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.