ANTILISTERIAL IMMUNITY INCLUDES SPECIFICITY TO LISTERIOLYSIN-O (LLO) AND NON-LLO-DERIVED DETERMINANTS

Subclinical infection of BALB/c mice with virulent Listeria monocytoge nes leads to the generation of Listeria-specific T-cell populations re quired for the expression of protective immunity. The L. monocytogenes -produced hemolysin listeriolysin O (LLO) is a virulence factor which appears to be crucial for the induction of protective antilisterial im munity. Analysis of the specificity of antilisterial cytotoxic cells f rom Listeria-immune BALB/c donors has shown a dominant response to an epitope corresponding to amino acids 91 to 99 of LLO. Demonstration of antilisterial T cells with specificity to non-LLO-derived epitopes ha s been difficult to achieve because of the requirement of LLO in facil itating escape of the bacteria to the cytoplasm of the host cell and t he apparent dominance of an anti-LLO response in antilisterial immunit y. In this study we show that antilisterial immunity also includes spe cificity to non-llO-derived determinants. We used as an immunogen an L LO(-) mutant of L. monocytogenes which expresses the hemolysin perfrin golysin O (PFO). The LLO(-)PFO(+)L. monocytogenes mutant possesses inv asive properties similar to those of wild-type L. monocytogenes and es capes from the phagocytic vacuole because of the activity of PFO. We f ound that J774 target cells infected ,vith the LLO(-) PFO+ L. monocyto genes mutant were lysed by antilisterial cytotoxic T cells obtained fr om BALB/c mice immunized,vith wild-type L. monocytogenes. In addition, BALB/c mice immunized with the LLO PFO+ L. monocytogenes mutant were immune to challenge with LLO(+) wild-type L. monocytogenes, a finding indicative of protective antilisterial immunity specific to Listeria-d erived epitopes other than LLO. Spleen cells from BALB/c mice immunize d with the LLO(-) PFO+ L. monocytogenes mutant adoptively transferred antilisterial protection to a subsequent challenge with wild-type L. m onocytogenes. This splenocyte population also contained cytotoxic cell s which lysed target cells infected with either the LLO(-) PFO+ L. mon ocytogenes mutant or wild-type LLO(+) L. monocytogenes but did not lys e target cells infected with an LLO-expressing Bacillus subtilis trans formant. These results establish that during the immune response to L. monocytogenes, immune splenocytes,vith specificity for LLO and other, non-llO-derived epitopes develop. These non-LLO epitopes serve as tar gets for antilisterial cytotoxic cells and for lymphocytes which adopt ively transfer antilisterial immunity.