Disease diagnosis is an essential first step in treatment of any illness. Patients often succumb to their diseases because they were not treated in time, and diagnosis is critical for improving prognosis. The antibody repertoire, the entire set of antibodies produced by an individual, may be the key to improving diagnosis. Because immune responses change the repertoire, an individual’s health history is recorded in the antibody repertoire from responses throughout their lifetime. Repertoire profiling may yield important immune status data and therefore may be applicable in disease diagnosis. De novo sequencing is a method in which a novel sequence is determined without reference sequences. Sequencing the repertoire reveals antibody binding capabilities and the individual’s genome, and provides understanding of immune responses to infection, vaccination, and cancers. In this study, Immunoglobulin Y will act as a model. Chicken eggs are sources with high amounts of IgY, as the antibodies are passed from hen to offspring through passive immunization. Samples will be taken from groups of individuals that have undergone immunization and groups that have not undergone immunization to provide comparison. Immunoglobulin Y will be purified from the solutions, and samples will be analyzed using liquid chromatography-mass spectrometry, a tool that measures mass-to-charge ratio of ions with high accuracy and sensitivity. Peptides will be sequenced using mass spectrometry data and denovo sequencing.