Abstract: Objective To investigate the effects of psoriatic keratinocytes on the expression of CD25 and CD69 in T lymphocytes. Methods Keratinocytes were isolated from the biopsy samples resected from the lesions and adjacent non-lesional area of 10 patients with psoriasis, and cultured in 5% CO2 at 37 ℃ in 24-well plates. Density gradient centrifugalization and glass adherence method were applied to detach peripheral blood mononuclear cells （PBMC） and peripheral blood T lymphocytes （PBTL） from anticoagulant blood samples of the same 10 psoriatic patients and 10 normal controls. PBMCs of 1 × 105/well were added to the wells containing cultured keratinocytes of 1 × 105/well, then gamma rays were used to inactivate these cells. Following that, PBTLs of 1 × 106/well were inoculated into the 24-well plate containing inactivated keratinocytes and PBMCs, and cultured in 5% CO2 at 37 ℃. Those PBTLs cultured without the presence of keratinocytes or PBMCs served as the natural growth control. Three days later, flow cytometry was performed to detect the expression of CD25 and CD69 in PBTLs. Results There was a significant increase in the expression of CD25 and CD69 in psoriatic PBTLs cocultured with lesional keratinocytes compared with those cocultured with non-lesional keratinocytes and natural psoriatic controls. Also, the expression of CD25 and CD69 was increased in normal PBTLs cocultured with lesional or non-lesional keratinocytes of psoriatc patients than those in the natural normal controls. No significant difference was observed in the expression of CD25 or CD69 between psoriatic PBTLs cocultured with non-lesional keratinocytes and natural psoriatic PBTLs, or between the normal PBTLs cocultured with lesional keratinocytes and those with non-lesional keratinocytes （P > 0.05）. Conclusions Psoriatic keratinocytes may act as an autoantigen to trigger autoimmune response and eventually lead to a chronic local inflammation in patients with psoriasis.