Fc Gamma Receptors on Keratinocytes in Psoriasis

Epidermis in cryostat sections of skin biopsy specimens from patients with psoriasis and from healthy individuals bound bovine erythrocytes (E) sensitized with rabbit IgG antibodies (A)(EA). No binding occurred using E or E sensitized with IgM or F(ab')2 fragments of IgG. The binding of EA was inhibited by human IgG and by Fc fragments of IgG, whereas human IgA, IgM, albumin, and F(ab)2 fragments of IgG did not inhibit the binding, indicating the presence of receptors for the Fc part of IgG (FcR). EA bound mainly to stratum spinosum and most strongly above FcR-positive cell infiltrates in dermal papillae. The binding of EA to sections from patients with active psoriasis was stronger than to sections from patients with stationary psoriasis vulgaris. Sections of unaffected skin from patients with psoriasis and healthy individuals also bound EA, but the binding was weaker than to sections of psoriatic lesions. The receptors were sensitive to periodic acid, formaldehyde, and heat. Using immune complexes of horseradish peroxidase (HRP) and rabbit IgG antibodies to HRP, the receptors were localized to the outer aspect of the keratinocytes and to the inflammatory cells in the microabscesses. The strongest binding occurred in the same areas which adhered EA most strongly. FcR on dendritic epidermal cells could not be demonstrated in situ. A monoclonal antibody against FcR also stained the outer aspect of most keratinocytes throughout the epidermis. FcR on keratinocytes support the assumption that these cells contribute to immune reactions in the skin.