Vimentin is a cytoskeleton intermediate filament protein present in cells of mesenchymal origin, including leukocytes, endothelial cells, and smooth muscle cells. It is subject to citrullination by peptidyl arginine deiminase 2 under high calcium concentrations, which can occur during macrophage apoptosis. Citrullinated vimentin has been shown to have a role in the production of anti-citrullinated protein antibodies (ACPAs). ACPAs against citrullinated proteins, such as vimentin, are considered to be highly specific markers for rheumatoid arthritis and other autoimmune diseases.