Nevus Cells of Nerve Sheath Origin

To the Editor.— The immunohistochemical demonstration factor XIIIa expression in more than 50 of the cells in 10 of 10 neurofibromas, but in 0 of 10 schwannomas, by Gray and coworkers was very interesting. 1 The authors also observed considerable staining for factor XIIIa among the spindleshaped cells in partly neurotized nevi (their Figs 3 and 4). They chose to interpret these as entrapped dermal fibroblasts, pointing out that similar cells in the upper dermis also stain for factor XIIIa (their Fig 5). However, they also reported that spindle-shaped cells of normal nerves can stain positively for factor XIIIa. I would therefore like to suggest the alternative interpretation that at least some of the factor XIIIa-positive spindle cells in their partly neurotized nevi may have been cells of nerve sheath origin, which may have been inherent nonmelanocytic elements of these nevi, rather than entrapped normal dermal fibroblasts. In support of