Effect of age on the intrinsic regulation of murine hemopoiesis.

As a part of studies conducted to determine the cause(s) of the decline in hemoglobin and peripheral blood lymphocytes observed in old mice, young mice were lethally irradiated and protected with bone marrow cells from young and old donors. Four months later the recipients of marrow from old mice had depressed hemoglobin and absolute lymphocyte levels in 4 of 6 and 5 of 6 experiments, respectively. Six months after lethally irradiated 20-month-old hosts were given marrow from young or 20-month-old donors, the recipients of old marrow had decreased lymphocyte counts but their hemoglobin levels were not different from those observed in mice given marrow from young donors. These results suggest that peripheral blood lymphocytes counts and to a lesser degree hemoglobin levels are at least partially controlled by mechanisms intrinsic to the marrow itself.