On day nine post infection, we observed systemic dissemination in all mice that had been reconstituted with Irf1–/– bone marrow, while spread in the control group was significantly lower (Fig. 3b) suggesting that Irf1 expression in the hematopoietic compartment is required to provide the host with the capacity to mount an efficient C. rodentium directed immune response. The gene discussed is IRF1; the disease is infection.