Cutaneous infiltrates of histiocytosis X contain plasminogen activator-bearing epidermotropic dendritic cells different from Langerhans cells.

Plasminogen activators (PA) play an important role in cell migration and tissue degradation. Considering the strong epidermotropism of atypical mononuclear cells in histiocytosis X (HX) skin infiltrates leading to intraepidermal abscess formation, it was the purpose of this study to look for tissue-type PA (t-PA) and/or urokinase-type PA (u-PA) on HX cells. Four monoclonal antibodies against PA were used, employing the alkaline phosphatase anti-alkaline phosphatase (APAAP) technique on cryostat sections from four patients with HX. Twenty percent to 40% of infiltrating cells in the epidermis expressed the t-PA antigen. t-PA+ cells were present in the follicular centers of human tonsil, absent in normal epidermis and scanty in cutaneous infiltrates from mycosis fungoides and lupus erythematosus. Double labeling with anti-PA and T6 (CD1) or S100 protein revealed some of the HX cells to express both antigens (t-PA+ CD1+ or t-PA+ S100+). We conclude that cutaneous infiltrates of HX contain PA+ dendritic cells which are different from normal Langerhans cells and which may be responsible for the strong epidermal alterations in HX.