ULTRASTRUCTURAL AND IMMUNOCYTOCHEMICAL STUDY ON NORMAL HUMAN PALMAR APONEUROSES

Background: Human palmar aponeurosis can be affected by a fibrotic pro cess whose aetiopathology is unknown. As the organization of that norm al tissue has not been completely investigated, the aim of the present study was to define the ultrastructure of the aponeurosis in order to better understand its biology and behaviour in pathology. Methods: Bi optic samples from normal subjects of different ages were analysed by optical and electron microscopy and by immunocytochemistry. Results: T he aponeurotic branches consisted of thick, almost parallel collagen b undles containing columns of prominent cells, characterized by long cy toplasmic projections. Cells did not change in number and distribution with age and appeared longer and slighter in the old than in the youn g subjects. They exhibited plasma membrane almost completely decorated by pinocytic vesicles, intracytoplasmic bundles of thin filaments wit h zonal thickenings close to the cell membrane, and well-developed sub cellular structures. Cells expressed smooth muscle cell alpha-actin, a s revealed by immunostaining. The external surface of the plasma membr ane was underlined by a discontinuous basement membrane-like structure and by a thick coat of interwoven filaments, highly positive to hyalu ronan-recognizing antibodies. Immunocytochemical analyses revealed tha t collagen fibrils were positive for collagen types I, III, and VI and that elastin fiber composition was rather complex. Conclusions: Indep endently of the age, normal palmar aponeurotic cells show peculiar mor phological features and peculiar cell-matrix interactions, very likely mediated by hyaluronan. These findings indicate that normal aponeurot ic cells cannot be regarded as typical tenocytes and suggest the need for a better definition of their phenotype in order to understand thei r behaviour in pathological processes. (C) 1994 Wiley-Liss, Inc.