THBS1 and rheumatoid arthritis: These early studies, combined with the significant role integrins play in the process of leukocytes crossing the blood vessel barrier to reach inflammatory sites (16), lead to the hypothesis that the interaction between TSP-1, CD47, and integrins may play a vital role in the infiltration of immune cells, especially T cells, across the blood vessel barrier into synovial membrane tissue during the development of rheumatoid arthritis.