Abstract: LIU Rui-feng, ZHAO Xin-cheng, YANG Yuan-wen, ZHANG Kai-ming. Department of Dermatology, Taiyuan City Centre Hospital, Taiyuan 030009, China Correponding author: ZHANG Kai-ming, Email: zhangkaiming@sina.com 【Abstract】 Objective To evaluate the inhibitory effect of mesenchymal stem cells （MSCs） in lesions of patients with psoriasis on T lymphocyte proliferation. Methods Tissue specimens were obtained from the lesions of 15 patients with psoriasis vulgaris （7 at progressive stage and 8 at resting stage） and normal skin of 15 human controls from the Department of Urology and Plastic Surgery, Taiyuan City Centre Hospital. MSCs were isolated from these skin specimens, cultured, and identified using flow cytometry and in vitro differentiation assay. Enzyme-linked immunosorbent assay （ELISA） was performed to detect the concentration of interleukin （IL）-6, IL-11, hepatocyte growth factor （HGF） and transforming growth factor （TGF）-β1 in the culture supernatant of third-passage MSCs. Peripheral blood T cells were obtained from a healthy adult and cocultured with the third-passage MSCs for four days. Then, cells were counted and methyl thiazolyl tetrazolium （MTT） assay was conducted to evaluate the proliferation of T cells. One-way analysis of variance （ANOVA） and Student-Newman-Keuls （SNK） test were carried out to compare the proliferation of T lymphocytes, and two independent samples t test to compare the concentrations of cytokines. Results Inverted microscopy revealed that the patient- and control-derived MSCs shared similar morphological properties and multi-directional differentiation capacity, along with the expression of CD29, CD44, CD73, CD90 and CD105, but absence of CD34, CD45 and HLA-DR on cell surface. After coculture with MSCs from the patients and controls for four days, the count of T lymphocytes per milliliter was （1.67 ± 0.34） × 105 and （1.04 ± 0.29） × 105 respectively （P ＜ 0.01）, and the proliferative activity （expressed as absorbence at 492 nm） was 0.317 ± 0.021 and 0.275 ± 0.007 respectively （P ＜ 0.01）. Compared with the control-derived MSCs, the patient-derived MSCs showed a significantly higher level of IL-11 （（181.37 ± 31.74） vs. （130.07 ± 29.20） ng/L, t = 5.32, P ＜ 0.01）, but a lower level of IL-6 （（61.67 ± 17.53） vs. （76.74 ± 18.96） ng/L, t = 2.61, P ＜ 0.05） and HGF （（319.24 ± 41.03） vs. （352.35 ± 51.47） ng/L, t = 2.25, P ＜ 0.05）, as well as a similar level of TFG-β1, in the culture supernatant. Conclusions The inhibitory effect of MSCs in psoriatic lesions on T lymphocyte proliferation is diminished, which may contribute to the pathogenesis of psoriasis. 【Key words】 Psoriasis; Mesenchymal stem cells; T-lymphocytes