Unmethylated oligo-DNA containing CpG motifs aggravates collagen-induced arthritis in mice

To investigate the effects of an intradermal injection of an unmethylated oligodeoxynucleotide (ODN) containing CpG motifs on the severity of collagen-induced arthritis (CIA).

CIA was induced in DBA/1 LacJ mice by immunization with bovine type II collagen (CII) in Freund's complete adjuvant followed 3 weeks later by immunization with CII in Freund's incomplete adjuvant (yielding CIA mice). Unmethylated ODN containing a CpG motif was injected intradermally into DBA/1 LacJ mice at a dosage of 20 microg (yielding CpG-CIA mice) 1 week prior to the first immunization with CII. Unmethylated ODN containing a GpC motif instead of a CpG motif and ODN containing a methylated CpG motif were used to produce controls (GpC-CIA mice and mCpG-CIA mice, respectively). After the second immunization with CII, arthritis scores were measured weekly up to the eighth week. At the eighth week, the mice were killed, histopathologic changes in the ankle joints were examined, and titers of interferon-gamma (IFNgamma) in the supernatants of splenocytes (1 x 10(7)) stimulated in culture by CII for 3 days were determined by enzyme-linked immunosorbent assay.

CpG-CIA mice had significantly higher arthritis scores than CIA mice. CpG-CIA mice had more severe histopathologic changes than CIA mice and mCpG-CIA mice. Moreover, splenocytes in CpG-CIA mice produced higher IFNgamma titers in response to CII than did splenocytes in CIA mice and mCpG-CIA mice.

Injection of unmethylated oligo-DNA containing CpG motifs aggravated CIA through activation of the Th1-type immune response, suggesting that microbial infection could be one of the mechanisms for aggravation or exacerbation of arthritis or, alternatively, that such infection could be an adjuvant in the induction of arthritis in rheumatoid arthritis.