ULTRASTRUCTURAL-LOCALIZATION OF FACTOR-XIIIA

Thin sections of dermatofibromas, of a basal cell epithelioma, a patch stage lesion of Kaposi's sarcoma, a case of angiolymphoid hyperplasia with eosinophilia, and one case of malignant mastocytosis were incuba ted with antibody to factor XIIIa (FXIIIa). Regardless whether the tis sue had been embedded in Lowicrvl K4M, Epon, or Araldite, labeling was found in dermal dendrocytes, mast cells, and endothelial cells. In de rmal dendrocytes, the reaction product was seen in dilated cisternae o f the rough endoplasmic reticulum as well as free within the cytoplasm . In endothelial cells, FXIIIa was localized within Weibel Palade bodi es, free within the cytoplasm, and in villous projections into the vas ucular lumen. In mast cells, the reaction was found in mast cell granu les exclusively. Mast cells, dermal dendrocytes, and endothelial cells have in common that all three express FXIIIa, belong to the microvasc ular unit, and are increased in number during angiogenesis and in fibr ovascular processes. It thus seems that these cells are functionally r elated.