Decreased expression of the human progenitor cell antigen (CD34) in morphea.

Morphea is an idiopathic disorder the hallmark of which is fibrosis of the skin. The regulatory factors resulting in the increased collagen production have not been determined. Within the dermis there are dendritic cells with possible immunological functions that express either the human progenitor cell antigen (CD34) or factor XIIIa. Immunohistochemical stains for factor XIIIa, CD34, S100, proliferating nuclear cell antigen, and vimentin were performed on 26 skin biopsies from patients with morphea and 11 biopsies from normal skin. A decreased number of CD34-expressing cells was seen in the affected skin from morphea patients, while there was an increased number of cells expressing factor XIIIa and vimentin. We hypothesize that CD34-positive dendritic cells may have a regulatory role in collagen synthesis and that lack of CD34 expression can be used as a marker for morphea.