CD8+ T Cells Induce Fatal Brainstem Pathology during Cerebral Malaria via Luminal Antigen-Specific Engagement of Brain Vasculature

Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection that results in thousands of deaths each year, mostly in African children. The in vivo mechanisms underlying this fatal condition are not entirely understood. Using the animal model of experimental cerebral malaria (ECM), we sought mechanistic insights into the pathogenesis of CM. Fatal disease was associated with alterations in tight junction proteins, vascular breakdown in the meninges / parenchyma, edema, and ultimately neuronal cell death in the brainstem, which is consistent with cerebral herniation as a cause of death. At the peak of ECM, we revealed using intravital two-photon microscopy that myelomonocytic cells and parasite-specific CD8+ T cells associated primarily with the luminal surface of CNS blood vessels. Myelomonocytic cells participated in the removal of parasitized red blood cells (pRBCs) from cerebral blood vessels, but were not required for the disease. Interestingly, the majority of disease-inducing parasite-specific CD8+ T cells interacted with the lumen of brain vascular endothelial cells (ECs), where they were observed surveying, dividing, and arresting in a cognate peptide-MHC I dependent manner. These activities were critically dependent on IFN-γ, which was responsible for activating cerebrovascular ECs to upregulate adhesion and antigen-presenting molecules. Importantly, parasite-specific CD8+ T cell interactions with cerebral vessels were impaired in chimeric mice rendered unable to present EC antigens on MHC I, and these mice were in turn resistant to fatal brainstem pathology. Moreover, anti-adhesion molecule (LFA-1 / VLA-4) therapy prevented fatal disease by rapidly displacing luminal CD8+ T cells from cerebrovascular ECs without affecting extravascular T cells. These in vivo data demonstrate that parasite-specific CD8+ T cell-induced fatal vascular breakdown and subsequent neuronal death during ECM is associated with luminal, antigen-dependent interactions with cerebrovasculature.

脑型疟（Cerebral malaria, CM）是恶性疟原虫（Plasmodium falciparum）感染引发的严重并发症，每年造成数千人死亡，其中以非洲儿童居多。目前学界尚未完全阐明该致命病症的体内发病机制。本研究借助实验性脑型疟（experimental cerebral malaria, ECM）动物模型，旨在阐明脑型疟的致病机制。致命性疾病进展与紧密连接蛋白（tight junction proteins）表达异常、脑膜与脑实质的血管破坏、水肿形成，最终导致脑干神经元细胞死亡密切相关，该病理特征与脑疝致死的表现一致。在ECM病程峰值阶段，我们通过活体双光子显微镜（intravital two-photon microscopy）成像发现，髓单核细胞与寄生虫特异性CD8+ T细胞主要黏附于中枢神经系统（Central Nervous System, CNS）血管的腔面。髓单核细胞可参与清除脑血管内被寄生虫感染的红细胞（parasitized red blood cells, pRBCs），但并非疾病发生所必需。值得注意的是，多数诱导疾病发生的寄生虫特异性CD8+ T细胞与脑血管内皮细胞（vascular endothelial cells, ECs）的管腔表面相互作用，在此过程中可观察到它们以同源肽-MHC I类分子（cognate peptide-MHC I）依赖的方式进行抗原监测、增殖及黏附停滞。上述过程严格依赖干扰素-γ（IFN-γ），该细胞因子可激活脑血管内皮细胞，使其上调黏附分子与抗原呈递分子的表达。重要的是，在无法通过MHC I类分子呈递内皮细胞抗原的嵌合小鼠（chimeric mice）中，寄生虫特异性CD8+ T细胞与脑血管的相互作用受到损害，此类小鼠也对致命性脑干病理产生了抵抗力。此外，针对淋巴细胞功能相关抗原1与极晚活化抗原4（LFA-1 / VLA-4）这两类黏附分子的治疗，可通过快速将腔面CD8+ T细胞从脑血管内皮细胞上解离且不影响血管外T细胞，从而阻止致命性疾病的发生。本研究的体内实验数据表明，在ECM病程中，寄生虫特异性CD8+ T细胞诱导的致命性血管破坏及后续神经元死亡，与细胞在管腔面与脑血管发生的抗原依赖性相互作用密切相关。