Regulatory Role of Interleukin 5 and Its Receptor in the Bcell Growth and Differentiation

我们以鼠IL-5 R α链cDNA为探针，通过跨物种杂交克隆cDNA，对人IL-5受体（hIL-5 R）进行了表征。一个cDNA克隆编码420个氨基酸的糖蛋白（Mr 47，670）具有N-末端疏水区（20个氨基酸），糖基化的胞外结构域（324个氨基酸），跨膜结构域（21个氨基酸）和胞质结构域用cDNA转染的COS 7细胞表达60 kD蛋白，并以单一类别的亲和力（Kd：250-590 pM）结合IL-5。Kd值与正常人嗜酸性粒细胞中观察到的相似。人IL-5 R α链在小鼠IL-3依赖性细胞系FDC-P1中表达后，可使细胞对IL-5产生应答，是信号转导的重要分子。人IL-5 R α链与小鼠IL-5的结合亲和力较低（Kd =-10nM），而人IL-5 R α链与小鼠IL-5的结合亲和力较高。在鼠系统中，β链（AIC 2B，IL-3R同源物）与α链的共表达使亲和力增加至单独α链的亲和力的至少100倍。虽然hIL-5 R α链可能与人GM-CSF受体β链（与IL-3受体共享）产生外差作用，但hIL-5 R β链对α链亲和力增加的贡献似乎是微不足道的。我们还鉴定了其它几个3'末端不同的hIL-5 R α链cDNA克隆。其中之一不具有跨膜和胞质结构域，并且可能编码可溶形式的IL-5 R α链。这些多样化的3'端可能参与调节人嗜酸性粒细胞的生长和分化。

We have characterized human IL-5 receptor (hIL-5R) by cloning cDNA with cross-species hybridization using murine IL-5R alpha chain cDNA as a probe. One cDNA clone encodes a glycoprotein of 420 amino acids (Mr 47, 670) with an N-terminal hydrophobic region (20 amino acids), a glycosylated extracellular domain (324 amino acids), a transmembrane domain (21 amino acids) and a cytoplasmic domain (55 amino acids).COS7 cells transfected with the cDNA expressed a 6OkD protein and bound IL-5 with a single class of affinity (Kd : 250-590 pM). The Kd values were similar with that observed in normal human eosinophils. The hIL-5R alpha chain characterized in this paper is an essential molecule for signal transduction, because expression of this molecule in murine IL-3 dependent cell line FDC-P1 allow these cells to proliferate in response to IL-5.In contrast to murine 60 kD alpha chain that binds IL-5 with low affinity (Kd : -IO nM), human alpha chain can bind IL-5 With much higher affinity by itself. In murine system, coexpression of beta chain (AIC2B, IL-3R homologue) with alpha chain increased the affinity at least 100-fold to that of alpha chain alone. Although hIL-5R alpha chain probably makes heterodyne with human GM-CSF receptor beta chain shared with IL-3 receptor, the contribution of hIL-5R beta chain to the increase of the affinity of alpha chain seems to be marginal. This may provide us an easier way to regulate eosinophil growth in human by designing an antagonist to hIL-5R alpha chain.We have also characterized several other cDNA clones for hIL-5R alpha chain with diversified 3' end. One of which does not have the transmembrane and cytoplasmic domains and probably codes for a soluble form of IL-5R alpha chain. These diversified 3' end may be involved in the regulation of the growth and differentiation of human eosinophils.