Receptors involved in the phagocytosis of microorganisms under nonopsonic conditions have been little studied in neutrophils. Complement receptor type 3 (CR3) is a pattern recognition receptor able to internalize zymosan and C3bi-coated particles. We report that Abs directed against CR3 strongly inhibited nonopsonic phagocytosis of Mycobacterium kansasii in human neutrophils. In these cells CR3 has been found associated with several GPI-anchored proteins localized in cholesterol-rich microdomains (rafts) of the plasma membrane. Cholesterol sequestration by nystatin, filipin, or beta-cyclodextrin as well as treatment of neutrophils with phosphatidylinositol phospholipase C to remove GPI-anchored proteins from the cell surface markedly inhibited phagocytosis of M. kansasii, without affecting phagocytosis of zymosan or serum-opsonized M. kansasii. Abs directed against several GPI-anchored proteins inhibited phagocytosis of M. kansasii, but not of zymosan. N:-acetyl-D-glucosamine, which is known to disrupt interactions between CR3 and GPI proteins, also strongly diminished phagocytosis of these mycobacteria. In conclusion, phagocytosis of M. kansasii involved CR3, GPI-anchored receptors, and cholesterol. In contrast, phagocytosis of zymosan or opsonized particles involved CR3, but not cholesterol or GPI proteins. We propose that CR3, when associated with a GPI protein, relocates in cholesterol-rich domains where M. kansasii are internalized. When CR3 is not associated with a GPI protein, it remains outside of these domains and mediates phagocytosis of zymosan and opsonized particles, but not of M. kansasii.

译文

:在中性粒细胞中很少研究非调理条件下参与微生物吞噬作用的受体。 3型补体受体(CR3)是一种模式识别受体,能够内化酵母聚糖和C3bi包被的颗粒。我们报道,针对CR3的Abs强烈抑制人嗜中性粒细胞中堪萨斯分枝杆菌的非调理吞噬作用。在这些细胞中,已发现CR3与定位在质膜富含胆固醇的微区(筏)中的几种GPI锚定蛋白有关。制霉菌素,菲利普林或β-环糊精的胆固醇隔离以及用磷脂酰肌醇磷脂酶C处理嗜中性白细胞从细胞表面去除GPI锚定的蛋白显着抑制了堪萨斯支原体的吞噬作用,而又不影响酵母聚糖的吞噬作用或血清调理的M.堪萨斯州。针对几种GPI锚定蛋白的Abs抑制了堪萨斯分枝杆菌的吞噬作用,但抑制了酵母聚糖的吞噬作用。众所周知,N:-乙酰基-D-葡萄糖胺会破坏CR3和GPI蛋白之间的相互作用,也大大降低了这些分枝杆菌的吞噬作用。总之,堪萨斯分枝杆菌的吞噬作用涉及CR3,GPI锚定受体和胆固醇。相反,酵母聚糖或调理过的颗粒的吞噬作用涉及CR3,但不涉及胆固醇或GPI蛋白。我们建议CR3,当与GPI蛋白相关时,重新定位在坎萨西分枝杆菌被内化的富含胆固醇的域中。当CR3与GPI蛋白不相关时,它将保留在这些结构域之外,并介导酵母聚糖和调理过的颗粒的吞噬作用,而不是堪萨斯分枝杆菌的吞噬作用。

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