Existence of activated and memory CD4+ T cells in peripheral blood and their skin infiltration in CD8 deficiency
CD8 deficiency is a rare primary immunodeficiency caused by the defect of a tyrosine kinase, ZAP‐70, which transduces signals from the T cell receptor. We report here a case of CD8 deficiency, having CD4+ T cells with a unique phenotype. The patient's T cells did not respond to anti‐CD3 stimulation in vitro, suggesting that they were naive. However, many CD4+ T cells with activated and memory phenotypes, which expressed CD45RO+, HLA‐DR+ and CD25+, were present in the peripheral blood, and these cells accumulated in the perivascular area of his infiltrative erythematous skin lesions. The patient's T cells could be activated by a high concentration of phytohaemagglutinin (PHA), indicating the presence of an alternate signalling pathway which bypasses ZAP‐70 and activates CD4+ T cells in vivo. The origin and role of activated CD4+ T cells in the pathogenesis involved in the skin lesions are discussed.