Human FcγRII Cytoplasmic Domains Differentially Influence Antibody-Mediated Dengue Virus Infection

Ab-dependent enhancement (ADE) of dengue virus (DENY) infection is mediated through the interaction of viral immune complexes with Fc gamma Rs, with notable efficiency of Fc gamma RII. Most human dengue target cells coexpress activating (Fc gamma RIIa) and inhibitory (Fc gamma RIIb) isoforms, but their relative roles in ADE are not well understood. We studied the effects of Fc gamma RIIa and Fc gamma RIIb by transfecting cells to express each individual receptor isoform or through coexpression of both isoforms. We showed that although both isoforms similarly bind dengue-immune complexes, Fc gamma RIIa efficiently internalized virus leading to productive cellular infection, unlike Fc gamma RIIb. We next focused on the main discriminating feature of these isoforms: their distinct intra-cytoplasmic tails (Fcy gamma IIa with an immunoreceptor tyrosine-based activation motif [ITAM] and Fc gamma RIIb with an immunoreceptor tyrosine-based inhibitory motif [ITIM]). We engineered cells to express "swapped" versions of their Fc gamma RII by switching the cytoplasmic tails containing the ITAM/ITIM motifs, leaving the remainder of the receptor intact. Our data show that both Fc gamma RIIa and Fc gamma RIIb comparably bind dengue immune complexes. However, wild type Fc gamma RIIa facilitates DENY entry by virtue of the ITAM motif, whereas the swapped version Fc gamma RIIa-ITIM significantly inhibited ADE. Similarly, replacing the inhibitory motif in Fc gamma RIIb with an ITAM (Fc gamma RIIb-ITAM) reconstituted ADE capacity to levels of the wild type activating counterpart, Fc gamma RIIa. Our data suggest that Fc gamma RIIa and Fc gamma RIIb isoforms, as the most abundantly distributed class II Fc gamma receptors, differentially influence Ab-mediated DENY infection under ADE conditions both at the level of cellular infection and viral production.