Epitope specificity plays a critical role in regulating antibody-dependent cell-mediated cytotoxicity against influenza A virus

Abstract

The generation of strain-specific neutralizing antibodies against influenza A virus is known to confer potent protection against homologous infections. The majority of these antibodies bind to the hemagglutinin (HA) head domain and function by blocking the receptor binding site, preventing infection of host cells. Recently, elicitation of broadly neutralizing antibodies which target the conserved HA stalk domain has become a promising "universal" influenza virus vaccine strategy. The ability of these antibodies to elicit Fc-dependent effector functions has emerged as an important mechanism through which protection is achieved in vivo. However, the way in which Fc-dependent effector functions are regulated by polyclonal influenza virus-binding antibody mixtures in vivo has never been defined. Here, we demonstrate that interactions among viral glycoprotein-binding antibodies of varying specificities regulate the magnitude of antibody-dependent cell-mediated cytotoxicity induction. We show that the mechanism responsible for this phenotype relies upon competition for binding to HA on the surface of infected cells and virus particles. Nonneutralizing antibodies were poor inducers and did not inhibit antibody-dependent cell-mediated cytotoxicity. Interestingly, anti-neuraminidase antibodies weakly induced antibody-dependent cell-mediated cytotoxicity and enhanced induction in the presence of HA stalk-binding antibodies in an additive manner. Our data demonstrate that antibody specificity plays an important role in the regulation of ADCC, and that cross-talk among antibodies of varying specificities determines the magnitude of Fc receptor-mediated effector functions.T he discovery and ongoing characterization of broadly neutralizing antibodies (bnAbs) that bind to the hemagglutinin (HA) stalk domain of influenza A viruses (IAVs) has galvanized promising new efforts to generate a universal influenza virus vaccine (1). A number of studies have now firmly established that stalk-specific bnAbs, normally present in low quantities, can be boosted substantially in humans following exposure to HA subtypes with antigenically foreign head domains (2-8). Sequential vaccination of animals with chimeric HAs or with "headless" vaccine constructs have effectively recapitulated the boosting of bnAbs observed in humans after exposure to foreign HAs, and also are protective against heterologous and heterosubtypic IAV challenge (9-15). These strategies are now being tested as promising "universal" influenza virus vaccine candidates (16).Whereas traditional strain-specific antibodies neutralize virus by inhibiting receptor binding, stalk-binding bnAbs neutralize virus by distinct postbinding mechanisms (17). A direct comparison of in vitro neutralization has revealed that strain-specific mAbs that inhibit receptor binding tend to be more potent at neutralizing virus compared with monoclonal stalk-binding bnAbs (18, 19); however, this difference is minimized in the context of a polyclonal response (18). In addition to virus neutralization,...

Divergent Requirement of Fc-Fcγ Receptor Interactions for In Vivo Protection against Influenza Viruses by Two Pan-H5 Hemagglutinin Antibodies

“…The data indicate that different neutralizing and binding activities of these cAbs against different H5 strains have little influence on their ADCC activity. These paradoxical results could be explained by the recent finding that optimal activation of Fc-mediated effector functions by anti-HA antibodies requires not only Fc-Fc␥R interactions but also interactions between HA and sialic acid receptor on effector cells (36)(37)(38). Since in our previous study we found that both 65C6 and 100F4 bind and neutralize H5 viruses before and after viruses bind to target cells (27), we speculate that binding of 65C6 and 100F4 to HA probably does not interfere with the interaction between HA and the sialic acid receptor.…”

“…The results of in vivo testing indicate that both Fc-Fc␥R interactions and Fc-complement interac-tions contribute to the protective effect of 1H5. More recently, it has been shown that optimal activation of Fc-mediated effector functions by anti-HA antibodies requires not only Fc-Fc␥R interactions but also interactions between HA and sialic acid receptor on effector cells (36)(37)(38). Since the requirement of the Fc-Fc␥R interactions for in vivo protection by the Abs in these studies was studied using a single-challenge virus strain and because among antihead Abs tested, 1H5 is the only Ab whose epitope was tentatively mapped to the head region outside the RBS, it remains to be determined whether the observed association between Fc-Fc␥R interactions and in vivo protection by these Abs is strain specific or epitope specific.…”

Immunological responses to influenza vaccination: lessons for improving vaccine efficacy

“…Systematic comparison of the in vivo protective activity of a panel of anti-influenza mAbs with differential neutralizing potency and breadth revealed that strain-specific, neutralizing mAbs directed against the globular head of the influenza HA confer protective activity without a requirement for FcγR engagement [29–31]. In contrast, broadly protective mAbs that target highly conserved influenza epitopes rely on interactions with activating Type I FcγRs to mediate antiviral activity in vivo [29–33].…”

The Vestigial Esterase Domain of Haemagglutinin of H5N1 Avian Influenza A Virus: Antigenicity and Contribution to Viral Pathogenesis

“…To a certain extent, the antibody's binding epitope can affect its ability to stimulate Fc dependent responses, presumably due to accessibility of its Fc region when bound [25]. Furthermore, the binding site of the antibody can subject it to competitive binding with other IAV antibodies in a polyclonal setting and negatively impact its ability to induce ADCC [28].…”