Exogenous IL-15 negatively regulates expression of endogenous mouse CX3CR1 in vivo. Freshly isolated bone marrow, splenocytes, and PBMCs from PBS-injected (PBS), IL-15-injected (IL-15), and noninjected (nil) C57Bl/6 mice were examined for CX3CR1 protein (A) and mRNA (B) expression 1, 5, and 7 days after injection (AI). (B) CCR5, CXCR4, and β₂-microglobulin mRNA expression was also analyzed. (C-D) Results in panels A and B, respectively, were quantitated by densitometry. Protein and RNA analysis was performed on samples pooled from 5 mice in each group, to have sufficient material for protein analysis in the PBMCs.