Comparison of the effectiveness of bone marrow and spleen stem cells for platelet repopulation in lethally irradiated mice.

To determine whether stem cells from spleen differ from those of bone marrow in their ability to support platelet repopulation after lethal irradiation we compared normal, splenectomized and plethoric (3 weeks exposure to CO) spleen cell recipients with similar groups of mice reconstituted with comparable numbers of bone marrow stem cells. Female LAF1 mice were given 825-950 R from a 60Co source and were transplanted with 0, 0.5, 1, 2, or 4 x 10(6) bone marrow or 10-64 x 10(6) spleen cells. CFUs content of the transplant was calculated from day 9 splenic nodules in mice receiving 5 x 10(4) bone marrow or 1.0-1.6 x 10(6) spleen cells. Blood volumes, platelet counts and hematocrits were determined on day 12. Total circulating platelets increased with increasing stem cell dose (range 50-1000 CFUs) after both types of transplant. Plethoric mice always had lower platelet levels than controls even when corrected for expanded blood volume. There was little difference between values for normal and splenectomized mice. Platelet production per CFUs in all groups except splenectomized spleen cell recipients declined with large transplants presumably because of feedback inhibition. Although the number of splenic megakaryocytes in spleen cell recipients was approximately 2.5 times as great as in bone marrow recipients, platelet levels were significantly higher only in normal and splenectomized mice receiving more than 300 CFUs. No differences were found between the two types of transplant when plethoric hosts were used.