IL-17A-producing gammadelta T and Th17 lymphocytes mediate lung inflammation but not fibrosis in experimental silicosis.

IL-17-producing T lymphocytes play a crucial role in inflammation, but their possible implication in fibrosis remains to be explored. In this study, we examined the involvement of these cells in a mouse model of lung inflammation and fibrosis induced by silica particles. Upregulation of IL-17A was associated with the development of experimental silicosis, but this response was markedly reduced in athymic, gammadelta T cell-deficient or CD4(+) T cell-depleted mice. In addition, gammadelta T lymphocytes and CD4(+) T cells, but not macrophages, neutrophils, NK cells or CD8 T cells, purified from the lungs of silicotic mice markedly expressed IL-17A. Depletion of alveolar macrophages or neutralization of IL-23 reduced upregulation of IL-17A in the lung of silicotic mice. IL-17R-deficient animals (IL-17R(-/-)) or IL-17A Ab neutralization, but not IL-22(-/-) mice, developed reduced neutrophil influx and injury during the early lung response to silica. However, chronic inflammation, fibrosis, and TGF-beta expression induced by silica were not attenuated in the absence of IL-17R or -22 or after IL-17A Ab blockade. In conclusion, a rapid lung recruitment of IL-17A-producing T cells, mediated by macrophage-derived IL-23, is associated with experimental silicosis in mice. Although the acute alveolitis induced by silica is IL-17A dependent, this cytokine appears dispensable for the development of the late inflammatory and fibrotic lung responses to silica.

ZONAB promotes proliferation and represses differentiation of proximal tubule epithelial cells.

Epithelial polarization modulates gene expression. The transcription factor zonula occludens 1 (ZO-1)-associated nucleic acid binding protein (ZONAB) can shuttle between tight junctions and nuclei, promoting cell proliferation and expression of cyclin D1 and proliferating cell nuclear antigen (PCNA), but whether it also represses epithelial differentiation is unknown. Here, during mouse kidney ontogeny and polarization of proximal tubular cells (OK cells), ZONAB and PCNA levels decreased in parallel and inversely correlated with increasing apical differentiation, reflected by expression of megalin/cubilin, maturation of the brush border, and extension of the primary cilium. Conversely, ZONAB reexpression and loss of apical differentiation markers provided a signature for renal clear cell carcinoma. In confluent OK cells, ZONAB overexpression increased proliferation and PCNA while repressing megalin/cubilin expression and impairing differentiation of the brush border and primary cilium. Reporter and chromatin immunoprecipitation assays demonstrated that megalin and cubilin are ZONAB target genes. Sparsely plated OK cells formed small islands composed of distinct populations: Cells on the periphery, which lacked external tight junctions, strongly expressed nuclear ZONAB, proliferated, and failed to differentiate; central cells, surrounded by continuous junctions, lost nuclear ZONAB, stopped proliferating, and engaged in apical differentiation. Taken together, these data suggest that ZONAB is an important component of the mechanisms that sense epithelial density and participates in the complex transcriptional networks that regulate the switch between proliferation and differentiation.