Microfibrillar-associated protein 4 (MFAP4) is an integrin ligand localized to extracellular matrix fibers in the vascular wall. Microfibrillar-associated protein 4 (MFAP4) is an extracellular protein belonging to the fibrinogen-related protein superfamily and plays a potential role in extracellular matrix (ECM) turnover and was recently identified as a biomarker for hepatic fibrosis in hepatitis C patients. Microfibrillar-associated protein 4 (MFAP4) is a non-structural matrix protein with cell regulatory activities and a potential seromarker for fibrosis. MFAP4 regulates integrin αVβ3-induced VSMC proliferation and migration, as well as monocyte chemotaxis, and accelerates neointimal hyperplasia after vascular injury. MFAP4 plays multifaceted roles in innate immunity and normal endothelial function. It has been proposed that MFAP4 promotes the development of asthma in vivo and proasthmatic pathways of bronchial smooth muscle cells in vitro.