Modulation of inflammation by immunostimulatory DNA

Abstract

The aim of this thesis was to elucidate the roles of different types of DNA in inflammatory responses. We compared the immune responses to nuclease-protected phosphorothioate oligodeoxynucleotides (S-ODNs) and phosphodiester oligodeoxynucleotides (O-ODNs) that either contained or lacked CpG motifs. The combination of CpG motif and S-ODN backbone was strongly synergistic for immunostimulation and caused the highest frequency of arthritis in intra-articularly injected mice. CpG-S induced arthritis correlated with a strong induction of NFkappaB, whereas S-ODN-induced immune activation and arthritis appeared to be independent of NFkappaB. Furthermore, we studied the in vivo and in vitro inflammatogenic properties of CpG ODNs, that contained a specific nucleobase deletion either upstream or downstream of the CpG motif. Depending on the location, nucleobase deletions reduced the arthritogenicity of CpG-S DNA, while retaining potent immunostimulatory activity, in terms of the induction of cytokines, chemokines and lymphocyte proliferation. CpG-S stimulation of splenocyte proliferation was significantly reduced by the addition of O-ODNs. Furthermore, CpG-S-induced production of IL-6 and IL-10, which both promote B-cell differentiation, was also downregulated when O-ODNs were added in combination with CpG-S. Since the O-ODN-mediated inhibition of proliferation was less pronounced in IL-10-/- mice, it appears that the anti-proliferative effects of O-ODNs are partially mediated by the downregulation of IL-10 production. B-cell responses to CpG DNA-containing immune complexes may play a role in chronic autoimmunity and in immune responses to bacterial components. Therefore, we investigated the potential interaction between CpG DNA stimulation and FcgammaR clustering on B-cell activities. We found that CpG DNA and FcgammaR clustering synergized to enhance B-cell proliferation, having also impact on several maturation stages in the late differentiation stage of splenic B cells. In conclusion, the inflammatogenic and arthritogenic properties of DNA could be modulated by changing the DNA sequence or backbone, or by modifying the nucleobases. Thus, ODNs may be tailor-made to provide directed immune responses. Furthermore, CpG DNA and FcgammaR clustering were synergistic with respect to B-cell activation. CpG DNA-containing immune complexes may play a role in the host defense against pathogens and as adjuvants in vaccines. However, certain properties of immunostimulatory DNA may, in a given host environment, lead to the development or aggravation of autoimmune disease.