Role of IgE and Eosinophils: The Use of Type 2 Biomarkers in Practice

Most patients with asthma and some patients with chronic obstructive pulmonary disease (COPD) demonstrate the features of type 2 inflammation. The association between eosinophils and pathophysiology is less clear in COPD than in asthma, but eosinophil testing in COPD is important to determine patients with response to steroids, and a blood eosinophil count of 300/μl is listed as an item in the guidelines for asthma–COPD overlap (ACO). Allergic sensitization is related to increased symptoms and risk of exacerbations in COPD, and some guidelines for ACO have introduced immunoglobulin E (IgE) into the diagnostic criteria. We comprehensively compared the positivity of specific IgE between ACO and non-ACO COPD, and only the positivity for house dust and Dermatophagoides pteronyssinus was significantly higher in ACO, indicating the specifically important role of mite-specific IgE in diagnosing ACO among COPD. This chapter discusses the role of eosinophils and IgE in the diagnosis and treatment of ACO.