Infection of mice with Mycobacterium avium primes CD8(+) lymphocytes for apoptosis upon exposure to macrophages

Mycobacterial infection is associated with granuloma formation in which the presence of apoptosis has been recognized. The role of CD4(+) T and CD8(+) T cells in host protection against mycobacterial infections has been demon strated. Previous studies, however, have shown that CD8(+) T cells have a l imited role in host defense against Mycobacterium avium infection, and we h ypothesize that M. avium infection could lead to T cell apoptosis, To inves tigate this hypothesis, C57BL/6 mice were infected with M. avium strain 101 , and the rate of apoptosis of splenic lymphocytes cultured ex vivo with pe ritoneal macrophages was determined and compared with that of controls. Whe n exposed to infected macrophages ex vivo, splenic lymphocytes from M. aviu m-infected mice underwent apoptosis, as determined by the TUNEL assay. This increased T cell apoptosis above the control Level was observed after 3 we eks but not after only 1 week of infection in mice. No splenic T cell apopt osis was observed when lymphocytes from Mycobacterium smegmatis-infected mi ce were cultured in the presence of M. smegmatis-infected peritoneal macrop hages, Likewise, macrophages infected in vitro with heat-killed M, avium di d not trigger T cell apoptosis, Culture of macrophages in different chamber from lymphocytes, separated by a transwell membrane, was not associated wi th increase of apoptosis compared with uninfected control, suggesting a req uirement for direct cell-cell interactions to trigger lymphocyte apoptosis, Using a double staining TUNEL followed by anti-mouse CD4 or anti-mouse CD8 monoclonal antibodies, it was observed that only CD8(+) T cells but not CD 4(+) T cells underwent apoptosis at 3 weeks of infection. In conclusion, M. avium infection in C57/BL6 mice for 3 weeks renders CD8(+) T cells prone t o apoptosis when exposed ex vivo to macrophages infected with M. avium. (C) 2001 Academic Press.