Socolovsky M, Hockaday A R, Allen J M
Physiological Laboratory, University of Cambridge, United Kingdom.
Eur J Cell Biol. 1994 Jun;64(1):29-44.
The high-affinity receptor (Fc gamma RI) for the constant (Fc) portion of immunoglobulin G (IgG) is one of three Fc IgG receptor classes (Fc gamma Rs) found on mononuclear phagocytes. The functional specialization of each of the Fc gamma R classes is not well understood. Previous studies utilizing anti-Fc gamma R monoclonal antibodies (mAbs) as opsonins suggest that Fc gamma RI, like the other Fc gamma Rs expressed by macrophages, is able to mediate phagocytosis. The ability of Fc gamma RI to mediate pinocytosis, however, had not been certain, since it binds, but does not mediate, internalization of monomeric IgG in the monocytoid U937 cells. We studied Fc gamma RI-mediated internalization by introducing it into the Fc gamma R-negative fibroblastic COS cells. We found, using electron microscopy and fluorescence microscopy, that COS cells expressing Fc gamma RI are able to phagocytose IgG-coated zymosan particles and sheep red blood cells (SRBC), as well as pinocytose cross-linked IgG. There was no intracellular accumulation of monomeric IgG. Chimeric receptors which retain the extracellular domains of Fc gamma RI but lack the entire wild-type transmembrane and intracellular regions of the receptor mediated both phagocytosis and pinocytosis with equal or increased efficiency when compared to the wild-type receptor. Control COS cells transfected with CD2 rosetted, but did not phagocytose, SRBC. Attachment of phagocytic targets to COS cells is therefore not sufficient for phagocytosis. Taken together, this suggests that the extracellular domain of Fc gamma RI is sufficient for it to mediate phagocytosis and pinocytosis in this system.
免疫球蛋白G（IgG）恒定（Fc）部分的高亲和力受体（FcγRI）是单核吞噬细胞上发现的三种Fc IgG受体类别（FcγRs）之一。对每种FcγR类别的功能特化了解尚不充分。以往利用抗FcγR单克隆抗体（mAb）作为调理素的研究表明，FcγRI与巨噬细胞表达的其他FcγRs一样，能够介导吞噬作用。然而，FcγRI介导胞饮作用的能力并不确定，因为它能结合但不介导单核细胞样U937细胞中单体IgG的内化。我们通过将FcγRI导入FcγR阴性的成纤维细胞COS细胞来研究其介导的内化作用。我们利用电子显微镜和荧光显微镜发现，表达FcγRI的COS细胞能够吞噬IgG包被的酵母聚糖颗粒和绵羊红细胞（SRBC），也能胞饮交联的IgG。单体IgG在细胞内没有积累。与野生型受体相比，保留FcγRI细胞外结构域但缺乏整个野生型跨膜和细胞内区域的嵌合受体介导吞噬作用和胞饮作用的效率相同或更高。转染了CD2的对照COS细胞能形成玫瑰花结，但不吞噬SRBC。因此，吞噬靶标与COS细胞的附着不足以引发吞噬作用。综上所述，这表明FcγRI的细胞外结构域足以在该系统中介导吞噬作用和胞饮作用。
