CD45 Epitope Mapping of Human CD1a+ Dendritic Cells and Peripheral Blood Dendritic Cells

The authors studied the pattern of leukocyte common antigen (CD45) epitope expression on dendritic cells in sections of human epidermis, tonsillar epithelium, dermatopathic lymph nodes, and in isolates from blood. The monoclonal antibodies (MAb) used were specific for all known CD45 epitopes, including the seven different CD45 common epitopes as well as the four known CD45R epitopes (two CD45RA, one CD45RB, and one CD45RO). Dendritic cells in all sites were uniformly reactive for the CD45 common epitopes tested except 2B11, which may recognize a CD45R rather than CD45 epitope. By single-label immunoperoxidase and double-label immunofluorescence epitope mapping of CD1a+ dendritic cells in tissue sections, it was generally difficult or impossible to detect expression of CD45RA, CD45RB, CD45RO, or 2B11. In blood dendritic cells, however, low levels of these CD45R epitopes were detected consistently using single-label immunoperoxidase staining of cytocentrifuge preparations. Monocytes were similar to blood dendritic cells except that the staining with MAb to CD45RO and 2B11 was slightly stronger. The authors conclude that dendritic cells differ from most subpopulations of lymphocytes in that CD45 common epitopes are readily detectable but the existing RA, RB, and RO epitopes are either undetectable or expressed at relatively low levels. These studies raise the possibility that CD1a+ dendritic cells may express a novel dominant CD45 isoform.