Two studies have identified CXCR4 as a critical regulator of B1 cell migration to the bone marrow, as CXCR4 deficiency resulted in decreased B1 cells in the bone marrow, reduced IgM levels [124], and elevated atherosclerosis in B-cell-specific CXCR4-deficient female Apoe−/− mice [125]. The gene discussed is APOE; the disease is atherosclerosis.