ADGRE2 and rheumatoid arthritis: In both receptors the fourth EGF domain binds chondroitin sulphate10,20,21 which, in EMR2, may recruit macrophages in the inflamed synovium of rheumatoid arthritis patients20; however, the prevailing CD97 variant on leukocytes contains only EGF domains 1, 2 and 522, indicating that the receptors have non-redundant functions.