonged to ST78. Among 40 mating tests, lsa(E) was successfully transferred through one conjugation at a frequency of 1.125 × 10-7 transconjugants per donor. The QDA resistance of the transconjugant N7435-R3645 was expressed at a higher level (MIC = 16 mg/L) than that of the parent S. aureus strain (MIC = 0.38 mg/L). Next-generation sequencing (NGS) analysis of the transconjugant N7435-R3645 showed that the complete sequence of the lsa(E)-carrying plasmid pN7435-R3645 had a size of 92,396 bp and a G + C content of 33% (accession no. MT022086). The genetic map of pN7435-R3645 had high nucleotide similarity and shared the main open reading frame (ORF) features with two plasmids: E. faecium pMG1 (AB206333.1) and E. faecium LS170308 (CP025078.1). The rep gene of pN7435-R3645 showed 100% identity with that of pMG1, although it did not belong to the rep1-19 family but instead a unique rep family. Multiple antibiotic resistance genes, including lsa(E), aadE and lnu(B), erm(B), ant6-Ia, and lnu(B), were present on the plasmid. In conclusion, an lsa(E)-carrying plasmid that can be transferred by conjugation from E. faecium to S. aureus in vitro was identified. This multidrug resistance (MDR) pMG1-like plasmid may act as a vector in the dissemination of antimicrobial resistance among species.

Highly flexible and mechanically strong polyaniline nanostructure @ aramid nanofiber films for free-standing supercapacitor electrodes.

A key challenge for the fabrication of flexible electrochemical capacitors is to prepare robust electrode materials with excellent integration of high specific capacitances and superior mechanical properties. Aramid nanofibers (ANFs) are emerging candidates for constructing flexible electrode materials due to their superior mechanical properties. However, the present ANF based electrode materials are generally designed by mixing ANFs with electrochemically active components, which results in an unfavorable trade-off in mechanical and electrochemical properties. In this work, we reported flexible, mechanically strong, and free-standing supercapacitor electrodes based on polyaniline (PANI) nanostructure functionalized ANF films for the first time. The flexible PANI@ANF film electrodes achieved an efficient combination of mechanical and electrochemical performance in a single platform with a specific capacitance of 441.0 F g-1 at a current density of 1 A g-1 and a tensile strength of 233.3 MPa, respectively. This kind of free-standing electrode material may have great potential in the development of flexible energy-storage devices. Furthermore, we anticipate that this study may provide insight into the functionalization of aramid nanofiber-based materials for structural energy and power systems with high mechanical performance.

Emergency Biosafety Management Practice in Laboratory of Shelter Hospital.

At the end of 2019, the novel coronavirus infection outbroke in Wuhan, Hubei Province. On Feb. 2, 2020, Wuhan, as the worst-hit region, began to build "shelter hospital" rapidly to treat patients with mild illness. The shelter hospital has multiple functions such as emergency treatment, surgical treatment and clinical test, which can adapt to emergency medical rescue tasks. Based on the characteristics that shelter hospital only treats patients with mild illness, tests of shelter laboratory, including coronavirus nucleic acid detection, IgM/IgG antibody serology detection, monitoring and auxiliary diagnosis and/or a required blood routine, urine routine, C-reactive protein, calcitonin original, biochemical indicators (liver enzymes, myocardial enzymes, renal function, etc.) and blood coagulation function test etc, were used to provide important basis for the diagnosis and treatment of the disease. In order to ensure laboratory biosafety, it is necessary to first evaluate the harm level of various specimens. In the laboratory biosafety management, the harm level assessment of microorganisms is the core work of biosafety, which is of great significance to guarantee biosafety. As an emergency deployment affected by the environment, shelter laboratory must possess strong mobility. This paper will explore how to combine the biosafety model of traditional laboratory with the particularity of shelter laboratory to carry out effective work in response to the current epidemic.

Electronic currents and the formation of nanopores in porous anodic alumina.

The formation processes of barrier anodic alumina (BAA) and porous anodic alumina (PAA) are discussed in detail. The anodizing current J(T) within the oxide includes ionic current j(ion) and electronic current j(e) during the anodizing process. The j(ion) is used to form an oxide and the j(e) is used to give rise to oxygen gas or sparking. The j(e) results from the impurity centers within the oxide. For a given electrolyte, the j(e) is dependent on the impurity centers and independent of the J(T). The formation of nanopores can be ascribed to the oxygen evolution within the oxide. Oxygen gas will begin to be released at the critical thickness d(c). The manner of the development of PAA is in accordance with that of BAA. The differences between PAA and BAA are the magnitude of j(e) or the continuity of oxygen evolution. There are two competitive reactions, i.e. oxide growth (2Al3 + 3O2- --> Al2O3) and oxygen evolution (2O2- --> O2 up arrow + 4e). The former keeps the wall of the channel lengthened, the latter keeps the channel open. By controlling the release rate of oxygen gas under different pressures, the shape of the channels can be adjusted. The present results may open up some opportunities for fabricating special templates.

The type VI secretion system protein AsaA in Acinetobacter baumannii is a periplasmic protein physically interacting with TssM and required for T6SS assembly.

Type VI secretion system (T6SS) is described as a macromolecular secretion machine that is utilized for bacterial competition. The gene clusters encoding T6SS are composed of core tss genes and tag genes. However, the clusters differ greatly in different pathogens due to the great changes accumulated during the long-term evolution. In this work, we identified a novel hypothetical periplasmic protein designated as AsaA which is encoded by the first gene of the T6SS cluster in the genus Acinetobacter. By constructing asaA mutant, we delineated its relative contributions to bacterial competition and secretion of T6SS effector Hcp. Subsequently, we studied the localization of AsaA and potential proteins that may have interactions with AsaA. Our results showed that AsaA in Acinetobacter baumannii (A. baumannii) localized in the bacterial periplasmic space. Results based on bacterial two-hybrid system and protein pull-down assays indicated that it was most likely to affect the assembly or stability of T6SS by interacting with the T6SS core protein TssM. Collectively, our findings of AsaA is most likely a key step in understanding of the T6SS functions in A. baumannii.

Surfactant-Dependent Charge Transfer between Polyoxometalates and Single-Walled Carbon Nanotubes: A Fluorescence Spectroscopic Study.

Hybridizations of redox-active polyoxometalates (POMs) with single-walled carbon nanotubes (SWNTs) have been widely investigated for their diverse applications. For the purpose of constructing high-quality electronic devices, controlling charge transfer within POM/SWNT hybrids is an inevitable issue. As determined by means of fluorescence spectroscopy, electron transfer between SWNTs and a common POM dopant, phosphomolybdic acid (PMo12 ), can be tuned simply by an alteration of nanotube surfactant type from anionic to nonionic. The mechanism is attributed to the influence of surfactant type on the stabilization of the electron donor-acceptor hybrid and effect of surfactant-nanotube interactions. These results will be important to control charge-transport behavior in nanohybrids consisting of carbon nanotubes.

Reduced serum club cell protein as a pulmonary damage marker for chronic fine particulate matter exposure in Chinese population.

BACKGROUND: Exposure to fine particulate matter (PM2.5) pollution is associated with increased morbidity and mortality from respiratory diseases. However, few population-based studies have been conducted to assess the alterations in circulating pulmonary proteins due to long-term PM2.5 exposure. METHODS: We designed a two-stage study. In the first stage (training set), we assessed the associations between PM2.5 exposure and levels of pulmonary damage markers (CC16, SP-A and SP-D) and lung function in a coke oven emission (COE) cohort with 558 coke plant workers and 210 controls. In the second stage (validation set), significant initial findings were validated by an independent diesel engine exhaust (DEE) cohort with 50 DEE exposed workers and 50 controls. RESULTS: Serum CC16 levels decreased in a dose response manner in association with both external and internal PM2.5 exposures in the two cohorts. In the training set, serum CC16 levels decreased with increasing duration of occupational PM2.5 exposure history. An interquartile range (IQR) (122.0µg/m3) increase in PM2.5 was associated with a 5.76% decrease in serum CC16 levels, whereas an IQR (1.06µmol/mol creatinine) increase in urinary 1-hydroxypyrene (1-OHP) concentration was associated with a 5.36% decrease in serum CC16 levels in the COE cohort. In the validation set, the concentration of serum CC16 in the PM2.5 exposed group was 22.42% lower than that of the controls and an IQR (1.24µmol/mol creatinine) increase in urinary 1-OHP concentration was associated with a 12.24% decrease in serum CC16 levels in the DEE cohort. CONCLUSIONS: Serum CC16 levels may be a sensitive marker for pulmonary damage in populations with high PM2.5 exposure.