Due to the association between osteopontin and RA, several anti-osteopontin antibodies have been developed and studies of these antibodies in animal RA models show promising results.23–25 The antibody M5 recognizes and binds to a cryptic epitope of thrombin-cleaved mouse osteopontin (147SLAYGLR153) and thereby blocks the binding of cleaved osteopontin to α9 and α4 integrins, which result in abrogation of monocyte migration.18 Here, SPP1 is linked to rheumatoid arthritis.