Partially TAP-independent protection against Listeria monocytogenes by H2-M3-restricted CD8(+) T cells

Effective protection against Listeria monocytogenes requires Ag-specific CD 8(+) T cells.-A substantial proportion of CD8(+) T cells activated during L . monocytogenes infection of C57BL/6 mice are restricted by the MHC class I b molecule H2-M3. In this study, an H2-M3-restricted CD8(+) T cell clone sp ecific for a known H2-M3 epitope (fMIGWII) was generated from L, monocytoge nes-infected mice. The clone was cytotoxic, produced IFN-gamma, and could m ediate strong protection against L, monocytogenes when transferred to infec ted mice. Macrophages pulsed with heat-killed Listeriae presented Ag to the clone in a TAP-independent manner. Both TAP-independent and -dependent pro cessing occurred in vivo, as TAP-deficient mice infected,vith L, monocytoge nes were partially protected by adoptive transfer of the clone, This is the first example of CD8(+) T cell-mediated, TAP-independent protection agains t a pathogen in vivo, confirming the importance of alternative MHC class I processing pathways in the antibacterial immunity.