Accumulation of cells containing factor XIII subunit a around the foci of intense fibrosis in human epulides.

On the basis of clinical and biochemical findings, Factor XIII subunit a (FXIII A) has been conjectured to play an important role in fibrotic processes. Epulis samples at different stages of fibrotic tissue formation were used as a model system for studying the localization and tissue distribution of FXIII A during the course of connective tissue generation. Marker characteristics of cells containing FXIII A (FXIII A+ cells) were determined as well. In double immunofluorescent labelling systems, FXIII A was localized in monocyte-derived (CD-14+), activated (HLA-DR+), and phagocytosing (Ki-M7+) tissue macrophages, which are widely distributed homogeneously in granulation tissues, but start to accumulate around foci of fibrosis as soon as the foci appear. During the relatively long process of fibrosis, FXIII A+ macrophages continuously decrease in number, and their morphological appearance changes from stellate to spindle-shaped. The nuclei of these cells were not labelled by Ki-67 monoclonal antibody; this indicating that they represent a non-proliferating cell population in the connective tissue stroma. The present findings may help to link theories concerning the role of FXIII A and those of macrophages in the connective tissue formation so far found separately in the literature.