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Background/purpose: Antibodies against type II collagen (anti-CII) are arthritogenic and central to the initiation of the disease. An animal model of collagen type II-specific monoclonal antibody-induced arthritis (CAIA) has been used for the evaluation of various therapeutic effects in rheumatoid arthritis (RA). We aimed to measure the expression of matrix metalloproteinase (MMP)-9 (gelatinase B), tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in the acute and chronic stages of the CAIA model for application as a therapeutic marker.Methods: A commercially available antibody cocktail containing four monoclonal anti-type II collagen antibodies were injected into 6 to 8-week-old male BALB/c mice (n=20) and 50 microL lipopolysaccharide was injected 3 days later. The clinical manifestations of RA were recorded and scored at 10 days (acute stage) and 21 days (chronic stage). Then the mice were sacrificed for histologic analysis of the inflamed footpad and gene expression of IL-1beta, TNF-alpha and MMP-9 by ELISA and quantitative polymerase chain reaction amplification.Results: Marked inflammation was found in the limb joints of mice at 10 days. Both IL-1beta and MMP-9 expression played a central role in the inflammatory reaction in the acute stage. The expression level of MMP-9 mRNA remained high in the chronic stage of CAIA, but that of IL-1beta mRNA was unexpectedly negligible; the serum level of TNF-alpha in CAIA was undetectable in the acute stage. The expression level of TNF-alpha mRNA was also lower than IL-1beta and MMP-9 in the acute inflammatory stage.Conclusion: The CAIA model is a fast and highly replicable model of RA. MMP-9 and IL-1beta were highly expressed in the acute stage of CAIA. It is suggested the MMP-9 mRNA level is a suitable marker for both acute and chronic stage, whereas IL-1beta is a marker only for the acute stage of the CAIA murine model. [ABSTRACT FROM AUTHOR]