DEFINING THE MYOFIBROBLAST - NORMAL-TISSUES, WITH SPECIAL REFERENCE TO THE STROMAL CELLS OF WHARTONS JELLY IN HUMAN UMBILICAL-CORD

Cells differing widely in tissue distribution, immunophenotype and ult rastructure have been described as myofibroblasts. The definition of t he myofibroblast was analysed as applied to normal tissues, with origi nal observations on Wharton's jelly stromal cells as an example. Strom al cells in Wharton's jelly were studied by conventional histology, im munohistochemistry, and electron microscopy. The normal architecture o f the cord was confirmed by light microscopy. Stromal cells and the sm ooth-muscle cells of the umbilical vessels were positive for vimentin, desmin and alpha-smooth muscle actin, while only the stromal cells we re positive for prolyl 4-hydroxylase. Electron microscopy revealed var iable but sometimes only moderate amounts of rough endoplasmic reticul um, bundles of smooth-muscle type filaments with focal densities, a la rge Golgi apparatus with collagen secretion granules, lipid and glycog en. There was no convincing evidence for either lamina or fibronexus j unctions. The nature of the stromal cell was discussed in the light of these findings. It was concluded that a myofibroblastic designation w as inappropriate and that these cells had phenotypic similarities to v ascular smooth muscle cells. The possibility is proposed that most exa mples of spindle cells cited in the literature as being myofibroblasts and seen in normal tissues not subjected to trauma or showing patholo gy may be pericytic or smooth-muscle in nature.