Generation of long-lived plasma cells (LLPCs) continues with age and disease progression. Frequencies (left) and absolute number (right) of bromodeoxyuridine (BrdU)-positive newly generated LLPCs enumerated in the spleen and bone marrow of young and old mice. Young (4 weeks of age) and old (20 weeks of age) NZB/W F1 mice were fed BrdU for six weeks, and BrdU incorporation studies were performed six weeks after the end of BrdU feeding. Cells were gated on CD138 + BrdU+ lymphocytes, which are newly generated LLPCs formed during the BrdU feeding period. Data are presented as mean and standard error of the mean (SEM). n = 5 mice. Numbers and horizontal bars represent P values from statistical comparison between groups by two-tailed unpaired t test. n.s., nonsignificant.