This mouse has been generated by targeted gene disruption. The mouse provides a model to investigate the function of the chemokine receptor CX3CR1, which is a proinflammatory receptor for the leukocyte chemoattractant CX3CL1 (aka fractalkine). As an example, the mouse is in use in the study of atherosclerosis. Further, the mouse may serve as a model study the role of the immune system during infection with pathogens as well as other immunologically mediated diseases and responses to tumors.