Enhancing effect of cyclosporins A and G on bone marrow colony formation.

The development of the number of colonies (cell colony-forming units, CFU-C) in soft agar from normal mouse bone marrow (BM) cells was enhanced 60% when total bone marrow cells (BMC) were preincubated for 1 h with either cyclosporin A (CsA) or cyclosporin G (CsG) before plating. Using cell fractionation techniques we found that the removal of macrophages enhanced CFU-C in noncyclosporin-treated BM and that cyclosporins mediated an additional enhancing effect. A similar enhancing effect on CFU-C in noncyclosporin-treated BM was obtained by depleting it of total T cells or Lyt-2.2+ cells. However, CFU-C growth in the residual BM population was no longer enhanced by cyclosporin. Conversely, removal of Lyt-1.2+ cells did not enhance CFU-C in noncyclosporin-treated BM, but the CFU-C in this population were enhanced by cyclosporin treatment. These results suggest that CsA and CsG can increase the cloning efficiency of normal mouse BMC, possibly by inhibiting an endogenous Lyt-2.2+ suppressor cell.