B-1a cells acquire their unique characteristics by bypassing the pre-BCR selection stage

B-1a B cells are innate-like cells with biased reactivity to bacteria and self-antigens. Here the authors show that reduced interleukin-7 in developing fetal liver-derived pro-B cells induces premature immunoglobulin κ rearrangement, alleviating the requirement for a pre-BCR selection stage and allowing the generation of autoreactive B1-a B cells.