Updated project metadata. Proteomic identification and characterization of antibodies comprising the serological response to antigen can provide unique insight into the functional dynamics of adaptive immunity. We have developed a novel method to overcome the technical challenges which previously limited the direct analysis of immunoglobulin proteins in serum, as demonstrated by the identification of human anti-tetanus toxoid (TT) immunoglobulin G (IgG) proteins following booster vaccination. We analyzed the serum IgG repertoire across four time-points corresponding to pre-vaccination, 7 days, 3 months, and 9 months post vaccination. Antigen-specific antibodies were affinity purified against immobilized TT protein and sequenced by bottom-up nanoLC-MS/MS. Interpretation of mass spectra required a custom reference database of IgG heavy and light chain variable sequences determined by NextGen RNA sequencing of the donor's circulating plasmablasts and memory B cells following booster vaccination.