van Vugt M J, Heijnen I A, Capel P J, Park S Y, Ra C, Saito T, Verbeek J S, van de Winkel J G
Department of Immunology, University Hospital Utrecht, The Netherlands.
Blood. 1996 May 1;87(9):3593-9.
Most Ig receptors exist as hetero-oligomeric complexes with separate ligand binding (alpha) and signal transducing (beta, gamma, or zeta) subunits. For Fc gamma RIIIa and Fc epsilon RI, association with the FcR gamma-chain is essential for surface expression. However, the human high affinity IgG receptor, hFc gamma RI, was found to be surface-expressed by itself in transient transfection models. We have now analyzed the integrity of hFc gamma RI expression in more detail in stable transfectants. In vitro we noted that, in the absence of FcR gamma-chain, surface expression of hFc gamma RI rapidly declined to background levels, in both IIA1.6 B cells and NIH3T3 fibroblasts. The effect of FcR gamma-chain on hFc gamma RI surface expression in vivo was evaluated by using two newly generated transgenic mouse lines, selectively expressing hFc gamma RI on myeloid cells. These transgenic mice were crossed with FcR gamma-chain-deficient mice. Analysis of blood monocytes and peritoneal macrophages showed that surface expression of hFc gamma RI was reduced by approximately 80%. The remaining approximately 20% of receptors were still capable of binding IgG-opsonized RBC, suggesting FcR gamma-chain not to be critical for hFc gamma RI ligand-binding capacity. Importantly, however, hFc gamma RI signaling capacity was lost in FcR gamma-chain-deficient cells. No phagocytosis could be observed using either ligand sensitized (EA-IgG2a) or CD64-targeted erythrocytes (using a bispecific antibody) in both hFc gamma RI transgenic lines. This documents the FcR gamma-chain to be indispensable for both surface membrane expression and function of human Fc gamma RI in vivo.
大多数免疫球蛋白（Ig）受体以异源寡聚体复合物的形式存在，具有独立的配体结合（α）和信号转导（β、γ或ζ）亚基。对于FcγRIIIa和FcεRI，与FcRγ链的结合对于其表面表达至关重要。然而，在瞬时转染模型中发现人类高亲和力IgG受体hFcγRI可自行在表面表达。我们现在在稳定转染细胞中更详细地分析了hFcγRI表达的完整性。在体外，我们注意到，在没有FcRγ链的情况下，hFcγRI在IIA1.6 B细胞和NIH3T3成纤维细胞中的表面表达均迅速下降至背景水平。通过使用两个新生成的转基因小鼠品系来评估FcRγ链在体内对hFcγRI表面表达的影响，这两个品系在髓系细胞上选择性表达hFcγRI。将这些转基因小鼠与FcRγ链缺陷小鼠杂交。对血液单核细胞和腹腔巨噬细胞的分析表明，hFcγRI的表面表达降低了约80%。其余约20%的受体仍能够结合IgG调理的红细胞，这表明FcRγ链对于hFcγRI的配体结合能力并非至关重要。然而，重要的是，在FcRγ链缺陷细胞中hFcγRI的信号传导能力丧失。在两个hFcγRI转基因品系中，无论是使用配体致敏的（EA-IgG2a）还是靶向CD64的红细胞（使用双特异性抗体），均未观察到吞噬作用。这证明FcRγ链对于人类FcγRI在体内的表面膜表达和功能均不可或缺。
