Original article Enhanced soluble interleukin-5 receptor alpha expression in nasal polyposis Interleukin-5 (IL-5) is a haematopoietic growth factor essential for eosinophil development, activation, and survival. Eosinophil is regarded as an important effector cell in various chronic pathologies including asthma, allergic rhinitis, and nasal polyposis (NP). However, the recent failure to demonstrate clinical efficacy of human- ized antibodies directed against IL-5 in human asthma trials has led to a re-evaluation of the role of eosinophils (1). A better understanding of the biology of IL-5 and the regulation of its receptors seems to be mandatory for understanding the effect of anti-IL-5 treatment in eosi- nophil-associated diseases. Nasal polyposis is an excellent model for eosinophil- associated diseases, as 80–90% of bilateral nasal polyps are characterized by abundant eosinophilic infiltration. Nasal polyps are swellings of the lamina propria mucosa, a pathology that is frequently associated with asthma and often treated by surgical removal of polyps that block airways, facilitating the use of this tissue for investigation. High amounts of IL-5 can be detected at the mRNA as well as at the protein level in NP (2, 3). The highest levels of IL-5 protein were observed in polyp homogenates of patients with generalized eosinophilic diseases such as asthma and aspirin sensitivity (2, 4, 5). The biological signal from IL-5 is mediated through a receptor consisting of a specific IL-5-binding a-chain, and a signal-transducing common b-chain, which is shared with the receptors for IL-3 and granulocyte macrophage- colony stimulating factor (GM-CSF) (6, 7). When the b-chain associates with the specific IL-5-binding a-chain, a high affinity complex is formed (8). In contrast to the pan- haemopoietic bc-chain, the IL-5Ra receptor seems to be expressed on a restricted range of cell types in humans, principally eosinophils, basophils, and their precursors. However, recent publications have demonstrated eosino- phil-independent airway hyperresponsiveness and IL-5Ra gene expression in human bronchus smooth muscle (9, 10). The IL-5 receptor a-subunit (IL-5Ra) can appear in either a membrane-anchored (TM) active form or a soluble (SOL) variant with antagonistic properties in vitro (6, 11). The various expression patterns of these forms are regulated at the transcriptional level by alternative splicing (12). The antagonistic properties of SOL IL-5Ra have been demonstrated in binding assays, eosinophil differentiation assays (11), and in nasal tissue explants (13). It is suggested that eosinophils are able to control Background: Alternative splicing of the interleukin-5 receptor alpha (IL-5Ra)- subunit leads to the generation of a signalling, membrane-anchored (TM) iso- form, or a secreted [soluble (SOL)], antagonistic variant. Given the key role of IL-5 in eosinophil function, we investigated SOL IL-5Ra expression pattern in an eosinophil-associated disease such as nasal polyposis (NP). Methods: An SOL IL-5Ra enzyme-linked immunosorbent assay and quantita- tive real-time polymerase chain reaction (PCR) were established and applied in serum, nasal secretion and nasal tissue of controls (n ¼ 12), and NP patients (n ¼ 42) with or without asthma. Results: Analysis of serum, nasal secretion, and nasal tissue samples revealed that SOL IL-5Ra protein concentrations were significantly increased in NP vs control tissue. Within the NP group, there was a significant up-regulation of SOL IL-5Ra in patients with systemic airway disease. These findings were confirmed at the mRNA level, using an optimized real-time reverse-transcriptase PCR procedure. Conclusions: This report demonstrates SOL IL-5Ra transcript and protein up-regulation in NP. Soluble IL-5Ra differentiates nasal polyps with or without concomitant asthma. As SOL IL-5Ra is strongly up-regulated for disease and has antagonistic properties in vitro, our studies shed new light on the mecha- nisms of specific immunomodulatory therapies, such as anti-IL-5. P.Gevaert 1 ,C.Bachert 1 , G. Holtappels 1 ,C.P.Novo 1 , J. Van der Heyden 2 ,L.Fransen 3 , S. Depraetere 3 ,H.Walter 3 , P.vanCauwenberge 1 ,J.Tavernier 2 1 Department of Otorhinolaryngology, Ghent University Hospital, Belgium; 2 VIB09 Department of Medical Protein Research, Ghent University, Belgium; 3 Innogenetics, Ghent, Belgium Key words: asthma; enzyme-linked immunosorbent assay; eosinophils; interleukin-5 receptor alpha; nasal polyps; polymerase chain reaction. Philippe Gevaert, MD DepartmentofOtorhinolaryngologyGhentUniversity Hospital B-9000 Ghent Belgium Accepted for publication 13 January 2003 Abbreviations: SOL IL-5Ra, soluble interleukin-5 receptor alpha; TM IL-5Ra, membrane-anchored interleukin-5 receptor alpha; NP, nasal polyposis; ECP, eosinophil cationic protein; CV, coefficient of variation; ROC, receiver operating characteristic; IQR, interquartile ranges. Allergy 2003: 58: 371–379 Printed in UK. All rights reserved Copyright Ó Blackwell Munksgaard 2003 ALLERGY ISSN 0105-4538 371