The important role of Perforin in protecting against Mycobacterium avium infection in mice.

Mycobacterium avium is a drug-resistant bacterium that causes refractory respiratory infection. Perforin protects hosts against viral infection and tumors by inducing apoptosis. It is also thought to be important in innate immunity against intracellular pathogen infection, although its role remains controversial. The role of perforin in M. avium infection prevention was examined using perforin-deficient mice. Clinically-isolated strains of M. avium were used, along with perforin-deficient and wild-type C57Bl/6 mice. M. avium (1 × 107 CFU/mouse) was administered intratracheally. Mice were euthanized 7, 21, and 60 days after infection. Lung homogenates were inoculated onto Middlebrook 7H10 agar plates for colony counting. Bronchoalveolar lavage was also performed. Lung tissue sections were stained with hematoxylin-eosin and the Ziehl-Neelsen method. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling using lung histology, and a cell death detection kit using lavage fluid, were used to detect apoptosis in the lungs. Perforin-deficient mice demonstrated severe pulmonary involvement after M. avium infection compared with wild-type mice. Colony counts indicated increased M. avium in the lungs of perforin-deficient mice. More apoptotic cells were detected in the lungs of wild-type mice compared with perforin-deficient mice. Histone-complexed DNA fragments were more prevalent in lavage fluids from wild-type mice compared with perforin-deficient mice. These results confirmed that perforin plays an important role in protection against M. avium infection in mice through the induction of apoptosis in infected cells. Perforin might therefore be a therapeutic target for drug-resistant pulmonary M. avium infection.