While LCMV, as expected, induced a strong gp61-specific systemic CD4 T cell response, we could not detect any gp61-specific CD4 T cells by tetramer staining following priming with either of the E. coli strains including E. coli ompC_gp61 (Figure 2A) This is likely due to the very low frequency of gp61-specific CD4 T cells present in naïve C57BL/6 mice (37–39) and much weaker T cell priming by E. coli compared to a productive viral infection with a replicating virus. The gene discussed is CD4; the disease is viral infectious disease.