Background and objectives: Interleukin-18 (IL-18) is a pleiotropic cytokine involved in rheumatoid arthritis (RA) pathogenesis. This studywas carried out to evaluate the efficicacy of interleukin-18 binding protein (IL-18BP) gene therapy in the rat adjuvant-induced arthritis (AIA) model and to decipher the mechanisms by which IL-18BP delivery lessens bone destruction. Materials and methods: Arthritis was induced in female Lewis rat by Mycobacterium butyricum and the mRNA expression of IL-18 and IL-18BP was determined in the joints. In a preventative study, rats were divided into an adenovirus producing IL-18BP-Fc (AdmIL-18BP-Fc) group (n=8) and an adenovirus producing green fluorescent protein (AdGFP) group (n=7). On day 8 after AIA induction, adenoviruses were injected. Clinical parameters were assessed. At day 18, during maximal arthritis, the rats were euthanized, ankles were collected, and X-rays were performed. mRNA and protein were extracted from joints for analyses by qRT-PCR, multiplex, Western blot, and zymography. Results: We observed a decrease in the [IL-18BP/IL-18] ratio from day 7 to day 45. Administration of AdmIL-18BPd-Fc decreased clinical parameters and prevented bone and joint destruction compared to AdGFP administration. IL-18BP delivery reduced the metalloproteinase 9 (MMP-9) levels by 33% (at protein level (Fig. 1B) and functional level (Fig. 1C) and the tartrate-resistant acid phosphatase (TRAP) level by 44% (Fig. 1D) in the joint homogenates from AdmIL-18BPd-Fc compared to AdGFP treated rats.However, no variationwas observed forMMP-2 at the protein level (Fig.1A) and functional level (Fig. 1C). Conclusions: In rat AIA, a decrease in the [IL-18BP/ IL-18] ratio was observed. IL-18BP delivery prevented joint and bone destruction by downregulating MMP-9 and TRAP, suggesting a potential benefit of a similar therapy in RA.