Acidic isoferritins and E-type prostaglandins in sources of colony stimulatory factors mask detection of cycling granulocyte-macrophage progenitor cells

The effect of granulocyte-macrophage colony stimulatory factors (GM- CSF), acidic isoferritins, and E-type prostaglandins on the detection of the cycle status of human granulocyte-macrophage progenitor cells (CFU-GM) was investigated. Bone marrow cells were pulse-treated with control medium or high specific activity tritiated thymidine [3HTdr) and subsequently plated over feeder layers containing mononuclear blood leukocytes prepared in the absence or presence of anti-acidic isoferritins and/or indomethacin, or plated in the presence of medium conditioned by placental cell or GCT-conditioned media free of acidic isoferritins and prostaglandin-E. The presence of anti-acidic isoferritins and/or indomethacin in the blood leukocyte feeder layers increased the detectable stimulatory capacity of these cells and permitted detection of a larger proportion of marrow CFU-GM in cycle than in control cultures. The cycle status was not influenced by GM-CSF in conditioned medium regardless of the dilution of conditioned medium used to stimulate colony formation. This suggests that GM-CSF, supplied to the cells after treatment with 3HTdr, does not itself influence the detection of CFU-GM in cycle, but using sources of GM-CSF that contain acidic isoferritins or prostaglandin-E will underestimate the actual number of CFU-GM in S-phase.