IgA Potentiates NETosis in Response to Viral Infection

IgA is the second most abundant antibody present in circulation and is enriched at mucosal surfaces. As such, IgA plays a key role in protection against a variety of mucosal pathogens, including viruses. In addition to neutralizing viruses directly, IgA can also stimulate Fc-dependent effector functions via engagement of Fc alpha receptors (FcαRI) expressed on the surface of certain immune effector cells. Neutrophils are the most abundant leukocyte, express FcαRI, and are often the first to respond to sites of injury and infection. Here, we describe a novel function for IgA:virus immune complexes (ICs) during viral infections. We show that IgA:virus ICs potentiate NETosis, the programmed cell death pathway through which neutrophils release neutrophil extracellular traps (NETs). Mechanistically, IgA:virus ICs potentiated a suicidal NETosis pathway via engagement of FcαRI on neutrophils through a toll-like receptor (TLR)-independent, NADPH oxidase complex-dependent pathway. NETs also were capable of trapping and inactivating viruses, consistent with an antiviral function.