IL-15 is present in synovial tissue in rheumatoid arthritis before and after treatment with infliximab. Sections of synovial biopsy tissue from patient no. 5 show diaminobenzidine staining (haematoxylin counterstained) for IL-15 neutralizing antibody before (a) and after (b) treatment with infliximab, and for IL-15 non-neutralizing antibody before (c) and after (d) treatment with infliximab. In (a) and (c) solid arrows indicate synovial lining layer and dotted arrows indicate endothelial cells. Original magnification × 250.