Increased density of histiocytes in uterine leiomyomas

The histiocyte content of leiomyomata and adjacent, histologically normal myometrium has been quantified morphometrically with the help of recently developed immunostaining for tissue macrophages. Histiocytes identified by immunoreaction for Factor XII subunit A and by double immunofluorescent labelings were found to be identical with tissue macrophages present in normal uteri. Histiocyte counts were significantly higher in leiomyomatous areas than in adjacent normal myometrium, and the distribution of these cells was also changed. In the normal uterine wall, histiocytes could be detected only in the connective tissue septa separating smooth muscle bundles, while in the myomatous nodules they were diffusely scattered throughout the whole area. In addition to providing new information on the cellular composition of leiomyomas, the present observations also raise several questions concerning the possible pathogenetic role of FXIII-positive histiocytes in neoplastic proliferation of uterine smooth muscle.