Alteration of fibroblast phenotype by asbestos-induced autoantibodies

Pulmonary fibrosis is a relentlessly progressive disease for which the etiology can be idiopathic or associated with environmental or occupational exposures. There is not a clear explanation for the chronic and progressive nature of the disease, leaving treatment and prevention options limited. However, there is increasing evidence of an autoimmune component, since fibrotic diseases are often accompanied by production of autoantibodies. Because exposure to silicates such as silica and asbestos can lead to both autoantibodies and pulmonary/pleural fibrosis, these exposures provide an excellent tool for examining the relationship between these outcomes. This study explored the possibility that autoantibodies induced by asbestos exposure in mice would affect fibroblast phenotype. L929 fibroblasts and primary lung fibroblasts were treated with serum IgG from asbestos- or saline-treated mice, and tested for binding using cell-based ELISA, and for phenotypic changes using immunofluorescence, laser scanning cytometry and Sirius Red collagen assay. Autoantibodies in the serum of C57Bl/6 mice exposed to asbestos (but not sera from untreated mice) bound to mouse fibroblasts. The autoantibodies induced differentiation to a myofibroblast phenotype, as demonstrated by increased expression of smooth muscle alpha alpha-actin (SMA), which was lost when the serum was cleared of IgG. Cells treated with purified IgG of exposed mice produced excess collagen. Using ELISA, we tested serum antibody binding to DNA topoisomerase (Topo) I, vimentin, TGF beta beta-R, and PDGF-R alpha alpha. Antibodies to DNA Topo I and to PDGF-R alpha alpha were detected, both of which have been shown by others to be able to affect fibroblast phenotype. The anti-fibroblast antibodies (AFA) also induced STAT-1 activation, implicating the PDGF-R pathway as part of the response to AFA binding. These data support the hypothesis that asbestos induces AFA that modify fibroblast phenotype, and suggest a mechanism whereby autoantibodies may mediate some of the fibrotic manifestations of asbestos exposure.