Monocytes and Macrophages: Emerging Mechanisms and Novel Therapeutic Targets in Pulmonary Fibrosis.

Abstract

Pulmonary fibrosis (PF) results from a plethora of abnormal pathogenetic events. In Idiopathic Pulmonary Fibrosis (IPF), inhalational, environmental, or occupational exposures in genetically and epigenetically predisposed individuals, triggers recurrent cycles of alveolar epithelial cell injury, activation of coagulation pathways, chemoattraction, and differentiation of monocytes into monocyte-derived alveolar macrophages (Mo-AMs). When these events happen intermittently and repeatedly throughout the individual's life cycle, the wound repair process becomes aberrant leading to bronchiolization of distal airspaces, fibroblast accumulation, extracellular matrix deposition and loss of the alveolar-capillary architecture. The role of immune dysregulation in IPF pathogenesis and progression has been underscored in the past mainly after the disappointing results of immunosuppressant use in IPF patients, however, recent reports highlighting the prognostic and mechanistic roles of monocytes and Mo-AMs revived the interest of immune dysregulation in IPF. In this review, we will discuss the role of these cells in the onset and progression of IPF, as well as potential targeted therapies.