Silicosis is characterized by chronic lung inflammation and fibrosis, which are seriously harmful to human health. Previous research demonstrated that uncontrolled T-helper (Th) cell immune responses were involved in the pathogenesis of silicosis. Lymphocytes also are reported to have important roles. Existing studies on lymphocyte regulation of Th immune responses were limited to T cells, such as the regulatory T (Treg) cell, which could negatively regulate inflammation and promote the process of silicosis. However, other regulatory subsets in silicosis have not been investigated in detail, and the mechanism of immune homeostasis modulation needs further exploration. Another regulatory lymphocyte, the regulatory B cell, has recently drawn increasing attention. In this study, we comprehensively showed the role of IL-10-producing regulatory B cell (B10) in a silicosis model of mice. B10 was inducible by silica instillation. Insufficient B10 amplified inflammation and attenuated lung fibrosis by promoting the Th1 immune response. Insufficient B10 clearly inhibited Treg and decreased the level of IL-10. Our study indicated that B10 could control lung inflammation and exacerbate lung fibrosis by inhibiting Th1 response and modulating the Th balance. The regulatory function of B10 could be associated with Treg induction and IL-10 secretion.

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Silicosis is an occupational lung disease caused by the inhalation of silica dust and characterized by lung inflammation and fibrosis. Interleukin (IL)-1β is induced by silica and functions as the key pro-inflammatory cytokine in this process. The Th17 response, which is induced by IL-1β, has been reported very important in chronic human lung inflammatory diseases. To elucidate the underlying mechanisms of IL-1β and IL-17 in silicosis, we used anakinra and an anti-IL-17 monoclonal antibody (mAb) to block the receptor of IL-1β (IL-RI) and IL-17, respectively, in a mouse model of silicosis. We observed increased IL-1β expression and an enhanced Th17 response after silica instillation. Treatment with an IL-1 type I receptor (IL-1RI) antagonist anakinra substantially decreased silica-induced lung inflammation and the Th17 response. Lung inflammation and the accumulation of inflammatory cells were attenuated in the IL-17-neutralized silicosis group. IL-17 may promote lung inflammation by modulating the differentiation of Th1 and regulatory T cells (Tregs) and by regulating the production of IL-22 and IL-1β during the lung inflammation of silicosis. Silica may induce IL-1β production from alveolar macrophages and promote inflammation by initiating a Th17 response via an IL-1β/IL-1RI-dependent mechanism. The Th17 response could induce lung inflammation during the pathogenesis of silicosis by regulating the homoeostasis of the Th immune responses and affecting the production of IL-22 and IL-1β. This study describes a potentially important inflammatory mechanism of silicosis that may bring about novel therapies for this inflammatory and fibrotic disease.

Silicosis is an inflammatory and fibrotic lung disease caused by inhalation of silica. Th17 cells play a key role in causing silica-induced lung inflammation and fibrosis. Baicalin, a compound isolated from the Chinese herb Huangqin, could suppress the differentiation of Th17 cells and alleviate inflammation. However, there are very few reports of the immunoregulatory mechanisms of baicalin in experimental silica-induced lung inflammation and fibrosis. In our study, mice were exposed to silica by intratracheal instillation, and in this way we established an experimental silicosis model. To elucidate the effects and mechanisms of baicalin in silica-induced inflammation and fibrosis, we used baicalin to treat the developed mouse model of silicosis. Treatment with baicalin attenuated the accumulation of inflammatory cells and led to milder pathological inflammatory and fibrotic changes in lung tissues. Baicalin affected the immunological balance between Th17 and Treg responses. Therefore, baicalin caused a decrease in Th17 cells by stimulating Treg cells and by inhibiting IL-6 and IL-23. We further demonstrated that silica-induced Th1 and Th2 immune responses were both inhibited by increased Treg activation, which was promoted by baicalin. Our findings confirmed the potential functions of baicalin in inhibiting the Th17 response and reducing silica-induced inflammation and fibrosis.

CD4+ T cells play an important role in regulating silica-induced inflammation and fibrosis. Recent studies showed that Wnt/β-catenin pathway could modulate the function and the differentiation of CD4+ T cells. Therefore, Wnt/β-catenin pathway may participate in the development and progress of silicosis. To investigate the role of Wnt/β-catenin pathway, we used lentivirus expressing β-catenin shRNA to block the Wnt/β-catenin pathway by intratracheal instillation to the mice model of silicosis. Treatment of lentivirus could significantly aggravate the silica-induced lung inflammation and attenuated the fibrosis at the late stage. By analyzing CD4+ T cells, we found that blockade of Wnt/β-catenin pathway suppressed regulatory T cells (Tregs). Reciprocally, enhanced Th17 response was responsible for the further accumulation of neutrophils and production of proinflammatory cytokines. In addition, blockade of Wnt/β-catenin pathway delayed the Th1/Th2 polarization by inhibiting Tregs and Th2 response. These results indicated that Wnt/β-catenin pathway could regulate Tregs to modulate Th immune response, which finally altered the pathological character of silicosis. Our study suggested that Wnt/β-catenin pathway might be a potential target to treat the silica-induced inflammation and fibrosis.