Restoration of prostaglandin releasing macrophage populations in lethally irradiated mice with spleen cells from bone marrow-depleted donors.

Previous studies in mice severely depleted of bone marrow cells by 89Sr showed persistent monocytopenia and impaired expression of prostaglandin E2-releasing splenic macrophages (PGSM) despite the occurrence in the spleen of more than 10-fold increases in pluripotential stem cells and M phi colony-forming cells. To determine whether the observed deficits were due to a lack of precursors of blood monocytes and PGSM in the spleens of 89Sr-treated mice, radiation chimeras were established by i.v. infusion of 2 x 10(6) spleen cells from 89Sr donor CBA/J or semisyngeneic B6CB F1 hybrid mice into lethally gamma-irradiated CBA/J recipients. Blood monocyte levels were greater than normal by day 14 and PGSM induced by Corynebacterium parvum were demonstrated by day 28. These restored M phi populations expressed the donor haplotype detected in vitro with haplotype-specific monoclonal anti-H-2K plus complement. 89Sr treatment of the chimeras resulted in profound depletion of monocytes and PGSM. The data indicate that the spleen of the 89Sr-treated mouse, which is an ineffective source of circulating monocytes and PGSM, contains cells which can generate both of these populations following infusion into lethally irradiated recipients. Since the bone marrow of such recipients was capable of being repopulated, the aggregate observations suggest that functional bone marrow is obligatory for the generation of blood monocytes and PGSM populations.