Chemokine (C-C motif) ligand 2 mediates direct and indirect fibrotic responses in human and murine cultured fibrocytes

Following optimized and identical human and murine fibrocyte isolation, both cell sources were shown to be positive for CCR2 by flow cytometry and this expression colocalized with collagen I and CD45. Human blood fibrocytes stimulated with the CCR2 ligand chemokine (C-C motif) ligand 2 (CCL2), demonstrated increased proliferation (P < 0.005) and differentiation into myofibroblasts (P < 0.001), as well as a chemotactic response (P < 0.05). Murine fibrocytes also responded to CCR2 stimulation, with CCL12 being more potent than CCL2.This study directly compares the functional responses of human and murine fibrocytes to CCR2 ligands, and following comparable isolation techniques. We have shown comparable biological effects, strengthening the translatability of the murine models to human disease with respect to targeting the CCR2 axis to ameliorate disease in IPF patients.Fibrocytes are a population of circulating cells that have been reported to express a variety of markers including leukocyte markers (CD45, CD34), mesenchymal markers (collagen I, fibronectin) and chemokine receptors (chemokine (C-C motif) receptor 3 (CCR3), CCR5, CCR7 and C-X-C chemokine receptor type 4 (CXCR4)) [1]. Human and mouse studies have demonstrated that fibrocytes from peripheral blood migrate to skin wound chambers [1-3] and bronchial mucosa after antigen challenge [4]. Furthermore, these cells have been reported in disease states with fibrotic pathologies including hypertrophic scars, asthma and idiopathic pulmonary fibrosis (IPF) [4-7]. Fibrocytes are functionally pleiotropic, potentially contributing to fibrogenesis by directly producing collagen, as well as inflammatory cytokines, hematopoietic growth factors, and chemokines [6-10].In preclinical models of lung fibrosis, inhibition of various chemokine receptor/ligand pathways reduces lung fibrosis and it has been hypothesized to be in part due to a reduction in fibrocyte recruitment [6-9]. However, the effect of inhibiting specific chem