CD4 and infection: Figure 4D shows the frequencies of MAH-specific CD4+ T helper 1 cells producing IFN-γ effector cytokine after infection. Interestingly, the frequencies of IFN-γ-producing CD4+ T cells were found to be lower in MAH 11-infected mice than in MAH 104-infected mice after 50 days of infection, possibly reflecting the lower organ bacterial loads (Fig. 4A and B).