Antigen-independent development of B cells o Bcell subsets and development Fetus liver: B1 B Bone marrow: HsC→proB→preB→imB→mB spleen: NFB FP FOB○ MZB⊙B cell subsets and development Fetus liver：B1 B Bone Marrow： HSC proB preB imB mB spleen：NF B FP FO B MZ B Antigen-independent development of B cells