B cell memory: building two walls of protection against pathogens.

Surviving a single infection often results in lifelong immunity to the infecting pathogen. Such protection is mediated, in large part, by two main B cell memory 'walls' - namely, long-lived plasma cells and memory B cells. The cellular and molecular processes that drive the production of long-lived plasma cells and memory B cells are subjects of intensive research and have important implications for global health. Indeed, although nearly all vaccines in use today depend on their ability to induce B cell memory, we have not yet succeeded in developing vaccines for some of the world's most deadly diseases, including AIDS and malaria. Here, we describe the two-phase process by which antigen drives the generation of long-lived plasma cells and memory B cells and highlight the challenges for successful vaccine development in each phase.