De novo recruitment of antigen-experienced and naive T cells contributes to the long-term maintenance of antiviral T cell populations in the persistently infected central nervous system.

Mice infected with attenuated strains of mouse hepatitis virus, strain JHM, develop a chronic infection in the brain and spinal cord characterized by low levels of viral Ag persistence and retention of virus-specific CD4 and CD8 T cells at the site of infection. It is not known whether these cells are maintained by proliferation of T cells that entered the CNS during acute infection or are newly recruited from Ag-experienced or naive T cell pools. In this study, using adoptive transfer experiments and bone marrow chimeras, we show that at least some of these cells are recruited from the periphery, predominantly from the viral Ag-experienced T cell pool. Both virus-specific CD4 and CD8 T cells are functional, as assessed by cytokine expression and degranulation after peptide exposure. In addition, populations of virus-specific CD4 T cells undergo dynamic changes in the infected CNS, as previously shown for CD8 T cells, because ratios of cells responding to two CD4 T cell epitopes change by a factor of five during the course of persistence. Collectively, these results show that maintenance of T cell responses in the virus-infected CNS is a dynamic process. Further, virus-specific T cell numbers at this site of infection are maintained by recruitment from peripheral Ag-experienced and naive T cell pools.