IL-23-deficient Rag1−/− mice, which only develop mild colitis after T cell transfer (Hue et al., 2006), had a reduced absolute number and percentage of eosinophils among CD45+ leukocytes compared to colitic IL-23 competent mice, suggesting a link between intestinal eosinophil accumulation and IL-23-driven inflammation (Figure S1B). The gene discussed is RAG1; the disease is colitis.