Effects of IL-4 and IL-13 on Human Fibrocyte Differentiation

Fibrocytes are bone marrow-derived spindle-shaped circulating precursors of fibroblasts. They are CD45 + and Col1a + and their primary role is to provide extracellular matrix deposition following injury during tissue repair. Fibrocytes are associated with fibrotic diseases like idiopathic pulmonary fibrosis (IPF), asthma, ischemic cardiomyopathy, liver fibrosis and kidney fibrosis and in autoimmune diseases like scleroderma related lung fibrosis (SSc-ILD), rheumatoid arthritis and autoimmune thyroiditis. Increased numbers of circulating fibrocytes have been observed in IPF patients and correlated with a faster disease progression (Moeller, 2008).  Recent publications describe a number of agents, including IL-4, IL-13 and TGFβ1, can influence the differentiation of fibrocytes in vitro . We confirmed the role of IL-4 and IL-13 on fibrocyte differentiation of human CD14 + cells in vitro .  The in vitro differentiated, spindle shaped CD45 + /Col1 + fibrocytes also express characteristic markers like PDGF-a and a-SMA.  We also show an in vivo role for IL-4 and IL-13 in fibrocyte differentiation and tissue repair using the FRA2 transgenic mouse model of SSc-ILD and a modified bleomycin model of pulmonary fibrosis.