Kottom Theodore J, Hebrink Deanne M, Jenson Paige E, Gudmundsson Gunnar, Limper Andrew H
Thoracic Diseases Research Unit, Departments of Medicine and Biochemistry, Mayo Clinic College of Medicine, Rochester, Minnesota, USA University of Iceland School of Health Sciences, Reykjavík, Iceland.
Thoracic Diseases Research Unit, Departments of Medicine and Biochemistry, Mayo Clinic College of Medicine, Rochester, Minnesota, USA.
Infect Immun. 2015 Jul;83(7):2816-26. doi: 10.1128/IAI.00196-15. Epub 2015 Apr 27.
Inflammation is a major cause of respiratory impairment during Pneumocystis pneumonia. Studies support a significant role for cell wall β-glucans in stimulating inflammatory responses. Fungal β-glucans are comprised of d-glucose homopolymers containing β-1,3-linked glucose backbones with β-1,6-linked glucose side chains. Prior studies in Pneumocystis carinii have characterized β-1,3 glucan components of the organism. However, recent investigations in other organisms support important roles for β-1,6 glucans, predominantly in mediating host cellular activation. Accordingly, we sought to characterize β-1,6 glucans in the cell wall of Pneumocystis and to establish their activity in lung cell inflammation. Immune staining revealed specific β-1,6 localization in P. carinii cyst walls. Homology-based cloning facilitated characterization of a functional P. carinii kre6 (Pckre6) β-1,6 glucan synthase in Pneumocystis that, when expressed in kre6-deficient Saccharomyces cerevisiae, restored cell wall stability. Recently synthesized β-1,6 glucan synthase inhibitors decreased the ability of isolated P. carinii preparations to generate β-1,6 carbohydrate. In addition, isolated β-1,6 glucan fractions from Pneumocystis elicited vigorous tumor necrosis factor alpha (TNF-α) responses from macrophages. These inflammatory responses were significantly dampened by inhibition of host cell plasma membrane microdomain function. Together, these studies indicate that β-1,6 glucans are present in the P. carinii cell wall and contribute to lung cell inflammatory activation during infection.
炎症是卡氏肺孢子虫肺炎期间呼吸功能损害的主要原因。研究支持细胞壁β-葡聚糖在刺激炎症反应中起重要作用。真菌β-葡聚糖由d-葡萄糖同聚物组成，含有β-1,3-连接的葡萄糖主链和β-1,6-连接的葡萄糖侧链。先前对卡氏肺孢子虫的研究已对该生物体的β-1,3葡聚糖成分进行了表征。然而，最近对其他生物体的研究支持β-1,6葡聚糖起重要作用，主要是介导宿主细胞活化。因此，我们试图表征卡氏肺孢子虫细胞壁中的β-1,6葡聚糖，并确定它们在肺细胞炎症中的活性。免疫染色显示β-1,6在卡氏肺孢子虫包囊壁中有特异性定位。基于同源性的克隆有助于表征卡氏肺孢子虫中一种功能性的卡氏肺孢子虫kre6（Pckre6）β-1,6葡聚糖合酶，当在kre6缺陷型酿酒酵母中表达时，可恢复细胞壁稳定性。最近合成的β-1,6葡聚糖合酶抑制剂降低了分离的卡氏肺孢子虫制剂产生β-1,6碳水化合物的能力。此外，从卡氏肺孢子虫中分离出的β-1,6葡聚糖组分可引发巨噬细胞强烈的肿瘤坏死因子α（TNF-α）反应。宿主细胞质膜微区功能的抑制可显著减弱这些炎症反应。这些研究共同表明，β-1,6葡聚糖存在于卡氏肺孢子虫细胞壁中，并在感染期间促成肺细胞炎症激活。
