IMMUNOMORPHOLOGICAL CHARACTERIZATION OF FC-EPSILON-RI-BEARING CELLS WITHIN THE HUMAN DERMIS

Recently we reported that the high-affinity receptor for IgE, FcepsilonRI, is constitutively expressed on normal epidermal Langerhans cells (LC) and on certain cells within the dermis. To study the nature of these cells we performed immunofluorescence double-labeling experiments using an anti-FcepsilonRI reagent (MoAb 15-1) as well as monoclonal antibodies (MoAb) against leukocyte differentiation antigens expressed on LC, interdigitating cells and macrophages. Avidin-fluorescein isothiocyanate was used to distinguish mast cells. We found that dermal FcepsilonRI+ cells are bone marrow derived (CD45+). Further, we found that a subset of 15-1+ dermal cells coexpresses antigens present on certain members of the LC/DC family: the majority of FcepsilonRI+ cells reacted with MoAb anti - HLA-DR and RFD1, the latter recognizes an antigenic moiety on interdigitating cells, and a small subpopulation coexpressed CD1a. In reverse fashion, virtually all CD1a+ cells and most RFD1+ cells reacted with the anti-FcepsilonI reagent. Approximately one third of 15-1+ cells represented avidin-FITC+ mast cells whereas FcepsilonRI expression was not detected on FXIIIa+ dermal dendrocytes or CD3+ lymphocytes. By immunoelectronmicroscopy, we found that perivascularly located 15-1-reactive cells exhibited pronounced dendrites, an indented nucleus, numerous mitochondria, and abundant endo-/lysosomal structures. However, Birbeck granules or granules specific for basophils or eosinophils were never detected in these cells. Collectively, our data suggest that the pool of dermal FcepsilonRI+ cells consists mainly of cells of the LC (CD1a+)/FXIIIa+ dermal macrophages.