Rodrigo W W Shanaka I, Jin Xia, Blackley Shanley D, Rose Robert C, Schlesinger Jacob J
Division of Infectious Diseases, Department of Medicine, University of Rochester School of Medicine and Dentistry, Box 689, 601 Crittenden Avenue, Rochester, NY 14642, USA.
J Virol. 2006 Oct;80(20):10128-38. doi: 10.1128/JVI.00792-06.
Fcgamma receptor (FcgammaR)-mediated entry of infectious dengue virus immune complexes into monocytes/macrophages is hypothesized to be a key event in the pathogenesis of complicated dengue fever. FcgammaRIA (CD64) and FcgammaRIIA (CD32), which predominate on the surface of such dengue virus-permissive cells, were compared for their influence on the infectivity of dengue 2 virus immune complexes formed with human dengue virus antibodies. A signaling immunoreceptor tyrosine-based activation motif (ITAM) incorporated into the accessory gamma-chain subunit that associates with FcgammaRIA and constitutively in FcgammaRIIA is required for phagocytosis mediated by these receptors. To determine whether FcgammaRIA and FcgammaRIIA activation functions are also required for internalization of infectious dengue virus immune complexes, we generated native and signaling-incompetent versions of each receptor by site-directed mutagenesis of ITAM tyrosine residues. Plasmids designed to express these receptors were transfected into COS-7 cells, and dengue virus replication was measured by plaque assay and flow cytometry. We found that both receptors mediated enhanced dengue virus immune complex infectivity but that FcgammaRIIA appeared to do so far more effectively. Abrogation of FcgammaRIA signaling competency, either by expression without gamma-chain or by coexpression with gamma-chain mutants, was associated with significant impairment of phagocytosis and of dengue virus immune complex infectivity. Abrogation of FcgammaRIIA signaling competency was also associated with equally impaired phagocytosis but had no discernible effect on dengue virus immune complex infectivity. These findings point to fundamental differences between FcgammaRIA and FcgammaRIIA with respect to their immune-enhancing capabilities and suggest that different mechanisms of dengue virus immune complex internalization may operate between these FcgammaRs.
Fcγ受体（FcγR）介导感染性登革病毒免疫复合物进入单核细胞/巨噬细胞被认为是重症登革热发病机制中的关键事件。比较了在此类登革病毒易感细胞表面占主导的FcγRIA（CD64）和FcγRIIA（CD32）对与人类登革病毒抗体形成的登革2病毒免疫复合物感染性的影响。这些受体介导的吞噬作用需要一个基于免疫受体酪氨酸的激活基序（ITAM），该基序整合到与FcγRIA相关的辅助γ链亚基中，并在FcγRIIA中组成性存在。为了确定感染性登革病毒免疫复合物的内化是否也需要FcγRIA和FcγRIIA的激活功能，我们通过对ITAM酪氨酸残基进行定点诱变，生成了每种受体的天然和无信号传导能力版本。将设计用于表达这些受体的质粒转染到COS-7细胞中，并通过空斑试验和流式细胞术测量登革病毒复制情况。我们发现两种受体都介导登革病毒免疫复合物感染性增强，但FcγRIIA似乎更有效。通过不与γ链一起表达或与γ链突变体共表达来消除FcγRIA的信号传导能力，与吞噬作用和登革病毒免疫复合物感染性的显著受损有关。消除FcγRIIA的信号传导能力也与吞噬作用同样受损有关，但对登革病毒免疫复合物感染性没有明显影响。这些发现指出了FcγRIA和FcγRIIA在免疫增强能力方面的根本差异，并表明这些FcγR之间可能存在不同的登革病毒免疫复合物内化机制。
