RECOMBINANT HUMAN INTERLEUKIN-4 INHIBITS THE PRODUCTION OF GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR BY BLOOD MONONUCLEAR-CELLS

The effect of recombinant human (rh) interleukin-4 4 (rIL-4) on human blood BFU-E was investigated using two populations of cells: platelet- depleted low-density mononuclear cells (PH,Pl(-) cells), as unpurified cells, and highly purified BFU-E. When FH,Pl(-) cells were cultured w ith rherythropoietin (rEp), rIL-4 inhibited BFU-E growth in a dose-dep endent manner. However, the addition of rIL-4 did not affect rh-interl eukin-3 (rIL-3) supported BFU-E growth. Limiting dilution analysis (LD A) of FH,Pl(-) cells showed that rIL-4 suppressed endogenous productio n of burst-promoting activity (BPA) by accessory cells. Highly purifie d BFU-E were used as target cells to measure BPA in the conditioned me dium (CM) that was prepared by FH,Pl(-) cells. When 100 purified BFU-E were cultured in 0.5 ml clots with 20% (vol/ vol) of the CM, the numb er of BFU-E colonies was increased by the CM. The increase was signifi cantly reduced by the addition of the CM prepared in the presence of r IL-4, but anti-IL-4 blocked the effect of rIL-4. The concentration of IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF) in CM was determined by an enzyme-linked immuno-adsorbent assay (ELISA). The spontaneous production of GM-CSP but not IL-3 was detected, and th is was significantly decreased in the presence of rIL-4. Anti-GM-CSF b ut not anti-IL-3 inhibited CM supported BFU-E growth, indicating that the main BPA in the CM is GM-CSF and that rIL-4 suppresses the spontan eous production of GM-CSF by accessory cells. From these studies, we c onclude that rIL-4 has a unique mechanism as a negative regulator on e rythropoiesis through the inhibition of BPA production by blood mononu clear accessory cells.