THE ADAPTIVE IMMUNE RESPONSE TO PHAGES
对噬菌体的适应性免疫反应
Adaptive immunity provides targeted defense against specific pathogens. The ability of phages to elicit antibody (humoral immunity) and T cell responses (cellular immunity) has important implications for phage display vaccines, phage therapy, and interactions with our microbiome. A schematic for how phages are known to elicit adaptive immunity is shown in Figure 4.
适应性免疫提供了针对特定病原体的针对性防御。噬菌体激发抗体（体液免疫）和 T 细胞反应（细胞免疫）的能力对噬菌体展示疫苗、噬菌体疗法以及与微生物组的相互作用具有重要意义。图 4 显示了已知噬菌体如何激发适应性免疫的示意图。
Humoral Immunity to Phages
噬菌体的体液免疫
Phages are able to elicit neutralizing antibodies that promote their uptake and clearance. Studies involving engineered and environmental phages suggest that most of these induce neutralizing antibodies in the absence of additional adjuvant (120–124).
噬菌体能够诱发中和抗体，从而促进噬菌体的吸收和清除。对工程噬菌体和环境噬菌体的研究表明，在没有额外佐剂的情况下，大多数噬菌体都能诱导中和抗体（120- 124）。
The mechanisms by which some phages stimulate antibody production have been described in animal models. These studies indicate that the spleen is required for a humoral response to circulating phages (125, 126) and that phagocytes play a central role in uptake, processing, and presentation of phage antigens by antigen-presenting cells (APCs) (127). The target peptides are then presented through on major histocompatibility complex (MHC)-I and MHC-II pathways, resulting in B and T cell responses against the relevant viral or tumor antigen in vitro (127, 128) and in vivo (93, 129). Antiphage antibodies are predominately IgM isotype, but IgG and IgA responses are induced as well (130). In a study of heterogenous phage therapy cases, local phage administration at the site of an infection elicited more robust antibody responses than phages administered orally in humans (131) but has not been examined in controlled trials.
一些噬菌体刺激抗体产生的机制已在动物模型中得到描述。这些研究表明，循环噬菌体的体液反应需要脾脏（125，126），吞噬细胞在抗原呈递细胞（APCs）摄取、处理和呈递噬菌体抗原的过程中起着核心作用（127）。然后，目标肽通过主要组织相容性复合体（MHC）-I 和 MHC-II 途径呈现，在体外（127、128）和体内（93、129）产生针对相关病毒或肿瘤抗原的 B 细胞和 T 细胞反应。抗噬菌体抗体主要是 IgM 同型，但也会诱导 IgG 和 IgA 反应（130）。在一项关于异源噬菌体疗法病例的研究中，与人类口服噬菌体相比，在感染部位局部注射噬菌体能引起更强的抗体反应（131），但尚未进行对照试验。
The long history of research on the coliphage phiX174 as a diagnostic for evaluating adaptive immune responses provides an important body of research on the human antiphage antibody responses in humans (132). In healthy controls, phiX174 circulates for 3–4 days following primary IV immunization (133). IgM antibodies specific to phage arise in this time frame and peak at 2 weeks, and secondary immunization 6 weeks later leads to a larger IgG/IgM peak after 1 week (133). Patients with X-linked agammaglobulinemia, who exhibit a complete lack of functional B cells, have dramatically prolonged active phage circulation and do not show any antiphage antibody response (69). Because these patients can neither produce natural antibodies nor mount an adaptive response, clearance of phage is impossible. However, when B cells are depleted through anti-CD19 antibody (Rituximab) administration, clearance of phiX174 is normal despite impaired primary and secondary antibody responses (133). As anti-CD19 therapy would not affect the patients’ pool of circulating natural IgM/IgA antibodies and complement, this study underscores the importance of these humoral proteins in phage clearance.
将噬菌体 phiX174 作为评估适应性免疫反应的诊断方法的研究由来已久，为人类抗噬菌体抗体反应的研究提供了重要依据 ( 132)。在健康对照组中，phiX174 在初次静脉免疫后会循环 3-4 天 ( 133)。噬菌体特异性 IgM 抗体在这段时间内产生，并在 2 周时达到峰值，6 周后的二次免疫会在 1 周后产生更大的 IgG/IgM 峰值（133）。X 连锁无噬菌体球蛋白血症患者完全缺乏功能性 B 细胞，他们的噬菌体循环活跃时间显著延长，却没有表现出任何抗噬菌体抗体反应（69）。由于这些患者既不能产生天然抗体，也不能做出适应性反应，因此不可能清除噬菌体。然而，当通过服用抗 CD19 抗体（利妥昔单抗）来消耗 B 细胞时，尽管一级和二级抗体反应受损，但 phiX174 的清除率却正常（133）。由于抗 CD19 治疗不会影响患者循环中的天然 IgM/IgA 抗体和补体，这项研究强调了这些体液蛋白在噬菌体清除中的重要性。
Antiphage antibodies may function as a check on the bioactivity of phages against our microbiome. Antiphage IgAs arose in response to repeated ingestion of T4 phages and limited its bioactivity (130). Antiphage adaptive immunity is likewise suspected to adversely affect the outcome of intravenous phage therapy. Although research on antiphage antibodies in humans is limited, one study suggests that many individuals have preexisting, neutralizing antibodies against phages commonly used in phage therapy (134). This may reflect the fact that many chronic infections are caused by opportunistic pathogens that under other circumstances are part of our commensal flora, thereby providing opportunity for exposure to those microbes’ phages. Patients also develop neutralizing antibodies over the course of treatment with phages (131, 135).
抗噬菌体抗体可以抑制噬菌体对微生物群的生物活性。抗噬菌体 IgAs 是对反复摄入 T4 噬菌体的反应，它限制了噬菌体的生物活性 ( 130)。抗噬菌体适应性免疫同样被怀疑会对静脉注射噬菌体疗法的结果产生不利影响。虽然对人类抗噬菌体抗体的研究有限，但一项研究表明，许多人体内存在针对噬菌体疗法中常用噬菌体的中和抗体（134）。这可能反映了一个事实，即许多慢性感染是由机会性病原体引起的，而这些病原体在其他情况下是我们共生菌群的一部分，因此提供了接触这些微生物噬菌体的机会。在噬菌体治疗过程中，患者还会产生中和抗体（131，135）。
However, the effect of antiphage antibodies on the success of phage therapy is ultimately unclear. In one report of 122 patients receiving a diversity of phages for a variety of infections, there was no clear correlation between patients developing strong humoral immunity and the outcome of phage treatment (131). Systematically monitoring the development of antiphage antibodies in patients and their effect on treatment outcome has been made difficult by the lack of controlled trials using standardized phage product, administration modes, and length of treatment.
然而，抗噬菌体抗体对噬菌体疗法成功与否的影响尚不明确。一份研究 122 名接受多种噬菌体治疗的各种感染患者的报告显示，患者产生强大的体液免疫与噬菌体治疗效果之间没有明显的相关性（131）。由于缺乏使用标准化噬菌体产品、给药方式和治疗时间的对照试验，因此很难系统监测患者体内抗噬菌体抗体的发展及其对治疗效果的影响。
The available data are also difficult to interpret, as phages engineered to have altered capsid structures (e.g., through peptide display protocols) may be more immunogenic than their unmodified parent phages (136, 137) and may be cleared from circulation more quickly (138). Moreover, phages delivered intravenously or at the site of infection may be more immunogenic than phages in the gastrointestinal tract (131).
现有数据也很难解释，因为改变了噬菌体外壳结构的噬菌体（如通过多肽展示方案）可能比未修饰的母体噬菌体具有更强的免疫原性（136、137），而且可能更快地从血液循环中清除（138）。此外，静脉注射或在感染部位注射噬菌体可能比在胃肠道中注射噬菌体更具免疫原性（131）。
Both antiphage antibodies and complement contribute to the removal of phages from peripheral circulation. Sokoloff et al. (139) injected a T7 phage library displaying random peptides into rats. They observed that IgM and IgG depletion in rat serum prolonged phage survival by 62% and 16%, respectively (139). Dabrowska et al. (123) described a critical role for complement in the phage-inactivating ability of serum antibodies. Taken together, these findings suggest that antibody binding and complement fixation promote opsonization and clearance of phages from circulation.
抗噬菌体抗体和补体都有助于从外周循环中清除噬菌体。Sokoloff 等人（139）向大鼠注射了显示随机肽的 T7 噬菌体库。他们观察到，大鼠血清中 IgM 和 IgG 的消耗分别使噬菌体存活时间延长了 62% 和 16% ( 139)。Dabrowska 等人（123）描述了补体在血清抗体灭活噬菌体能力中的关键作用。综上所述，这些研究结果表明，抗体结合和补体固定促进了噬菌体的憎溶性和从循环中清除噬菌体。
Much remains unknown about the antibody response to phages. For example, it is unclear to what extent humoral immunity exists against the broader pool of phages within the body and what roles these antibodies play in modulating phage activity; influencing phage transcytosis; or, perhaps, promoting opsonization of either commensal or pathogenic bacteria targeted by phages. A better understanding of these and related topics will be essential for the further development of phage therapy and phage display vaccines.
关于噬菌体的抗体反应，还有很多未知。例如，目前还不清楚针对体内更广泛的噬菌体库存在多大程度的体液免疫，也不清楚这些抗体在调节噬菌体活性、影响噬菌体转囊、或促进噬菌体靶向的共生或致病细菌的疏松化方面发挥什么作用。更好地了解这些及相关主题对于噬菌体疗法和噬菌体展示疫苗的进一步发展至关重要。