As GFP (CX3CR1) expression separates memory CD8+ T cells into two populations (Fig. 1), we addressed the question whether antigen-specific GFP+ (CX3CR1+) and GFPneg (CX3CR1neg) memory CD8+ T cells generated after viral or bacterial infections in CX3CR1+/GFP reporter mice had distinct functional properties. This evidence concerns the gene CX3CR1 and bacterial infectious disease.