Distribution of EGF receptor expressing and DNA replicating epidermal cells in psoriasis vulgaris and Bowen's disease

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Abstract
We have examined the localization of DNA replicating cells and EGF receptor‐expressing cells in the epidermis of psoriasis vulgaris, a benign hyperproliferative skin disease, and Bowen's disease, a pre‐malignant hyperproliferative skin disease, and normal skin. DNA replicating cells were detected by anti‐BrdU monoclonal antibody after incubating tissue sections with BrdU, and EGF receptors were detected by the anti‐EGF receptor monoclonal antibody B4G7. In normal skin, DNA replicating cells were localized exclusively in the basal and suprabasal layers. EGF receptor expression was observed most strongly in the basal and parabasal layers, but diminished gradually towards the upper squamous layer. In psoriatic skin, DNA replicating cells were also localized in the basal and parabasal layers, but the number of these mitotic cells was about 10 times higher than in normal skin. In this case, more EGF receptors were detected in all viable layers of the epidermis. Apparently normal skin adjacent to psoriasis lesions showed persistent expression of EGF receptors in the upper squamous layer without an increased number of DNA replicating cells in the basal and parabasal layers. In Bowen's disease, DNA replicating cells and EGF receptor expressing cells were distributed in all layers of the epidermis. These findings indicate that the increased production of EGF receptors may be, in part, responsible for the hyperproliferative state of the epidermis and that cells in the upper squamous layer of psoriasis may have lost a mechanism by which EGF receptor expression is diminished thus allowing differentiation. This altered process of EGF receptor production may be involved in the onset of psoriasis vulgaris.