Interaction of interleukin-5 with its receptors on murine leukemic BCL1 cells and its implication in biological activity

Interaction of interleukin (IL)-5 with its receptors on murine leukemic cell line, BCL1 cells was examined. 125I-labeled recombinant murine IL-5(rmIL-5) bound specifically to high-affinity receptors on BCL1 cells. rmIL-5, which was about 2500-fold more active than recombinant human IL-5(rhIL-5) in IgM-inducing activity on BCL1 cells, also showed about 5000-fold higher affinity to receptors. These results suggest that the bioactivity of IL-5 correlates with its receptor-binding activity. When disulfide bond formation was blocked, rmIL-5 dissociated into a monomer and lost its biological activity. This monomeric form of rmIL-5 also lost its ability to bind to cells, suggesting that dimer formation is essential for the biological activity of IL-5.