We studied the direct effects of interferon‐γ (IFN‐γ) in single cell colony assays of CD34+HLA‐DR++ bone marrow progenitor cells stimulated by either granu‐locyte‐colony‐stimulating factor (G‐CSF), interleukin(IL)‐3, granulocyte/macro‐phage‐colony‐stimulating factor (GM‐CSF), combinations of these CSF or medium conditioned by the 5637 human bladder carcinoma cell line. In this culture system IFN‐γ stimulated monocytic colonies (CFU‐M) no matter which CSF or CSF combination was used to support them and inhibited granulocytic colonies (CFU‐G) if they were generated in the presence of G‐CSF. IL‐4 antagonized the myelopoietic effects of IFN‐γ: the IFN‐γ induced suppression of G‐CSF‐supported CFU‐G, as well as the stimulation of CFU‐M, were reversed by IL‐4. In all cultures, IFN‐γ had a limited, but statistically non‐significant, inhibitory effect on CFU‐GM, which was not affected by the presence of IL‐4. These data show that IFN‐γ and IL‐4 reciprocally regulate the generation of myeloid cells involved in humoral (neutrophils) and cellular (macrophages) immune responses through a direct effect on monopotential myeloid progenitor cells.
- Progenitor cells