The aim of this study was to examine whether inhibition of Interleukin (IL)-6 signaling by MR16-1, an IL-6 receptor antibody, attenuates aortitis, cardiac hypertrophy, and arthritis in IL-1 receptor antagonist deficient (IL-1RA KO) mice.  Four weeks old mice were intraperitoneally administered with either MR16-1 or non-immune IgG at dosages that were adjusted over time for 5 weeks.  These mice were stratified into 4 groups: MR16-1 treatment groups, KO/MR low group (first 2.0 mg, following 0.5 mg/week, n=14) and KO/MR high group (first 4.0 mg, following 2.0 mg/week, n=19) in IL-1RA KO mice, and IgG treatment groups, KO/IgG group (first 2.0 mg, following 1.0 mg/week, n=22) in IL-1RA KO mice, and wild/IgG group (first 2.0 mg, following 1.0 mg/week, n=17) in wild mice.  Aortitis, cardiac hypertrophy and arthropathy were histologically analyzed.  Sixty-eight % of the KO/IgG group developed aortitis (53% developed severe aortitis).  In contrast, only 21% of the KO/MR high group developed mild aortitis, without severe aortitis (P<0.01, vs KO/IgG group).  Infiltration of inflammatory cells, such as neutrophils, T cells, and macrophages, was frequently observed around aortic sinus of the KO/IgG group.  Left ventricle and cardiomyocyte hypertrophy were observed in IL-1RA KO mice.  Administration of high dosage of MR16-1 significantly suppressed cardiomyocyte hypertrophy.  MR16-1 attenuated the incidence and severity of arthritis in IL-1RA KO mice in a dose-dependent manner.  In conclusion, blockade of IL-6 signaling may exert a beneficial effect to attenuate severe aortitis, left ventricle hypertrophy, and arthritis

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