The algorithm assembled to classify patients with leprosy into subgroups according to the presence of leprosy reactions proposed the use of IL-9 as the root attribute (cutoff = 9 pg/ml) followed by IL-6 (cutoff = 0.4 pg/ml) and CXCL10 (cutoff = 350 pg/ml) as branch biomarkers for classifying T1RL and T2RL. This evidence concerns the gene IL9 and leprosy.