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 now 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.