Resistome analyses of sputum from COPD and healthy subjects reveals bacterial load-related prevalence of target genes.

BACKGROUND: Antibiotic resistance is a major global threat. We hypothesised that the chronic obstructive pulmonary disease (COPD) airway is a reservoir of antimicrobial resistance genes (ARGs) that associate with microbiome-specific COPD subgroups. OBJECTIVE: To determine the resistance gene profiles in respiratory samples from COPD patients and healthy volunteers. METHODS: Quantitative PCR targeting 279 specific ARGs was used to profile the resistomes in sputum from subjects with COPD at stable, exacerbation and recovery visits (n=55; COPD-BEAT study), healthy controls with (n=7) or without (n=22) exposure to antibiotics in the preceding 12 months (EXCEED study) and in bronchial brush samples from COPD (n=8) and healthy controls (n=7) (EvA study). RESULTS: ARG mean (SEM) prevalence was greater in stable COPD samples (35.2 (1.6)) than in healthy controls (27.6 (1.7); p=0.004) and correlated with total bacterial abundance (r2=0.23; p<0.001). Prevalence of ARG positive signals in individuals was not related to COPD symptoms, lung function or their changes at exacerbation. In the COPD subgroups designated High γProteobacteria and High Firmicutes, ARG prevalence was not different at stable state but significantly declined from stable through exacerbation to recovery in the former (p=0.011) without changes in total bacterial abundance. The ARG patterns were similar in COPD versus health, COPD microbiome-subgroups and between sputum and bronchoscopic samples independent of antibiotic exposure in the last 12 months. CONCLUSIONS: ARGs are highly prevalent in sputum, broadly in proportion to bacterial abundance in both healthy and COPD subjects. Thus, COPD appears to be an ARG reservoir due to high levels of bacterial colonisation.

Blood eosinophil count and airway epithelial transcriptome relationships in COPD versus asthma.

BACKGROUND: Whether the clinical or pathophysiologic significance of the "treatable trait" high blood eosinophil count in COPD is the same as for asthma remains controversial. We sought to determine the relationship between the blood eosinophil count, clinical characteristics and gene expression from bronchial brushings in COPD and asthma. METHODS: Subjects were recruited into a COPD (emphysema versus airway disease [EvA]) or asthma cohort (Unbiased BIOmarkers in PREDiction of respiratory disease outcomes, U-BIOPRED). We determined gene expression using RNAseq in EvA (n = 283) and Affymetrix microarrays in U-BIOPRED (n = 85). We ran linear regression analysis of the bronchial brushings transcriptional signal versus blood eosinophil counts as well as differential expression using a blood eosinophil > 200 cells/µL as a cut-off. The false discovery rate was controlled at 1% (with continuous values) and 5% (with dichotomized values). RESULTS: There were no differences in age, gender, lung function, exercise capacity and quantitative computed tomography between eosinophilic versus noneosinophilic COPD cases. Total serum IgE was increased in eosinophilic asthma and COPD. In EvA, there were 12 genes with a statistically significant positive association with the linear blood eosinophil count, whereas in U-BIOPRED, 1197 genes showed significant associations (266 positive and 931 negative). The transcriptome showed little overlap between genes and pathways associated with blood eosinophil counts in asthma versus COPD. Only CST1 was common to eosinophilic asthma and COPD and was replicated in independent cohorts. CONCLUSION: Despite shared "treatable traits" between asthma and COPD, the molecular mechanisms underlying these clinical entities are predominately different.

slan-defined subsets of CD16-positive monocytes: impact of granulomatous inflammation and M-CSF receptor mutation.

Human monocytes are subdivided into classical, intermediate, and nonclassical subsets, but there is no unequivocal strategy to dissect the latter 2 cell types. We show herein that the cell surface marker 6-sulfo LacNAc (slan) can define slan-positive CD14(+)CD16(++) nonclassical monocytes and slan-negative CD14(++)CD16(+) intermediate monocytes. Gene expression profiling confirms that slan-negative intermediate monocytes show highest expression levels of major histocompatibility complex class II genes, whereas a differential ubiquitin signature is a novel feature of the slan approach. In unsupervised hierarchical clustering, the slan-positive nonclassical monocytes cluster with monocytes and are clearly distinct from CD1c(+) dendritic cells. In clinical studies, we show a selective increase of the slan-negative intermediate monocytes to >100 cells per microliter in patients with sarcoidosis and a fivefold depletion of the slan-positive monocytes in patients with hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS), which is caused by macrophage colony-stimulating factor (M-CSF) receptor mutations. These data demonstrate that the slan-based definition of CD16-positive monocyte subsets is informative in molecular studies and in clinical settings.

Emphysema- and airway-dominant COPD phenotypes defined by standardised quantitative computed tomography.

EvA (Emphysema versus Airway disease) is a multicentre project to study mechanisms and identify biomarkers of emphysema and airway disease in chronic obstructive pulmonary disease (COPD). The objective of this study was to delineate objectively imaging-based emphysema-dominant and airway disease-dominant phenotypes using quantitative computed tomography (QCT) indices, standardised with a novel phantom-based approach.441 subjects with COPD (Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages 1-3) were assessed in terms of clinical and physiological measurements, laboratory testing and standardised QCT indices of emphysema and airway wall geometry.QCT indices were influenced by scanner non-conformity, but standardisation significantly reduced variability (p<0.001) and led to more robust phenotypes. Four imaging-derived phenotypes were identified, reflecting "emphysema-dominant", "airway disease-dominant", "mixed" disease and "mild" disease. The emphysema-dominant group had significantly higher lung volumes, lower gas transfer coefficient, lower oxygen (PO2 ) and carbon dioxide (PCO2 ) tensions, higher haemoglobin and higher blood leukocyte numbers than the airway disease-dominant group.The utility of QCT for phenotyping in the setting of an international multicentre study is improved by standardisation. QCT indices of emphysema and airway disease can delineate within a population of patients with COPD, phenotypic groups that have typical clinical features known to be associated with emphysema-dominant and airway-dominant disease.

Comparison of two different strategies for human monocyte subsets gating within the large-scale prospective CARE FOR HOMe Study.

Monocytes are heterogeneous cells consisting of (at least) three subsets: classical, intermediate, and nonclassical monocytes. Correct enumeration of cell counts necessitates well-defined gating strategies, which are essentially based upon CD14 and CD16 expression. For the delineation of intermediate from nonclassical monocytes, a "rectangular gating (RG) strategy" and a "trapezoid gating (TG) strategy" have been proposed. We compared the two gating strategies in a well-defined clinical cohort of patients with chronic kidney disease (CKD). Within the ongoing CARE FOR HOMe study, monocyte subsets were reanalyzed in 416 CKD patients, who were followed 3.6 ± 1.6 years for the occurrence of a cardiovascular event. Gating was performed by either RG or TG. We analyzed the expression of surface markers, and compared the predictive role of cell counts of monocyte subsets, as defined by RG and TG, respectively. With both gating strategies, higher intermediate monocyte counts predicted the cardiovascular endpoint in Kaplan-Meier analyses (P < 0.001 with RG; P < 0.001 with TG). After correction for confounders, intermediate monocyte counts remained independent predictors in Cox-Regression analyses (HR = 1.013 [95% CI: 1.006-1.020; P < 0.001] with RG; HR = 1.015 [95% CI: 1.006-1.024; P = 0.001] with TG). NRI was 3.9% when reclassifying patients from quartiles of intermediate monocyte counts with RG strategy toward quartiles of intermediate monocytes counts with TG strategy. In expression analysis, those monocytes which are defined as intermediate monocytes by the RG strategy and as nonclassical monocytes by the TG strategy share characteristics of both subsets. In conclusion, intermediate monocytes were independent predictors of cardiovascular outcome irrespective of the applied gating strategy. Future studies should aim to identify markers that allow for an unequivocal definition of intermediate monocytes, which may further improve their power to predict cardiovascular events.

Reprint of: Monocyte subsets in man and other species.

Monocytes are white blood cells that belong to the mononuclear phagocyte system. They derive from precursors in bone marrow, from there they go into blood, where they have a half-life of 1-2 days, and then they migrate into the various tissues. Monocyte subsets were discovered by means of flow cytometry in human blood some 20 years ago and their phenotype and function has been characterized in detail in health and disease. The subset classification as classical, intermediate and non-classical monocytes appears to apply to other species as well, as reviewed in here by comparing data on human monocytes with the respective cells in the mouse, the rat, the pig, the cow and the horse. The data show that the subsets are homologous between the species but there are important differences in subset-specific gene expression such that findings in a given species cannot be directly translated to man.

Monocyte subsets in man and other species.

Monocytes are white blood cells that belong to the mononuclear phagocyte system. They derive from precursors in bone marrow, from there they go into blood, where they have a half-life of 1-2 days, and then they migrate into the various tissues. Monocyte subsets were discovered by means of flow cytometry in human blood some 20 years ago and their phenotype and function has been characterized in detail in health and disease. The subset classification as classical, intermediate and non-classical monocytes appears to apply to other species as well, as reviewed in here by comparing data on human monocytes with the respective cells in the mouse, the rat, the pig, the cow and the horse. The data show that the subsets are homologous between the species but there are important differences in subset-specific gene expression such that findings in a given species cannot be directly translated to man.

Transcript profiling of CD16-positive monocytes reveals a unique molecular fingerprint.

CD16-positive (CD14(++) CD16(+) and CD14(+) CD16(++) ) monocytes have unique features with respect to phenotype and function. We have used transcriptional profiling for comparison of CD16-positive monocytes and classical monocytes. We show herein that 187 genes are greater than fivefold differentially expressed, including 90 genes relevant to immune response and inflammation. Hierarchical clustering of data for monocyte subsets and CD1c(+) myeloid blood dendritic cells (DCs) demonstrate that CD16-positive cells are more closely related to classical monocytes than to DCs. Reverse transcriptase polymerase chain reaction for ten genes with the strongest differential expression confirmed the pattern including a lower messenger RNA level for CD14, CD163, and versican in CD16-positive monocytes. The pattern was similar for CD16-positive monocytes at rest and after exercise mobilization from the marginal pool. By contrast, alveolar macrophages, small sputum macrophages, breast milk macrophages, and synovial macrophages all showed a different pattern. When monocyte-derived macrophages (MDMs) were generated from CD16-positive monocytes by culture with macrophage colony-stimulating factor in vitro, then the MDMs maintained properties of their progeny with lower expression of CD14, CD163, and versican compared with CD14(++) CD16(-) MDMs. Furthermore, CD16-positive MDMs showed a higher phagocytosis for opsonized Escherichia coli. The data demonstrate that CD16-positive monocytes form a distinct type of cell, which gives rise to a distinct macrophage phenotype.

The EvA study: aims and strategy.

The EvA study is a European Union-funded project under the Seventh Framework Programme (FP7), which aims at defining new markers for chronic obstructive pulmonary disease (COPD) and its subtypes. The acronym is derived from emphysema versus airway disease, indicating that the project targets these two main phenotypes of the disease. The EvA study is based on the concept that emphysema and airway disease are governed by different pathophysiological processes, are driven by different genes and have differential gene expression in the lung. To define these genes, patients and non-COPD controls are recruited for clinical examination, lung function analysis and computed tomography (CT) of the lung. CT scans are used to define the phenotypes based on lung density and airway wall thickness. This is followed by bronchoscopy in order to obtain samples from the airways and the alveoli. These tissue samples, along with blood samples, are then subjected to genome-wide expression and association analysis and markers linked to the phenotypes are identified. The population of the EvA study is different from other COPD study populations, since patients with current oral glucocorticoids, antibiotics and exacerbations or current smokers are excluded, such that the signals detected in the molecular analysis are due to the distinct inflammatory process of emphysema and airway disease in COPD.

Comparison of gene expression profiles between human and mouse monocyte subsets.

Blood of both humans and mice contains 2 main monocyte subsets. Here, we investigated the extent of their similarity using a microarray approach. Approximately 270 genes in humans and 550 genes in mice were differentially expressed between subsets by 2-fold or more. More than 130 of these gene expression differences were conserved between mouse and human monocyte subsets. We confirmed numerous of these differences at the cell surface protein level. Despite overall conservation, some molecules were conversely expressed between the 2 species' subsets, including CD36, CD9, and TREM-1. Other differences included a prominent peroxisome proliferator-activated receptor gamma (PPARgamma) signature in mouse monocytes, which is absent in humans, and strikingly opposed patterns of receptors involved in uptake of apoptotic cells and other phagocytic cargo between human and mouse monocyte subsets. Thus, whereas human and mouse monocyte subsets are far more broadly conserved than currently recognized, important differences between the species deserve consideration when models of human disease are studied in mice.

Nomenclature of monocytes and dendritic cells in blood.

Monocytes and cells of the dendritic cell lineage circulate in blood and eventually migrate into tissue where they further mature and serve various functions, most notably in immune defense. Over recent years these cells have been characterized in detail with the use of cell surface markers and flow cytometry, and subpopulations have been described. The present document proposes a nomenclature for these cells and defines 3 types of monocytes (classical, intermediate, and nonclassical monocytes) and 3 types of dendritic cells (plasmacytoid and 2 types of myeloid dendritic cells) in human and in mouse blood. This classification has been approved by the Nomenclature Committee of the International Union of Immunological Societies, and we are convinced that it will facilitate communication among experts and in the wider scientific community.

Preparations of intravenous immunoglobulins diminish the number and proinflammatory response of CD14+CD16++ monocytes in common variable immunodeficiency (CVID) patients.

We have studied the effect of intravenous immunoglobulins (IVIG) on monocyte subpopulations and cytokine production in patients with CVID. The absolute number of CD14(+)CD16(++) monocytes decreased on average 2.5-fold 4h after IVIG and after 20h returned to the baseline. The cytokine level in the supernatants of peripheral blood mononuclear cells (PBMC) after ex vivo LPS stimulation demonstrated the >2-fold decrease in TNF production 4h after IVIG. The TNF expression, which is higher in the CD14(+)CD16(++) monocytes, was decreased in these cells by IVIG in 4/7 CVID cases. In vitro exposure of the healthy individuals' monocytes to the IVIG preparation resulted in reduced TNF production, which was overcome by blockade of the FcγRIIB in the CD14(+)CD16(++) CD32B(high) monocytes. Our data suggest that reduction in the number of CD14(+)CD16(++) monocytes and the blockade of their cytokine production via triggering CD32B can contribute to the anti-inflammatory action of IVIG.

Chemokine expression by small sputum macrophages in COPD.

Small sputum macrophages represent highly active cells that increase in the airways of patients with inflammatory diseases such as chronic obstructive pulmonary disease (COPD). It has been reported often that levels of cytokines, chemokines and pro-teases are increased in sputum supernatants of these patients. In COPD, the small sputum macrophages may contribute to these supernatant proteins and recruit additional cells via specific chemokine expression patterns. We therefore investigated the expression profile of chemokines in sputum macrophages obtained from COPD patients in comparison to cells from healthy donors and cells isolated after inhalation of lipopolysaccharide (LPS). We used the minimally invasive procedure of sputum induction and have purified macrophages with the RosetteSep technology. Using macrophage purification and flow cytometry we show that in COPD small sputum macrophages account for 85.9% ± 8.3% compared with 12.9% ± 7.1% of total macrophages in control donors. When looking at chemokine expression we found, for the small macrophages in COPD, increased transcript and protein levels for CCL2, CCL7, CCL13 and CCL22 with a more than 100-fold increase for CCL13 mRNA (P < 0.001). Looking at active smokers without COPD, there is a substantial increase of small macrophages to 60% ± 15% and, here, chemokine expression is increased as well. In a model of airway inflammation healthy volunteers inhaled 20 µg of lipopolysaccharide (LPS), which resulted in an increase of small sputum macrophages from 18% ± 19% to 64% ± 25%. The pattern of chemokine expression was, however, different with an upregulation for CCL2 and CCL7, while CCL13 was downregulated three-fold in the LPS-induced small macrophages. These data demonstrate that sputum macrophages in COPD show induction of a specific set of CCL chemokines, which is distinct from what can be induced by LPS.

Lung microbiome composition and bronchial epithelial gene expression in patients with COPD versus healthy individuals: a bacterial 16S rRNA gene sequencing and host transcriptomic analysis.

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is associated with airway inflammation and bacterial dysbiosis. The relationship between the airway microbiome and bronchial gene expression in COPD is poorly understood. We aimed to identify differences in the airway microbiome from bronchial brushings in patients with COPD and healthy individuals and to investigate whether any distinguishing bacteria are related to bronchial gene expression. METHODS: For this 16S rRNA gene sequencing and host transcriptomic analysis, individuals aged 45-75 years with mild-to-moderate COPD either receiving or not receiving inhaled corticosteroids and healthy individuals in the same age group were recruited as part of the Emphysema versus Airways Disease (EvA) consortium from nine centres in the UK, Germany, Italy, Poland, and Hungary. Individuals underwent clinical characterisation, spirometry, CT scans, and bronchoscopy. From bronchoscopic bronchial brush samples, we obtained the microbial profiles using 16S rRNA gene sequencing and gene expression using the RNA-Seq technique. We analysed bacterial genera relative abundance and the associations between genus abundance and clinical characteristics or between genus abundance and host lung transcriptional signals in patients with COPD versus healthy individuals, and in patients with COPD with versus without inhaled corticosteroids treatment. FINDINGS: Between February, 2009, and March, 2012, we obtained brush samples from 574 individuals. We used 546 of 574 samples for analysis, including 207 from healthy individuals and 339 from patients with COPD (192 with inhaled corticosteroids and 147 without). The bacterial genera that most strongly distinguished patients with COPD from healthy individuals were Prevotella (median relative abundance 33·5%, IQR 14·5-49·4, in patients with COPD vs 47·7%, 31·1-60·7, in healthy individuals; p<0·0001), Streptococcus (8·6%, 3·8-15·8, vs 5·3%, 3·0-10·1; p<0·0001), and Moraxella (0·05%, 0·02-0·14, vs 0·02%, 0-0·07; p<0·0001). Prevotella abundance was inversely related to COPD severity in terms of symptoms and positively related to lung function and exercise capacity. 446 samples had assessable RNA-seq data, 257 from patients with COPD (136 with inhaled corticosteroids and 121 without) and 189 from healthy individuals. No significant associations were observed between lung transcriptional signals from bronchial brushings and abundance of bacterial genera in patients with COPD without inhaled corticosteroids treatment and in healthy individuals. In patients with COPD treated with inhaled corticosteroids, Prevotella abundance was positively associated with expression of epithelial genes involved in tight junction promotion and Moraxella abundance was associated with expression of the IL-17 and TNF inflammatory pathways. INTERPRETATION: With increasing severity of COPD, the airway microbiome is associated with decreased abundance of Prevotella and increased abundance of Moraxella in concert with downregulation of genes promoting epithelial defence and upregulation of pro-inflammatory genes associated with inhaled corticosteroids use. Our work provides further insight in understanding the relationship between microbiome alteration and host inflammatory response, which might lead to novel therapeutic strategies for COPD. FUNDING: EU Seventh Framework Programme, National Institute for Health Research.

Gender specific airway gene expression in COPD sub-phenotypes supports a role of mitochondria and of different types of leukocytes.

Chronic obstructive pulmonary disease (COPD) is a destructive inflammatory disease and the genes expressed within the lung are crucial to its pathophysiology. We have determined the RNAseq transcriptome of bronchial brush cells from 312 stringently defined ex-smoker patients. Compared to healthy controls there were for males 40 differentially expressed genes (DEGs) and 73 DEGs for females with only 26 genes shared. The gene ontology (GO) term "response to bacterium" was shared, with several different DEGs contributing in males and females. Strongly upregulated genes TCN1 and CYP1B1 were unique to males and females, respectively. For male emphysema (E)-dominant and airway disease (A)-dominant COPD (defined by computed tomography) the term "response to stress" was found for both sub-phenotypes, but this included distinct up-regulated genes for the E-sub-phenotype (neutrophil-related CSF3R, CXCL1, MNDA) and for the A-sub-phenotype (macrophage-related KLF4, F3, CD36). In E-dominant disease, a cluster of mitochondria-encoded (MT) genes forms a signature, able to identify patients with emphysema features in a confirmation cohort. The MT-CO2 gene is upregulated transcriptionally in bronchial epithelial cells with the copy number essentially unchanged. Both MT-CO2 and the neutrophil chemoattractant CXCL1 are induced by reactive oxygen in bronchial epithelial cells. Of the female DEGs unique for E- and A-dominant COPD, 88% were detected in females only. In E-dominant disease we found a pronounced expression of mast cell-associated DEGs TPSB2, TPSAB1 and CPA3. The differential genes discovered in this study point towards involvement of different types of leukocytes in the E- and A-dominant COPD sub-phenotypes in males and females.

Standardized single-platform assay for human monocyte subpopulations: Lower CD14+CD16++ monocytes in females.

We present a novel single-platform assay for determination of the absolute number of human blood monocyte subpopulations, i.e., the CD14(++)CD16(-) and the CD14(+)CD16(++) monocytes. A four-color combination of antibodies to CD14, CD16, CD45, and HLA-DR reduces the spill-over of natural killer cells and of granulocytes into the CD14(+)CD16(++) monocyte gate. For these CD14(+)CD16(++) monocytes, the intra-assay coefficient of variation (CV) was 4.1% and the inter-assay CV was 8.5%. Looking at a cohort of 40 donors aged 18-60 years, we found no age dependence. There was however an effect of gender in that females had lower CD14(+)CD16(++) monocytes (45.4 +/- 13.5 cells/microl) compared with males (59.1 +/- 20.3 cells/microl) (P < 0.02). Using this novel approach, we can confirm that exercise will lead to more than three-fold increase of the CD14(+)CD16(++) monocytes. Also, we show that therapy with low doses of glucocorticoids will deplete these cells. This robust single-platform assay may be a useful tool for monitoring the absolute number of monocyte subpopulations in health and disease.

Subsets of CD1c+ DCs: Dendritic Cell Versus Monocyte Lineage.

Currently three bona fide dendritic cell (DC) types are distinguished in human blood. Herein we focus on type 2 DCs (DC2s) and compare the three defining markers CD1c, CD172, and CD301. When using CD1c to define DC2s, a CD14+ and a CD14- subset can be detected. The CD14+ subset shares features with monocytes, and this includes substantially higher expression levels for CD64, CD115, CD163, and S100A8/9. We review the current knowledge of these CD1c+CD14+ cells as compared to the CD1c+CD14- cells with respect to phenotype, function, transcriptomics, and ontogeny. Here, we discuss informative mutations, which suggest that two populations have different developmental requirements. In addition, we cover subsets of CD11c+CD8- DC2s in the mouse, where CLEC12A+ESAMlow cells, as compared to the CLEC12A-ESAMhigh subset, also express higher levels of monocyte-associated markers CD14, CD3, and CD115. Finally, we summarize, for both man and mouse, the data on lower antigen presentation and higher cytokine production in the monocyte-marker expressing DC2 subset, which demonstrate that the DC2 subsets are also functionally distinct.

Epigenetics in non-classical monocytes support their pro-inflammatory gene expression.

Non-classical human monocytes are characterized by high-level expression of cytokines like TNF, but the mechanisms involved are elusive. We have identified miRNAs and CpG-methylation sites that are unique to non-classical monocytes, defined via CD14 and CD16 expression levels. For down-regulated miRNAs that are linked to up-regulated mRNAs the dominant gene ontology term was intracellular signal transduction. This included down-regulated miRNA-20a-5p and miRNA-106b-5p, which both are linked to increased mRNA for the TRIM8 signaling molecule. Methylation analysis revealed 16 hypo-methylated CpG sites upstream of 14 differentially increased mRNAs including 2 sites upstream of TRIM8. Consistent with a positive role in signal transduction, high TRIM8 levels went along with high basal TNF mRNA levels in non-classical monocytes. Since cytokine expression levels in monocytes strongly increase after stimulation with toll-like-receptor ligands, we have analyzed non-classical monocytes (defined via slan expression) after stimulation with lipopolysaccharide (LPS). LPS-stimulated cells continued to have low miRNA-20a and miRNA-106b and high TRIM8 mRNA levels and they showed a 10-fold increase in TNF mRNA. These data suggest that decreased miRNAs and CpG hypo-methylation is linked to enhanced expression of TRIM8 and that this can contribute to the increased TNF levels in non-classical human monocytes.

Ultrafine carbon particles down-regulate CYP1B1 expression in human monocytes.

BACKGROUND: Cytochrome P450 monoxygenases play an important role in the defence against inhaled toxic compounds and in metabolizing a wide range of xenobiotics and environmental contaminants. In ambient aerosol the ultrafine particle fraction which penetrates deeply into the lungs is considered to be a major factor for adverse health effects. The cells mainly affected by inhaled particles are lung epithelial cells and cells of the monocyte/macrophage lineage. RESULTS: In this study we have analyzed the effect of a mixture of fine TiO2 and ultrafine carbon black Printex 90 particles (P90) on the expression of cytochrome P450 1B1 (CYP1B1) in human monocytes, macrophages, bronchial epithelial cells and epithelial cell lines. CYP1B1 expression is strongly down-regulated by P90 in monocytes with a maximum after P90 treatment for 3 h while fine and ultrafine TiO2 had no effect. CYP1B1 was down-regulated up to 130-fold and in addition CYP1A1 mRNA was decreased 13-fold. In vitro generated monocyte-derived macrophages (MDM), epithelial cell lines, and primary bronchial epithelial cells also showed reduced CYP1B1 mRNA levels. Benzo[a]pyrene (BaP) is inducing CYB1B1 but ultrafine P90 can still down-regulate gene expression at 0.1 muM of BaP. The P90-induced reduction of CYP1B1 was also demonstrated at the protein level using Western blot analysis. CONCLUSION: These data suggest that the P90-induced reduction of CYP gene expression may interfere with the activation and/or detoxification capabilities of inhaled toxic compounds.