Modulation of inflammation by immunostimulatory DNA

Sammanfattning: 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.