Immunofluorescence photomicrograph of cultured rat myofibroblasts from vein wall reacted with antibody against vimentin. The micrograph illustrates indirect immunofluorescence with antivimentin in cultured cells of mesenchymal origin derived from the wall of a vein. These filament bundles are not stained by antibody raised against keratin. A myofibroblast is a cell that is in-between a fibroblast and a smooth muscle cell in differentiation.