CD40 and severe combined immunodeficiency: The intestinal bacterium Hh is associated with IBD and induces spontaneous colitis in mice with severe combined immunodeficiency or IL10-deficiency.16,18 The fact that we found Hh-specific Ig in sera of DC-LMP1/CD40 mice suggested that this mouse colony was endemically infected by Hh. To test this, we screened the fecal content from mice for the presence of Helicobacter by genus-specific and species-specific PCR (Figure 3(a)).