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

以小鼠IL-5R α链cDNA为探针，采用跨种杂交技术克隆人类IL-5受体（IL-5R）。一个cDNA克隆编码一个包含420个氨基酸（Mr 47670）的糖蛋白，包含一个n端疏水区（20个氨基酸）、一个糖基化的胞外结构域（324个氨基酸）、一个跨膜结构域（21个氨基酸）和一个细胞质结构域（55个氨基酸）。转染cDNA的COS7细胞表达6OkD蛋白，并以单一类亲和力结合IL-5 （Kd: 250-590 pM）。Kd值与正常人嗜酸性粒细胞相似。本文描述的hIL-5R α链是信号转导的重要分子，因为该分子在小鼠IL-3依赖性细胞系FDC-P1中的表达允许这些细胞响应IL-5增殖。与小鼠60kd α链结合IL-5的亲和力较低（kD: -IO nM）相比，人α链能以更高的亲和力单独结合IL-5。在小鼠系统中，β链（AIC2B， IL-3R同源物）与α链共表达，其亲和力比α链单独表达提高了至少100倍。虽然hIL-5R α链可能与人GM-CSF受体β链与IL-3受体共享外差，但hIL-5R β链对α链亲和力增加的贡献似乎是边际的。这可能为我们设计il - 5r α链拮抗剂调控人嗜酸性粒细胞生长提供一种更简单的方法。我们还鉴定了其他几个具有多样化3'端hIL-5R α链的cDNA克隆。其中一个没有跨膜和细胞质结构域，可能编码可溶形式的IL-5R 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.