B cells are primarily produced in the bone marrow after birth, where they develop from hematopoietic stem cells through several stages of differentiation and selection to ensure proper function and self-tolerance

. In fetuses, B cells are initially produced in the fetal liver before the bone marrow takes over this role postnatally

. Once immature B cells are formed in the bone marrow, they migrate to secondary lymphoid organs such as the spleen and lymph nodes, where they mature further and differentiate into various types of mature B cells capable of responding to antigens