The effect of dexamethasone on the growth of bone marrow fibroblasts in aplastic anemia.

To study the characteristics of the microenvironment of human bone marrow, fibroblasts derived from normal and aplastic anemia bone marrow aspirates or core biopsies were grown in culture. Normal bone marrow fibroblasts had a slow logarithmic phase of growth (8 days) with doubling times of 2 to 3 days. Aplastic anemia bone marrow fibroblasts had a rapid logarithmic phase of growth (5 to 6 days) and doubling times of 1 day. Dexamethasone (1 X 10(-8) M) stimulated the growth of normal fibroblasts. Growth of fibroblasts derived from aplastic anemia marrows was, however, inhibited by dexamethasone. Specific binding sites for the hormone were present in the normal fibroblasts (Bmax: 460-770 fmole/mg protein) whereas in the aplastic anemia fibroblasts the amount was very low (Bmax 27-215 fmole/mg protein). These observations suggest that in aplastic anemia, the bone marrow fibroblast, a cell constituent of the marrow microenvironment, has the capacity to develop and grow in vitro. However, this cell is different from normal bone marrow fibroblasts in its growth characteristics and response to dexamethasone.