IL5 receptor complex

The receptor complex consists of an a chain and a fic chain. Both chains have structures characteristic of the hematopoietin receptor superfamily. The c* chain is a glycoprotein of 415 amino acids and binds with low affinity to IL-5. The |3 chain itself does not bind to IL-5, but associates with the a chain to generate the high-affinity receptor. The (3 chain is common to the receptors for IL-3 and GM-CSF.

Because of the difficulty in obtaining sufficient numbers of eosinophils, progress in characterizing the eosinophil IL-5R has been slow. Murine eosinophils have been calculated to express approximately 50 high-affinity receptors (Kj in the range 4— 6x10 11 m), and approximately 5000 low-affinity receptors (Kd in the range 0.3-2.0 x 109m). Initial work on the human receptor used a clone of the human promyelocytic leukemia cell line HL-60.

These cells express only a single population of high-affinity IL-5-binding sites and cross-linking studies show IL-5 associating with two membrane proteins of Mr 60 000 and 13 000. Similarly, only a single high-affinity receptor population has been identified on human eosinophils. This was found to be a high-affinity receptor in the range Kl( 170-330 pm (3-6 x 10"" m).

Human eosinophils express three different transcripts from the same IL-5 Ret locus. In addition to the membrane-anchored receptor, two soluble iso forms can be produced. Intriguingly, one of these soluble variants is the predominant (>90%) transcript detected in mature, circulating eosinophils or in eosinophils obtained from cord blood cultures. This major soluble isoform arises from splicing to a soluble-specific exon, which preceeds the exons encoding the transmembrane anchor.

See also: Cytokines; Cytokine receptors; Eosinophils. Further reading

Corrigan CJ and Kay AB (1992) T cells and eosinophils in the pathogenesis of asthma. Immunology Today 13: 501-507.

Goodall GJ, Bagley CJ, Vadas MA and Lopez AF (1993) A model for the interaction of the GM-CSF, 11.-3 and IL-5 receptors with their ligands. Growth Factors 8: 87-97.

Karlcn S, Mordvinov S and Sanderson CJ (1996) How is the expression of the intcrleukin-5 gene regulated? Immunology and Cell Biology 74: 218-223. Sanderson CJ (1992) IL5, eosinophils and disease. Blood

79: 3101-3109. Sanderson CJ (1993) In: Smith H and Cook R (eds! Immunopharmacology of Eosinophils, pp I 1-24. London: Academic Press.

Sanderson CJ (1994) In: Thompson AW (ed) The Cytokine Handbook, pp 127-143. London: Academic Press.

Tavernier J, Devos R, Cornells S et al (1991) A human high affinity interleukin-5 receptor (IL5R) is composed of an IL5-specific a chain and a (3 chain shared with the receptor for GM-CSF. Cell 66: 1175-1184.

Tuypens T, Plaetinck G, Baker E et al (1992) Organization and chromosomal localization of the human interleukin 5 receptor alpha-chain gene. European Cytokine Network 3: 451-459.

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