In certain strains of mice, such as C57BL/6, Toxoplasma infection leads to an acute, CD4+ T cell-dependent ileitis characterized by an influx of neutrophils and monocytes (7, –, 10), along with increased levels of interferon gamma (IFN-γ) (11, 12), tumor necrosis factor alpha (TNF-α) (11), interleukin 18 (IL-18) (13), IL-22 (14), IL-23 (14), and nitric oxide (NO) (11). The gene discussed is CD4; the disease is Crohn ileitis.