Microbial Activation of B-cells by Pattern Recognition Receptors Contributes to the Proinflammatory and Profibrotic Milieu in Patients with Idiopathic Pulmonary Fibrosis

Abstract

Abstract We hypothesize that B-lymphocytes are conducive to the pathogenesis of idiopathic pulmonary fibrosis (IPF), a progressive and fatal interstitial lung disease. B-lymphocytes aggregate in the lungs of IPF patients to form tertiary lymphoid follicles. How these follicles are formed and their role in the pathogenesis of IPF is not known. Hence, we sought to characterize how the activation of B-lymphocytes from IPF patients may contribute to the disease. Methods IPF patients defined by ATS guidelines were identified and recruited under local IRB #14-004714. B-lymphocytes were then isolated by negative selection. Cytokines and immunoglobulins from plasma or B-lymphocyte supernatants were measured by ELISA and signaling pathways were elucidated from whole-cell lysates by immunoblotting. Our results show that B-lymphocyte aggregates are present within fibrotic areas of the lung of IPF patients and that activated B-lymphocytes induce fibroblast migration. This effect was abrogated by nintedanib inhibition of B-lymphocyte activation. Furthermore, microbial antigen (β-glucan and CpG) activation of B-lymphocytes through pattern recognition receptors (PRRs; TLR9 and Dectin-1) contributed to the proinflammatory and profibrotic milieu seen in IPF patients. Stimulation of TLR9 and Dectin-1 resulted in activation of mTOR-dependent and -independent pathways, respectively. Rapamycin decreased TLR9 signaling, but not Dectin-1 mediated pathways. Nintedanib abrogated B-cell activation, IgM production, and the profibrotic milieu by interfering with both the mTOR-dependent and -independent pathways. In conclusion, our findings implicate activated B-lymphocytes in IPF pathogenesis highlighting the role of PRRs in this disease.