A central feature of the remarkable success of our immune system in keeping us upright and functional for potentially 80 years or more, is its adaptive learning from its previous experiences. The system retains samplings of the elements generated in body’s previous responses to invaders in the form of antibody produce plasma cells and memory cells, now known to occur within multiple haematopoietic lineages. These retained learnings provide either immediate or sentinel defence, or they act as a rapid response force, shortening the time from infection to resolution. The components of our potentially ever-expanding immune defenses have quite different properties, both between the cell types generated in a single response and between the same cell types generated to different antigens. It is on these differences that much interest is focused in order to maximise the protection provided by designer vaccines, both in breadth and duration. And that turns out to lead to some interesting and fundamental questions.