The circumventricular organs (CVOs) in the brain are without a blood-brain barrier (BBB) and as such directly exposed to blood plasma constituents and blood-borne pathogens. In light of previous studies showing discrepancies regarding the immunocompetence of these organs, we initiated the present study to provide a comprehensive immunohistochemical analysis of the cellular expression of immune-associated antigens within the pineal gland, area postrema and the subfornical organ. In all CVOs, subpopulations of cells morphologically similar to complement receptor type 3 immunoreactive microglial/macrophage cells expressed major histocompatibility complex (MHC) class II antigen, leucocyte common antigen (LCA/CD45), as well as CD4 and ED1 antigen. Based on morphological criteria the MHC class II antigen expressing cells could be grouped into a major population of classical parenchymal and perivascular ramified microglial cells and a minor population presenting itself as scattered or small groups of rounded macrophage-like cells. CD4 and ED1 antigen were expressed by both cell types. CD45 was preferentially expressed by macrophage-like cells. MHC class I antigen was expressed by the vascular endothelium in both BBB-protected and BBB-deficient areas and was additionally present as a lattice-like network throughout the BBB-deficient parenchyma in all CVOs. The results suggest that the BBB-free areas of the brain besides being constantly surveyed by blood-borne macrophages, possess an intrinsic immune surveillance system based on resting and activated microglial cells, which may function as a non-endothelial, cellular barrier against blood-borne pathogens.

译文

大脑中的室间隔器官(CVO)没有血脑屏障(BBB),因此直接暴露于血浆成分和血源性病原体。鉴于先前的研究表明这些器官的免疫能力存在差异,我们启动了本研究,以提供对松果体,视网膜后区域和分支下器官内免疫相关抗原的细胞表达的全面免疫组织化学分析。在所有CVO中,与补体受体3型免疫反应性小胶质细胞/巨噬细胞细胞形态相似的细胞亚群表达了主要的组织相容性复合物(MHC)II类抗原,白细胞常见抗原(LCA / CD45)以及CD4和ED1抗原。根据形态学标准,可以将表达MHC II类抗原的细胞分为经典的实质和血管周围分枝的小神经胶质细胞的主要群体,以及表现为散在的或成团的圆形巨噬细胞样细胞的少数群体。 CD4和ED1抗原通过两种细胞类型表达。 CD45优先由巨噬细胞样细胞表达。 MHC I类抗原在BBB保护区和BBB缺失区均由血管内皮表达,并在所有CVO中的整个BBB缺失实质中均呈格子状网络存在。结果表明,除了大脑中无血脑屏障的区域不断被血源性巨噬细胞检查外,还具有基于静止和活化的小胶质细胞的内在免疫监视系统,该系统可能起非内皮细胞屏障的作用。传播的病原体。

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