Recent functional studies indicate a further subdivision of labor assigning B1a cells as the producers of natural serum antibody (7). In contrast, B1b cells appear to be the primary source of dynamic T cell independent (TI) antibody production and long-term protection after bacterial infection such as Borrelia hermsii and Streptococcus pneumoniae. These studies indicate preexisting subset differences in B-cell receptor (BCR) specificity and antigen-driven B cell fate that remain important unresolved features of the system.
