TY - JOUR T1 - Granzyme B Induces Apoptosis of Chondrocytes with Natural Killer Cell-like Cytotoxicity in Rheumatoid Arthritis JF - The Journal of Rheumatology JO - J Rheumatol SP - 1932 LP - 1943 VL - 35 IS - 10 AU - SEIJI SAITO AU - KAORU MURAKOSHI AU - SHIGERU KOTAKE AU - NAOYUKI KAMATANI AU - TAISUKE TOMATSU Y1 - 2008/10/01 UR - http://www.jrheum.org/content/35/10/1932.abstract N2 - Objective Granzyme B, an apoptosis-inducing factor, is expressed in natural killer (NK) cells, an important factor in innate immunity. We previously reported that granzyme B is expressed in arthritic cartilage and chondrocytes, and suggested that granzyme B expression is related to apoptosis distribution. We have now investigated whether granzyme B directly induces apoptosis in chondrocytes and whether chondrocytes possess NK cell-like function. Methods Chondrocytes included the human C-28/12 chondrocyte cell line, normal chondrocytes, and rheumatoid arthritis (RA) chondrocytes. Apoptosis was analyzed by ELISA and TUNEL after C-28/12 cells were incubated with active granzyme B. NK cell markers were examined in chondrocytes by FACS and immunohistochemistry. Chondrocytes with or without Z-AAD-CMK, a known granzyme B inhibitor, were stimulated with PHA (20 μg/ml), followed by coculture with K562 cells in order to test chondrocyte cytotoxity. Results Granzyme B was successfully introduced into C-28/12 chondrocytes, and was confirmed to dose-dependently induce apoptosis. Immunohistochemically, chondrocytes expressed the surface antigens of NK cells and exhibited cytotoxicity against K562 cells, which served as an indicator of cytotoxicity. Z-AAD-CMK inhibited cytotoxicity against K562 cells in a dose-dependent manner, thus confirming that chondrocyte cytotoxicity against K562 cells is dependent on granzyme B. Conclusion Our findings indicate that chondrocytes possess NK cell-like activity related to innate immunity, and that apoptosis is induced in these cells by granzyme B. Our findings suggest that inflammation activates granzyme B, which participates in the destruction of RA-affected joints. ER -