Abstract. The human dermis contains a series of dendritic cells which express different phenotypes including Factor XIIIa immunoreactivity. This compound is related to a blood coagulation factor participating in angiogenesis, in the final stages of the clotting cascade and in wound healing. In normal skin, Factor XIIIa is expressed in specific dermal dendrocytes (DD) derived from the monocyte/macrophage lineage or from a mesenchymal origin. DD are located predominantly around the microvasculature in the adventitial dermis, at the dermo-epidermal junction, and around skin appendages, but normally not within the epidermis. Increased numbers of Factor XIIIa + DD are present in a host of specific cutaneous inflammatory and fibrotic conditions. In tumor pathology, immunophenotypic differences are found between dermatofibromas and other fibrohistiocytic entities, most notably dermatofibrosarcoma protuberans. In addition, Factor XIIIa + DD are likely to be involved in the progression and regression of some malignancies including cutaneous melanoma and basal cell carcinoma.

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