Limitations of the adoptive immunity assay for analyzing anti-Listeria immunity.

The usefulness of adoptive immunization as a method for analyzing mechanisms responsible for resolution of Listeria monocytogenes infection was studied. Results showed that, although mice resolving primary infection acquire CD8+ T cells that are exclusively capable of adoptively immunizing recipient mice against an L. monocytogenes challenge infection, these T cells are protective only if given to recipients at very early stages of infection (soon after the infection is cleared from the blood by fixed phagocytes of the liver and spleen). In contrast the same T cells failed to mediate adoptive immunity against infection if given to recipients 24 h after infection was initiated, when L. monocytogenes is no longer in fixed phagocytes but is confined to granulomas. These results indicate that specific CD8+ T cells produced in response to infection contribute minimally to resolution of established infection in the donor.