Cytokine expression in CD4-CD8- double-negative (DN) T cells of autoimmune lymphoproliferative syndrome (ALPS) was analysed. Two patients with DN αβT-cell expansion showed higher serum interleukin 10 (IL-10) levels than one patient without it. Intracellular flow-cytometric analysis indicated the IL-10-expressing CD3+CD4-CD8- cells in patients with lymphoproliferation. Quantitative real-time polymerase chain reaction revealed ∼100 times higher IL-10, but not interferon-γ or transforming growth factor-β in DN than in single-positive T cells. IL-10 was exclusively expressed in DN αβ but not γδT cells. Circulating DN αβT cells may constitutively express IL-10 and contribute to the ALPS phenotype.
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