We previously reported that B lymphocyte chemoattractant (BLC; CXCL13) was highly and ectopically expressed in aged (NZB× NZW) F 1 (BWF 1) mice developing lupus nephritis, and that B1 cells were preferentially chemoattracted toward BLC. We demonstrate in this study that B1 cells fail to home to the peritoneal cavity in aged BWF 1 mice developing lupus nephritis, and that they are preferentially recruited to the target organs including the kidney, lung, and thymus when injected iv In contrast, B1 cells homed to the peritoneal cavity in aged BALB/c mice as effectively as in young mice. Accumulation of B1 cells to the omentum milky spots was also impaired in aged BWF 1 mice compared with young mice. CD11b high F4/80 high cells with macrophage morphology were confirmed to be a major cell source for BLC in the peritoneal cavity both in young and aged BWF 1 mice. However, the number of BLC-producing peritoneal macrophages was markedly decreased in aged BWF 1 mice. These results suggest that the decreased number of BLC-producing peritoneal macrophages together with ectopic high expression of BLC in aged BWF 1 mice result in abnormal B1 cell trafficking during the development of murine lupus.