Granzyme B is dispensable for immunologic tolerance to self in a murine model of systemic lupus erythematosus

• Published in: Arthritis and rheumatism 2005-06, Vol.52 (6), p.1684-1693
• Main Authors: Graham, Kareem L., Thibault, Donna L., Steinman, Jonathan B., Okeke, Lance, Kao, Peter N., Utz, Paul J.
• Format: Article
• Language: English
• Subjects: Animals; Autoantibodies - immunology; Autoantigens - immunology; Autoimmunity - immunology; Biological and medical sciences; Female; Granzymes; Immune Tolerance - immunology; Lupus Erythematosus, Systemic - immunology; Medical sciences; Mice; Models, Animal; Sarcoidosis. Granulomatous diseases of unproved etiology. Connective tissue diseases. Elastic tissue diseases. Vasculitis; Serine Endopeptidases - immunology
• ISSN: 0004-3591; 1529-0131
• DOI: 10.1002/art.21092

Objective Proteolytic autoantigen cleavage by the serine protease granzyme B has been implicated in the development of systemic autoimmune disease; however, there has been no conclusive demonstration of a pathogenic role for granzyme B in autoimmunity. In this study, we evaluated the role of granzyme B in a murine model of autoimmunity. Methods To identify potential novel granzyme B substrates, complementary DNAs encoding nuclear factor 45 (NF45) and NF90 were used to generate 35S‐methionine–labeled proteins by coupled in vitro transcription/translation. Radiolabeled proteins were then incubated with purified recombinant granzyme B or caspases, and the cleavage products were analyzed by autoradiography. We also immunized granzyme B–deficient and granzyme B–intact mice with the mineral oil pristane. Production of autoantibodies directed against granzyme B substrates in response to pristane was evaluated by Western blotting, immunoprecipitation, and enzyme‐linked immunosorbent assay. Results The double‐stranded RNA–binding protein NF90 was identified as a novel substrate for caspases and granzyme B, both in vitro and in vivo. NF90 is uniquely cleaved by granzyme B in vitro; however, pristane immunization still induced anti‐NF90 antibodies in granzyme B–deficient mice. Pristane‐treated granzyme B–deficient mice also produced antibodies directed against the U1–70‐kd antigen, a previously identified granzyme B substrate. Last, antibodies directed against U1–70 kd arose spontaneously in granzyme B–deficient mice. Conclusion These results demonstrate that granzyme B is not required for the production of autoantibodies directed against antigens that are granzyme B substrates in vitro. The data also suggest a protective role for this proapoptotic protease in systemic autoimmunity.