Mast cells and myofibroblasts in keloid: a light microscopic, immunohistochemical and ultrastructural study.

A light microscopic, immunohistochemical and ultrastructural study was done on 2 patients with active pruritic keloids. The primary cell was the myofibroblast with prominent rough endoplasmic reticulum and bundles of myofilaments with focal densities in the cytoplasm. Enhanced secretory activity was reflected in the prominence of the Golgi apparatus and the frequent presence of intracellular collagen within the tubular membranes. The number of mast cells was increased and they were closely associated with myofibroblasts with frequent direct cell contacts. The filopodia of the mast cells were seen intimately applied along the cell membrane of the myofibroblasts. Degranulated mast cells contained few and electron-lucent granules. Discharge of the contents of granules into the interstitial matrix was encountered. Mast cell granules were also seen lying free in the interstitium. In the vicinity of the degranulated mast cells the interstitial matrix was oedematous containing granular material and the myofibroblasts showed considerable dilation of the rough endoplasmic reticulum and vacuole formation. The intimate relationship and interaction between mast cells and myofibroblasts support the important role of mast cells and their mediators in the pathogenesis of keloid.