CD319 is expressed on RA synovial tissue (IHC) and is a marker of plasma cells. FFPE samples of synovial tissues from RA patients were used for IHC analysis of CD319 using (A) 1G9 alone and co-stained with cell surface markers for leukocyte subsets (B-F). Double labeling studies were performed using 1G9 in combination with (B) anti-CD3 (T cells), (C) anti-CD20 (B cells), (D) anti-CD56 (NK cells), (E) anti-CD68 (macrophages), and (F) CD138 for plasma cells. Brown staining represented CD319 reactivity while other cell surface markers stained red. Double staining cells are purple. FFPE, formalin fixed paraffin embedded; IHC, immunohistochemistry; RA, rheumatoid arthritis.