Immunohistopathologic studies in the development of psoriatic lesion influenced by gamma-interferon and the producing cells.

Immunological studies on psoriasis have been done using monoclonal antibodies (MoAbs) to elucidate the relation between gamma-interferon (IFN-gamma) secreted from inflammatory infiltrate, and the expression of HLA-DR molecule on epidermal keratinocytes in the lesion. In highly inflamed psoriatic lesions, IFN-gamma producing cells were found in the inflammatory infiltrate of the dermal papillae, while keratinocytes located near IFN-gamma+ cells expressed HLA-DR molecules on the surface. In fully developed psoriatic lesions, HLA-DR+ keratinocytes were mainly found in the thin epidermis over the elongated dermal papillae where IFN-gamma deposited not only at infiltrates but also in teh dermal components. The IFN-gamma+ cells were activated T cells which exhibited HLA-DR and interleukin 2 receptor. Munro's microabscess under the horny layer also included IFN-gamma producing cells. A radioimmunoassay by the sandwich method with anti-human IFN-gamma and anti-recombinant IFN-gamma MoAbs found that extracts from psoriatic scales contained IFN-gamma. The results suggest that HLA-DR+ keratinocytes are due to the effect of IFN-gamma secreted by activated T cells in psoriatic lesions. The proliferation of keratinocytes over the dermal papillae in fully developed lesions seemed to be inhibited by IFN-gamma from the inflammatory infiltrate. We consider that cell-mediated immune reaction plays an important role in the development of psoriatic eruption.