Intraepidermal lymphocytes in psoriatic lesions are activated GMP‐17(TIA‐1)+CD8+CD3+ CTLs as determined by phenotypic analysis

The onset and persistence of psoriatic lesions are linked to the presence of an inflammatory infiltrate of CD3+ lymphocytes that includes CD4+ and CD8+ subsets. Since a primary susceptibility factor for psoriasis is the Class I HLA-Cw6 molecule, we set out to learn more about the features of the epidermal CD8+ lymphocytes. The markers tested were GMP-17, a cytotoxic granule protein found in activated cytotoxic lymphocytes (CTLs), and the alpha chain of the IL-2 receptor (CD25), a plasma membrane molecule found on activated T cells. Lymphocytes in lesional skin expressed the GMP-17 protein, whereas lymphocytes in non-lesional skin, resolving lesional skin and normal skin had little or no GMP-17. By flow cytometry analysis, lesional epidermal GMP-17+ cells were CD8+CD3+, with a subpopulation expressing the activation marker CD25+. Due to the abundance of activated GMP-17+CD8+CD3+ lymphocytes (the phenotype of activated cytotoxic cells) in psoriatic lesions compared to non-lesional and normal skin, we hypothesize that they are contributing directly to the psoriatic phenotype.