Abstract -- Project 1 Project 1 will study the updating of imprinted responses to influenza infection and vaccination that occurs during subsequent influenza vaccination. The hypothesis is that imprinting of B cell memory to influenza by initial infection will induce more neutralization but less breadth directed at heterologous strains, while initial imprinting by influenza vaccine will provide greater breadth but less neutralizing activity. Project 1 will test this hypothesis in a series of experiments in humans and rhesus macaques, in which we will probe the B cell repertoires in response to combinations of influenza infection and vaccination. Project 1 will perform experiments in non-human primates where the exposure to influenza antigens can be tighly controlled and will collect samples from humans of all ages receiving influenza vaccination to quantify responses in a “real world” setting. For all aims, the goals will be to 1) quantify the effect of exposure to different influenza subtypes by infection and vaccination, 2) quantify recall upon antigenic challenge by vaccination or infection and 3) quantify the epitope specific response to influenza. We will pursue these golas using serology, Nojima cultures, and monoclonal antibody (mAb) isolation, for epitope mapping and structural studies, in collaboration with Project 4.