Class Ia MHC-deficient BALB/c mice generate CD8⁺ T cell-mediated protective immunity against listeria monocytogenes infection

CD8⁺ T cells are required for protective immunity against intracellular pathogens such as Listeria monocytogenes. In this study, we used class Ia MHC-deficient mice, which have a severe reduction in circulating CD8⁺ T cells, to determine the protective capacity of class Ib MHC-restricted T cells during L. monocytogenes infection. The K^b-/-D^b-/- mutation was backcrossed onto a C.B10 (BALB/c congenic at H-2 locus with C57BL/10) background, because BALB/c mice are more susceptible to Listeria infection than other commonly studied mouse strains such as C57BL/6. C.B10 K^b-/-D^b-/- mice immunized with a sublethal dose of L. monocytogenes were fully protected against a subsequent lethal infection. Adoptive transfer of Listeria-immune splenocyte subsets into naive K^b-/-D^b-/- mice indicated that CD8⁺ T cells were the major component of this protective immune response. A CD8⁺ T cell line isolated from the spleen of a Listeria-infected class Ia MHC-deficient mouse was shown to specifically recognize Listeria-infected cells in vitro, as determined by IFN-γ secretion and cytotoxicity assays. Adoptive transfer of this T cell line alone resulted in significant protection against L. monocytogenes challenge. These results suggest that even a limited number of class Ib MHC-restricted T cells are sufficient to generate the rapid recall response required for protection against secondary infection with L. monocytogenes.