Eosinophils and airway hyper-responsiveness

Authors' reply Sir—In our preliminary study of interleukin 5 antibody, the study was powered for effects on the late asthmatic reaction. In a crossover design, fewer than eight participants are required to show a 50% attenuation in this response with 90% power.1Inman MD Watson R Cockroft DW et al.Reproducibility of allergen-induced early and late asthmatic responses.J Allergy Clin Immunol. 1995; 95: 1191-1195Summary Full Text Full Text PDF PubMed Scopus (74) Google Scholar However, studying three groups of eight patients is probably insufficient to draw firm conclusions about effects on baseline airways hyper-responsiveness measured as a histamine PC20 because hyperresponsiveness can vary day to day, even in mild asthma.2Josephs LK Gregg I Mullee MA Holgate ST Non-specific bronchial reactivity and its relationship to the clinical expression of asthma: a longitudinal study.Am Rev Respir Dis. 1989; 140: 350-357Crossref PubMed Scopus (189) Google Scholar We used ANCOVA to allow for the baseline value (−14 days). The baseline value for histamine PC20 was included in the model, and the analysis took into account the baseline value. In our view, this approach is similar but preferable to looking at the change from baseline. We agree that more pronounced effects on baseline airway hyperresponsiveness might be expected in patients with a greater degree of blood eosinophilia. Patients with mild asthma had a mean baseline eosinophil count of 0·4×109/L, which is just higher than normal for healthy non-atopic individuals. In a preliminary report of a different monoclonal interleukin 5 antibody in patients with symptomatic asthma despite inhaled corticosteroid therapy, the fall in circulating eosinophils was similar to that seen in our study, but there was little effect on asthma symptoms or lung function.3Kips JC O'Connor BJ Langley SJ et al.Results of a phase I trial with SCH55700, a humanized anti-IL-5 antibody in severe persistent asthma.Am J Respir Crit Care Med. 2000; 161: A505Crossref Scopus (194) Google Scholar This finding provides further support for the idea that eosinophils do not play a critical part in asthma. However, eosinophils might be important in more long-term processes in asthma such as the structural remodelling changes that underlie irreversible airflow obstruction. Eosinophils and airway hyper-responsivenessIn their report, M Leckie and coworkers (Dec 23/30, p 2144)1 show that a monoclonal antibody to interleukin 5 lowers sputum and blood eosinophils without affecting airway hyper-responsiveness or the late-phase allergen response. Full-Text PDF