IFNG and infection: At five weeks post-infection, strong IFN-γ production was detected in response to M. avium culture filtrate (and PPD, data not shown) in mice infected with MST12 and MST22 isolates (ranging between 20,000 and 40,000 pg/mL), whereas IFN-γ levels were about tenfold lower in mice infected with MST91 isolates (Fig 2).