I read with interest the article by Allaire et al1
that appeared in this journal on malignant fibrous histiocytoma of the conjunctiva,
but would like to express reservations on certain aspects of the ultrastructural
In Figure 6 (top), the authors describe "subplasmalemmal fusiform densities
suggesting myofibroblastic differentiation." In my view, the multiple small
subplasmalemmal densities clearly illustrated in the figure are not a feature
of myofibroblasts. Although these cells have submembranous densities, they
do not appear in large numbers and tend to be associated with the microtendon.
This is the fibronectin-containing fibril believed to mediate contact between
the surface of the myofibroblast and the extracellular matrix, and is regarded
as an important marker of myofibroblastic differentiation.2,3
Further, the cell in Figure 6 clearly displays a continuous, well-formed lamina.
Despite citations in the literature that myofibroblasts have a lamina,4 this idea is controversial; most authors accept
that if the lamina is present, it is mostly focal.4,5
My own belief is that the principal structure on the surface of the myofibroblast
is the fibronexus junction2,3
and that cells with a well-defined and continuous lamina are more likely to
show an alternative line of differentiation. In the context of the authors'
Figure 6, I think the cell in question is a pericyte—moreover, a pericyte
of a nonneoplastic vessel. It has a close association with a lamina-bearing
cell, which would be endothelium (although the micrograph does not include
a lumen), and has the features of a poorly differentiated smooth-muscle cell
(subplasmalemmal densities and lamina). This, in a cell biological sense,
is what a pericyte is.
Eyden B. Reactive Pericytes vs Myofibroblastic Tumor Cells. Arch Ophthalmol. 2001;119(3):459. doi: