Human B-cell memory is shaped by age- and tissue-specific T-independent and GC-dependent events

Switched and IgM memory B cells execute different and non-interchangeable functions. We studied memory B cells in children of different ages, in peripheral blood and spleen and compared them with those of children born asplenic or unable to build germinal centers. We show that, whereas switched memory B cells are mostly generated in the germinal centers at all ages, IgM memory B cells can be distinct in three types with different developmental history. Innate IgM memory B cells, the largest pool in infants, are generated in the spleen by a germinal center-independent mechanism. With age, if the spleen is present and germinal centers are functional, innate IgM memory B cells are remodelled and accumulate somaticmutations. The third type of IgM memory B cell a by-product ofthe germinal center reaction. Our data suggest that the B-cell memory developmental program is implemented during the first 5–6 years of life. This article is protected by copyright. All rights reserved