Podoplanin is expressed in human synovial tissue in RA. Immunohistochemistry (IHC) of human synovial tissue from (A-D, I) rheumatoid arthritis (RA), (E-H, J) osteoarthritis (OA) (A-D, E-H, J) using antipodoplanin antibody (D2-40) or (I) mouse immunoglobulin G1. (J) Positive control showing lymph vessels (arrow). (K) IHC staining score of podoplanin on human synovial tissue from 18 RA and 9 OA patients. Double immunofluorescence staining of (L and M) RA and (N) OA synovium using antipodoplanin (green) and anti-cadherin-11 (red) antibodies. Note the extensive hyperplasia of the podoplanin-positive lining layer cells (C and D, L) and the podoplanin-positive lymph vessel (arrowhead in N) but negative lining layer in OA (N). L, lumen. ***statistical significance P < 0,0001.