Just Published in Science Immunology: Sandra Weller and coll. in the former team of Claude-Agnès Reynaud and Jean-Claude Weill, in collaboration with the group of Pr. Guy Gorochov (CIMI, Paris and AP-HP) investigated the B cell subsets involved in T-independent (TI) responses. Such responses are directed against nonproteins with repeated structure such as bacterial capsular polysaccharides (capPS). Unlike T-dependent responses, TI responses do not elicit germinal centers or a memory response, but in humans, antibodies specific to bacterial capPS harbor somatic mutations, which appears as a paradox. Using High throughput BCR repertoire sequencing, Weller et al studied TI responses in healthy individuals vaccinated with Pneumovax, a model TI vaccine composed of pneumococcal polysaccharides. They showed that they largely mobilize Marginal Zone (MZ) and clonally related switched B cells that most likely prediversified their antibody repertoire during immune responses taking place in Gut-associated lymphoid tissues and directed against gut bacteria harboring cross-reactive glycans.