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Identification of the second subunit of the murine interleukin‐5 receptor: interleukin‐3 receptor‐like protein, AIC2B is a component of the high affinity interleukin‐5 receptor.

Murine interleukin‐5 (IL‐5) binds to its receptor with high and low affinity. It has been shown that the high affinity IL‐5 receptor (IL‐5‐R) is composed of at least two membrane protein subunits and is responsible for IL‐5‐mediated signal transduction. One subunit of the high affinity IL‐5‐R is a 60 kDa membrane protein (p60 IL‐5‐R) whose cDNA was isolated using the anti‐IL‐5‐R monoclonal antibody (mAb), H7. This subunit alone binds IL‐5 with low affinity. The second subunit does not bind IL‐5 by itself, and is expressed not only on IL‐5‐dependent cell lines but also on an IL‐3‐dependent cell line, FDC‐P1. Expression of the p60 IL‐5‐R cDNA in FDC‐P1 cells, which do not bind IL‐5, reconstituted the high affinity IL‐5‐R. We have characterized the second subunit of the IL‐5‐R by using another anti‐IL‐5‐R mAb, R52.120, and the anti‐IL‐3‐R mAb, anti‐Aic‐2. The anti‐Aic‐2 mAb down‐regulated binding of IL‐5 to an IL‐5‐dependent cell line, Y16. Both R52.120 and anti‐Aic‐2 mAbs recognized membrane proteins of 130–140 kDa expressed on FDC‐P1 and Y16 cells. The R52.120 mAb recognized both murine IL‐3‐R (AIC2A) and its homologue (AIC2B) expressed on L cells transfected with suitable cDNAs. The high affinity IL‐5‐R was reconstituted on an L cell transfectant co‐expressing AIC2B and p60 IL‐5‐R, whereas only the low affinity IL‐5‐R was detected on a transfectant co‐expressing AIC2A and p60 IL‐5‐R.(ABSTRACT TRUNCATED AT 250 WORDS)