An ultrastructural and immunohistochemical study of elastofibroma: CD 34, MEF-2, prominin 2 (CD133), and factor XIIIa-positive proliferating fibroblastic stromal cells connected by Cx43-type gap junctions.

Elastofibromas have been described as ill-defined tumors, composed of fibroblastic stromal cells and a dense collagenous stroma. A total of 5 elastofibromas from 4 Japanese patients were examined by ultrastructural and immunohistochemical methods. The proliferating fibroblastic stromal cells in the lesion showed Cx43-type gap junctions, isolated cilia, prominent nuclear fibrous laminae, and primitive cellular junctions with incomplete laminae. The active proliferating fibroblastic cells showed positive staining for vimentin, CD34, factor XIIIa, prominin 2 (CD133), and MEF 2. Conspicuous cell-to-matrix interactions were observed with abnormally unique elastins, collagens (type I, III, and IV), laminin, fibronectin, and amorphous extracellular matrix (GAGs; glycosaminoglycans). As for the origin of elastofibromas, the tumors in the present study were suggested to arise from subscapular or periosteal connective tissue, but further revealed some similarities to other tissues, such as human skin dermal tissue, as exemplified by the presence of an abundance of type I and III collagen, CD34/factor XIIIa-expressing stromal fibroblast-like cells, amorphous extracellular matrix, and a unique abnormal elastin. The elastofibromas might have arisen from stromal stem cell candidate populations of stromal fibroblastic cells (CD34(+), MEF2(+), prominin 2(CD133)(+), and factor XIIIa(+)).