YKL-40 is unregulated in the bronchial tissue of patients with asthma. Specific staining for YKL-40 is brown, whereas nuclei are stained blue. Representative photomicrographs are present from a) a healthy individual, b) a patient with mild asthma, c) a patient with moderate asthma, and d) a patient with severe asthma. YKL-40-positive and -negative cells were counted in the epithelium and submucosa (expressed as a percentage of total cells). The data are presented as medians. e) YKL-40 is increased in both severe and moderate asthma compared with mild asthma, and there is a significant difference found between the two patient groups.