Lopez A F, Vadas M A, Woodcock J M, Milton S E, Lewis A, Elliott M J, Gillis D, Ireland R, Olwell E, Park L S
Division of Human Immunology, Institute of Medical and Veterinary Science, Adelaide, Australia.
J Biol Chem. 1991 Dec 25;266(36):24741-7.
Human interleukin (IL)-5 receptors were characterized by means of binding studies using bioactive 125I-labeled IL-5. Of purified primary myeloid cells, eosinophils and basophils but not neutrophils or monocytes expressed surface receptors for IL-5. Binding studies showed that eosinophils expressed a single class of high affinity receptors (Ka = 1.2 x 10(10) M-1) with the number of receptors being small (less than 1000 receptors/cell) and varying between individuals. Among several cell lines examined only HL-60 cells showed detectable IL-5 receptors which were small in numbers (200 receptors/cell) and also bound 125I-IL-5 with high affinity. The binding of IL-5 was rapid at 37 degrees C while requiring several hours to reach equilibrium at 4 degrees C. Specificity studies revealed that the two other human eosinophilopoietic cytokines IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF) inhibited the binding of 125I-IL-5 to eosinophils. No competition was observed by other eosinophil activating or nonactivating cytokines. The inhibition of 125I-IL-5 binding by IL-3 and GM-CSF was partial up to a concentration of competitor of 10(-7) M with GM-CSF consistently being the stronger competitor. Converse experiments using IL-5 as a competitor revealed that this cytokine inhibited the binding of 125I-IL-3 and of 125I-GM-CSF in some but not all the individuals tested, perhaps reflecting eosinophil heterogeneity in vivo. Cross-linking experiments on HL-60 cells demonstrated two IL-5-containing complexes of Mr 150,000 and Mr 80,000 both of which were inhibited by GM-CSF. The competition between IL-5, IL-3, and GM-CSF on the surface of mature eosinophils may represent a unifying mechanism that may help explain the common biological effects of these three eosinophilopoietic cytokines on eosinophil function. This unique pattern of competition may also be beneficial to the host by preventing excessive eosinophil stimulation.
利用具有生物活性的125I标记的白细胞介素（IL）-5，通过结合研究对人IL-5受体进行了表征。在纯化的原代髓细胞中，嗜酸性粒细胞和嗜碱性粒细胞表达IL-5的表面受体，而中性粒细胞或单核细胞则不表达。结合研究表明，嗜酸性粒细胞表达一类单一的高亲和力受体（Ka = 1.2×10¹⁰ M⁻¹），受体数量较少（每个细胞少于1000个受体），且个体之间存在差异。在所检测的几种细胞系中，只有HL-60细胞显示出可检测到的IL-5受体，其数量较少（200个受体/细胞），并且也以高亲和力结合125I-IL-5。IL-5在37℃时结合迅速，而在4℃时需要数小时才能达到平衡。特异性研究表明，另外两种人嗜酸性粒细胞生成细胞因子IL-3和粒细胞-巨噬细胞集落刺激因子（GM-CSF）可抑制125I-IL-5与嗜酸性粒细胞的结合。其他嗜酸性粒细胞激活或非激活细胞因子未观察到竞争作用。在竞争者浓度达到10⁻⁷ M之前，IL-3和GM-CSF对125I-IL-5结合的抑制作用是部分性的，GM-CSF始终是更强的竞争者。使用IL-5作为竞争者的反向实验表明，这种细胞因子在部分但并非所有测试个体中抑制125I-IL-3和125I-GM-CSF的结合，这可能反映了体内嗜酸性粒细胞的异质性。对HL-60细胞进行的交联实验显示出两种分子量分别为150,000和80,000的含IL-5复合物，两者均被GM-CSF抑制。IL-5、IL-3和GM-CSF在成熟嗜酸性粒细胞表面的竞争可能代表一种统一机制，有助于解释这三种嗜酸性粒细胞生成细胞因子对嗜酸性粒细胞功能的共同生物学效应。这种独特的竞争模式也可能通过防止嗜酸性粒细胞过度刺激而对宿主有益。
