Bacteriophages and the Immune System噬菌体与免疫系统

Phages and Bacterial Clearance
噬菌体和细菌清除

Along with conflicting data regarding the roles of specific PRRs in phage recognition, there are likewise contradictory data on the effect of phages on inflammation and bacterial clearance. Key elements of these data are summarized in Figure 3.
除了关于特定 PRR 在噬菌体识别中的作用的相互矛盾的数据外，关于噬菌体对炎症和细菌清除的影响的数据也同样相互矛盾。图 3 总结了这些数据的主要内容。

Phage vaccines using modified T4 or other phages are typically proinflammatory (93–95). There are reports of induction of mixed T helper (Th) 1 and Th2 responses and robust proinflammatory cytokine induction in response to such phages (96–99) consistent with a resounding antibacterial response. However, endotoxin levels are often not quantified in phage vaccine preparations, and some studies use bacterial lysates as an immunogen (100). Bacterial contaminants may therefore contribute to the immunogenicity of these preparations.
使用改良 T4 或其他噬菌体的噬菌体疫苗通常具有促炎作用 ( 93- 95)。有报告称，此类噬菌体可诱导混合 T 辅助细胞（Th）1 和 Th2 反应，并诱导大量促炎细胞因子（96-99），从而产生明显的抗菌反应。然而，噬菌体疫苗制剂中的内毒素水平往往没有量化，有些研究使用细菌裂解液作为免疫原（100）。因此，细菌污染物可能会影响这些制剂的免疫原性。

Consistent with these proinflammatory effects, there are indications that phages may act synergistically with the innate immune response to promote bacterial clearance. Using an innovative fluorescent lysis reporter system, Bodner et al. (101) detected lysis of E. coli by a lambda prophage in response to ROS present within a macrophage phagosome. This suggests that phages provide an alternative bacterial killing pathway for macrophages. Tiwari et al. (102) evaluated the efficacy of phage therapy on P. aeruginosa infection in wild-type and neutropenic mice. While wild-type mice exhibited 100% survival with phage injection, neutropenic mice were not rescued. In vitro, phage cocultured with isolated neutrophils were better able to kill bacteria than phage alone, suggesting phage-neutrophil synergy is essential in bacterial clearance. Conversely, in a Pseudomonas lung infection model, treatment with the lytic phage PAK_P1 was of equal benefit in wild-type and Rag2^−/−IL2rg^−/− mice, which lack lymphocytes, indicating that lymphocytes are not significantly involved in bacterial clearance in this time frame (103). In this same study, phage therapy was relatively ineffective in both mice lacking neutrophils and MyD88^−/− mice. These data suggest that phage control of a bacterial infection depends on collaboration with the host immune system, in particular with neutrophils and TLR-sensing pathways in myeloid cells.
与这些促炎作用相一致，有迹象表明噬菌体可能与先天性免疫反应协同作用，促进细菌清除。Bodner 等人（101）使用一种创新的荧光裂解报告系统，检测到λ噬菌体在巨噬细胞吞噬体中的 ROS 作用下裂解大肠杆菌。这表明噬菌体为巨噬细胞提供了另一种杀死细菌的途径。Tiwari 等人（102）评估了噬菌体疗法对野生型小鼠和中性粒细胞减少小鼠铜绿假单胞菌感染的疗效。注射噬菌体后，野生型小鼠的存活率达到 100%，而中性粒细胞减少的小鼠则没有得到救治。在体外，噬菌体与离体中性粒细胞共培养比单独使用噬菌体更能杀死细菌，这表明噬菌体与中性粒细胞的协同作用对细菌清除至关重要。相反，在假单胞菌肺部感染模型中，溶菌噬菌体 PAK_P1 对野生型和 Rag2 ^−/− IL2rg {{1} 的益处相同。IL2rg ^−/− 小鼠（这些小鼠缺乏淋巴细胞）同样获益，这表明淋巴细胞在这一时期并没有显著参与细菌清除（103）。在同一项研究中，噬菌体疗法对缺乏中性粒细胞的小鼠和MyD88 ^−/− 小鼠相对无效。这些数据表明，噬菌体对细菌感染的控制取决于与宿主免疫系统的合作，特别是与中性粒细胞和骨髓细胞中的 TLR 传感途径的合作。

Other studies have demonstrated minimal inflammatory responses to phage (104–106) and no effect on phagocytosis (107). T4 phages added to naive and LPS-activated monocytes induced no change in activation or release of proinflammatory cytokines (108, 109). Monocyte and neutrophil ROS production in response to purified T4 and A3/R phages was similarly minimal (110). In humans, both endogenous phages in circulation and infusion of phages administered in the context of lytic phage therapy are generally well tolerated with minimal inflammation (111).
其他研究表明，噬菌体的炎症反应极小（104-106），对吞噬作用没有影响（107）。T4噬菌体加入天真单核细胞和 LPS 激活的单核细胞后，促炎细胞因子的激活或释放没有变化 ( 108, 109)。单核细胞和中性粒细胞对纯化的 T4 和 A3/R 噬菌体产生的 ROS 反应同样微乎其微（110）。在人体中，无论是循环中的内源性噬菌体还是溶解性噬菌体疗法中的噬菌体输注，一般都能很好地耐受，炎症反应极小 ( 111)。

Still other studies have reported that phages inhibit bacterial phagocytosis and dampen proinflammatory cytokine production in response to bacterial endotoxin. Pf4 phages produced by P. aeruginosa suppressed both phagocytosis and production of tumor necrosis factor in response to LPS, contributing to chronicity of P. aeruginosa infections in mouse wound (90) and lung infection models (76, 112) and to an association with chronic wound and lung infections in humans (90, 113). These effects were mediated by induction of type 1 IFN-dominated antiviral responses that antagonized bacterial clearance (90). T4 and F8 phages produced by E. coli similarly inhibited phagocytosis and ROS production in response to E. coli (114) but not ROS in response to phorbol myristate acetate (115). Jahn et al. (116) uncovered a phage-expressed protein, ANKp, that when inserted in E. coli under an inducible promoter significantly reduced proinflammatory cytokine production and phagocytosis of ANKp-expressing E. coli by macrophages. Van Belleghem et al. (117) investigated the transcriptional changes resulting from human peripheral blood mononuclear cell stimulation with a variety of S. aureus and P. aeruginosa phages and found that these altered the transcriptional response to endotoxin. Together, these studies indicate that some phages can directly influence local immune responses in ways that alter susceptibility to bacterial infections. They also raise the intriguing possibility that phages modulate local immunity to protect their bacterial hosts.
还有其他研究报告称，噬菌体可抑制细菌的吞噬作用，并抑制细菌内毒素引起的促炎细胞因子的产生。铜绿假单胞菌产生的 Pf4 噬菌体抑制了对 LPS 的吞噬作用和肿瘤坏死因子的产生，从而导致铜绿假单胞菌在小鼠伤口（90）和肺部感染模型（76，112）中的慢性感染，并与人类的慢性伤口和肺部感染有关（90，113）。这些效应是通过诱导 1 型 IFN 主导的抗病毒反应来拮抗细菌清除的（90）。由大肠杆菌产生的 T4 和 F8 噬菌体同样抑制了大肠杆菌的吞噬作用和 ROS 产生（114），但没有抑制乙酸薄荷醇肉豆蔻酯的 ROS 产生（115）。Jahn 等人（116）发现了一种噬菌体表达的蛋白质 ANKp，将其插入大肠杆菌的诱导启动子后，可显著减少促炎细胞因子的产生以及巨噬细胞对 ANKp 表达的大肠杆菌的吞噬作用。Van Belleghem 等人（117）研究了人外周血单核细胞受多种金黄色葡萄球菌和铜绿假单胞菌噬菌体刺激后的转录变化，发现这些变化改变了对内毒素的转录反应。这些研究共同表明，某些噬菌体能直接影响局部免疫反应，从而改变对细菌感染的易感性。这些研究还提出了一个令人感兴趣的可能性，即噬菌体可以调节局部免疫以保护细菌宿主。

How can we make sense of these contradictory data regarding the pro- and anti-inflammatory effects of phages? It is notable that the same phages (i.e., T4) are proinflammatory in some contexts (118) and anti-inflammatory in others (109, 110, 114, 115). This suggests that the purity of the phage preparation in question may be a critical determinant of the immune response (119). Further, the immunomodulatory effects of phage may be context- and perhaps phage-dependent; there are indications that phages dampen the immune response to bacteria but little evidence that they affect other inflammatory settings. One way this could occur mechanistically is if many phages trigger IFN responses that antagonize bacterial immunity but enhance other kinds of inflammatory responses.
如何理解这些关于噬菌体促炎和抗炎作用的矛盾数据？值得注意的是，同样的噬菌体（如 T4）在某些情况下具有促炎作用（118），而在另一些情况下则具有抗炎作用（109、110、114、115）。这表明噬菌体制剂的纯度可能是决定免疫反应的关键因素（119）。此外，噬菌体的免疫调节作用可能与环境有关，也可能与噬菌体有关；有迹象表明，噬菌体会抑制对细菌的免疫反应，但很少有证据表明它们会影响其他炎症环境。如果许多噬菌体引发的 IFN 反应能拮抗细菌免疫，但却能增强其他类型的炎症反应，那么就有可能从机理上出现这种情况。

Much remains unknown about innate immune responses to phages. Most of our data are from a small handful of phages; it would be important to know whether common responses to phages exist. It is also unclear to what extent distinct sets of phages (e.g., lytic versus filamentous phages) stimulate different immune responses.
关于噬菌体的先天性免疫反应，还有很多未知因素。我们的大多数数据都来自少数噬菌体；了解噬菌体是否存在共同的反应非常重要。目前还不清楚不同的噬菌体（如溶解性噬菌体与丝状噬菌体）在多大程度上会激发不同的免疫反应。