PRF1 and infection: In contrast to the infection with R. australis where the release of IFNγ by CD8+ T cells was found to be not essential for protection [111], IFNγ was even more important than the cytotoxic activity of CD8+ T cells in long-term control of R. typhi. Persisting bacteria were not found in BALB/c CB17 SCID mice that received CD8+ Perforin-/- T cells but were detectable by quantitative polymerase chain reaction (qPCR) in CD8+ IFNγ-/- T cell recipients, predominantly in the brain [122].