Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska, USA.
College of Information Science and Technology, University of Nebraska at Omaha, Omaha, Nebraska, USA.
Infect Immun. 2018 Nov 20;86(12). doi: 10.1128/IAI.00684-18. Print 2018 Dec.
Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature monocytes and granulocytes. While neutrophils (polymorphonuclear leukocytes [PMNs]) are classically identified as highly differentiated cells specialized for antimicrobial defense, our laboratory has reported minor contributions of PMNs to the immune response during biofilm infection. However, these two cell types can be difficult to differentiate because of shared surface marker expression. Here we describe a more refined approach to distinguish MDSCs from PMNs utilizing the integrin receptor CD11b combined with conventional Ly6G and Ly6C expression. This approach separated the Ly6G Ly6C population that we previously identified in a mouse model of orthopedic implant infection into two subsets, namely, CD11b Ly6G Ly6C MDSCs and CD11b Ly6G Ly6C PMNs, which was confirmed by characteristic nuclear morphology using cytospins. CD11b Ly6G Ly6C MDSCs suppressed T cell proliferation throughout the 28-day infection period, whereas CD11b Ly6G Ly6C PMNs had no effect early (day 3 postinfection), although this population acquired suppressive activity at later stages of biofilm development. To further highlight the distinctions between biofilm-associated MDSCs and PMNs versus monocytes, transcriptional profiles were compared by transcriptome sequencing (RNA-Seq). A total of 6,466 genes were significantly differentially expressed in MDSCs versus monocytes, whereas only 297 genes were significantly different between MDSCs and PMNs. A number of genes implicated in cell cycle regulation were identified, and ethynyldeoxyuridine (EdU) labeling revealed that approximately 50% of MDSCs proliferated locally at the site of biofilm infection. Based on their similar transcriptomic profiles to those of PMNs, biofilm-associated MDSCs are of a granulocytic lineage and can be classified as granulocytic MDSCs (G-MDSCs).
髓系来源的抑制细胞 (MDSCs) 是一种异质性的未成熟单核细胞和粒细胞群体。虽然中性粒细胞（多形核白细胞 [PMN]）被经典地鉴定为专门用于抗微生物防御的高度分化细胞，但我们的实验室报告称，PMN 在生物膜感染期间对免疫反应的贡献较小。然而，由于共同的表面标志物表达，这两种细胞类型可能难以区分。在这里，我们描述了一种更精细的方法，利用整合素受体 CD11b 结合传统的 Ly6G 和 Ly6C 表达来区分 MDSC 和 PMN。这种方法将我们之前在骨科植入物感染的小鼠模型中鉴定的 Ly6G Ly6C 群体分为两个亚群，即 CD11b Ly6G Ly6C MDSC 和 CD11b Ly6G Ly6C PMN，这通过使用细胞涂片确认了特征性的核形态得到证实。CD11b Ly6G Ly6C MDSC 在整个 28 天的感染期间抑制 T 细胞增殖，而 CD11b Ly6G Ly6C PMN 在感染后 3 天（早期）没有影响，尽管该群体在生物膜发育的后期获得了抑制活性。为了进一步强调生物膜相关 MDSC 和 PMN 与单核细胞之间的区别，通过转录组测序 (RNA-Seq) 比较了转录谱。MDSC 与单核细胞相比，共有 6466 个基因显著差异表达，而 MDSC 与 PMN 之间仅有 297 个基因显著不同。鉴定出一些与细胞周期调节相关的基因，并且 EdU 标记显示大约 50%的 MDSC 在生物膜感染部位局部增殖。基于它们与 PMN 相似的转录组谱，生物膜相关的 MDSC 具有粒细胞谱系，可以被分类为粒细胞 MDSC (G-MDSC)。
