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The fibronexus in reactive and tumoral myofibroblasts: further
characterisation by electron microscopy
B. Eyden
Department of Histopathology, Christie Hospital
NHS Trust, Manchester, United Kingdom
Offprint requests to:
Brian Eyden PhD, Department of Histopathology, Christie Hospital
NHS Trust, Manchester M20 4BX, United Kingdom. Fax: +44 161 446
3300
Summary. Forty
two surgical specimens containing myofibroblasts were studied
to clarify the criteria for identifying the fibronexus, an ultrastructural
feature regarded as a marker for myofibroblastic differentiation.
Granulation tissue, tumour stroma, fibro-proliferative lesions
(nodular fasciitis, myofibromatosis, inflam-matory myofibroblastic
tumour) and malignancies (myofibrosarcoma and fibrosarcoma) were
studied. Comparable results were found throughout these specimens,
although fibronexus junctions were better developed in reactive
compared with tumoral myofibroblasts. By electron microscopy,
myofibroblasts were identified by abundant rough endoplasmic reticulum,
peripheral smooth-muscle myofilaments with focal densities, and
fibronexus junctions. The latter were recognised as the points
of convergence on the myofibroblast surfaces of intracellular
myofilaments and extracellular fibronectin fibrils. The fibronectin
fibrils were often co-linear with myofilaments. Also, fibronectin
fibrils were dark-staining, straight and rigid-looking, and had
a longitudinal filamentous substructure. A striking feature was
the tendency of fibronectin fibrils to project into the surrounding
extracellular space, away from the myofibroblast surface: in these
respects, they differed significantly from lamina ("basement
membrane"). The presence of fibronectin fibrils correlated
positively with fibronectin immunostaining by light and electron
microscopy. Laminin and collagen IV showed variable and weak staining
in the intercellular spaces in a minority of cases and never strongly
stained myofibroblast surfaces. The data emphasise that the fibronexus
has a number of distinctive features permitting identification,
and constitute a reference-point for pathologists wishing to use
electron microscopy to refine light microscopy diagnoses of putative
myofibroblastic lesions. The role of the fibronexus in the definition
of the myofibroblast is discussed. Histol. Histopathol. 16,
57-70 (2001)
Key words: Fibronexus,
Myofibroblast, Electron-microscopy, Fibronectin , Basement-membrane
DOI: 10.14670/HH-16.57
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