carried out the analysis. Here, the authors isolate an antibody from an H5N6 infected patient, characterize the epitope within the N6 tetramer, and display that its protecting in female mice. == Intro == Influenza viruses are continuing to develop and cause seasonal flu and occasional worldwide pandemics, which have posed a great challenge to general public health14. Influenza viruses have two major surface glycoproteins, hemagglutinin (HA), and neuraminidase (NA). HA mediates the binding of viruses to the cellular sialic acid receptors and fusion of the virion membrane with the Aniracetam intracellular endosome membranes5. Aniracetam NA removes decoy receptors from mucins and cleaves off the sialic acid, allowing the release of progeny viruses from the infected cells6,7. Human being protecting antibodies elicited by vaccination or illness can bind to both the HA and NA proteins8,9. In the past years, the NA has been historically understudied compared to the surface protein counterpart HA. However, increasing studies highlighted the importance of NA-targeting antibodies and their implications for therapy and design of common flu vaccines, as they have shown that NA-targeted immunity can confer protecting effectiveness against influenza computer virus challenge in animal models1013. NA-targeting monoclonal antibodies (mAbs) are shown to reduce the viral lots and symptoms in infected mice and even correlate with the safety in humans1416, and antigenic drifts also occurred on NA protein1620. Most of the NA-targeting antibodies directly inhibit enzymatic activity of the NA via binding to enzyme active site2125, or indirectly inhibit enzymatic activity of the NA through steric hindrance24,2628. Otherwise, there are some additional NA antibodies with no inhibitory activity to the NA, could also contribute to safety through antibody-dependent cellular cytotoxicity (ADCC) or antibody-dependent cellular phagocytosis (ADCP)16. In addition to seasonal H1N1, H3N2 influenza A computer virus and influenza B computer virus, the recent rise in the rate of recurrence of avian influenza viruses (AIVs) illness has also raised serious public health issues4,5,29. Among them, H5N6 AIV offers obtained global attention. Severe disease occurred in 93.8% of human H5N6 infection cases, and the case fatality rate was >50%30. However, the part of NA in human being immune response to H5N6 AIV Aniracetam illness has not been well investigated. Here, we isolated an N6-specific antibody, 18_14D, from an H5N6-infected human being case in Shenzhen, China, in 2015. Antibody 18_14D can bind to N6 and weakly inhibit enzymatic activity of the H5N6 computer virus at a high concentration. Moreover, 18_14D could protect mice from lethal computer virus illness via ADCC function. Further cryo-electron microscopy (cryo-EM) structure exposed that 18_14D identify a distinctive epitope within the lateral surface of NA, and the antibody binding would induce conformational switch to generate steric conflict in the interface of NA protomer in the tetramer under closed state, acting like a bayonet to unclench the N6 tetramer and keep the NA tetramer in an open state. These findings will contribute to the molecular understanding of protecting immune response to the NA of AIVs in human being, and provide a new direction for the rational design of NA-based vaccines. == Results == Isl1 == Human being illness with H5N6 AIV induces anti-N6 mAb == Peripheral blood mononuclear cell (PBMC) samples were collected at 18 days post illness onset (d.p.o) from a hospitalized H5N6 AIV infected patient in Shenzhen, China31. IgG+memory space B cells were selected and cultured. Within the 13thday of the tradition, the positive rate of IgG+B cells was 34.3%, and the positive rate of H5N6-positive B cells was 10.1%. A total of 9 cell wells were successfully amplified with weighty chain and light chain genes of antibodies and the antibody genes were analyzed (Supplementary Table.1). The putative antibodies from your H5- or N6-positive cell wells were indicated by 293 T cells, and ELISA was used to measure their binding activities for H5 HA or N6 NA (Supplementary Table.2)..