THY1 and rheumatoid arthritis: previously showed localization of PG staining from synovial samples only within cells expressing markers of antigen presentation (HLA-DR, CD40, CD80, CD86) in situ. However, we and others have subsequently shown that synovia from Lyme arthritis [17] and rheumatoid arthritis [49] contain distinct populations of HLA-DR + CD90 + synovial fibroblasts, particularly within the synovial sub-lining and perivascular regions.