Immunohistochemistry of CXCR5 in the intima and postcapillary venules in rheumatoid arthritis synovia. (a) CD68+ cells in the intima. (b) Serial section to (a) stained for CXCR5. Note the colocalization of CXCR5 and CD68 to the same group of cells. (c) and (d) Sections from the same region as (a) and (b), treated with isotype-matched control immunoglobulin instead of CD68 and CXCR5 antibodies, respectively. (e) Postcapillary venule positive for CXCR5 within a lymphoid aggregate. Labelling was revealed using 3,3'-diaminobenzidine substrate. (f) Isotype control for (e). (a), (b), (e) and (f) Original magnification, 420 ×; (c) and (d) original magnification, 350 ×.