Neutrophils, the first line of defense against pathogens, are critical in the host response to acute and chronic infections. In Gram-negative pathogens, the bacterial outer membrane (OM) is a key mediator of pathogen detection; nonetheless, the effects of variations in its molecular structure on the neutrophil migratory response to bacteria remain largely unknown. Here, we developed a quantitative microfluidic assay that precludes physical contact between bacteria and neutrophils while maintaining chemical communication, thus allowing investigation of both transient and steady-state responses of neutrophils to a library of Salmonella enterica serovar Typhimurium OM-related mutants at single-cell resolution. Using single-cell quantitative metrics, we found that transient neutrophil chemokinesis is highly gradated based upon OM structure, while transient and steady-state chemotaxis responses differ little between mutants. Based on our finding of a lack of correlation between chemokinesis and chemotaxis, we define “stimulation score” as a metric that comprehensively describes the neutrophil response to pathogens. Complemented with a killing assay, our results provide insight into how OM modifications affect neutrophil recruitment and pathogen survival. Altogether, our platform enables the discovery of transient and steady-state migratory responses and provides a new path for quantitative interrogation of cell decision-making processes in a variety of host-pathogen interactions.

中文翻译：

---

肠沙门氏菌的外膜结构缺陷鼠伤寒血清型影响中性粒细胞趋化作用但不影响趋化作用

中性粒细胞是抵御病原体的第一道防线，在宿主对急性和慢性感染的反应中至关重要。在革兰氏阴性病原体中，细菌外膜 (OM) 是病原体检测的关键介质；尽管如此，其分子结构的变化对中性粒细胞对细菌的迁移反应的影响仍然很大程度上未知。在这里，我们开发了一种定量微流体分析，在保持化学通讯的同时排除了细菌和中性粒细胞之间的物理接触，从而允许研究中性粒细胞对肠道沙门氏菌库的瞬态和稳态反应单细胞分辨率下鼠伤寒 OM 相关突变体的血清型。使用单细胞定量指标，我们发现瞬态中性粒细胞趋化作用基于 OM 结构高度分级，而瞬态和稳态趋化反应在突变体之间差异不大。基于我们发现趋化作用和趋化性之间缺乏相关性，我们将“刺激评分”定义为全面描述中性粒细胞对病原体反应的指标。辅以杀灭试验，我们的结果提供了对 OM 修饰如何影响中性粒细胞募集和病原体存活的见解。总而言之，我们的平台能够发现瞬态和稳态迁移反应，并为在各种宿主 - 病原体相互作用中对细胞决策过程进行定量询问提供了新途径。