中文摘要：

背景：Faecalibacterium prausnitzii（Fp）是一种具有抗炎和免疫调节作用的肠道共生菌,研究发现结直肠癌患者肠道内Fp数量明显减少,可能与肿瘤发生有关。目的：探讨Fp及其基因组DNA（fDNA）干预对外周血单个核细胞（PBMCs）对人结肠癌LoVo细胞杀伤活性的影响及其免疫学机制。方法：将Fp、fDNA或酶解fDNA（d-fDNA）与分离自健康成人的PBMCs体外共培养,MTT实验检测PBMCs对LoVo细胞的杀伤活性,ELISA法检测PBMCs培养上清液中的Th1、Th2型细胞因子干扰素-γ（IFN-γ）、白细胞介素-4（IL-4）含量,real-time PCR检测PBMCs Th1、Th2特异性转录因子T-bet、GATA3表达。结果：与未予干预的PBMCs相比,fDNA干预能显著增强PBMCs对LoVo细胞的杀伤活性（P〈0.05）,同时促进PBMCs的IFN-γ分泌和T-bet mRNA表达（P〈0.05）,抑制IL-4分泌和GATA3mRNA表达（P〈0.05）。Fp和d-fDNA均未显示出上述作用。结论：fDNA能增强PBMCs对人结肠癌细胞的杀伤活性,其机制可能与上调Th1型免疫应答有关。

英文摘要：

Background： Faecalibacterium prausnitzii （Fp） is a commensal intestinal bacterium that exhibits anti-inflammatory and immunomodulatory capacity in vivo and in vitro. It has been reported that Fp in intestinal lumen was reduced in patients with colorectal cancer, which might be a factor associated with cancer development. Aims： To investigate the effect and immunological mechanism of Fp and its genomic DNA （fDNA） on the killing activity of peripheral blood mononuclear cells （PBMCs） against human colon cancer LoVo cells. Methods： PBMCs derived from healthy adults were co-cultured in vitro with Fp, fDNA, or the digested fDNA （d-fDNA）, respectively. Killing activity of PBMCs against LoVo cells was measured by MTY assay; concentrations of interferon-gamma （ INF-γ）, a Thl-type cytokine and interleukin-4 （ IL-4）, a Th2-type cytokine in culture supernatant of PBMCs were determined by ELISA; and expressions of T-bet and GATA3, the transcription factors specific for Thl and Th2 cells, were measured by real-time PCR. Results： Compared with the PBMCs not treated, fDNA could significantly enhance the killing activity of PBMCs against LoVo cells （P 〈 0.05） ; meanwhile, it promoted IFN-γ secretion, upregulated T-bet mRNA expression and inhibited IL-4 secretion and GATA3 mRNA expression in PBMCs （P 〈 0.05）. Similar effects were not observed in PBMCs treated with Fp and d-fDNA. Conclusions： fDNA enhances the killing activity of PBMCs against human colon cancer cells by upregulating Thl immune response.