Pretreatment Sublethal B. Anthracis Lethal Toxin in Rats

在体外实验中，炭疽芽孢杆菌LeTx的致死因子组分灭活了丝裂原活化的蛋白激酶激酶，抑制了tnf fa和NO的释放。这些抗炎作用是否与炭疽杆菌感染的致病性有关尚不清楚。然而，如果它们是，我们假设亚致死剂量的LeTx在体内致命LPS攻击期间也可能具有抗炎作用。实验中，在LPS输注24小时前3小时，采用静脉和动脉导管的Sprague-Dawley大鼠随机接受低、中、高亚致死剂量的LeTx或稀释剂注射。在LPS输注期间，测量平均动脉血压（MAP） （q1h）、血浆细胞因子（IL-1a和b、IL-2、4、6和10、IFNg、TNFa、GM-CSF、MIP1、2和3a、RANTES）和NO水平（2,8和24 h）。动物观察168小时。与高剂量LeTx相比，中、低剂量LeTx导致的生存危险比降低接近显著性（高剂量vs中、低剂量联合p=0.08）。与仅用稀释液相比，LeTx在2 h降低了12种细胞因子中的10种（无显著性），在8 h降低了全部13种细胞因子，其中4种细胞因子（IL-6、IL-10、IFNg、MIP2a,p<=0.08），在2 - 24 h显著降低了NO水平（LeTx对时间的影响p=0.02），在24 h显著增加了MAP （p=0.001）。因此，与体外数据一致，亚致死LeTx降低了LPS刺激大鼠的细胞因子和NO水平。这与血压升高有关，在低剂量和中剂量的情况下，有利于生存趋势。在细菌感染期间，LeTx的这些相同的抗炎作用是有益的还是损害宿主的防御还需要进一步的研究。目前正在进行研究，以调查在大肠杆菌感染大鼠模型之前低亚致死剂量LeTx的影响。

In vitro the lethal factor component of B. anthracis LeTx inactivated mitogen-activated protein kinase kinases and inhibited TNFa and NO release in response to LPS and IFNg. Whether these anti-inflammatory effects are relevant to the pathogenicity of B. anthracis infection is not known. If they are however, we hypothesized that sublethal doses of LeTx might also have anti-inflammatory effects in vivo during lethal LPS challenge. In experiments, 3 h before a 24 h infusion with LPS, Sprague-Dawley rats with venous and arterial catheters were randomized to receive injections of low, medium or high sublethal doses of LeTx or diluent only. During LPS infusion, mean arterial blood pressure (MAP) (q1h) and plasma cytokines (IL-1a and b, IL-2, 4, 6, and 10, IFNg, TNFa, GM-CSF, MIP1,2 and 3a, and RANTES) and NO levels (2, 8, and 24 h) were measured. Animals were observed for 168 h. Compared to high doses of LeTx, medium and low doses caused decreases in the hazards ratio of survival approaching significance (p=0.08 for high vs low and medium doses combined). Compared to diluent only, LeTx decreased 10 of 12 cytokines at 2 h (none significantly), all 13 cytokines, 4 of them significantly or approaching it (IL-6, IL-10, IFNg, MIP2a,p<=0.08) at 8 h, and NO levels significantly from 2 to 24 h (p=0.02 for the effect of LeTx across time) and increased MAP significantly over the 24 h (p=0.001). Thus, consistent with in vitro data, sublethal LeTx decreased cytokine and NO levels in LPS challenged rats. This was associated with increased blood pressure and, with low and medium doses, beneficial survival trends. Whether these same anti-inflammatory effects with LeTx would be beneficial or instead impair host defense during bacterial infection requires further study. Studies are ongoing to investigate the effects of low sublethal doses of LeTx before E. coli infection in this rat model.