Given that B2 lymphocytes are dependent on the interaction of BAFF (B cell activation factor of the TNF family) with BAFF-receptor (BAFFR) for their survival and maturation [10], [11], we crossed BAFFR-deficient mice to ApoE−/− mice and examined how BAFFR deficiency affected development of atherosclerosis. The gene discussed is TNFSF13B; the disease is atherosclerosis.