CX3CR1 and rheumatoid arthritis: One of the most important candidate genes studied is CX3CR1. This gene encodes C-X3-C motif chemokine receptor 1, a transmembrane protein involved in leukocyte adhesion and migration [9] and in modulating cellular immune responses in inflammatory and viral diseases [10, 11], including coronary heart disease [12], hypertension [13], rheumatoid arthritis [14], liver disease [15], and AIDS [16].