Simon Raphael, Heithoff Douglas M, Mahan Michael J, Samuel Charles E
Department of Molecular, Cellular and Developmental Biology, University of California at Santa Barbara, Santa Barbara, CA 93106, USA.
Infect Immun. 2007 Dec;75(12):5627-39. doi: 10.1128/IAI.01021-07. Epub 2007 Sep 24.
Mutants of Salmonella enterica serovar Typhimurium deficient in DNA adenine methylase (Dam) are attenuated for virulence in mice and confer heightened immunity in vaccinated animals. In contrast, infection of mice with wild-type (WT) strains or flagellin-deficient mutants of Salmonella causes typhoid fever. Here we examined the bacterial load and spatiotemporal kinetics of expression of several classes of host genes in Peyer's patches, the liver, and the spleen following oral infection of mice with WT, dam mutant, or flagellin-deficient (flhC) Salmonella. The genes evaluated included inflammatory (interleukin-1beta [IL-1beta], tumor necrosis factor alpha), chemokine (macrophage inflammatory protein 2), Th1/Th2 indicator (IL-12p40, IL-4), and interferon system (beta interferon [IFN-beta], IFN-gamma, protein Mx1 GTPase, RNA-dependent protein kinase, inducible nitric oxide synthase, suppressor of cytokine signaling 1) beacons. We showed that maximal interferon system and proinflammatory gene induction occurred by 5 days after infection and that the levels were comparable for the WT and flhC strains but were significantly lower for the dam mutant. Additionally, host gene expression in systemic tissues of individual animals was dependent on the bacterial load in the Peyer's patches for mice infected with WT, dam mutant, or flhC mutant Salmonella as early as 8 h after infection. Moreover, a bacterial load threshold in the Peyer's patches was necessary to stimulate the host gene induction in the liver and spleen. Taken together, these results suggest that bacterial load and the accompanying strain-specific cytokine signature are important determinants of the host innate immune response and associated disease manifestations observed in dam mutant Salmonella-infected animals compared to the immune response and disease manifestations observed in WT and flhC mutant Salmonella-infected animals.
鼠伤寒沙门氏菌DNA腺嘌呤甲基化酶（Dam）缺陷型突变体在小鼠体内的毒力减弱，且能使接种动物的免疫力增强。相比之下，用野生型（WT）菌株或沙门氏菌鞭毛蛋白缺陷型突变体感染小鼠会引发伤寒热。在此，我们检测了用WT、dam突变体或鞭毛蛋白缺陷型（flhC）沙门氏菌经口感染小鼠后，派尔集合淋巴结、肝脏和脾脏中几类宿主基因的细菌载量及表达的时空动力学。评估的基因包括炎性基因（白细胞介素-1β [IL-1β]、肿瘤坏死因子α）、趋化因子（巨噬细胞炎性蛋白2）、Th1/Th2指标（IL-12p40、IL-4）以及干扰素系统（β干扰素 [IFN-β]、IFN-γ、Mx1 GTP酶蛋白、RNA依赖性蛋白激酶、诱导型一氧化氮合酶、细胞因子信号传导抑制因子1）信标。我们发现，感染后5天干扰素系统和促炎基因诱导达到最大值，WT和flhC菌株的诱导水平相当，但dam突变体的水平显著更低。此外，早在感染后8小时，感染WT、dam突变体或flhC突变体沙门氏菌的小鼠个体全身组织中的宿主基因表达就依赖于派尔集合淋巴结中的细菌载量。而且，派尔集合淋巴结中的细菌载量阈值对于刺激肝脏和脾脏中的宿主基因诱导是必要的。综上所述，这些结果表明，与WT和flhC突变体沙门氏菌感染动物所观察到的免疫反应和疾病表现相比，细菌载量以及随之而来的菌株特异性细胞因子特征是dam突变体沙门氏菌感染动物中宿主先天免疫反应及相关疾病表现的重要决定因素。
