VH and V genes from each cell were amplified by RT-PCR and nested PCR reactions using cocktails of primers as previously described15,24 and then sequenced. B cell receptor (BCR) repertoire that in some donors were dominated by only a few B cell clones. This pauci-clonal response, however, showed extensive intraclonal diversification from accumulated somatic mutations. We used the immunoglobulin variable regions isolated from sorted single ASCs to produce over fifty human monoclonal antibodies (mAbs) that bound to the three influenza vaccine strains with high affinity. This strategy demonstrates that we can generate multiple high affinity mAbs from humans within a month after vaccination. The Rabbit Polyclonal to PGLS panel of influenza virus specific human mAbs allowed us to address the issue of original antigenic sin (OAS) – the phenomenon where the induced antibody shows higher affinity to a previously encountered influenza virus strain compared to the virus strain present in the vaccine1. However, we found that the vast majority of the influenza virus specific mAbs showed the highest affinity for the current vaccine strain. Thus, OAS does not seem to Apaziquone be a common occurrence in normal healthy adults receiving influenza vaccination. Influenza causes 36,000 deaths annually in the United States alone and the influenza pandemic of 1918 caused an estimated 50 million deaths worldwide2. Outbreaks Apaziquone of avian influenza infections in human populations that caused substantially higher mortality rates foresee the possibility of another deadly pandemic3. The challenge of influenza has long been to design vaccines that induce long lasting immunity against a pathogen that rapidly alters its appearance to the immune system by mutating (antigenic drift) and exchanging (antigenic shift) its components. Antibodies play a key role in protection against influenza infection4-7. However, the underlying B cell response leading to the rapid production of ASCs that secrete antibodies is only beginning to be understood8-12. Critically, we do not yet know if B cell memory can provide sufficient protection early in the response to counteract variant strains of influenza or if rather the response is dominated by antibodies previously generated against divergent viruses in an OAS fashion. Finally, of profound clinical significance is the possibility that the early ASC response observed after immunization can be exploited to rapidly generate therapeutic or diagnostic mAbs to emerging influenza virus strains, or in fact to any immunizing antigen. In order to determine the dynamics and magnitude of the human anti-influenza response we analyzed the frequency of ASCs and Apaziquone memory B cells in a time-course following vaccination. The ASC response was quite transient, peaking at approximately day seven and returning to barely detectable levels by day 14 after vaccination (Fig. 1a and 1b). The frequency of influenza-specific ASCs averaged 6.4% (or 2,500 ASCs per ml of blood) at day 7, and accounted for up Apaziquone to 16% of all B cells (range for ten donors: 1.1-16%, Fig. 1b). Also, most of these ASCs were generated during the vaccination response as they were almost entirely Ki-67 positive, indicating recent proliferation, and most expressed homogenously high levels of HLA-DR13 (Fig. 1c). Importantly, analysis of IgG secreting ASCs isolated by cell sorting at day 7 post-immunization demonstrated that the vast majority were influenza vaccine specific (ranging from 20-85% and averaging 70%, Fig. 1d). The ASCs were mainly IgG positive, with minor components of IgA and IgM positive cells (data not shown), suggesting an origin from the memory B cell compartment. The memory B cell response was also quantified14. Increasing from low levels prior to vaccination, influenza-specific memory B cells peaked a week after the ASC response at 14 to 28 days after vaccination and averaged 8.2% of the IgG+ memory B Apaziquone cells or 1% of all B cells (Fig. 1e). We conclude that influenza vaccination results in a massive burst of IgG+ ASCs that are predominantly influenza-reactive and peak at approximately day 7 post-immunization. Open in a separate window Figure 1 Analysis of the B cell response.