B-1 cells: orthodox or conformist?

B-1 cells differ from conventional peripheral B cells (B-2) by anatomical location, surface marker expression, antibody repertoire and growth properties. The lineage hypothesis of B-1 cell development attributes the properties of B-1 cells to their unique origin. The induced differentiation hypothesis suggests the surface-immunoglobulin-driven development of B-1 cells from common B-1/B-2 cell progenitors. In both models self-antigen-induced signalling plays the central role in positive selection of B-1 cells. The ability of B-1 cells to be positively selected by self-antigens raises questions about the mechanism of this phenomenon.