MOLECULAR CHARACTERIZATION OF THE BETA-CHAIN OF THE MURINE INTERLEUKIN-5 RECEPTOR

Interleukin 5 (IL-5) is a multifunctional cytokine that regulates the proliferation and differentiation of hematopoietic cells including B cells and eosinophils. The murine IL-5 acts on target cells via an IL-5 specific high-affinity receptor (K(d) congruent-to 150 pM) that has been proposed to be composed of at least two membrane polypeptide chains. The p60 component recognized by anti-murine IL-5 receptor mAbs H7 and T21 binds IL-5 with low affinity (K(d) congruent-to 10 nM). The other component is p130, detectable by following cross-linking experiments with IL-5. Using H7, T21, and R52.120 mAbs specific to murine IL-5 receptor, we characterized the molecular nature of the p130 of the high affinity receptor for murine IL-5. R52.120 mAb did not recognize the IL-5 binding recombinant p60 expressed on COS7 cells, but reacted with p130/140 on IL-5-dependent cell lines. R52.120 mAb showed partial inhibition of the IL-5-induced proliferation of the IL-5-dependent early B cell line Y16 at high IL-5 concentrations. Addition of R52.120 mAb together with H7 or T21 mAb caused more striking inhibition of the IL-5-dependent proliferation than that caused by either of them alone. R52.120 mAb down-regulated the number and dissociation constant of IL-5 binding sites with high affinity without affecting the levels of these with low-affinity. It also preferentially inhibited the formation of the cross-linked complex of p130 with radiolabeled IL-5. These results indicate that p130/p140, recognized by R52.120 mAb, is indispensable, together with p60, for the formation of high affinity IL-5 receptor. We propose to designate p60 and p130/p140 as the alpha and beta-chain of IL-5 receptor, respectively.