Lung fibrosis induced by silica particles in NMRI mice is associated with an upregulation of the p40 subunit of interleukin-12 and Th-2 manifestations

A novel experimental model to investigate fungal involvement shows expression of Dectin-1 in periapical lesion pathogenesis

BACKGROUND

Candida albicans is linked to persistent endodontic lesions. However, the recognition receptor that identifies it is not explored previously.

OBJECTIVES

The aim of this study was to (1) establish a zymosan-induced model of apical periodontitis in mouse, (2) observe the expression of Dectin-1 and its possible relationship with toll-like receptor (TLR) 2 and (3) observe relationship between Osteopontin (OPN) and inflammatory cytokines.

METHODS

A total of 138 Naval Medical Research Institute (NMRI) mice were randomly divided into; Experimental Group n = 69 and Zymosan Group n = 69. Periapical periodontitis was developed in right maxillary molar. The animals were sacrificed at 7, 21 and 42 days. Bone blocks containing the mesial root (n = 15 for qRT-PCR, n = 45 for enzyme-linked immune sorbent assay (ELISA)) were collected for mRNA expression and ELISA. While whole maxilla (n = 3 from each time interval) were used for histology and immunohistochemical analysis. One way analysis of variance (ANOVA) and Tuckey's posthoc was used for statistical analysis at p ≤ .05.

RESULTS

TLR-2, Dectin-1 and TLR4-positive cells was detected at all time intervals in both groups. A strong positive correlation was observed between TLR-2 and Dectin-1 in both lesions (regular r = .680, p = .015, zymosan (r = .861, p < .001)). A significant correlation was found between OPN and tumour necrosis factor-alpha (TNF-α) in zymosan lesion (r = .827, p = .001).

CONCLUSIONS

Immune cells of inflamed periapical tissue expressed Dectin-1 receptor in response to the microbial challenge from infected root canals and showed positive correlation with TLR-2 and OPN suggesting a possible receptor collaboration mediated by OPN. The expression of OPN and TNF-α showed positive correlation in response to fungal antigen, indicating a possible relationship.

Gasdermin D membrane pores orchestrate IL-1α secretion from necrotic macrophages after NFS-rich silica exposure

IL-1α is an intracellular danger signal (DAMP) released by macrophages contributing to the development of silica-induced lung inflammation. The exact molecular mechanism orchestrating IL-1α extracellular release from particle-exposed macrophages is still unclear. To delineate this process, murine J774 and bone-marrow derived macrophages were exposed to increasing concentrations (1-40 cm²/ml) of a set of amorphous and crystalline silica particles with different surface chemical features. In particular, these characteristics include the content of nearly free silanols (NFS), a silanol population responsible for silica cytotoxicity recently identified. We first observed de novo stocks of IL-1α in macrophages after silica internalization regardless of particle physico-chemical characteristics and cell stress. IL-1α intracellular production and accumulation were observed by exposing macrophages to biologically-inert or cytotoxic crystalline and amorphous silicas. In contrast, only NFS-rich reactive silica particles triggered IL-1α release into the extracellular milieu from necrotic macrophages. We demonstrate that IL-1α is actively secreted through the formation of gasdermin D (GSDMD) pores in the plasma membrane and not passively released after macrophage plasma membrane lysis. Our findings indicate that the GSDMD pore-dependent secretion of IL-1α stock from macrophages solely depends on cytotoxicity induced by NFS-rich silica. This new regulated process represents a key first event in the mechanism of silica toxicity, suitable to refine the existing adverse outcome pathway (AOP) for predicting the inflammatory activity of silicas.

IL-10 is not anti-fibrotic but pro-fibrotic in endometriosis: IL-10 treatment of endometriotic stromal cells in vitro promotes myofibroblast proliferation and collagen type I protein expression

STUDY QUESTION

Is interleukin-10 (IL-10) anti-fibrotic in endometriosis?

SUMMARY ANSWER

IL-10 is not anti-fibrotic but pro-fibrotic in endometriosis, because IL-10 treatment of endometriotic stromal cells in vitro promotes myofibroblast proliferation and collagen type I protein expression.

WHAT IS KNOWN ALREADY

We previously showed that persistent activation of signal transducer and activator of transcription 3 (STAT3) via IL-6 trans-signaling promotes fibrosis of endometriosis. Studies showed marked anti-fibrotic effects of IL-10 via the STAT3 signaling pathway, which is generally considered to be anti-inflammatory, in various organs.

STUDY DESIGN, SIZE, DURATION

Endometrial and/or endometriotic samples of 54 patients who had histological evidence of deep endometriosis, and endometrial samples from 30 healthy fertile women were analyzed.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The effects of IL-10/STAT3 signaling as well as inhibition of STAT3 activation by knockdown of STAT3 gene on the pro-fibrotic phenotype in endometrial and endometriotic stromal cells in vitro were investigated. Then, the effects of various time points of IL-10 treatment in combination with transforming growth factor (TGF)-β1 and/or IL-6/soluble IL-6 receptor (sIL-6R) on the profibrotic phenotype of endometrial and endometriotic stromal cells were investigated.

MAIN RESULTS AND THE ROLE OF CHANCE

IL-10 induced pro-fibrotic phenotype (cell proliferation, collagen type I synthesis, α-smooth muscle actin positive stress fibers and collagen gel contraction) of endometriotic stromal cells. Knockdown of STAT3 gene decreased the IL-10 induced pro-fibrotic phenotype of endometriotic stromal cells. In contrast, IL-10 had no significant effects on pro-fibrotic phenotype of endometrial stromal cells of healthy women. Sequential IL-10 treatment with or without TGF-β1 and/or IL-6/sIL-6R induced persistent activation of STAT3 and significantly increased proliferation of myofibroblasts (cells with α-smooth muscle actin positive stress fibers) and protein expression of collagen type I in endometriotic stromal cells. TGF-β1 and/or IL-6/sIL6RIL-6/sIL6R treatment significantly increased tissue inhibitor of metalloproteinase 1 (TIMP1) protein expression, whereas IL-10 had no significant effects. Knockdown of STAT3 gene significantly decreased the TGF-β1 and/or IL-6/sIL6R induced TIMP1 protein expression. In contrast, pre-treatment with IL-10 before TGF-β1 and/or IL-6/sIL-6R treatment and sequential IL-10 treatment with or without TGF-β1 and/or IL-6/sIL-6R significantly decreased proliferation of fibroblasts (cells without α-smooth muscle actin positive stress fibers) and collagen type I protein expression in endometrial stromal cells of healthy women.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Given the large number of complex interactions and signaling pathways of pro- and anti-inflammatory mediators that are involved in the pathophysiology of endometriosis, the present study investigated only a very small portion of the whole. Further in vivo studies are required to validate the present findings.

WIDER IMPLICATIONS OF THE FINDINGS

Inflammatory mediators in the pathophysiology of endometriosis have been extensively investigated as potential therapeutic targets. However, the present study showed that anti-inflammatory signals of IL-10 and IL-6 through persistent STAT3 activation may promote endometriosis fibrosis. Therapeutic strategies, such as suppression of 'inflammation', might dysregulate the cross-regulation of 'pro- and anti-inflammatory mediators', leading to detrimental effects in patients with endometriosis, such as fibrosis. To develop new, but not deleterious, therapeutic strategies, studies are required to investigate whether, how and what 'anti-inflammatory mediators' along with pro-inflammatory mediators are involved in individual patients with endometriosis.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported in part by KARL STORZ SE & Co. KG (Tuttlingen, Germany). The authors have no conflict of interest to disclose.

IL-12p40 deletion aggravates lipopolysaccharide-induced cardiac dysfunction in mice

Background

Cardiac dysfunction is one of the most common complications of sepsis and is associated with the adverse outcomes and high mortality of sepsis patients. IL-12p40, the common subunit of IL-12 and IL-23, has been shown to be involved in a variety of inflammation-related diseases, such as psoriasis and inflammatory bowel disease. However, the role of IL-12p40 in lipopolysaccharide (LPS)-induced cardiac dysfunction remains obscure. This study aimed to explore the role of IL-12p40 in LPS-induced cardiac dysfunction and its potential mechanisms.

Methods

In this study, mice were treated with LPS and the cardiac expression of IL-12p40 was determined. Then, IL-12p40–/– mice were used to detect the role and mechanisms of IL-12p40 in LPS-induced cardiac injury. In addition, monocytes were adoptively transferred to IL-12p40–/– mice to explore their effects on LPS-induced cardiac dysfunction.

Results

The results showed that cardiac IL-12p40 expression was significantly increased after treated with LPS. In addition, IL-12p40 deletion significantly aggravated LPS-induced cardiac dysfunction, evidenced by the increased serum levels of cardiomyocyte injury markers and heart injury scores, as well as by the deteriorated cardiac function. Moreover, IL-12p40 deletion increased LPS-induced monocyte accumulation and cardiac expression of inflammatory cytokines, as well as enhanced the activation of the NF-κB and MAPK pathways. Furthermore, adoptive transfer WT mouse monocytes to IL-12p40−/− mice alleviated LPS-induced cardiac dysfunction and decreased the phosphorylation of p65.

Conclusion

IL-12p40 deletion significantly aggravated LPS-induced cardiac injury and cardiac dysfunction in mice by regulating the NF-κB and MAPK signaling pathways, and this process was related to monocytes. Therefore, IL-12p40 show a protective role in SIC, and IL-12p40 deficiency or anti-IL-12p40 monoclonal antibodies may be detrimental to patients with SIC.

Pulmonary Toxicity of Silica Linked to Its Micro- or Nanometric Particle Size and Crystal Structure: A Review

Silicon dioxide (SiO2) is a mineral compound present in the Earth’s crust in two mineral forms: crystalline and amorphous. Based on epidemiological and/or biological evidence, the pulmonary effects of crystalline silica are considered well understood, with the development of silicosis, emphysema, chronic bronchitis, or chronic obstructive pulmonary disease. The structure and capacity to trigger oxidative stress are recognized as relevant determinants in crystalline silica’s toxicity. In contrast, natural amorphous silica was long considered nontoxic, and was often used as a negative control in experimental studies. However, as manufactured amorphous silica nanoparticles (or nanosilica or SiNP) are becoming widely used in industrial applications, these paradigms must now be reconsidered at the nanoscale (<100 nm). Indeed, recent experimental studies appear to point towards significant toxicity of manufactured amorphous silica nanoparticles similar to that of micrometric crystalline silica. In this article, we present an extensive review of the nontumoral pulmonary effects of silica based on in vitro and in vivo experimental studies. The findings of this review are presented both for micro- and nanoscale particles, but also based on the crystalline structure of the silica particles.

Mouse innate-like B-1 lymphocytes promote inhaled particle-induced in vitro granuloma formation and inflammation in conjunction with macrophages

The current paradigm for explaining lung granulomatous diseases induced by inhaled particles is mainly based on macrophages. This mechanism is now challenging because B lymphocytes also infiltrate injured tissue, and the deficiency in B lymphocytes is associated with limited lung granulomas in silica-treated mice. Here, we investigated how B lymphocytes respond to micro- and nanoparticles by combining in vivo and in vitro mouse models. We first demonstrated that innate-like B-1 lymphocytes (not conventional B-2 lymphocytes or plasma cells) specifically accumulated during granuloma formation in mice instilled with crystalline silica (DQ12, 2.5 mg/mouse) and carbon nanotubes (CNT Mitsui, 0.2 mg/mouse). In comparison to macrophages, peritoneal B-1 lymphocytes purified from naïve mice were resistant to the pyroptotic activity of reactive particles (up to 1 mg/mL) but clustered to establish in vitro cell/particle aggregates. Mouse B-1 lymphocytes (not B-2 lymphocytes) in coculture with macrophages and CNT (0.1 µg/mL) organized three-dimensional spheroid structures in Matrigel and stimulated the release of TIMP-1. Furthermore, purified B-1 lymphocytes are sensitive to nanosilica toxicity through radical generation in culture. Nanosilica-exposed B-1 lymphocytes released proinflammatory cytokines and alarmins. In conclusion, our data indicate that in addition to macrophages, B-1 lymphocytes participate in micrometric particle-induced granuloma formation and display inflammatory functions in response to nanoparticles.

Crystalline Silica Impairs Efferocytosis Abilities of Human and Mouse Macrophages: Implication for Silica-Associated Systemic Sclerosis

Inhalation of crystalline silica (SiO2) is a risk factor of systemic autoimmune diseases such as systemic sclerosis (SSc) and fibrotic pulmonary disorders such as silicosis. A defect of apoptotic cell clearance (i.e., efferocytosis, a key process in the resolution of inflammation) is reported in macrophages from patients with fibrotic or autoimmune diseases. However, the precise links between SiO2 exposure and efferocytosis impairment remain to be determined. Answering to this question may help to better link innate immunity and fibrosis. In this study, we first aim to determine whether SiO2 might alter efferocytosis capacities of human and mouse macrophages. We secondly explore possible mechanisms explaining efferocytosis impairment, with a specific focus on macrophage polarization and on the RhoA/ROCK pathway, a key regulator of cytoskeleton remodeling and phagocytosis. Human monocyte-derived macrophages (MDM) and C57BL/6J mice exposed to SiO2 and to CFSE-positive apoptotic Jurkat cells were analyzed by flow cytometry to determine their efferocytosis index (EI). The effects of ROCK inhibitors (Y27632 and Fasudil) on EI of SiO2-exposed MDM and MDM from SSc patients were evaluated in vitro. Our results demonstrated that SiO2 significantly decreased EI of human MDM in vitro and mouse alveolar macrophages in vivo. In human MDM, this SiO2-associated impairment of efferocytosis, required the expression of the membrane receptor SR-B1 and was associated with a decreased expression of M2 polarization markers (CD206, CD204, and CD163). F-actin staining, RhoA activation and impairment of efferocytosis, all induced by SiO2, were reversed by ROCK inhibitors. Moreover, the EI of MDM from SSc patients was similar to the EI of in vitro- SiO2-exposed MDM and Y27632 significantly increased SSc MDM efferocytosis capacities, suggesting a likewise activation of the RhoA/ROCK pathway in SSc. Altogether, our results demonstrate that SiO2 exposure may contribute to the impairment of efferocytosis capacities of mouse and human macrophages but also of MDM in SiO2-associated autoimmune diseases and fibrotic disorders such as SSc; in this context, the silica/RhoA/ROCK pathway may constitute a relevant therapeutic target.

Development of experimental silicosis in inbred and outbred mice depends on instillation volume

There is considerable variation in methods to induce experimental silicosis with the effects of dose and route of exposure being well documented. However, to what extent the volume of silica suspension alters the dispersion and severity of silicosis has not been adequately investigated. In this study, the optimal volume of a crystalline silica suspension required to obtain uniform distribution and greatest incidence and severity of silicosis was determined in inbred and outbred mice. Silica dispersal, detected by co-inspiration with India ink and polarized light microscopy, was highly dependent upon volume. Furthermore, although peribronchitis, perivasculitis, and increases in bronchoalveolar lavage fluid cell numbers were detected a lower doses and volumes, significant alveolitis required exposure to 5 mg of silica in 50 μl. This dose and volume of transoral instillation led to a greater penetrance of silicosis in the genetically heterogeneous Diversity Outbred strain as well as greater alveolar inflammation typical of the silicosis in human disease. These findings underscore the critical importance of instillation volume on the induction, severity, and type of inflammatory pathology in experimental silicosis.

Immunity to the Dual Threat of Silica Exposure and Mycobacterium tuberculosis

Exposure to silica and the consequent development of silicosis are well-known health problems in countries with mining and other dust producing industries. Apart from its direct fibrotic effect on lung tissue, chronic and immunomodulatory character of silica causes susceptibility to tuberculosis (TB) leading to a significantly higher TB incidence in silica-exposed populations. The presence of silica particles in the lung and silicosis may facilitate initiation of tuberculous infection and progression to active TB, and exacerbate the course and outcome of TB, including prognosis and survival. However, the exact mechanisms of the involvement of silica in the pathological processes during mycobacterial infection are not yet fully understood. In this review, we focus on the host's immunological response to both silica and Mycobacterium tuberculosis, on agents of innate and adaptive immunity, and particularly on silica-induced immunological modifications in co-exposure that influence disease pathogenesis. We review what is known about the impact of silica and Mycobacterium tuberculosis or their co-exposure on the host's immune system, especially an impact that goes beyond an exclusive focus on macrophages as the first line of the defense. In both silicosis and TB, acquired immunity plays a major role in the restriction and/or elimination of pathogenic agents. Further research is needed to determine the effects of silica in adaptive immunity and in the pathogenesis of TB.

New interplay between interstitial and alveolar macrophages explains pulmonary alveolar proteinosis (PAP) induced by indium tin oxide particles

Occupational exposure to indium tin oxide (ITO) particles has been associated with the development of severe lung diseases, including pulmonary alveolar proteinosis (PAP). The mechanisms of this lung toxicity remain unknown. Here, we reveal the respective roles of resident alveolar (Siglec-F^high AM) and recruited interstitial (Siglec-F^low IM) macrophages contributing in concert to the development of PAP. In mice treated with ITO particles, PAP is specifically associated with IL-1α (not GM-CSF) deficiency and Siglec-F^high AM (not Siglec-F^low IM) depletion. Mechanistically, ITO particles are preferentially phagocytosed and dissolved to soluble In³⁺ by Siglec-F^low IM. In contrast, Siglec-F^high AM weakly phagocytose or dissolve ITO particles, but are sensitive to released In³⁺ through the expression of the transferrin receptor-1 (TfR1). Blocking pulmonary Siglec-F^low IM recruitment in CCR2-deficient mice reduces ITO particle dissolution, In³⁺ release, Siglec-F^high AM depletion, and PAP formation. Restoration of IL-1-related Siglec-F^high AM also prevented ITO-induced PAP. We identified a new mechanism of secondary PAP development according to which metal ions released from inhaled particles by phagocytic IM disturb IL-1α-dependent AM self-maintenance and, in turn, alveolar clearance.

The alarmin IL-1α is a master cytokine in acute lung inflammation induced by silica micro- and nanoparticles

Background

Inflammasome-activated IL-1β plays a major role in lung neutrophilic inflammation induced by inhaled silica. However, the exact mechanisms that contribute to the initial production of precursor IL-1β (pro-IL-1β) are still unclear. Here, we assessed the implication of alarmins (IL-1α, IL-33 and HMGB1) in the lung response to silica particles and found that IL-1α is a master cytokine that regulates IL-1β expression.

Methods

Pro- and mature IL-1β as well as alarmins were assessed by ELISA, Western Blot or qRT-PCR in macrophage cultures and in mouse lung following nano- and micrometric silica exposure. Implication of these immune mediators in the establishment of lung inflammatory responses to silica was investigated in knock-out mice or after antibody blockade by evaluating pulmonary neutrophil counts, CXCR2 expression and degree of histological injury.

Results

We found that the early release of IL-1α and IL-33, but not HMGB1 in alveolar space preceded the lung expression of pro-IL-1β and neutrophilic inflammation in silica-treated mice. In vitro, the production of pro-IL-1β by alveolar macrophages was significantly induced by recombinant IL-1α but not by IL-33. Neutralization or deletion of IL-1α reduced IL-1β production and neutrophil accumulation after silica in mice. Finally, IL-1α released by J774 macrophages after in vitro exposure to a range of micro- and nanoparticles of silica was correlated with the degree of lung inflammation induced in vivo by these particles.

Conclusions

We demonstrated that in response to silica exposure, IL-1α is rapidly released from pre-existing stocks in alveolar macrophages and promotes subsequent lung inflammation through the stimulation of IL-1β production. Moreover, we demonstrated that in vitro IL-1α release from macrophages can be used to predict the acute inflammogenic activity of silica micro- and nanoparticles.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-014-0069-x) contains supplementary material, which is available to authorized users.

Uncoupling between inflammatory and fibrotic responses to silica: evidence from MyD88 knockout mice

The exact implication of innate immunity in granuloma formation and irreversible lung fibrosis remains to be determined. In this study, we examined the lung inflammatory and fibrotic responses to silica in MyD88-knockout (KO) mice. In comparison to wild-type (WT) mice, we found that MyD88-KO animals developed attenuated lung inflammation, neutrophil accumulation and IL-1β release in response to silica. Granuloma formation was also less pronounced in MyD88-KO mice after silica. This limited inflammatory response was not accompanied by a concomitant attenuation of lung collagen accumulation after silica. Histological analyses revealed that while pulmonary fibrosis was localized in granulomas in WT animals, it was diffusely distributed throughout the parenchyma in MyD88-KO mice. Robust collagen accumulation was also observed in mice KO for several other components of innate immunity (IL-1R, IL-1, ASC, NALP3, IL-18R, IL-33R, TRIF, and TLR2-3-4,). We additionally show that pulmonary fibrosis in MyD88-KO mice was associated with the accumulation of pro-fibrotic regulatory T lymphocytes (T regs) and pro-fibrotic cytokine expression (TGF-β, IL-10 and PDGF-B), not with T helper (Th) 17 cell influx. Our findings indicate that the activation of MyD88-related innate immunity is central in the establishment of particle-induced lung inflammatory and granuloma responses. The development of lung fibrosis appears uncoupled from inflammation and may be orchestrated by a T reg-associated pathway.

Free IL-12p40 monomer is a polyfunctional adaptor for generating novel IL-12-like heterodimers extracellularly

IL-12p40 partners with the p35 and p19 polypeptides to generate the heterodimeric cytokines IL-12 and IL-23, respectively. These cytokines play critical and distinct roles in host defense. The assembly of these heterodimers is thought to take place within the cell, resulting in the secretion of fully functional cytokines. Although the p40 subunit alone can also be rapidly secreted in response to inflammatory signals, its biological significance remains unclear. In this article, we show that the secreted p40 monomer can generate de novo IL-12-like activities by combining extracellularly with p35 released from other cells. Surprisingly, an unbiased proteomic analysis reveals multiple such extracellular binding partners for p40 in the serum of mice after an endotoxin challenge. We biochemically validate the binding of one of these novel partners, the CD5 Ag-like glycoprotein, to the p40 monomer. Nevertheless, the assembled p40-CD5L heterodimer does not recapitulate the biological activity of IL-12. These findings underscore the plasticity of secreted free p40 monomer, suggesting that p40 functions as an adaptor that is able to generate multiple de novo composites in combination with other locally available polypeptide partners after secretion.

Positional cloning reveals strain-dependent expression of Trim16 to alter susceptibility to bleomycin-induced pulmonary fibrosis in mice

Pulmonary fibrosis is a disease of significant morbidity, with no effective therapeutics and an as yet incompletely defined genetic basis. The chemotherapeutic agent bleomycin induces pulmonary fibrosis in susceptible C57BL/6J mice but not in mice of the C3H/HeJ strain, and this differential strain response has been used in prior studies to map bleomycin-induced pulmonary fibrosis susceptibility loci named Blmpf1 and Blmpf2. In this study we isolated the quantitative trait gene underlying Blmpf2 initially by histologically phenotyping the bleomycin-induced lung disease of sublines of congenic mice to reduce the linkage region to 13 genes. Of these genes, Trim16 was identified to have strain-dependent expression in the lung, which we determined was due to sequence variation in the promoter. Over-expression of Trim16 by plasmid injection increased pulmonary fibrosis, and bronchoalveolar lavage levels of both interleukin 12/23-p40 and neutrophils, in bleomycin treated B6.C3H-Blmpf2 subcongenic mice compared to subcongenic mice treated with bleomycin only, which follows the C57BL/6J versus C3H/HeJ strain difference in these traits. In summary we demonstrate that genetic variation in Trim16 leads to its strain-dependent expression, which alters susceptibility to bleomycin-induced pulmonary fibrosis in mice.

Genetic differences within the population influence an individual's susceptibility to the lung disease pulmonary fibrosis. As environmental factors also have a tremendous effect on the development of this disease, investigations in an animal model can reveal the genetic basis of this trait, under controlled circumstances. Starting from previous work that had identified a genomic region linked to fibrosis susceptibility in mice, we assayed the fibrosis response of lines of mice specifically bred to contain reduced portions of the original genetic interval, and we narrowed our study to 13 genes. Genetic evaluation pointed to the gene Trim16 as a prime candidate for affecting fibrosis, and we identified genetic variations to alter its transcription. Our functional studies showed that Trim16 injected into the specifically bred, and bleomcyin-treated, mice significantly increased their pulmonary fibrosis levels. Further evaluation of the mice showed the increase to be associated with known enhancers of fibrosis, neutrophils and interleukin12/23-p40. This study shows that genetic variation in Trim16 affects both the lung tissue inflammatory response and the development of pulmonary fibrosis in mice and thus provides a novel pathway to fibrosis development for subsequent clinical investigation.

Targeting IL-12/IL-23 by employing a p40 peptide-based vaccine ameliorates TNBS-induced acute and chronic murine colitis

Interleukin (IL)-12 and IL-23 both share the p40 subunit and are key cytokines in the pathogenesis of Crohn's disease. Previously, we have developed and identified three mouse p40 peptide-based and virus-like particle vaccines. Here, we evaluated the effects and immune mechanisms of the optimal vaccine in downregulating intestinal inflammation in murine acute and chronic colitis, induced by intrarectal administrations of trinitrobenzene sulfonic acid (TNBS). Mice were injected subcutaneously with vaccine, vaccine carrier or saline three times, and then intrarectally administered TNBS weekly for 2 wks (acute colitis) or 7 wks (chronic colitis). The severity of colitis was evaluated by body weight, histology and collagen and cytokine levels in colon tissue. Th1 and Th17 cells in mesenteric lymph nodes (MLN) were determined. Our results showed the vaccine induced high level and long-lasting specific IgG antibodies to p40, IL-12 and IL-23. After administrations of TNBS, vaccinated mice had significantly less body weight loss and a significant decrease of inflammatory scores, collagen deposition and expression of p40, IL-12, IL-23, IL-17, TNF, iNOS and Bcl-2 in colon tissues, compared with carrier and saline groups. Moreover, vaccinated mice exhibited a trend to lower percentages of Th1 cells in acute colitis and of Th17 cells in chronic colitis in MLN than in controls. In summary, administration of the vaccine induced specific antibodies to IL-12 and IL-23, which was associated with improvement of intestinal inflammation and fibrosis. This suggests that the vaccine may provide a potential approach for the long-term treatment of Crohn's disease.

Time-response relationship of nano and micro particle induced lung inflammation. Quartz as reference compound

An increasing number of engineered particles, including nanoparticles, are being manufactured, increasing the need for simple low-dose toxicological screening methods. This study aimed to investigate the kinetics of biomarkers related to acute and sub-chronic particle-induced lung inflammation of quartz. Mice were intratracheal instilled with 50 µg of microsized or nanosized quartz. Acute inflammation was assessed 1, 2, 4, 8, 16 or 48 hours post exposure, whereas sub-chronic inflammation was investigated 3 months after exposure. Markers of acute inflammation in the bronchoalveolar lavage fluid (BALF) were neutrophils (PMN), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, macrophage inflammatory protein-2 (MIP-2), keratinocyte derived chemokine (KC) and total protein, which were all close to maximum 16 hours post instillation. No major differences were seen in the time-response profiles of nano- and micro-sized particles. The potency of the two samples cannot be compared; during the milling process, a substantial part of the quartz was converted to amorphous silica and contaminated with corundum. For screening, BALF PMN, either TNF-α or IL-1β at 16 hours post instillation may be useful. At 3 months post instillation, KC, PMN and macrophages were elevated. Histology showed no interstitial inflammation three months post instillation. For screening of sub-chronic effects, KC, PMN, macrophages and histopathology is considered sufficient.

IL-18 inhibits TNF-alpha-induced osteoclastogenesis possibly via a T cell-independent mechanism in synergy with IL-12 in vivo

It has recently been reported that tumor necrosis factor (TNF)-alpha has the ability to accelerate osteoclastogenesis. We previously reported that the proinflammatory cytokine interleukin (IL)-18 inhibits TNF-alpha-mediated osteoclastogenesis in mouse bone marrow cultures. In the present study, the effect of IL-18 on TNF-alpha-mediated osteoclastogenesis was investigated in vivo. We administered TNF-alpha with or without IL-18 into the supracalvaria of mice. The number of osteoclasts in the suture of the calvaria was increased in mice administered TNF-alpha. The number of osteoclasts in mice administered both TNF-alpha and IL-18 was lower than that in mice administered TNF-alpha alone. We previously showed that IL-12 and IL-18 synergistically inhibit TNF-alpha-mediated osteoclastogenesis in vitro. To assess the ability of these two cytokines to synergistically inhibit TNF-alpha-induced osteoclastogenesis in vivo, mice were administered the two cytokines at doses that did not inhibit osteoclast formation. The combination of IL-12 and IL-18 markedly inhibited TNF-alpha-induced osteoclastogenesis in vivo. To evaluate how IL-12 and IL-18 synergistically affect TNF-alpha-induced osteoclastogenesis, the IL-18 receptor (IL-18R) and IL-12R expression levels were analyzed by RT-PCR in bone marrow cells cultured with IL-12 or IL-18. IL-18R mRNA was increased in cells cultured with IL-12, while IL-12R mRNA was increased in cells cultured with IL-18. In addition, IL-18 inhibited TNF-alpha-induced osteoclastogenesis in mice with T-cell depletion caused by anti-CD4 and anti-CD8 antibodies. The present results suggest that IL-18 may inhibit TNF-alpha-mediated osteoclastogenesis in vivo via a T cell-independent mechanism.

Changes of cytokine production and cell viability of peripheral blood mononuclear cells from silicosis patients: effect of in vitro treatment with acetylsalicylic acid

In this study, IL-6 and IL-12p40 production and cell viability of peripheral blood mononuclear cells from silicosis patients after in vitro stimulation were investigated. Furthermore, the effects of introducing acetylsalicylic acid to stimulated patients’ peripheral blood mononuclear cells on cytokine production and cell viability were determined. Nine patients with moderate silicosis, 11 with severe silicosis and 14 healthy subjects were recruited for this study. The level of IL-6 produced by patients peripheral blood mononuclear cells decreased depending on the stage of the disease. The addition of acetylsalicylic acid had significantly suppressive effect on the IL-6 production by lipopolysaccharide—stimulated patients’ peripheral blood mononuclear cells. Acetylsalicylic acid treatment of C3 binding glycoprotein—stimulated patients’ peripheral blood mononuclear cells led to significant upregulation of IL-12p40 production. Results showed a stage-dependent decrease of cell viability of peripheral blood mononuclear cells from silicosis patients. Acetylsalicylic acid significantly decreased cell viability entirely in stimulated peripheral blood mononuclear cells from patients with severe silicosis. In conclusion, this study showed that the disease progression affects peripheral blood mononuclear cells in patients with silicosis and causes functional changes that became apparent after stimulation. Our study demonstrated that in severe silicosis the treatment with acetylsalicylic acid, as an anti-inflammatory agent, might not be beneficial for patients.

Altered cytokine profiles in patients with Chuvash polycythemia

Chuvash polycythemia results from a homozygous 598C>T mutation in exon 3 of the von Hippel-Lindau (VHL) gene. This disrupts the normoxia pathway for degrading hypoxia inducible factor (HIF)-1alpha and HIF-2alpha causing altered expression of HIF-1 and HIF-2 inducible genes. As hypoxia induces expression of pro-inflammatory cytokines, we hypothesized that there might be an elevation of Th1 cytokines in the setting of Chuvash polycythemia. We analyzed plasma concentrations of Th1 (interleukins-2 and 12, interferon-gamma, granulocyte-monocyte colony-stimulating factor, tumor necrosis factor-alpha) and Th2 cytokines (interleukins-4, 5, 10, and 13) using the Bio-Plex multiplex suspension array system in 34 VHL598C>T homozygotes and 32 VHL wild-type participants from Chuvashia. Concentrations of all the Th1 and Th2 cytokines measured were elevated in the VHL598C>T homozygotes compared with the control wild-type participants, but the ratios of Th1 to Th2 cytokines did not differ by genotype. In parallel, peripheral blood concentrations of CD4 positive T-helper cells and CD4/CD8 ratio were lower in the VHL598C>T homozygotes. In conclusion, the up-regulated hypoxic response in Chuvash polycythemia is associated with increased plasma products of both the Th1 and Th2 pathways, but the balance between the two pathways seems to be preserved.

Suppressive oligodeoxynucleotides inhibit silica-induced pulmonary inflammation

Inhalation of silica-containing dust particles induces silicosis, an inflammatory disease of the lungs characterized by the infiltration of macrophages and neutrophils into the lungs and the production of proinflammatory cytokines, chemokines, and reactive oxygen species (ROS). Synthetic oligodeoxynucleotides (ODN) expressing "immunosuppressive motifs" were recently shown to block pathologic inflammatory reactions in murine models of autoimmune disease. Based on those findings, the potential of suppressive ODN to prevent acute murine silicosis was examined. In vitro studies indicate that suppressive ODN blunt silica-induced macrophage toxicity. This effect was associated with a reduction in ROS production and p47phox expression (a subunit of NADPH oxidase key to ROS generation). In vivo studies show that pretreatment with suppressive (but not control) ODN reduces silica-dependent pulmonary inflammation, as manifest by fewer infiltrating cells, less cytokine/chemokine production, and lower levels of ROS (p < 0.01 for all parameters). Treatment with suppressive ODN also reduced disease severity and improved the survival (p < 0.05) of mice exposed to silica.

Sequential exposure to carbon nanotubes and bacteria enhances pulmonary inflammation and infectivity

Carbon nanotubes (CNT), with their applications in industry and medicine, may lead to new risks to human health. CNT induce a robust pulmonary inflammation and oxidative stress in rodents. Realistic exposures to CNT may occur in conjunction with other pathogenic impacts (microbial infections) and trigger enhanced responses. We evaluated interactions between pharyngeal aspiration of single-walled CNT (SWCNT) and bacterial pulmonary infection of C57BL/6 mice with Listeria monocytogenes (LM). Mice were given SWCNT (0, 10, and 40 mug/mouse) and 3 days later were exposed to LM (10(3) bacteria/mouse). Sequential exposure to SWCNT/LM amplified lung inflammation and collagen formation. Despite this robust inflammatory response, SWCNT pre-exposure significantly decreased the pulmonary clearance of LM-exposed mice measured 3 to 7 days after microbial infection versus PBS/LM-treated mice. Decreased bacterial clearance in SWCNT-pre-exposed mice was associated with decreased phagocytosis of bacteria by macrophages and a decrease in nitric oxide production by these phagocytes. Pre-incubation of naïve alveolar macrophages with SWCNT in vitro also resulted in decreased nitric oxide generation and suppressed phagocytizing activity toward LM. Failure of SWCNT-exposed mice to clear LM led to a continued elevation in nearly all major chemokines and acute phase cytokines into the later course of infection. In SWCNT/LM-exposed mice, bronchoalveolar lavage neutrophils, alveolar macrophages, and lymphocytes, as well as lactate dehydrogenase level, were increased compared with mice exposed to SWCNT or LM alone. In conclusion, enhanced acute inflammation and pulmonary injury with delayed bacterial clearance after SWCNT exposure may lead to increased susceptibility to lung infection in exposed populations.

Interleukin-12B-3'UTR polymorphism in association with IL-12p40 and IL-12p70 serum levels and silicosis severity

Susceptibility to silicosis and to disease severity is in part genetically determined. In this study, the role of IL-12B-3'UTR polymorphism in susceptibility and severity of silicosis and its influence on IL-12p40 and IL-12p70 serum level were investigated. The quantity of IL-12p40 and IL-12p70 was detected by enzyme-linked immunosorbent assay and the genotype of IL-12B was determined using the polymerase chain reaction-restriction fragment-length polymorphism method. We observed elevated IL-12p40 in contrast to IL-12p70 serum levels in a group of 62 silicosis patients compared with both control groups. In severe silicosis patients, we detected the highest IL-12p40 serum levels (129.1 +/- 67.7 pg mL(-1)); lower in patients with the moderate (94 +/- 41.6 pg mL(-1)), whereas in mild silicosis, the IL-12p40 levels (67 +/- 23.5 pg mL(-1)) was similar to these in healthy donors. According to IL-12B polymorphism, increased serum levels were observed in subjects with AA genotype (103.2 +/- 46.9 pg mL(-1)) compared to silicosis patients with AC genotype (82.7 +/- 38.3 pg mL(-1)). No significant differences of genotype and allele frequencies of the 3'UTR polymorphism were observed between silicosis patients and healthy controls. However, the heterozygous genotype was found approximately five times more frequently in patients with mild and moderate (48% and 52%) silicosis compared to patients with severe silicosis (11%), and that IL-12B polymorphism may contribute to silicosis severity rather than to susceptibility. Our data demonstrated that elevated serum IL-12p40, independently of IL-12p70 levels, is associated with severity of silicosis, and suggested that IL-12p40 profibrotic activity may contribute to silicosis severity.

Susceptibility of Hermansky-Pudlak mice to bleomycin-induced type II cell apoptosis and fibrosis

Pulmonary inflammation, abnormalities in type II cell and macrophage morphology, and pulmonary fibrosis are features of Hermansky-Pudlak Syndrome (HPS), a recessive disorder associated with intracellular trafficking defects. We have previously reported that "Pearl" (HPS2) and "Pale Ear" (HPS1) mouse models have pulmonary inflammatory dysregulation and constitutive alveolar macrophage (AM) activation (Young LR et al., J Immunol 2006;176:4361-4368). In the current study, we used these HPS models to investigate mechanisms of lung fibrosis. Unchallenged HPS1 and HPS2 mice have subtle airspace enlargement and foamy AMs, but little or no histologic evidence of lung fibrosis. Seven days after intratracheal bleomycin (0.025 units), HPS1 and HPS2 mice exhibited increased mortality and diffuse pulmonary fibrosis compared to strain-matched C57BL/6J wild-type (WT) mice. HPS mice had significantly increased collagen deposition, and reduced quasi-static and static compliance consistent with a restrictive defect. The early airway and parenchymal cellular inflammatory responses to bleomycin were similar in HPS2 and WT mice. Greater elevations in levels of TGF-beta and IL-12p40 were produced in the lungs and AMs from bleomycin-challenged HPS mice than in WT mice. TUNEL staining revealed apoptosis of type II cells as early as 5 h after low-dose bleomycin challenge in HPS mice, suggesting that type II cell susceptibility to apoptosis may play a role in the fibrotic response. We conclude that the trafficking abnormalities in HPS promote alveolar apoptosis and pulmonary fibrosis in response to bleomycin challenge.

Type 2 immune response associated with silicosis is not instrumental in the development of the disease

It has been proposed that the development of lung fibrosis is associated with a T helper type 2 response, mainly characterized by IL-4 and IL-13 production. We investigated the potential role of type 2 immune polarization in the silicotic process and examined the pulmonary response to silica particles in mice genetically deficient for IL-4. We found that IL-4−/− mice were not protected against the development of silicosis, suggesting that IL-4 is not essential for the development of this fibrotic disease. By evaluating the intensity of silica-induced lung fibrosis in mice deficient for IL-4 receptor α (IL-4Rα), we showed that the establishment of pulmonary fibrosis was independent of both IL-4 and IL-13. Strong impairment of the type 2 immune response (IgG1) in the lungs of IL-4−/− and IL-4Rα−/− mice did not affect the development of the disease. Measurement of IL-13α2 receptor expression and IgG2a, IL-12p70, and IFN-γ levels in silica-treated IL-4−/− and IL-4Rα−/− animals showed that the development of silicosis was not related to an IL-13 signaling pathway or a switch to a type 1 response in deficient animals. Our data clearly indicate that the type 2 immune response associated with silicosis in mice is not required for the development of this inflammatory and fibrotic disease.

IL-12p40: an inherently agonistic cytokine

IL-12p40 is known as a component of the bioactive cytokines interleukin (IL)-12 and IL-23 but it is not widely recognized as having intrinsic functional activity. Recent publications have altered this perception and support an independent role for IL-12p40. IL-12p40 is induced in excess over the other subunits of IL-12 and IL-23 and can exist in a monomeric or homodimeric form. Its most widely appreciated function is to provide a negative feedback loop by competitively binding to the IL-12 receptor. However, IL-12p40 acts as a chemoattractant for macrophages and promotes the migration of bacterially stimulated dendritic cells. It is associated with several pathogenic inflammatory responses such as silicosis, graft rejection and asthma but it is also protective in a mycobacterial model. An appreciation of the independent function of IL-12p40 is important for improving our understanding of both protective and pathogenic immune responses.

Interleukin-12 is not essential for silicosis in mice

BACKGROUND

Silicosis features foci of inflammation where macrophages and lymphocytes precede and accompany fibroblast proliferation, alveolar epithelial hyperplasia, and increased deposition of connective tissue matrix material. In the mouse following silica inhalation there is recruitment of natural killer-, B-, and CD4+ and CD8+ lymphocytes to the alveolar spaces, enlargement of bronchial-associated lymphoid tissues (BALT), and aggregation of lymphocytes surrounding small airways and blood vessels. A substantial fraction of the recruited lung lymphocytes produce interferon-gamma (IFN-gamma), and IFN-gamma gene-deleted mice develop less silicosis than wild-type mice. Interleukin-12 (IL-12) is an important pathway for driving the adaptive immune response towards a TH1-like phenotype. We hypothesized that IL-12 might stimulate lymphocyte activation and the up-regulation of IFN-gamma, and consequently be an essential mediator for silicosis.

RESULTS

C57Bl/6 wild-type (WT) and IL-12 deficient (IL-12 KO) mice were exposed to sham-air or crystobalite silica (61 mg/m3) by inhalation for 5 hours/day for 12 days and then studied from 1 to 112 days after exposure. Mice exposed to sham-air had normal lung histology at all time points. WT mice exposed to titanium dioxide (72 mg/m3) showed pulmonary macrophage recruitment but no increase in lung collagen. Both WT and IL-12 KO mice exposed to silica showed similar progressive lung pathology, increased wet lung weight and increased total lung collagen (hydroxyproline). IL-12 p35 mRNA was not increased in either strain after silica exposure; IL-12 p40 mRNA was up-regulated after silica in WT mice and constitutively absent in the IL-12 KO mice. IL-18 mRNA was not increased after silica exposure. The expression of IL-15 (an important driver for innate immunity, Natural Killer cell activation, and IFN-gamma production) was abundant in air-exposed mice and was increased slightly in the lungs of mice with silicosis.

CONCLUSION

The axis of IL-12 driving IFN-gamma production is not essential for the full manifestations of silicosis in mice exposed to a crystobalite silica aerosol.

Cytokine levels in the sera of patients with idiopathic pulmonary fibrosis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a fibroproliferative disorder. Cytokines contribute an important but yet undefined role to its pathogenesis.

OBJECTIVES

The present study aims to compare serum levels of cytokines involved in Th-1 and Th-2 immunity, such as interleukins (IL) IL-2, IL-4, IL-8, IL-10, interferon-gamma (IFN-gamma) and IL-12 (p40) in patients with IPF and healthy volunteers. Twenty patients with IPF and 40 healthy controls (HC) participated.

METHODS

Cytokines were assessed by enzyme-linked immunoabsorbent assay (ELISA).

RESULTS

Median values of serum IL-2, IL-8, IL-10, IL-12 (p40) were higher in the IPF than the control group: IPF group: 1.05 U/ml, 12.55, 10.13, 44.17 pg/ml; control group: 0.05 U/ml, 6.91, 0.75, 4.51 pg/ml, respectively (P<0.05). IFN-gamma serum levels were lower in the IPF (0.19 pg/ml) than in the control group (0.49 pg/ml). IL-4 values did not differ in a statistically significant way among the groups: 8.40 pg/ml in the IPF group, and 7.46 pg/ml in the control group (P>0.05). IL-4 positively correlated to fast expiratory volume in 1s (FEV1%) and forced vital capacity (FVC%), while IL-8 negatively correlated to the respective values (P<0.005).

CONCLUSIONS

IL-2, IL-8, IL-10 and IL-12 (p40) were found to be elevated in the sera of patients with IPF. IFN-gamma was found to be decreased in the sera of patients with IPF.

The role of pro- and anti-inflammatory responses in silica-induced lung fibrosis

Background

It has been generally well accepted that chronic inflammation is a necessary component of lung fibrosis but this concept has recently been challenged.

Methods

Using biochemical, histological, immunohistochemistry, and cellular analyses, we compared the lung responses (inflammation and fibrosis) to fibrogenic silica particles (2.5 and 25 mg/g lung) in Sprague-Dawley rats and NMRI mice.

Results

Rats treated with silica particles developed chronic and progressive inflammation accompanied by an overproduction of TNF-α as well as an intense lung fibrosis. Dexamethasone or pioglitazone limited the amplitude of the lung fibrotic reaction to silica in rats, supporting the paradigm that inflammation drives lung fibrosis.

In striking contrast, in mice, silica induced only a limited and transient inflammation without TNF-α overproduction. However, mice developed lung fibrosis of a similar intensity than rats. The fibrotic response in mice was accompanied by a high expression of the anti-inflammatory and fibrotic cytokine IL-10 by silica-activated lung macrophages. In mice, IL-10 was induced only by fibrotic particles and significantly expressed in the lung of silica-sensitive but not silica-resistant strains of mice. Anti-inflammatory treatments did not control lung fibrosis in mice.

Conclusion

These results indicate that, beside chronic lung inflammation, a pronounced anti-inflammatory reaction may also contribute to the extension of silica-induced lung fibrosis and represents an alternative pathway leading to lung fibrosis.

Overexpression of cathepsin K during silica-induced lung fibrosis and control by TGF-beta

Background

Lung fibrosis is characterized by tissue remodeling resulting from an imbalance between synthesis and degradation of extracellular organic matrices. To examine whether cathepsin(s) (Cat) are important in the development of pulmonary fibrosis, we assessed the expression of four Cat known for their collagenolytic activity in a model of silica-induced lung fibrosis.

Methods

Different strains of mice were transorally instilled with 2.5 mg crystalline silica or other particles. Cat expression (Cat K, S, L and B) was quantified in lung tissue and isolated pulmonary cells by quantitative RT-PCR. In vitro, we assessed the effect of different cytokines, involved in lung inflammatory and fibrotic responses, on the expression of Cat K by alveolar macrophages and fibroblasts.

Results

In lung tissue, Cat K transcript was the most strongly upregulated in response to silica, and this upregulation was intimately related to the fibrotic process. In mouse strains known for their differential response to silica, we showed that the level of Cat K expression following silica treatment was inversely related to the level of TGF-β expression and the susceptibility of these strains to develop fibrosis. Pulmonary macrophages and fibroblasts were identified as Cat K overproducing cells in the lung of silicotic mice. In vitro, Cat K was downregulated in mouse and human lung fibroblasts by the profibrotic growth factor TGF-β1.

Conclusion

Altogether, these data suggest that while Cat K may contribute to control lung fibrosis, TGF-β appears to limit its overexpression in response to silica particles.

Abrasive blasting agents: designing studies to evaluate relative risk

Workers exposed to respirable crystalline silica used in abrasive blasting are at increased risk of developing a debilitating and often fatal fibrotic lung disease called silicosis. The National Institute for Occupational Safety and Health (NIOSH) recommends that silica sand be prohibited as abrasive blasting material and that less hazardous materials be used in blasting operations. However, data are needed on the relative risks associated with exposure to abrasive blasting materials other than silica. NIOSH has completed acute studies in rats (Hubbs et al., 2001; Porter et al., 2002). To provide dose-response data applicable to making recommendation for occupational exposure limits, NIOSH has collaborated with the National Toxicology Program (NTP) to design longer term studies with silica substitutes. For risk assessment purposes, selected doses will include concentrations that are relevant to human exposures. Rat lung burdens achieved should be comparable to those estimated in humans with working lifetime exposures, even if this results in "overloading" doses in rats. To quantify both dose and response, retained particle burdens in the lungs and lung-associated lymph nodes will be measured, as well as biochemical and pathological indices of pulmonary response. This design will facilitate assessment of the pulmonary fibrogenic potential of inhaled abrasive blasting agents at occupationally relevant concentrations.

Pulmonary overexpression of IL-10 augments lung fibrosis and Th2 responses induced by silica particles

Chronic inflammation and proinflammatory cytokines as well as T helper type 2 (Th2) cytokines have been involved in the pathogenesis of pulmonary injury and lung fibrosis. The actual role of IL-10 in lung fibrosis is still unclear because this cytokine has been identified as Th2 but possesses strong anti-inflammatory properties. To better dissect the potential role of IL-10 in silica-induced lung fibrosis, IL-10 was overexpressed in the lung of mice by adenoviral gene transfer during the inflammatory (administered at day − 1) or the fibrotic (administered at day + 30) stages of the disease. Pulmonary overexpression of IL-10 during both silica-induced lung inflammation and fibrosis exacerbated the fibrotic lesions as estimated by the measurement of hydroxyproline and other biochemical and histological markers. Increased expression of IL-10 significantly enhanced the number of lung lymphocytes and bronchoalveolar lavage fluid IgG1 but not IgG2a levels, indicating the induction of a Th2-like immune response. In addition, the production of the profibrotic Th2 cytokines IL-4 and IL-13 was also significantly increased upon IL-10 overexpression. No difference in transforming growth factor-β or PGE2 production was noted after adenoviral IL-10 treatment of silica-treated mice. Together, these data indicate that the increased expression of IL-10 significantly contributed to silica-induced lung fibrosis by exacerbating the Th2 response and the production of the profibrotic cytokines IL-4 and IL-13.

Markers of macrophage differentiation in experimental silicosis

Macrophages are characterized by a marked phenotypic heterogeneity depending on their microenvironmental stimulation. Beside classical activation (M1), it has been shown that macrophages could follow a different activation pathway after stimulation with interleukin (IL)-4 or IL-13 (M2). Recently, it has been postulated that those "alternatively activated" macrophages may be critical in the control of fibrogenesis. In an experimental model of silicosis, where pulmonary macrophages play a central role, we addressed the question of whether lung fibrosis development would be associated with alternative macrophage activation. As available markers for alternative macrophage activation, type-1 arginase (Arg-1), Fizz1, Ym1/2, and mannose receptor expression were evaluated at the mRNA and/or protein levels at different stages of the disease. Nitric oxide synthase-2 (NOS-2) expression was also examined to investigate the classical counterpart. We found that the expression of Arg-1, Fizz1, and NOS-2 in adherent bronchoalveolar lavage cells was highly up-regulated 3 days after silica administration but returned to control levels during the fibrotic stage of the disease (60 days). By comparing the early response to silica in C57BL/6 and BALB/c mice, we observed that the amplitude of Arg-1 mRNA up-regulation was not associated with the severity of lung fibrosis. Using a model of manganese dioxide particles (resolutive alveolitis), we showed that this early Arg-1 mRNA was not specific to a fibrogenic lung response. Our data indicate that the modifications of M1/M2 marker expression are limited to the early inflammatory stage of silicosis and that the establishment of a fibrotic process is not necessarily associated with M2 polarization.

Characterization of p40 and IL-10 in the BALF of patients with pulmonary sarcoidosis

This study investigated cytokine protein levels (interleukin-12 p70 [IL-12p70], p40, and IL-10) in bronchoalveolar lavage fluid (BALF) from patients with pulmonary sarcoidosis (n = 59), healthy control subjects (n = 17), and patients with idiopathic pulmonary fibrosis (IPF) (n = 30). The relationship between cytokine levels and clinical course of sarcoidosis was also examined. Overall, p40 was far more abundant than IL-12p70. p40 levels (pg/ml, mean +/- SEM) were significantly higher in the BALF from patients with sarcoidosis (2.97 +/- 3.69) than in IPF patients (0.83 +/- 1.57) and healthy subjects (0.78 +/- 1.00). Size exclusion chromatography indicated that p40 detected in BALF from sarcoidosis patients corresponded to p40 monomers or (p40)(2) homodimers. Further, p40 levels were associated with (paralleled) the clinical course of sarcoidosis, with the highest levels detected in BALF from patients with persistent disease. Higher p40 levels were also found in the BALF from sarcoid patients who required corticosteroid treatment compared with patients with spontaneous regression (3.51 +/- 3.83 vs. 2.01 +/- 3.43, p = 0.03). IL-10 concentrations paralleled p40 changes. No similar association was found for IL-12p70 levels. In conclusion, this report shows that the BALF from patients with sarcoidosis contains elevated levels of p40, (p40)(2), and IL-10 protein but not of IL-12p70. The present data also suggest that BALF p40 concentrations may be indicative of the sarcoidosis clinical course.

Regulation of interleukin 12 p40 and p70 production by blood and alveolar phagocytes during severe sepsis

Paradoxically, the host response to severe sepsis may lead to immunosuppression, thereby favoring nosocomial infections. We examined the role of the two IL-12 isoforms, bioactive IL-12p70 and regulatory IL-12p40, in 16 patients with severe sepsis. We compared the capacity of purified blood and alveolar phagocytes [polymorphonuclear neutrophils (PMN) and monocytes/macrophages] to secrete each isoform. Blood monocytes had normal basal secretions. In contrast, a marked imbalance was observed after ex vivo stimulation by lipopolysaccharide plus IFN-gamma, with significantly lower IL-12p70 production and higher IL-12p40 production. Conversely, stimulated IL-12p40 production by the patients' blood PMN tended to be impaired, as was their cell-surface beta2 integrin and L-selectin expression, known as markers of cell activation. In the patient's bronchoalveolar lavage fluid, the production of both IL-12 isoforms after ex vivo stimulation was significantly lower with alveolar macrophages than with autologous blood monocytes and significantly higher with alveolar PMN than with autologous blood PMN. This sheds new light on the potential role of PMN in local modulation of inflammation, via secretion of the anti-inflammatory IL-12 p40 subunit. The imbalance between the bioactive and regulatory IL-12 isoforms, which is probably designed to control excessive inflammation, may also make septic patients more susceptible to nosocomial infection.

A profibrotic function of IL-12p40 in experimental pulmonary fibrosis

The p40 subunit of IL-12 (IL-12p40), but not the heterodimeric form IL-12p70, is secreted during the development of silica-induced lung fibrosis in C57BL/6 mice. To delineate the contribution of IL-12p40 to the lung inflammatory and fibrotic processes, we compared the pulmonary responses with silica particles of IL-12p35-deficient mice (IL-12p35(-/-), able to produce IL-12p40) and IL-12p40-deficient mice (IL-12p40(-/-)). IL-12p35(-/-) and IL-12p40(-/-) animals developed strikingly contrasting responses to silica in comparison with wild-type C57BL/6 mice. Although the IL-12p40(-/-) mice exhibited limited inflammatory and fibrotic reactions, the IL-12p35(-/-) mice presented a robust and well-developed pulmonary inflammation and fibrosis. Furthermore, the silica-induced increase in lung IL-12p40 content was significantly higher in IL-12p35(-/-) mice than in wild-type controls, and was associated with extensive lung fibrosis and pulmonary macrophage infiltration. The contrasting responses observed between these two IL-12 subunit-deficient murine strains were not accompanied by a strict type 1 or type 2 polarization as estimated by the measurements of lung IFN-gamma/IgG2a and IL-4/IgG1 content. In vitro proliferation, type I collagen expression, as well as myofibroblast differentiation of purified pulmonary fibroblasts were not affected by treatment with exogenous rIL-12p40. In vivo, supplementation with rIL-12p40 restored the impaired pulmonary fibrotic response and macrophage accumulation in silica-treated IL-12p40(-/-) mice, and also promoted fibrosis and macrophage influx in wild-type mice. Together, our data suggest that IL-12p40 plays an important role in silica-induced pulmonary inflammation and fibrosis, possibly by exacerbating macrophage recruitment.

IL-12: the role of p40 versus p75

Interleukin (IL)-12p75 is a heterodimeric cytokine composed of the product of two different genes that specify p35 and p40 subunits. The prevailing view is that IL-12 acts as a proinflammatory cytokine that bridges the innate and adaptive immune responses and skews T-cell reactivity toward a TH1 cytokine pattern. Though the terms IL-12 and IL-12p40 are often used interchangeably, and measurements of the p40 chain are often interpreted as measurements of the intact p75 heterodimer, such interchangeable usage may be incorrect. In the following discussion, I will delineate an alternative hypothesis for the roles of the p40 and p75 proteins, suggesting specifically, that: (1) in vivo, secretion of free p40 precedes that of p75 in response to pathogens; (2) induction of p40 is a T-independent response by antigen presenting cells (APCs) to early host-pathogen interactions; and (3) IL-12p75 is a late product, whose induction requires T-dependent signals. It is made as a result, rather than as a cause, of TH1 differentiation. Thus, it is the p40 protein, either alone or paired with other polypeptides, rather than p75, that acts as an interface between the innate and adaptive immune responses.

The importance of balanced pro-inflammatory and anti-inflammatory mechanisms in diffuse lung disease

The lung responds to a variety of insults in a remarkably consistent fashion but with inconsistent outcomes that vary from complete resolution and return to normal to the destruction of normal architecture and progressive fibrosis. Increasing evidence indicates that diffuse lung disease results from an imbalance between the pro-inflammatory and anti-inflammatory mechanisms, with a persistent imbalance that favors pro-inflammatory mediators dictating the development of chronic diffuse lung disease. This review focuses on the mediators that influence this imbalance.

Fibrosis of the lung and other tissues: new concepts in pathogenesis and treatment

Tissue fibrosis can lead to significant organ dysfunction and resulting patient morbidity and mortality. Unfortunately, the therapeutic repertoire is currently limited, nonspecific, and largely ineffective. While the pathogenesis is incompletely understood, evidence is accumulating that immune and cytokine mediated mechanisms are critical. In this review, data will be provided to support the role of Type 2 cytokines in the pathogenesis of fibrosis. The importance of the role of the pro-fibrogenic cytokine TGF-beta and CD40-CD40 ligand mediated fibroblast activation will also be evaluated. Finally, novel therapeutic options based on inhibiting these pathways will be described.

Attenuation of bleomycin-induced pneumopathy in mice by monoclonal antibody to interleukin-12

We previously demonstrated essential roles of the Fas-Fas ligand (FasL) pathway in bleomycin-induced pneumopathy in mice. T lymphocytes and natural killer cells express FasL on activation and use it as a cytotoxic effector molecule. Because interleukin (IL)-12 is known to play a critical role in cell-mediated immunity, we investigated whether anti-IL-12 antibody treatment suppresses the development of this model. The anti-IL-12 antibody treatment decreased the number of apoptotic cells and the degree of inflammation and fibrosis in lung tissue. The results of RT-PCR showed that IL-12p40, IL-12 receptor (R) β2, interferon-γ, tumor necrosis factor-α and FasL mRNAs were upregulated after bleomycin instillation. The upregulation of FasL, IL-12Rβ2, and tumor necrosis factor-α mRNA expression in lung tissue was suppressed by anti-IL-12 antibody treatment. The results of enzyme-linked immunosorbent assay showed that the levels of IL-12p40, but not of IL-12p70, were increased in lung tissue after bleomycin instillation. Although the increase in IL-12Rβ2 mRNA levels suggests that the T helper type 1 cell response may participate in lung injury, the increase in IL-12p40 supports T helper type 2 cell predominance in the fibrotic process of this model. The administration of anti-IL-12 antibody could be a novel therapy against lung injury and pulmonary fibrosis.

Interleukin-9 reduces lung fibrosis and type 2 immune polarization induced by silica particles in a murine model

We examined the effect of interleukin (IL)-9, a cytokine active on B and T lymphocytes and associated with bronchial asthma, on the development of lung fibrosis induced by crystalline silica particles. Therefore, we compared the response to silica (1 and 5 mg/animal, intratracheally) in transgenic mice that constitutively express high levels of IL-9 (Tg5) and their wild-type counterparts (FVB). At 2 and 4 mo after treatment with silica, histologic examination and measurement of lung hydroxyproline content showed that the severity of fibrosis was significantly less important in Tg5 mice than in their wild-type counterparts. Intraperitoneal injection of IL-9 in C57BL/6 mice also reduced the amplitude of silica-induced lung fibrosis. The reduction of lung fibrosis by IL-9 was associated with a significant expansion of the B-lymphocyte population, both in bronchoalveolar lavage (BAL) and in the pulmonary parenchyma. In wild-type animals, silica-induced fibrosis correlated with markers of a T helper 2-like response such as upregulation of IL-4 levels in lung tissue and an increased immunoglobulin (Ig) G1/IgG2a ratio in BAL. Immunohistochemical studies demonstrated that the upregulation of IL-4 associated with the development of fibrosis was mainly localized in inflammatory alveolar macrophages. In transgenic mice, the level of IL-4 in lung homogenates was not significantly affected by silica treatment, and a reduced IgG1/IgG2a ratio was observed upon treatment with silica. The levels of interferon-gamma were significantly decreased after silica treatment in both strains. Together, these observations point to an antifibrotic effect of IL-9 in pulmonary fibrosis associated with a limitation of the type 2 polarization which accompanies lung fibrosis.

Interferon-gamma production by specific lung lymphocyte phenotypes in silicosis in mice

We recently described overproduction of interferon (IFN)-gamma by lung lymphocytes in mice with silicosis (11% of cells in air-control versus 19% of cells from silica-exposed mice; Davis and colleagues, Am. J. Respir. Cell Mol. Biol. 1999;20:813-824). We hypothesized that the increased IFN-gamma production might be due to selective enrichment of one lymphocyte phenotype. To test this hypothesis, small mononuclear cells from lung digest preparations of mice exposed 4 mo previously to cristobalite silica (70 mg/m(3), 12 d, 5 h/d) or to sham-air were stained for intracellular cytokines and surface antigen phenotypes, and examined by flow cytometry. Air-sham mouse lung digests included CD4(+) (16%) and CD8(+) (6%) T cells, gammadelta T-cell antigen receptor (TCR)(+) CD4(-)CD8(-) T cells (3%), natural killer (NK) cells (15%), B cells (6%), and macrophages (12%). The total number of lung lymphocytes was increased 1.7-fold in silicosis, but the phenotype frequencies did not change significantly. In the control lungs IFN-gamma was produced by three major phenotypes of lymphocytes: 5% of CD4(+) T cells, 5% of gammadelta-TCR(+) CD4(-)CD8(-) T cells, and 2% of NK cells. The percentage of each type producing IFN-gamma was increased 2- to 3-fold in silicosis. When multiplied by cell number, the increased percentages yielded a 3- to 5-fold increase in the total number of each IFN- gamma-producing phenotype in the lung. Our results demonstrate no selective phenotype enrichment but upregulated IFN-gamma production by at least three lymphocyte phenotypes. IFN-gamma may be an important signal driving lymphocyte differentiation and macrophage activation in silicosis.