CXCR4 and systemic lupus erythematosus: The CXCL12/CXCR4 axis has been implicated in the pathogenesis of several types of inflammatory arthritis and autoimmune diseases, including rheumatoid arthritis (RA) [13,14], osteoarthritis (OA) [15,16], systemic lupus erythematosus (SLE) [17], and ankylosing spondylitis (AS) [18].