HEMATOPOIETIC GROWTH-FACTOR PRODUCTION BY NORMAL AND APLASTIC-ANEMIA STROMA IN LONG-TERM BONE-MARROW CULTURE

Defective marrow stroma, or microenvironment, have been proposed as on e of several mechanisms to account for bone marrow failure in aplastic anaemia (AA). This could involve defects in positive- or negative-act ing haemopoietic regulator expression by AA stroma, or alteration of n ormal stroma-stem cell interactions. We have used a sensitive bloassay to investigate production of granulocyte-colony stimulating factor (G -CSF), granulocyte-macrophage-colony stimulating factor (GM-CSF), inte rleukin (IL)-3, IL-6 and stem cell growth factor (SCF), by normal and AA stroma in long-term bone marrow culture (LTBMC). LTBMC were grown t o confluence, irradiated and harvested to yield a single cell suspensi on. These cells were cocultured with normal target bone marrow mononuc lear cells (BMMC), or CD34(+) cells, in clonogenic assays, in the abse nce of exogenous cytokines, Cytokines responsible for the colony-stimu lating activity (CSA) and burst-promoting activity (BPA) produced by s tromal cells were identified by neutralizing antibodies to specific cy tokines. All normal stroma populations produced G-CSF and GM-CSF, 93% produced IL-3, 80% produced IL-6, and 70% produced SCF. Similarly, all AA stroma produced G-CSF and GM-CSF, and 71% produced SCF. In contras t, only 71% of AA stroma produced IL-3 and 36% produced IL-6, Target c ell stimulation was not dependent on direct stroma-target cell contact , suggesting production of soluble cytokines, However, although both I L-6 and G-CSF were detected in LTBMC supernatants by enzyme-linked imm unoassay (ELISA), IL-3 and GM-CSF were undetectable, perhaps indicatin g low-level local production of these factors.