Ross Robbi L, Arias-Parbul Kassandra, Douglass Zane M, Adams Katrina L, Santiago-Tirado Felipe H
bioRxiv. 2025 Jul 18:2025.07.17.665466. doi: 10.1101/2025.07.17.665466.
the etiological agent of cryptococcal meningitis (CM), is a globally distributed environmental yeast that mainly causes infections in immunocompromised individuals. Particularly in low-resource countries, the mortality rate of CM can reach 81% and accounts for 19% of HIV/AIDS-related deaths each year. In immunocompromised individuals, once inhaled, escapes from the lungs and disseminates with special predilection for the central nervous system (CNS). Once in the brain, interacts with microglia, the tissue-resident macrophages of the CNS. Previous studies indirectly showed that microglia are ineffective at controlling this fungal infection. The mechanisms underlying this fungal survival and proliferation within the CNS, however, remain unclear. In this study, we use and validate the C20 immortalized human microglia cell line to study cryptococcal-microglia interactions. We show that microglia have limited phagocytic activity that is specific to and partly dependent on cryptococcal antiphagocytic proteins that alter cell size and cell wall structure. We also show human microglia respond to cryptococcal strains differently than peripheral macrophages. Further, we show that human microglia are ineffective at killing phagocytosed , and that this could be due to the ability of this yeast to disrupt phagosome maturation and induce phagosome membrane damage in these cells. These findings provide us with fundamental knowledge regarding cryptococcal pathogenesis in the CNS, specifically insight into how is recognized by microglia under different conditions and demonstrate the usefulness of C20 cells to further study how this yeast survives and replicates within the CNS environment.
While is acquired through inhalation, the fatal pathology of cryptococcal infection occurs when the yeast disseminates to the central nervous system (CNS) and causes cryptococcal meningitis. Microglia are the first immune cells that will encounter once it reaches the CNS, and they are the largest population of macrophages in the brain. While microglia are professional phagocytes, they are unable to control infection. The mechanisms behind uncontrolled growth of within the CNS remains understudied, partly due to a lack of knowledge regarding microglia-cryptococcal interactions. This study provides fundamental knowledge into these interactions and establishes a powerful model to specifically study how is recognized by microglia and how cryptococcal phagosomes mature in these phagocytes. This work opens new avenues of research to further our understanding of cryptococcal-host interactions which can be leveraged to develop more effective therapeutics for cryptococcal meningitis.
新型隐球菌性脑膜炎（CM）的病原体是一种全球分布的环境酵母，主要在免疫功能低下的个体中引起感染。特别是在资源匮乏的国家，CM的死亡率可达81%，每年占与艾滋病相关死亡人数的19%。在免疫功能低下的个体中，一旦吸入，（新型隐球菌）就会从肺部逃逸，并特别倾向于在中枢神经系统（CNS）中传播。一旦进入大脑，（新型隐球菌）就会与小胶质细胞相互作用，小胶质细胞是中枢神经系统中的组织驻留巨噬细胞。先前的研究间接表明，小胶质细胞在控制这种真菌感染方面无效。然而，这种真菌在中枢神经系统内存活和增殖的机制仍不清楚。在本研究中，我们使用并验证了C20永生化人小胶质细胞系来研究新型隐球菌与小胶质细胞的相互作用。我们发现，小胶质细胞的吞噬活性有限，这种活性是新型隐球菌特有的，并且部分依赖于改变细胞大小和细胞壁结构的新型隐球菌抗吞噬蛋白。我们还发现，人小胶质细胞对新型隐球菌菌株的反应与外周巨噬细胞不同。此外，我们发现人小胶质细胞在杀死吞噬的新型隐球菌方面无效，这可能是由于这种酵母能够破坏吞噬体成熟并诱导这些细胞中的吞噬体膜损伤。这些发现为我们提供了关于新型隐球菌在中枢神经系统发病机制的基础知识，特别是深入了解新型隐球菌在不同条件下如何被小胶质细胞识别，并证明了C20细胞在进一步研究这种酵母如何在中枢神经系统环境中存活和复制方面的有用性。
虽然新型隐球菌是通过吸入获得的，但当这种酵母扩散到中枢神经系统并引起新型隐球菌性脑膜炎时，就会发生致命的病理变化。小胶质细胞是新型隐球菌到达中枢神经系统后首先遇到的免疫细胞，并且它们是大脑中最大的巨噬细胞群体。虽然小胶质细胞是专业的吞噬细胞，但它们无法控制新型隐球菌感染。新型隐球菌在中枢神经系统内不受控制生长背后的机制仍未得到充分研究，部分原因是缺乏关于小胶质细胞与新型隐球菌相互作用的知识。本研究为这些相互作用提供了基础知识，并建立了一个强大的模型，以具体研究新型隐球菌如何被小胶质细胞识别以及新型隐球菌吞噬体在这些吞噬细胞中如何成熟。这项工作开辟了新的研究途径，以进一步加深我们对新型隐球菌与宿主相互作用的理解，从而可以利用这些知识开发更有效的新型隐球菌性脑膜炎治疗方法。
