THE HUMAN PROGENITOR-CELL ANTIGEN (CD34) IS LOCALIZED ON ENDOTHELIAL-CELLS, DERMAL DENDRITIC CELLS, AND PERIFOLLICULAR CELLS IN FORMALIN-FIXED NORMAL SKIN, AND ON PROLIFERATING ENDOTHELIAL-CELLS AND STROMAL SPINDLE-SHAPED CELLS IN KAPOSI-SARCOMA

The human progenitor cell antigen (CD34) is selectively expressed on hematopoietic progenitor cells in the bone marrow. In either cryostat sections of snap-frozen skin, or formalin-fixed paraffin-embedded sections of normal skin, anti-CD34 monoclonal antibody immunostained vascular endothelial cells and perivascular/interstitial dendritic cells, particularly in the reticular dermis. A distinctive population of perifollicular spindle-shaped cells in the midportion of the follicle (ie, bulge area), which is the site of the putative hair follicle stem cells, were CD34 positive, as were spindle-shaped cells in and around the eccrine glands accentuating their basement membrane zone. In patch/plaque- and tumor-stage acquired immunodeficiency syndrome-associated Kaposi's sarcoma lesions, CD34 expression was present on both the proliferating endothelial cells as well as the spindle-shaped stromal cells. CD34 positive endothelial cells and spindle-shaped stromal cells may play important participatory and supportive functions in both normal and diseased skin.