Analyses based on the magnitude order of the increase identified a higher number of immune mediators which were increased, six of these being the best biomarkers—the chemokines CXCL10, CCL3, and CXCL8; the pro-inflammatory cytokines IFN-γ and IL-6; and the regulatory cytokine IL-9—which showed greater clinical relevance and possible applicability in the diagnosis of leprosy. This evidence concerns the gene IL9 and leprosy.