Since the staining morphology of our anti-FLS rmAbs suggested partial binding to cytoskeletal proteins, either through direct biding or interaction with HSP60 (24), we performed double-immunofluorescence staining of the RA-rmAbs with an anti–human F-actin antibody showing variable but largely incomplete colocalization for the 3 RA-rmAbs with a structural FLS antigen (Supplemental Figure 5). Here, HSPD1 is linked to rheumatoid arthritis.