Collagen type IV staining in healthy and arthritic synovial tissue. Collagen type IV was found in the lining layer of synovial biopsies from (a) healthy human subjects and (c) rheumatoid arthritis (RA) patients. Relative isotype controls are shown in (b,d). Double staining was performed to reveal the cellular origin of the type IV collagen. (e) Double staining was found in the lining layer. For a clearer picture, succeeding slices were stained with (f) CD55 or (g) collagen type IV. (h) Isotype control. Arrows indicate collagen IV, CD55 or double staining in the lining layer. (i) PCR results: top, collagen type IV mRNA expression in fibroblast-like synoviocytes from 10 RA patients and 11 healthy controls; bottom, β2-microglobulin (β2M) mRNA expression in the same samples.