Inflammatory Phenotypes and Potential Bio-markers of ACO: What Is the Specific Feature of ACO?

Asthma-chronic obstructive pulmonary disease (COPD) overlap (ACO) is a chronic obstructive airway disease subtype. Therefore, it is essential to elucidate the phenotype and endotype of patients with ACO to develop personalized or stratified medicine in patients with asthma and COPD. Furthermore, clarification of these aspects could contribute to the development of useful biomarkers for identifying ACO patients. Many previous studies have focused on the contribution of inflammatory markers, including eosinophil, fractional exhaled nitric oxide (FeNO), and serum IgE levels, to ACO identification. Moreover, recent studies have attempted to develop specific markers for ACO using several analysis approaches, such as genomics, epigenetics, transcriptomics, and metabolomics. Therefore, it is highly anticipated that the multidimensional characterization of the pathophysiology of ACO would lead to the development of biomarkers that would be helpful in the discrimination of ACO.