CD4 and infection: However, our finding that CD4+ T cells which co-produced IFN-γ with either TNF-α or IL-2 (based on dual gating) were not associated with protection against reinfection seemed to suggest that a CD4+IFN-γ T cell response is sufficient for immune protection against CT reinfection; this has also been described for infection from another Gram-negative bacteria, Salmonella typhi (29).