However, wild-type mice had higher bacterial burden in their liver and spleen than the iNOS−/− mice during the initial three (liver) or four days (spleen) post-infection (Fig. 2k), indicating that NO production promotes S. Typhimurium intracellular replication at the early infection stage, which was in agreement with the macrophage replication assays (in vitro results). The gene discussed is NOS2; the disease is infection.