To analyze the specificity, breadth, and neutralizing capacity of these plasmablasts, we used single-cell PCR to amplify the heavy and light chain variable region genes from individually Hancock et al., 2009) . The Centers for Disease Control reports that there were an estimated 60 million cases of the 2009 H1N1 pandemic strain, which caused 256,000 hospitalizations. An unusually high frequency of severe disease occurred in younger and otherwise healthy patients (Hancock et al., 2009 ). In addition, rare infections with avian H5N1 influenza strains in humans had close to a 50% mortality rate (Subbarao and Joseph, 2007) . Emergence of a zoonotic or antigenically distinct strain that combined even a fraction of the morbidity and mortality of the pandemic H1N1 and H5N1 viruses would have dire consequences. Antibodies play a key role in protection against influenza infection in vivo (Puck et al., 1980; Gerhard et al., 1997; Luke et al., 2006; Simmons et al., 2007) . The fact that there were little or no preexisting antibody titers present before the emergence of this pandemic virus, and that the virus atypically caused such severe disease in young adult, illustrates the importance of comprehensively understanding the B cell responses and antibody specificities induced by infection with this influenza virus.