EFFECT OF AGE ON MARROW MACROPHAGE NUMBER AND FUNCTION

Employing flow cytometry and a monoclonal antibody against the murine macrophage antigen, Mac-1, we found a significant increase in the numb er of marrow macrophages in aged mice. This was reflected as significa nt increase with age in the number of alpha-naphthyl acetate esterase positive cells, as well as in colony forming unit-macrophage (CFU-M) p rogenitor cells. Macrophages from the marrow of old mice generated sig nificantly less tumor necrosis factor alpha (TNF alpha) than did macro phages from young mice, either spontaneously or when activated by gran ulocyte-macrophage colony stimulating factor (GM-CSF). Furthermore, co nditioned medium (CM) derived from either marrow or peritoneal macroph ages of old mice caused less suppression of burst forming unit-erythro id (BFU-E) colony growth than did CM obtained from young mice. Aging, therefore, is associated with an in crease in the number of marrow mac rophages that have an impaired ability to generate or release cytokine s. The increase in macrophage number may reflect a compensation for th eir reduced function. Altered macrophage number and Junction may contr ibute to the age-related decline in hematopoietic reserve capacity.