REAPPRAISAL OF IN-SITU IMMUNOPHENOTYPIC ANALYSIS OF PSORIASIS SKIN - INTERACTION OF ACTIVATED HLA-DR(-CELLS IS A MAJOR FEATURE OF PSORIATICLESIONS() IMMUNOCOMPETENT CELLS AND ENDOTHELIAL)

Psoriasis is an inflammatory skin disease of unknown aetiology. Many o bservations indicate that T cells play an important role in the pathog enesis of the disease. Upregulation of MHC class-II molecules on immun ocompetent cells, endothelial cells and keratinocytes on lesional psor iatic skin has been regarded as a hallmark of the disease. However, th ere is some controversy in the literature regarding the cell types exp ressing class-II molecules and there is limited information about the presence of immune cells other than T cells and antigen presenting cel ls in the cellular infiltrates of psoriatic skin. We therefore reinves tigated the subject using immunocytochemical single and multiple stain ing techniques. In agreement with earlier reports, our studies showed that the cellular infiltrates in lesional skin consist largely of HLA- DR(+)/IL-2R(+) T cells, HLA-DR(+)/CD1a(+) Langerhans cells, and HLA-DR (+)/CD68(+) macrophages. We found increased HLA-DR expression mostly o n immunocompetent cells and endothelial cells, but no prominent HLA-DR expression on keratinocytes in lesional psoriatic skin. Upregulation of HLA-DR on endothelial cells and in mononuclear infiltrates was also evident in the non-lesional skin of psoriatic patients as compared wi th normal controls. B cells and natural killer cells were also found i n the cellular infiltrates in lesional psoriatic skin. In spite of the presence of a large amount of activated T cells in the epidermis, we found that HLA-DR expression on keratinocytes was not a major feature of psoriatic skin.