Figure 3

Immunohistochemistry of CXCR5 in lymphoid cell aggregates of rheumatoid arthritis synovia. Sections of rheumatoid synovium were treated with (a) CXCR5 antibody or (b) isotype control. Serial sections were treated with (c) anti-CD20 as a marker of B lymphocytes or (d) isotype control. Arrows indicate B lymphocytes expressing CXCR5. (e) Rheumatoid synovium treated with the T-cell marker anti-CD3 followed by alkaline phosphatase and Vector red substrate (methyl green counterstain). T cells stain a light red colour. (f) Serial section from the same synovial sample as (e) treated with anti-CD3, alkaline phosphatase and Vector red followed by anti-CXCR5, peroxidase and 3,3'-diaminobenzidine (DAB)-Nickel substrate (no counterstain used). T cells that express CXCR5 are stained dark red whereas cells expressing CXCR5 alone are grey–black in colour. (g) Control for (e), in which isotype-matched rabbit immunoglobulin (Ig) was used instead of anti-CD3. (h) Control for (f), in which isotype-matched rabbit and mouse Ig were applied instead of CD3 and CXCR5 antibodies (no counterstain used). Unless stated otherwise, DAB substrate was used. (a), (c) and (e)–(h) Original magnification, 420 ×; isotype controls (b) and (d) original magnification, 280 ×.