Broadly Neutralizing Hemagglutinin Stalk-Specific Antibodies Induce Potent Phagocytosis of Immune Complexes by Neutrophils in an Fc-Dependent Manner

Abstract

Broadly neutralizing antibodies that recognize the conserved hemagglutinin (HA) stalk have emerged as exciting new biotherapeutic tools to combat seasonal and pandemic influenza viruses. Our general understanding of the mechanisms by which stalk-specific antibodies achieve protection is rapidly evolving. It has recently been demonstrated that broadly neutralizing HA stalk-specific IgG antibodies require Fc-Fcγ receptor (FcγR) interactions for optimal protection in vivo. Here we examine the neutrophil effector functions induced by stalk-specific antibodies. As the most abundant subset of blood leukocytes, neutrophils represent a critical innate effector cell population and serve an instrumental role in orchestrating downstream adaptive responses to influenza virus infection. Yet, the interplay of HA stalk-specific IgG, Fc-FcγR engagement, and neutrophils has remained largely uncharacterized. Using an in vitro assay to detect the production of reactive oxygen species (ROS), we show that human and mouse monoclonal HA stalk-specific IgG antibodies are able to induce the production of ROS by neutrophils, while HA head-specific antibodies do not. Furthermore, our results indicate that the production of ROS is dependent on Fc receptor (FcR) engagement and phagocytosis. We went on to assess the ability of monoclonal HA stalk-specific IgA antibodies to induce ROS. Consistent with our findings for monoclonal IgGs, only HA stalk-specific IgA antibodies elicited ROS production by neutrophils. This induction is dependent on the engagement of FcαR1. Taken together, our findings describe a novel FcR-dependent effector function induced by HA stalk-specific IgG and IgA antibodies, and importantly, our studies shed light on the mechanisms by which HA stalk-specific antibodies achieve protection.

Cross‐reactive antibody‐dependent cellular cytotoxicity antibodies are increased by recent infection in a household study of influenza transmission

“…Antibody‐dependent cellular cytotoxicity responses are reportedly highly cross‐reactive, and avian influenza‐specific ADCC antibodies can be found in healthy unexposed individuals and enriched for the HA stem . In our study, ADCC activity towards conserved NP, cross‐reactive H7‐HA, seasonal HA and NA proteins was boosted by recent H1N1 infection.…”

Roles of antibodies to influenza A virus hemagglutinin, neuraminidase, and M2e in conferring cross protection

“…These results suggest that Fc receptors partially contribute to the protection by NA antibodies. In line with the roles of Fc receptors in mediating protection, HA stalk-specific antibodies were shown to induce phagocytosis of immune complexes in a FcR dependent manner [19, 20]. Similarly, Fc receptors were required for M2e immune mediated protection [13].…”

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]. These findings clearly highlight that the broad antiviral activity of these IgG antibodies is achieved not only through the targeting of specific, highly conserved epitopes on HA, but also through their capacity to engage and activate distinct FcγR pathways to confer protective effector functions.…”