TLR are involved in the detection of microbial infection as well as endogenous ligands that signal tissue and cell damage in mammals. This recognition plays an essential role in innate immune response and the initiation of adaptive immune response. We have previously shown that murine CD8 T cells express TLR2, and that costimulation of Ag-activated CD8 T cells with TLR2 ligands enhances their proliferation, survival, and effector functions. We also demonstrated that TLR2 engagement on CD8 T cells significantly reduces their need for costimulatory signals delivered by APC. We show in this study that TLR2 engagement on CD8 T cells lowers the Ag concentration required for optimal activation, and converts a partial activation into a productive process leading to a significant expansion of cells. Using altered peptide ligands, we demonstrate that TLR2 engagement increases CD8 T cell activation and enables the generation of functional memory cells in response to a low TCR signal. This increased activation is associated with an augmented activation of the PI3K. Taken together, our results demonstrate that TLR2 engagement on CD8 T cells lowers their activation threshold for TCR signal strength and enables efficient memory cell generation in response to a weak TCR signal.

The spleen is a major homing site for NK cells. How they traffic to and within this site in homeostatic or inflammatory conditions is, however, mostly unknown. Here we show that NK cells enter the spleen through the marginal sinus and home to the red pulp via a pertussis toxin-insensitive mechanism. Upon inflammation induced by poly(I:C) injection or mouse cytomegalovirus infection, many NK cells left the red pulp while others transiently entered the white pulp, predominantly the T cell area. This migration was dependent on both CXCR3 and CCL5, suggesting a synergy between CXCR3 and CCR5, and followed the path lined by fibroblastic reticular cells. Thus, the entry of NK cells in the white pulp is limited by the expression of pro-inflammatory chemokines. This phenomenon ensures the segregation of NK cells outside of the white pulp and might contribute to the control of immunopathology.Key words: Chemokines Á Migration Á Natural killer cells Á Spleen Supporting Information available online Introduction Natural killer (NK) cells are large granular lymphocytes involved in defense mechanisms against several types of microbial infections and tumors [1][2][3]. In particular in the mouse, NK cells play a critical role in the defense against mouse cytomegalovirus (MCMV) by eliminating infected cells through their cytotoxic activity [4] and by regulating the immune response through their crosstalk with dendritic cells [5,6]. Consistent with their role in immune surveillance, NK cells are widely distributed in the body. They are present in lymphoid organs as well as in non-lymphoid peripheral tissues [7]. At steady state, the spleen is the largest reservoir of mouse NK cells [8].The spleen has a complex architecture owing to its dual roles in the filtration of exhausted red blood cells and as a secondary lymphoid organ. Blood is supplied through arterioles that are FrontlineClaude GrØgoire et al. Eur. J. Immunol. 2008. 38: 2076-2084 We and others have previously reported that most NK cells are located in the red pulp area of the spleen with NK cells occasionally present in the white pulp [8,[16][17][18][19]. Moreover, previous reports have suggested that NK cell trafficking was modified in the case of inflammation [16,17], possibly by inflammatory chemokines that are known to act on NK cells [20]. However, the pattern of NK cell trafficking within the spleen is not known. In particular, the route of entry, the migration tracts, and the guidance signals that allow NK cells to enter or leave the red pulp are all issues that need to be addressed.We recently described that the cell surface expression of the activating NK cell receptor NKp46 (CD336) defines NK cells across mammalian species and that staining for NKp46 enables the unambiguous in situ visualization of NK cells in tissue sections [19]. We took advantage of this tool to analyze NK cell trafficking under steady-state and inflammatory conditions. Results NK cells enter the spleen through the marginal zoneWe sought to determine how NK cells enter the spleen and reac...