Liu Wei, Li Hao, Kämpfe Nordström Charlotta, Danckwardt-Lillieström Niklas, Agrawal Sumit, Ladak Hanif M, Rask-Andersen Helge
Department of Surgical Sciences, Otorhinolaryngology and Head and Neck Surgery, Uppsala University, Uppsala, Sweden.
Department of Otolaryngology-Head and Neck Surgery, Western University, London, ON, Canada.
Front Neurol. 2024 May 16;15:1355785. doi: 10.3389/fneur.2024.1355785. eCollection 2024.
Despite its location near infection-prone areas, the human inner ear demonstrates remarkable resilience. This suggests that there are inherent instruments deterring the invasion and spread of pathogens into the inner ear. Here, we combined high-resolution light microscopy, super-resolution immunohistochemistry (SR-SIM) and synchrotron phase contrast imaging (SR-PCI) to identify the protection and barrier systems in the various parts of the human inner ear, focusing on the lateral wall, spiral ganglion, and endolymphatic sac.
Light microscopy was conducted on mid-modiolar, semi-thin sections, after direct glutaraldehyde/osmium tetroxide fixation. The tonotopic locations were estimated using SR-PCI and 3D reconstruction in cadaveric specimens. The sections were analyzed for leucocyte and macrophage activity, and the results were correlated with immunohistochemistry using confocal microscopy and SR-SIM.
Light microscopy revealed unprecedented preservation of cell anatomy and several macrophage-like cells that were localized in the cochlea. Immunohistochemistry demonstrated IBA1 cells frequently co-expressing MHC II in the spiral ganglion, nerve fibers, lateral wall, spiral limbus, and tympanic covering layer at all cochlear turns as well as in the endolymphatic sac. RNAscope assays revealed extensive expression of fractalkine gene transcripts in type I spiral ganglion cells. CD4 and CD8 cells occasionally surrounded blood vessels in the modiolus and lateral wall. TMEM119 and P2Y12 were not expressed, indicating that the cells labeled with IBA1 were not microglia. The round window niche, compact basilar membrane, and secondary spiral lamina may form protective shields in the cochlear base.
The results suggest that the human cochlea is surveilled by dwelling and circulating immune cells. Resident and blood-borne macrophages may initiate protective immune responses via chemokine signaling in the lateral wall, spiral lamina, and spiral ganglion at different frequency locations. Synchrotron imaging revealed intriguing protective barriers in the base of the cochlea. The role of the endolymphatic sac in human inner ear innate and adaptive immunity is discussed.
尽管人类内耳位于易感染区域附近，但其具有显著的抵抗力。这表明存在内在机制可阻止病原体侵入和扩散至内耳。在此，我们结合高分辨率光学显微镜、超分辨率免疫组织化学（SR - SIM）和同步辐射相衬成像（SR - PCI）来识别人类内耳各部分的保护和屏障系统，重点关注外侧壁、螺旋神经节和内淋巴囊。
在直接经戊二醛/四氧化锇固定后，对中轴位半薄切片进行光学显微镜检查。在尸体标本中使用SR - PCI和三维重建估计音频定位。分析切片中的白细胞和巨噬细胞活性，并将结果与共聚焦显微镜和SR - SIM免疫组织化学结果相关联。
光学显微镜显示细胞解剖结构得到前所未有的保存，且在耳蜗中发现了几种巨噬细胞样细胞。免疫组织化学表明，IBA1细胞在所有耳蜗转弯处的螺旋神经节、神经纤维、外侧壁、螺旋缘和鼓膜覆盖层以及内淋巴囊中频繁共表达MHC II。RNAscope分析显示I型螺旋神经节细胞中大量表达趋化因子基因转录本。CD4和CD8细胞偶尔围绕蜗轴和外侧壁的血管。未表达TMEM119和P2Y12，表明标记为IBA1的细胞不是小胶质细胞。圆窗龛、致密基底膜和第二螺旋板可能在耳蜗底部形成保护屏障。
结果表明人类耳蜗受到驻留和循环免疫细胞的监测。驻留和血源性巨噬细胞可能通过趋化因子信号通路在不同频率位置的外侧壁、螺旋板和螺旋神经节引发保护性免疫反应。同步辐射成像揭示了耳蜗底部有趣的保护屏障。对内淋巴囊在人类内耳固有免疫和适应性免疫中的作用进行了讨论。
