Fc-dependent effector functions of neutrophils induced by hemagglutinin stalk-specific antibodies

Abstract Broadly neutralizing antibodies that recognize the conserved hemagglutinin (HA) stalk have emerged as exciting new biotherapeutic tools to combat both 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-FcR interactions for optimal protection in vivo. Here we explore the relationship between such stalk-specific antibodies and neutrophils. Neutrophils represent a critical innate effector cell population and play an important role in orchestrating downstream adaptive responses to influenza virus infection. Yet, at present the interplay of HA stalk-specific IgG, Fc-FcR engagement, and neutrophils has remained largely uncharacterized. Using an in vitro assay to detect the production of reactive oxygen-species (ROS), we show that both human and mouse monoclonal HA stalk-specific IgG antibodies are able to induce the production of ROS in neutrophils, while antibodies specific to the HA head domain do not. Furthermore, our results indicate that the production of ROS is dependent on Fc receptor engagement and phagocytosis. We went on to assess the ability of monoclonal HA stalk-specific IgA antibodies to induce ROS. We found that monoclonal IgA lead to a greater induction of ROS as compared to monoclonal IgG. Our data demonstrate this activity 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.