天花粉蛋白免疫抑制作用的功能性肽段筛选及其作用机制

Screening of Trichosanthin-derived peptide with immune suppression function and exploration of related mechanisms

在人工合成天花粉蛋白(Tk)多个重叠肽段的基础上,采用前期工作中筛选出的天花粉蛋白高敏感(C57BL/6)和低敏感(C3H/He)小鼠近交系,建立OVA特异的体外二次应答增殖系统,检测各肽段抑制能力,并通过细胞剔除及过继试验确认发挥作用的细胞,采用ELISA方法检测细胞因子分泌格局的改变。结果筛选到5条具有明显免疫抑制功能的Tk衍生肽,其中PE和PS对两个品系皆显示抑制活性,而PQ、PB及PJ仅在C57BL/6小鼠中诱导抑制。Tk衍生肽段改变了OVA特异性增殖系统中细胞因子分泌的格局,使得以Th1/Tc1型细胞因子为主状态向Th2/Tc2偏移,表现为IL-4和IL-10分泌增加,而IFN-γ分泌减少。剔除CD8+T细胞明显解除Tk及其肽段的抑制作用。表明Tk的某些肽段与全蛋白一样具有免疫抑制功能,其机制可能与诱导T细胞向CD8+Tc2方向偏移有关。

To screen some Tk-derived segments or epitopes retaining suppression property but free from toxicity, 24 peptides were synthesized in this study and their suppression activity on the secondary response of the OVA-primed T cells were examined in vitro. Two inbred mouse strain were used： one （C57BL/6） was high susceptible and the other （C3H/He） was low susceptible to the Tk-induced suppression. Our result showed that 5 peptides with strong suppression activity were resulted from the screening. Among them, PE and PS could function both in C57BL/6 and C3H/He mice. Peptide PQ, PB and PJ, however, only induced snppression in C57BL/6 mice. This suggests that, like full-length native Tk molecule, some Tk-derived peptides could only behave as down modulators under certain MHC backgrounds. Furthermore, Tk derived-peptides changed the cytokine profile obviously by turning type Ⅰ cytokine profile to type Ⅱ. The fact that depletion of CD8^＋ T cells dramatically diminished the suppression, further implicates that the Tk-derived peptides are active in inducing immune suppression via activating a CD8^＋ Tc2 subset.