An impressive system for retrieving large numbers of antibodies from memory B cells has been developed. It has been put into practice in an investigation of immune responses to the human immunodeficiency virus.rnInfection of an individual with a virus or a bacterium triggers a vigorous response in white blood cells, some of which - B cells - are stimulated to produce antibodies that target the invading pathogen. The antibodies may be produced too late to prevent symptoms of infection, but the next contact with the same pathogen will probably be symptom-free as antibodies are rapidly deployed to clear the pathogen.rnThis antibody 'memory', which is crucial to vaccine efficacy, has two forms: antibodies circulating in the blood, made by a very-long-lived type of B cell in the bone marrow known as a plasma cell; and B cells in the blood that can be stimulated to make antibodies on contact with a pathogen1'2. The latter 'B-cell memory' carries a record of the antibodies an individual has made in response to a given pathogen, and is of great interest, not least in guiding the design of better vaccines. On page 636 of this issue, Scheid et al.
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