Defective erythropoietic responses of aged mice not improved by young marrow.

Defective responses to severe bleeding in 25-mo.-old C57BL/6J mice were not improved by injections of 8-mo.-old marrow cells. Such injections greatly improved responses of genetically anemic W/W-v mice that have defective erythropoietic stem cells. Apparently the defective responses of old mice were not intrinsic to their erythropoietic stem cells.