Immunohistochemical staining of the RA synovial membrane with the anti-Thy-1 mAb AS02. (A) This mAb strongly stained cells in the connective tissue layer beneath the lining layer (APAAP, red staining; arrows), while largely sparing cells of the lining layer (arrowhead). Endothelial cells (asterisk) and connective tissue cells in diffuse infiltrates were also stained, more weakly in the latter case. In serial sections, the anti-CD14 mAb MoS39 (kindly provided by Prof GR Burmester, Berlin, Germany) stained macrophages in the lining layer (arrowhead in (C)) and diffuse inflammatory infiltrates (peroxidase, brown staining; arrow in (C), (E)); the mAb against von Willebrand factor stained endothelial cells (peroxidase, brown staining; (D), (F), (G)). In double-staining experiments, the anti-Thy-1 mAb AS02 showed no overlap with anti-CD14 staining (E). In contrast, endothelial cells were double-stained with both the antibody against von Willebrand factor and the anti-Thy-1 mAb AS02 [arrowheads in (F) (G)]. There was no positive reaction with control isotype-matched mAbs (APAAP and peroxidase) (B), employed as controls for double-staining [(E), (F), (G)]. Original magnification: (A)-(D) and (F), 92 ×; (E) and (G), 184 ×.