Filtrate Antigens in Mycobacterium bovis Bacillus Calmette-Guérin-Infected Mice

CD81 T cells are essential for protection against mycobacteria, as is clearly demonstrated by the fatal outcome of experimental infection of b-2 microglobulin knockout mice. However, the mechanisms and antigens (Ags) leading to CD81 T-cell activation and regulation have been poorly characterized. Here we show that, upon immunization of major histocompatibility complex (MHC)-congenic mice with Mycobacterium bovis bacillus Calmette-Guérin (BCG), a cytotoxic response against BCG culture filtrate (CF) Ags (CFAgs) is induced in H-2b and H-2bxd haplotypes but not in H-2d haplotype. This response is mediated by CD81 T cells and absolutely requires the activation of CD41 T cells and their secretion of interleukin 2. The lack of cytotoxic response in H-2d mice cannot be explained by impaired cytokine production or by a defect in Ag presentation by H-2d macrophages. Using the MHC class I mutant B6.C-H-2bm13 mouse strain, we demonstrate that cytotoxic T lymphocytes (CTLs) recognize CFAgs exclusively in association with Db molecules. These Ags are cross-reactive in mycobacteria, since BCG-induced CTLs also recognize macrophages pulsed with CF from Mycobacterium tuberculosis H37Rv and H37Ra and from two virulent strains of M. bovis. Moreover, immuni-zation with Mycobacterium kansasii induces CTLs able to lyse macrophages pulsed with BCG CF. Finally, we have found that these Ags can be characterized as hydrophilic proteins, since they do not bind to phenyl-Sepharose CL-4B. Our results indicate that MHC-linked genes exert a profound influence on the generatio