Podoplanin and clusterin are reliable markers of nonneoplastic synovium at various sites

Clusterin (CLU) has been noted to mark synovium adjacent to tenosynovial tumors, and studies suggest that podoplanin (PP) is upregulated in inflammatory arthritis. Characterization of synovial staining with CLU and PP in various nonneoplastic disease states has not been described. Methods. A microarray was created from paraffin-embedded human synovium, including 19 normal/ noninflammatory (10 weight-bearing joints, 8 non-weight-bearing joints), 9 rheumatoid arthritis, 10 synovial cysts, and 3 osteoarthritis and stained with PP (D2-40) and CLU. Staining intensity was graded semiquantitatively (0-3+). Results. PP and CLU stained synovium in 88% and 95% cases, respectively. PP and CLU showed moderate to strong (3+) staining in 26% and 19% of noninflammatory and 44% and 0% of inflammatory synovia, respectively (P <.01). Conclusions. PP and CLU are reliable markers of human synovium and can confirm its presence in limited specimens. Although CLU was more sensitive, PP may be more useful in the setting of chronic inflammation.