Effect of fibroblast activation protein (FAP) deficiency on disease severity in arthritic mice. (A) Effect of FAP-deficiency on weight, grip strength, and paw swelling over time (weeks 6 to 12). All data are means ± standard error of the mean (SEM) of 7 FAP knockout (fap−/−), 13 human tumor necrosis factor alpha transgene (hTNFtg) and 13 (fap−/− hTNFtg) mice (B) Representative microphotographs of toluidine blue-stained joint sections at week 12 of fap−/−, hTNFtg, and fap−/−/ hTNFtg mice, illustrating inflammation and joint destruction. (C) Magnified representative cartilage areas, demonstrating destained cartilage caused by proteoglycan loss (arrows). (D) Tartrate-resistant acid phosphatase (TRAP) staining of corresponding joint sections, illustrating the presence of osteoclasts (red-brownish). Scale bars, 200 μm. (E) Quantitative histomorphometric assessment of synovial inflammation, bone erosion, cartilage degradation, and osteoclast numbers in tarsal joints. All data are means ± SEM of 7 fap−/−, hTNFtg, and fap−/− hTNFtg mice each (*
P <0.05, **
P <0.01). (F) Representative genotyping PCR for confirmation of FAP deficiency in the various mouse lines.