ITGB1 and rheumatoid arthritis: Furthermore, 99 ± 6% of RA-FLSs expressed the fibroblast marker CD90, 97 ± 1% of RA-FLSs expressed CD29 (β1-integrin) and less than 0.6 ± 0.5% of RA-FLSs expressed the macrophage marker CD68.