The CX3CL1 Chemokine in Bronchoalvelar Lavage Fluid and its Cellular Sources in Diffuse Parenchymal Lung Diseases

<bold>Background:</bold> Fractalkine (CX3CL1) is a unique chemokine that functions as a chemoattractant on cells expressing the fractalkine receptor (CX3CR1). Several recent studies proved the involvement of the CX3CL1-CX3CR1 axis in the process of pulmonary fibrosis. In this study, we evaluated the concentration of CX3CL1 in bronchoalveolar (BAL) fluid in selected diffuse parenchymal lung diseases (DPLD) and aimed to find CX3CL1-producing cell lines after BAL stimulation. <bold>Methods:</bold> CX3CL1 concentration was measured by enzyme-linked immunosorbent assay test in bronchoalveolar lavage fluid in sarcoidosis, idiopathic pulmonary fibrosis (IPF), and hypersensitivity pneumonitis (HP). Two cell lines, A549 (human lung epithelial cells) and MRC-5 (human fibroblasts), were stimulated by BAL fluid, and the concentration of CX3CL1 was estimated in the cell culture supernatants after 48 hours. <bold>Results:</bold> We found the highest concentration of CX3CL1 in IPF compared to the control group and sarcoidosis. A raised concentration was revealed in the fibrotic phenotype of HP in contrast to the inflammatory phenotype and stage IV sarcoidosis compared to stages I-III. We stimulated two cell lines, A549 and MRC-5 with BAL fluid, and the elevated concentration of CX3CL1 was discovered in the culture medium of MRC-5 cell after BAL stimulation in IPF. <bold>Conclusion:</bold> CX3CL1 acts in the pathogenesis of DPLDs, moreover its concentration increases in IPF, fibrotic HP, and stage IV sarcoidosis. In vitro study suggests that human fibroblasts are a possible source of CX3CL1.