In recent years, improved knowledge of eosinophilic inflammation has led to the approval of biologics aimed at inhibiting the pathways of eosinophilic activation, notably via the interleukin 5 pathway in eosinophilic asthmatic patients uncontrolled despite receiving maximum doses of standard drugs. These treatments showed efficacy in asthmatic patients with a high level of eosinophils in their induced sputum (\> 3%) and the criteria were extended to those with circulating eosinophilia (\> 300 / mm3). Eosinophils are therefore an important biomarker for phenotyping asthmatic patients. The Charcot-Leyden crystals are a reflection of the presence of eosinophils, and are sometimes found in some pathological samples. It is hypothesized that the presence of Charcot-Leyden crystals, a reflection of tissue eosinophilia, is a predictive factor for the efficacy of anti-IL5 biotherapies in patients with severe eosinophilic asthma.
