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Objective To study effects of phosphoinositide 3 kinase (PI3K) and Notch signaling pathway on the proliferation and activation of CD4+ T cells in peripheral blood of patients with psoriasis vulgaris. Methods Peripheral venous blood was collected from 28 patients with psoriasis vulgaris and 28 healthy controls. CD4+ T cells in peripheral blood were sorted by immunomagnetic bead method. CD4+T cells from peripheral blood of patients with psoriasis vulgaris were divided into four groups: the blank control group, and 10 μmol/L PI3K blocker group (LY294002 group), 25 μmol/L Notch blocker group (DAPT group), 10 μmol/L LY294002+25 μmol/L DAPT group (LY294002+DAPT group). CD4+T cells were stimulated with phytohemagglutinin (PHA) 10 μg/ml and interleukin (IL) -2 1000 U/ml for 6 hours. The protein levels of Cyclina, Cyclin D1 and P27kipl in CD4+T cells were detected by FCM, and the mRNA levels of Cyclin A, Cyclin D1 and P27kipl were detected by reverse transcription polymerase chain reaction (RT-PCR). Results The purity of CD4+ T cells were (90.00±3.90)%, and the survival rate of CD4+ T cells was (92.50±4.60)%. The protein levels of Cyclin A and Cyclin D1 in peripheral blood CD4+ T cells of patients with psoriasis vulgaris were (27.60±3.80)%, (14.70±3.20)%, and the mRNA levels were (0.56±0.14) and (1.37±0.39)%, respectively. Compared with the healthy control group (13.50±3.70)%, (7.80±2.00)% and (0.31±0.12), (0.93±0.35), the difference was statistically significant (P=0.002, 0.037, 0.008 and 0.043). The level of P27kipl Protein and mRNA of CD4+ T cells in peripheral blood of patients with psoriasis vulgaris were (23.50±3.60)% and (0.17±0.02)% respectively, which were significantly lower than those in healthy control group (36.80±5.60)% and (0.33±0.05) (P=0.007, P=0.001). The expression of Cyclin D1 protein and mRNA in CD4+ T cells of the blank control group were (12.30±3.50)% and (1.74±0.39), respectively, while the level in LY294002 group, DAPT group and LY294002+DAPT group decreased significantly, with (7.20±3.10)%, (8.20±2.50)%, (4.30±1.50)% and (1.11±0.29), (1.26±0.28), (0.63±0.20), respectively (all P<0.05). Compared with the blank control group, the level of P27kipl Protein of CD4+ T cells in LY294002 group, DAPT group and LY294002+DAPT group increased significantly with (30.90±5.10)%, (27.60±5.20)%, (43.90±3.00%) respectively (P=0.005, 0.006 and 0.001). Compared with the level of the blank control group (0.15±0.08), the level of CD4+T cell P27kipl mRNA of LY294002 group, DAPT group and LY294002+DAPT group increased significantly with (0.37±0.07), (0.62±0.09), (0.99±0.21), respectively (P=0.018, 0.002, 0.003). There was no significant difference in the expression of Cyclin A protein and mRNA in CD4+ T cells in blank control group, LY294002 group, DAPT group and LY294002+DAPT group (all P>0.05). Conclusions PI3K and Notch signaling pathway can synergistically enhance the increase of positive regulatory protein Cyclin D1 and the decrease of negative regulatory protein P27kipl in CD4+ T cells, suggesting that PI3K and Notch signaling pathway play a synergistic regulatory role in the proliferation and activation of peripheral blood CD4+ T cells in patients with psoriasis vulgaris.