Representative flow cytometry profiles and blood films of peripheral blood lymphocytes from a single (NZW x B10.NZW) F1 x B10.NZW backcross mouse carrying all Bpal-1, -2 and -3 alleles, at 8, 16, and 23 months of age. CD5⁺ B-1 cells are boxed. Cytospinned lymphocyte films were stained with Giemsa. Proportions of B-1 cells in total peripheral B cells and total white blood cell counts were 11% and 7,200/mm³ in mice at 8 months, 44% and 7,000/mm³ at 16 months, and 97% and 35,500/mm³at 23 months of age, respectively.