RAG1 and schistosomiasis: In mice, widely used to investigate various aspects of schistosomiasis, closer scrutiny of results suggests that serum factors may dominate the apparent inborn resistance to schistosomiasis: first, only ~30% of penetrating cercariae mature in the mouse (15), and, second, full-body irradiation or genetic ablation of RAG1, suppressing cellular immunity, does not notably improve S. mansoni maturation in mice (16, 17).