Department of Neurology, University of Texas John P. and Kathrine G. McGovern Medical School, Houston, TX, USA.
UTHealth Graduate School of Biomedical Sciences, University of Texas MD Anderson Cancer Center, Houston, USA.
J Neuroinflammation. 2020 Dec 1;17(1):366. doi: 10.1186/s12974-020-02019-5.
The ability to distinguish resident microglia from infiltrating myeloid cells by flow cytometry-based surface phenotyping is an important technique for examining age-related neuroinflammation. The most commonly used surface markers for the identification of microglia include CD45 (low-intermediate expression), CD11b, Tmem119, and P2RY12.
In this study, we examined changes in expression levels of these putative microglia markers in in vivo animal models of stroke, cerebral amyloid angiopathy (CAA), and aging as well as in an ex vivo LPS-induced inflammation model.
We demonstrate that Tmem119 and P2RY12 expression is evident within both CD45 and CD45 myeloid populations in models of stroke, CAA, and aging. Interestingly, LPS stimulation of FACS-sorted adult microglia suggested that these brain-resident myeloid cells can upregulate CD45 and downregulate Tmem119 and P2RY12, making them indistinguishable from peripherally derived myeloid populations. Importantly, our findings show that these changes in the molecular signatures of microglia can occur without a contribution from the other brain-resident or peripherally sourced immune cells.
We recommend future studies approach microglia identification by flow cytometry with caution, particularly in the absence of the use of a combination of markers validated for the specific neuroinflammation model of interest. The subpopulation of resident microglia residing within the "infiltrating myeloid" population, albeit small, may be functionally important in maintaining immune vigilance in the brain thus should not be overlooked in neuroimmunological studies.
通过流式细胞术表面表型鉴定来区分驻留小胶质细胞和浸润髓样细胞的能力是研究年龄相关神经炎症的重要技术。用于鉴定小胶质细胞的最常用表面标志物包括 CD45（低-中等表达）、CD11b、Tmem119 和 P2RY12。
在这项研究中，我们检查了这些假定的小胶质细胞标志物在中风、脑淀粉样血管病 (CAA) 和衰老的体内动物模型以及体外 LPS 诱导的炎症模型中的表达水平变化。
我们证明 Tmem119 和 P2RY12 的表达在中风、CAA 和衰老的模型中的 CD45 和 CD45 髓样细胞群体中都很明显。有趣的是，LPS 刺激 FACS 分选的成年小胶质细胞表明这些脑驻留的髓样细胞可以上调 CD45 并下调 Tmem119 和 P2RY12，使它们与外周来源的髓样细胞群体无法区分。重要的是，我们的研究结果表明，小胶质细胞的分子特征的这些变化可以在没有其他脑驻留或外周来源免疫细胞贡献的情况下发生。
我们建议未来的研究在使用流式细胞术鉴定小胶质细胞时要谨慎，特别是在没有使用针对特定神经炎症模型的组合标记物的情况下。尽管驻留在“浸润性髓样”群体中的小胶质细胞亚群很小，但在维持大脑中的免疫监视方面可能具有重要的功能，因此不应在神经免疫学研究中被忽视。
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