CD8A and infection: Finally, the physiological importance of the direct impact of TLR2 ligands on CD8 T cells has been established in vivo by the demonstration that TLR2 deficiency in CD8 T cells impairs clearance of the bacteria Listeria monocytogenes [28], and that TLR2 plays a critical T cell-intrinsic role in CD8 T cell expansion and memory formation during an infection by vaccinia virus [26].