Investigating distinct platelet populations and their function in immunopathology and hemostasis associated with sepsis.

血小板在先天免疫中起关键作用，在对感染的反应中具有复杂的作用。首先，血小板对感染组织中白细胞的有效募集和激活至关重要(Clark等人)。2007；Amison等人2018年)，并增强其他免疫细胞的抗菌活性(Tang等人。2002年)。其次，血小板似乎对病原体诱导的呼吸道-血管屏障破坏具有保护作用。最后，血小板致病相互作用的研究表明，除了在感染诱导的血栓形成中发挥作用外，血小板还通过病原内化或释放抗菌肽，如PF-4的裂解多肽，发挥直接的抗微生物作用(Youssefian等人)。2002年；Shannon等人。2015年)。临床上，ICU中的败血症患者表现出血小板减少，这被认为是预后不良的迹象，血小板减少的水平与器官衰竭和死亡率的增加密切相关，可能是通过败血症引起的凝血障碍(Venkata等人)。2013)。在UKRI最近资助的一个项目中，对已发表的严重炎症反应综合征(SIRS)和脓毒症数据集的荟萃分析发现了一种基因表达模式，强调了血小板在脓毒症中的参与，而不是SIRS。进一步的验证工作确定了中性粒细胞和血小板群体中潜在的细胞亚群，发现了3个不同的血小板群体。考虑到血小板在脓毒症相关感染中的多方面作用，识别CD41和CD61以及MYL9和CD274等特异性生物标记物可以为了解这些不同群体的功能及其与中性粒细胞的相互作用提供潜在的洞察，这些不同群体可能与疾病进展和患者生存相关(童等人)。由于这些临床研究只是在ICU入院时才开始，因此重要的是在整个败血症相关感染的整个病程中识别和表征这些不同的人群，这在临床研究中很难实现。因此，使用适合于早发性脓毒症的动物感染模型，复制人类脓毒症的血液标志物和治疗效果，可以模拟低度和高度感染的完整时间过程。来自PHE的专业知识将使这位博士生能够识别出以前在人类患者中发现的存活或死于疾病的独特的血小板群体。随后对这些血小板群体的分离和功能特征将调查它们在与脓毒症相关的免疫反应和止血中的个别、特定的作用。这需要跨学科的方法，学生将学习药理学/生理学(体外/体内分析)和生物信息学(RNA微阵列数据的参数统计和路径分析)方面的技术。

Platelets are critical in innate immunity and possess complex roles in responses to infections. Firstly, plateletsare critical for efficient leukocyte recruitment and activation in infected tissue (Clark et al. 2007; Amison et al2018), and augment antimicrobial activity of other immune cells (Tang et al. 2002). Secondly, platelets appearto possess a protective role against pathogen induced airway-vascular barrier disruption. Finally, plateletpathogeninteraction studies have suggested a direct anti-microbial role of platelets through either pathogeninternalisation or release of antimicrobial peptides e.g. cleaved peptides of PF-4, in addition to their role ininfection induced thrombosis (Youssefian et al. 2002; Shannon et al. 2015). Clinically, septic patients in theICU demonstrate thrombocytopenia that is recognised as a poor prognostic sign, with the level ofthrombocytopenia closely related to increased organ failure and mortality, potentially via sepsis inducedcoagulopathy (Venkata et al. 2013). In a recent UKRI funded project, metanalysis of published severeinflammatory response syndrome (SIRS) and sepsis datasets identified a pattern of gene expressionhighlighting platelet involvement in sepsis but not SIRS. Further validation work identified potential cellularsubgroups within both neutrophil and platelet populations, with 3 distinct platelet groups identified.Considering the multifaceted role of platelets in infections associated with sepsis, identification of specificbiomarkers such as CD41 & CD61 alongside MYL9 & CD274 provides potential insight as to the function ofthese different populations and their interactions with neutrophils potentially associated with diseaseprogression and patient survival (Tong et al. 2020).As these clinical studies only commenced upon ICU admission, it is important to identify and characterisethese distinct populations over the full time-course of sepsis associated infections difficult to achieve in clinicalstudies. Therefore, using animal infection models appropriate for early onset sepsis that reproduce both bloodmarkers of human sepsis and treatment efficacy, a complete time-course of both low and high grade infectionscan be modelled. Expertise from PHE will enable the PhD student to identify the distinct platelet populationspreviously identified in human patients that either survive or succumb to disease. Subsequent isolation andfunctional characterisation of these platelet populations will investigate their individual, specific roles withinthe immune response and hemostasis associated with sepsis. This requires an interdisciplinary approach,where the student will learn techniques in pharmacology/physiology (in vitro/ vivo assays) and Bioinformatics(parametric statistical and pathway analysis of RNA microarray data).