AIDS-Associated Cutaneous Kaposi's Sarcomas

Kaposi's sarcoma (KS) is an angioproliferative neoplasm that develops as multifocal lesions, often involving the skin, accompanied by the accumulation of perivascular and interstitial spindle-shaped cells (1). The nature of the proliferating spindle-shaped cells in KS has been a "riddle within a puzzle" for the past century [reviewed in (2) ]. While the endothelial cell has been linked to the spindle-shaped cells in KS lesions (3), twvo recent reports (4) suggest a nonvascular origin of the spindle-shaped cells in AIDS-associated KS lesions. Because the cultured cells derived from AIDS-associated KS lesions had morphological features including "dendritic" spindle cells (4), we asked whether these cells could be related to the dermal dendrocyte, a normal constituent of skin first described by Headington (5). The dermal dendrocyte is a member of the mononuclear phagocytic system (5) and shares with other monocytes/macrophages the expression of factor XIIIa antigen (6). Furthermore, both the dermal dendrocyte and cultured KS spindle-shaped cells possess the same enzymatic content, including acid phophatase and nonspecific esterase, while lacking adenosinetriphosphatase and factor VIII-related antigen; they also both have pinocytotic vesicles but no Birbeck granules (4, 5). To determine whether the spindle-shaped cell proliferation in AIDS-associated KS lesions included factor XIIIa antigen-expressing dermal dendrocytes, we analyzed 14 AIDSassociated cutaneous patch-and-plaque stage KS lesions obtained from 11 different patients. The KS lesions were characterized by a complex histological picture, including numerous slit-like vascular spaces, perivascular spindle-shaped cells that stained positively for factor XIIIa, lymphocytes, and plasma cells (Fig. 1 and Fig. 2). In four of the AIDS-associated KS cases, the factor XIIIapositive cells represented approximately 30 to 50% of the spindle-shaped cells within the lesions; in eight other cases they were between 10 and 30% of cells; in two cases they represented approximately 10% of the spindle-shaped cells. It appeared that in those cases in which there was a greater proportion of factor XIIIa-positive dermal dendrocytes among the spindle-shaped cells, there was a greater degree of lymphocytic inflammation. The factor XIIIa staining pattern in all 14 KS lesions was heterogeneous; this heterogeneity is similar to the staining pattern of another cutaneous neoplasm that contains a significant accumulation of dermal dendrocytes known as the dermatofibroma (7). The dermatofibroma, which may be difficult to distinguish from KS lesions (8), also contains proliferating small vessels and spindle-shaped cells embedded in a collagenous stroma with admixed lymphocytes. The factor XIIIa-positive cells in KS lesions appeared as fascicles of spindle-shaped cells, or as individual dendritic-shaped cells inter-