The migration of leukocytes from the bloodstream to sites of inflammation is a dynamic factor involving adhesion molecules and chemotactic factors. Chemokines play a role in the trafficking of leukocytes by inducing cellular motility and activating adhesion molecules within the immune system. Lymphotactin (also known as XCL1 and SCM-1) is a unique chemokine that retains only two of the four cysteine residues found in the CC, CXC and CX3C families of chemokines. A Gi-coupled receptor, XCR1, binds to lymphotactin and mediates its chemotactic effects. Chemokines promote accumulation of activated mononuclear cells (MNCs) in inflamed joints in rheumatoid arthritis (RA) and lymphotacin is highly expressed in synovial fluid of RA patients. In situ hybridization studies indicate that XCR1 expression was detected in both the infiltrated MNCs and the synoviocytes from synovial specimens taken from RA patients.