Ring A, Weiser J N, Tuomanen E I
Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
J Clin Invest. 1998 Jul 15;102(2):347-60. doi: 10.1172/JCI2406.
Although Streptococcus pneumoniae is a major cause of meningitis in humans, the mechanisms underlying its traversal from the circulation across the blood-brain barrier (BBB) into the subarachnoid space are poorly understood. One mechanism might involve transcytosis through microvascular endothelial cells. In this study we investigated the ability of pneumococci to invade and transmigrate through monolayers of rat and human brain microvascular endothelial cells (BMEC). Significant variability was found in the invasive capacity of clinical isolates. Phase variation to the transparent phenotype increased invasion as much as 6-fold and loss of capsule approximately 200-fold. Invasion of transparent pneumococci required choline in the pneumococcal cell wall, and invasion was partially inhibited by antagonists of the platelet-activating factor (PAF) receptor on the BMEC. Pneumococci that gained access to an intracellular vesicle from the apical side of the monolayer subsequently were subject to three fates. Most opaque variants were killed. In contrast, the transparent phase variants were able to transcytose to the basal surface of rat and human BMEC in a manner dependent on the PAF receptor and the presence of pneumococcal choline-binding protein A. The remaining transparent bacteria entering the cell underwent a previously unrecognized recycling to the apical surface. Transcytosis eventually becomes a dominating process accounting for up to 80% of intracellular bacteria. Our data suggest that interaction of pneumococci with the PAF receptor results in sorting so as to transcytose bacteria across the cell while non-PAF receptor entry shunts bacteria for exit and reentry on the apical surface in a novel recycling pathway.
尽管肺炎链球菌是人类脑膜炎的主要病因，但其从血液循环穿过血脑屏障（BBB）进入蛛网膜下腔的潜在机制仍知之甚少。一种机制可能涉及通过微血管内皮细胞的转胞吞作用。在本研究中，我们调查了肺炎球菌侵袭并穿过大鼠和人脑微血管内皮细胞（BMEC）单层的能力。临床分离株的侵袭能力存在显著差异。向透明表型的相变使侵袭增加了6倍，而荚膜缺失使侵袭增加了约200倍。透明肺炎球菌的侵袭需要肺炎球菌细胞壁中的胆碱，并且BMEC上血小板活化因子（PAF）受体的拮抗剂可部分抑制侵袭。从单层顶端进入细胞内囊泡的肺炎球菌随后有三种命运。大多数不透明变体被杀死。相反，透明相变变体能够以依赖于PAF受体和肺炎球菌胆碱结合蛋白A的存在的方式转胞吞至大鼠和人BMEC的基底表面。进入细胞的其余透明细菌经历了以前未被认识的向顶端表面的再循环。转胞吞作用最终成为一个占主导地位的过程，占细胞内细菌的80%。我们的数据表明，肺炎球菌与PAF受体的相互作用导致分选，以便细菌穿过细胞进行转胞吞，而非PAF受体进入则使细菌在一种新的再循环途径中从顶端表面排出并重新进入。
