CD11c-Expressing Cells Affect Regulatory T Cell Behavior in the Meninges during Central Nervous System Infection.

Regulatory T cells (Tregs) play an important role in the CNS during multiple infections, as well as autoimmune inflammation, but the behavior of this cell type in the CNS has not been explored. In mice, infection with Toxoplasma gondii leads to a Th1-polarized parasite-specific effector T cell response in the brain. Similarly, Tregs in the CNS during T. gondii infection are Th1 polarized, as exemplified by their T-bet, CXCR3, and IFN-γ expression. Unlike effector CD4+ T cells, an MHC class II tetramer reagent specific for T. gondii did not recognize Tregs isolated from the CNS. Likewise, TCR sequencing revealed minimal overlap in TCR sequence between effector T cells and Tregs in the CNS. Whereas effector T cells are found in the brain parenchyma where parasites are present, Tregs were restricted to the meninges and perivascular spaces. The use of intravital imaging revealed that activated CD4+ T cells within the meninges were highly migratory, whereas Tregs moved more slowly and were found in close association with CD11c+ cells. To test whether the behavior of Tregs in the meninges is influenced by interactions with CD11c+ cells, mice were treated with anti-LFA-1 Abs to reduce the number of CD11c+ cells in this space. The anti-LFA-1 treatment led to fewer contacts between Tregs and the remaining CD11c+ cells and increased the speed of Treg migration. These data suggest that Tregs are anatomically restricted within the CNS, and their interaction with CD11c+ populations regulates their local behavior during T. gondii infection.