Department of Microbiology and Immunology, Uniformed Services University, Bethesda, Maryland, USA.
Henry Jackson Foundation for the Advancement of Military Medicine, Bethesda, Maryland, USA.
Infect Immun. 2021 Jul 15;89(8):e0068520. doi: 10.1128/IAI.00685-20.
In response to stress, the obligate intracellular pathogen Chlamydia trachomatis stops dividing and halts its biphasic developmental cycle. The infectious, extracellular form of this bacterium is highly susceptible to killing by the host immune response, and by pausing development, Chlamydia can survive in an intracellular, "aberrant" state for extended periods of time. The relevance of these aberrant forms has long been debated, and many questions remain concerning how they contribute to the persistence and pathogenesis of the organism. Using reporter cell lines, fluorescence microscopy, and a dipeptide labeling strategy, we measured the ability of C. trachomatis to synthesize, assemble, and degrade peptidoglycan under various aberrance-inducing conditions. We found that all aberrance-inducing conditions affect chlamydial peptidoglycan and that some actually halt the biosynthesis pathway early enough to prevent the release of an immunostimulatory peptidoglycan component, muramyl tripeptide. In addition, utilizing immunofluorescence and electron microscopy, we determined that the induction of aberrance can detrimentally affect the development of the microbe's pathogenic vacuole (the inclusion). Taken together, our data indicate that aberrant forms of Chlamydia generated by different environmental stressors can be sorted into two broad categories based on their ability to continue releasing peptidoglycan-derived, immunostimulatory muropeptides and their ability to secrete effector proteins that are normally expressed at the mid- and late stages of the microbe's developmental cycle. Our findings reveal a novel, immunoevasive feature inherent to a subset of aberrant chlamydial forms and provide clarity and context to the numerous persistence mechanisms employed by these ancient, genetically reduced microbes.
面对压力,专性细胞内病原体沙眼衣原体停止分裂并停止其两相发育周期。这种细菌的感染性、细胞外形式极易受到宿主免疫反应的杀伤,通过暂停发育,衣原体可以在细胞内的“异常”状态下存活很长时间。这些异常形式的相关性长期以来一直存在争议,许多问题仍然存在,涉及它们如何有助于该生物的持续存在和发病机制。使用报告细胞系、荧光显微镜和二肽标记策略,我们测量了 C. trachomatis 在各种诱导异常条件下合成、组装和降解肽聚糖的能力。我们发现,所有诱导异常的条件都会影响衣原体的肽聚糖,并且有些条件实际上会提前阻止生物合成途径,从而防止释放免疫刺激性肽聚糖成分,即 muramyl tripeptide。此外,利用免疫荧光和电子显微镜,我们确定异常的诱导会对微生物致病空泡(包含体)的发育产生不利影响。总之,我们的数据表明,不同环境胁迫产生的衣原体异常形式可以根据其继续释放肽聚糖衍生的免疫刺激性 muropeptides 的能力以及分泌通常在微生物发育周期的中期和晚期表达的效应蛋白的能力分为两大类。我们的发现揭示了一种新的、免疫逃避特征,固有地存在于一组异常的衣原体形式中,并为这些古老的、遗传上减少的微生物所采用的许多持久性机制提供了清晰的认识和背景。