Microglia, the resident immune cells of the central nervous system, are not a homogeneous population; their morphology, molecular profile, and even their ultrastructure greatly vary from one cell to another. Recent advances in the field of neuroimmunology have helped to demystify the enigma that currently surrounds microglial heterogeneity. Indeed, numerous microglial subtypes have been discovered such as the disease-associated microglia, neurodegenerative phenotype, and Cd11c-positive developmental population. Another subtype is the dark microglia (DM), a population defined by its ultrastructural changes associated with cellular stress. Since their first characterization using transmission electron microscopy, they have been identified in numerous disease conditions, from mouse models of Alzheimer's disease, schizophrenia, fractalkine signaling deficiency to chronic stress, just to name a few. A recent study also identified the presence of cells with a similar ultrastructure to the DM in postmortem brain samples from schizophrenic patients, underlining the importance of understanding the function of these cells. In this minireview, we aim to summarize the current knowledge on the DM, from their initial ultrastructural characterization to their documentation in various pathological contexts across multiple species. We will also highlight the current limitations surrounding the study of these cells and the future that awaits the DM.

中文翻译：

---

在小胶质细胞的黑暗面发光。

小胶质细胞是中枢神经系统的常驻免疫细胞，它不是一个同质的群体。它们的形态、分子特征，甚至它们的超微结构因一个细胞而异。神经免疫学领域的最新进展有助于揭开目前围绕小胶质细胞异质性的谜团。事实上，已经发现了许多小胶质细胞亚型，例如疾病相关的小胶质细胞、神经退行性表型和 Cd11c 阳性发育群体。另一种亚型是暗小胶质细胞 (DM)，这是一种由与细胞压力相关的超微结构变化定义的群体。自从他们第一次使用透射电子显微镜进行表征以来，他们已经在多种疾病条件下被识别出来，从阿尔茨海默病、精神分裂症、fractalkine 信号缺陷导致慢性压力，仅举几例。最近的一项研究还发现，精神分裂症患者的死后大脑样本中存在与 DM 具有相似超微结构的细胞，这强调了了解这些细胞功能的重要性。在这篇小综述中，我们旨在总结关于 DM 的当前知识，从它们最初的超微结构表征到它们在多个物种的各种病理背景下的记录。我们还将强调围绕这些细胞研究的当前局限性以及等待 DM 的未来。强调了解这些细胞功能的重要性。在这篇小综述中，我们旨在总结关于 DM 的当前知识，从它们最初的超微结构表征到它们在多个物种的各种病理背景下的记录。我们还将强调围绕这些细胞研究的当前局限性以及等待 DM 的未来。强调了解这些细胞功能的重要性。在这篇小综述中，我们旨在总结关于 DM 的当前知识，从它们最初的超微结构表征到它们在多个物种的各种病理背景下的记录。我们还将强调围绕这些细胞研究的当前局限性以及等待 DM 的未来。