In adult mice, B1 cells constitute a minor fraction of the spleen and secondary lymphoid tissues but are enriched in the pleural and peritoneal cavities., B1 cells were shown to arise from precursors in the fetal liver and neonatal but not adult bone marrow and constitute the earliest wave of mature peripheral B cells.
In adult mice, B1 cells account for a small fraction of the spleen and secondary lymphoid tissues, whereas they are more prevalent in the pleural and peritoneal cavities. Research has shown that B1 cells develop from fetal liver and neonatal bone marrow precursors, but not those from adult bone marrow, and constitute the initial wave of mature peripheral B cells.