B lymphocytes are critical for lung fibrosis control and prostaglandin E2 regulation in IL-9 transgenic mice.

We previously showed that overexpression of IL-9 controls lung fibrosis induced by silica particles in mice (Arras and colleagues; Am J Respir Cell Mol Biol 2001;24:368-375). This protection was associated with an expansion of lung B lymphocytes. To explore the contribution of these cells in the protective effect of IL-9, we crossed IL-9 transgenic (IL-9+) and B-deficient (B-) mice. The antifibrotic effect of IL-9 was abolished in mice deficient in B lymphocytes (B-IL-9+) and restored by reconstituting these mice with B lymphocytes. The expression of the antifibrotic mediator prostaglandin (PG)E2 was markedly increased in the lung of IL-9+ mice at baseline, and similarly high levels were found in both wild-type and transgenic strains upon silica treatment. This PGE2 expression was completely abolished in B- mice, both at baseline and upon silica administration. In vitro, alveolar and peritoneal macrophages from IL-9+ mice had an increased capacity to produce PGE2 in response to LPS or silica. This capacity was markedly reduced in macrophages obtained from B- mice and restored by co-incubating macrophages with B lymphocytes from IL-9+ mice. The increased PGE2 response of IL-9+ macrophages was dependent on cyclooxygenase 2 expression, based on transcript analysis and inhibition by NS398. We conclude that B lymphocytes are essential for the protection against lung fibrosis and macrophage overexpression of PGE2 in IL-9 transgenic animals.

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-alpha 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-alpha 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.

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-beta or PGE(2) 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 the effect of interleukin-10 on silica-induced lung fibrosis in mice.

We previously described a reduction of silica-induced lung fibrosis in interleukin-10-deficient mice (IL-10-/-) (Huaux and colleagues; Am. J. Respir. Cell Mol. Biol. 1998;18:51-59). In the present study, we further dissect the exact functions of IL-10 in experimental silicosis. The reduced lung fibrotic response to silica in IL-10-/- mice was accompanied by a marked recruitment of TH1 CD4+ lymphocytes. However, treatment with anti-CD4 antibodies reduced silica-induced lung fibrosis in both IL-10-/- and IL-10+/+ mice, suggesting that this T cell population actually contributes to the extension of the fibrotic lesions in a manner that is independent of IL-10. In IL-10-/- mice, silica-induced lung production of the profibrotic mediator transforming growth factor (TGF)-beta1 and the antifibrotic eicosanoid PGE2 were reduced and increased, respectively, relative to that in IL-10+/+ mice. In addition, in vitro experiments indicated that recombinant IL-10 upregulated TGF-beta1 expression in alveolar macrophages while in contrast it downregulated PGE2 production and cyclooxygenase-2 expression in both lung fibroblasts and macrophages. Thus the net profibrotic activity of IL-10 in vivo appears to be mediated by its ability to stimulate the expression of the profibrotic cytokine TGF-beta1 while suppressing the expression of cyclooxygenase-2 and thus production of the antifibrotic eicosanoid PGE2. These effects appear to be independent of the enhanced lung CD4+ T-lymphocytosis observed in IL-10-deficient mice.

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.

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.