Immunomorphological and ultrastructural characterization of Langerhans cells and a novel, inflammatory dendritic epidermal cell (IDEC) population in lesional skin of atopic eczema

We investigated epidermal cell suspensions prepared from lesional and nonlesional atopic eczema skin, other inflammatory skin conditions, and normal human skin for high-affinity IgE receptor (Fc epsilon RI) expression on dendritic CD1a cells by quantitative flow cytometric analysis. A single CD1a(bright)/CD1b(neg)/Fc epsilon RI(dim)/CD23(neg)/CD32(dim)/HLA-DR(bright)/CD36(neg) population was found in normal skin. In contrast, lesional skin of atopic eczema and other inflammatory skin diseases harbored variable proportions of two distinct CD1a populations. Both populations exhibited typical ultrastructural features of Langerhans cells, but the second one lacked Birbeck granules and was unreactive to the Birbeck granules-specific LAG antibody. Both populations differed phenotypically: classical Langerhans cells were CD1a(bright)/CD1b(neg)/FC epsilon RI(dim)/CD23(neg)/CD32(dim)/HLA-DR(bright)/CD36(dim), while the second population was CD1a(dim)/CD1b(dim)/Fc epsilon RI(bright)/CD23(dim)/CD32(dim)/HLA- R(bright)/CD36(bright). The highest Fc epsilon RI expression was found on the second CD1a population in lesional atopic eczema skin. Furthermore, Fc epsilon RI expression on CD1a cells correlated significantly with the serum IgE level of the patients. Thus, a distinct population of CD1a inflammatory dendritic epidermal cells different from classical Langerhans cells appears in the epidermis of lesional skin and is subjected to specific signals leading to the upregulation of Fc epsilon RI in atopic eczema skin.