Expression of the same receptors could be observed on the non-RA membranes with the exception of Bob, CCR7 and CCR9. Bob/GPR15 is an orphan receptor that is a coreceptor for human and simian immunodeficiency viruses, and its expression in the RA synovium is a novel observation that might be worthy of further investigation. Here, CCR9 is linked to rheumatoid arthritis.