Kiss A L, Jost C R, Fransen J A, Onderwater J J, Ginsel L A
Laboratory I of Electron Microscopy, Semmelweis University of Medicine, Budapest, Hungary.
J Submicrosc Cytol Pathol. 1991 Oct;23(4):649-57.
The internalization of peroxidase-antiperoxidase (PAP) immune complexes by human neutrophil granulocytes was studied at an ultrastructural level. PAP initially bound to the plasma membrane at 4 degrees C accumulated in endosomes within 5 min of internalization. By that time, all of the ligand bound to the plasma membrane had been removed from the cell surface and the cells were able to bind newly added PAP. Pre-embedding labelling of FcRIII on these cells showed that this receptor was present on the cell surface, indicating involvement of FcRIII in the rebinding of PAP in neutrophils. The origin of FcRIII present on the plasma membrane after Fc receptor-mediated internalization of PAP was investigated in another series of experiments. Incubation of the cells with pronase eliminated the epitope on the Fc receptor recognized by anti-FcRIII. After the pronase treatment hardly any Fc receptors were detected on the plasma membrane. However, incubation of the cells for only 5 min in a protease-free medium after the pronase treatment led to an abundance of FcRIII on the plasma membrane of the neutrophils. These findings support the hypothesis that FcRIII on the plasma membrane of human neutrophil granulocytes is replenished from an internal source of free Fc receptors and suggest that at least some of the receptors present on the cell surface after the binding and internalization of PAP originate from this source in the cytoplasm.
在超微结构水平上研究了人中性粒细胞对过氧化物酶-抗过氧化物酶（PAP）免疫复合物的内化作用。PAP最初在4℃时结合到质膜上，内化5分钟内积聚在内体中。此时，所有结合到质膜上的配体已从细胞表面去除，细胞能够结合新添加的PAP。对这些细胞上的FcRIII进行预包埋标记表明，该受体存在于细胞表面，表明FcRIII参与了中性粒细胞中PAP的再结合。在另一系列实验中，研究了PAP经Fc受体介导内化后质膜上存在的FcRIII的来源。用链霉蛋白酶处理细胞消除了抗FcRIII识别的Fc受体上的表位。链霉蛋白酶处理后，在质膜上几乎检测不到任何Fc受体。然而，链霉蛋白酶处理后，将细胞在无蛋白酶培养基中仅孵育5分钟，导致中性粒细胞质膜上出现大量FcRIII。这些发现支持了这样的假说，即人中性粒细胞质膜上的FcRIII由游离Fc受体的内源性来源补充，并且表明PAP结合和内化后细胞表面存在的至少一些受体源自细胞质中的该来源。
