Transfer of both protection and delayed-type hypersensitivity against live Listeria is mediated by the CD8+ T cell subset: a study with Listeria-specific T lymphocytes recovered from murine infected liver.

The recruitment of specific T lymphocytes in murine liver is thought to be a key event in the ultimate control of Listeria monocytogenes growth during primary infection. However, there has been little functional characterization of the cell populations recruited in this non-lymphoid organ. Therefore in this study, the recruited lymphomyeloid cells were isolated from the liver of C57BL/6 mice at the peak of the immune response (day 7) triggered by a non-lethal L.monocytogenes infection. The anti-Listeria T lymphocytes were detected in vivo by their ability to transfer protection and delayed-type hypersensitivity (DTH) to live L.monocytogenes in naive recipients: protection was measured not only by the effect on reduction of the bacterial load in liver and spleen, but also on survival after the lethal challenge, and DTH was detected using as eliciting antigen, either live L.monocytogenes or heat-killed L.monocytogenes. When live pathogens were used, both functions were found to be mediated by T lymphocytes belonging to the CD8+ subset. However, when heat-killed L.monocytogenes were used as eliciting antigen in the DTH assay, Listeria-specific CD8+ T lymphocytes could not be restimulated in immune lymphoid cell populations recovered either from liver or spleen of Listeria-infected mice. Both populations were thus found to share the same qualitative properties in the DTH assay. The importance of the use of live pathogens versus heat-killed pathogens for detection of DTH and protection functions is discussed in the light of current concepts on processing and presentation pathways of Listeria-derived peptides.