XCL1 and rheumatoid arthritis: Xcr1 is the receptor for Xcl1 and Xcl2, which were not part of our microarray, but it is known that Xcrl also plays a role in rheumatoid arthritis (Wang et al., 2004) and in the recruitment of cells to arthritic joints (Coelho et al., 2008; Grespan et al., 2008).