An assessment of myeloid colony-forming-cell generation in liquid human bone marrow cultures : influence of accessory cells and cytokines IL-1α, β and IL-6

Liquid culture of Ficoll isolated human marrow mononuclear cells followed by secondary clonogenic assays has been used to study the involvement of specific accessory cells and cytokines on the kinetics in vitro of human granulocyte-macrophage-colony forming cells (CFU-GM). Primary cultures produced an oscillation in CFU-GM numbers, typified by increases in CFU-GM after 4 and 9 days and reductions on days 2 and 4. Cultures of marrow cells depleted of mononuclear phagocytes produced a steady decline in CFU-GM number over a similar period. Removal of T cells was without effect. Comparison of colony assays using conditioned medium (CM) from the human bladder carcinoma cell line 5637 and 5637CM plus interleukin (IL)-3 revealed the decline of CFU-GM in mononuclear phagocyte depleted cultures due to lack of maturation of early myeloid progenitors. The cytokines IL-6 and IL-1 beta were detectable in the supernatant from whole marrow cultures and from cultures depleted of T cells but not in cultures depleted of mononuclear phagocytes. Using neutralizing polyclonal antibodies directed against IL-1 and IL-6, singly or in combination, in whole marrow cultures we showed that anti-IL-6 antibody alone had no effect on the number of colonies detected in the secondary clonogenic assay whilst anti-IL-1 and anti-IL-1 plus anti-IL-6 reduced colony counts by 44 and 83% respectively. Thus, endogenously produced IL-1 and IL-6 are involved in the dynamic changes in CFU-GM numbers when marrow mononuclear cells are cultured. Possible synergistic interactions are discussed.