Immunostimulatory DNA and the innate immune response to Trypanosoma brucei rhodesiense

The work presented in this thesis describes the role of immunostimulatory DNA in the immune response to Trypanosoma brucei rhodesiense. Relative resistance to trypanosome infection is dependent on a strong type I cytokine response that is generated in part by TLR9-dependent innate immune responses. We hypothesized that trypanosome DNA would stimulate macrophages to produce immunoregulatory molecules that are part of the type I immune response to trypanosomes. We began by measuring the amount of accessible cell-free trypanosome DNA in the plasma of infected mice. Trypanosome DNA was detectable during the initial phase of infection, as trypanosome numbers increase. Using an in vitro macrophage model system and purified trypanosome DNA, we identified several macrophage responses to trypanosome DNA. Our results showed that several molecules involved in the TLR9 signal transduction cascade were activated in macrophages in response to trypanosome DNA. Subsequently, the cells demonstrated increased expression of several proinflammatory and immunoregulatory genes. Ultimately, trypanosome DNA induced macrophages to produce NO, TNF-alpha, IL-10, IL-6, IL-12, and PGE2. These results demonstrate that macrophages activation in response to trypanosome DNA leads to the production of several molecules that play a role in the immune response to trypanosomes.; Because responses to DNA contribute to the type I cytokine response, we then hypothesized that enhancement of this response by synthetic CpG oligodeoxynucleotides (ODNs) would lead to enhanced resistance to trypanosome infection. CpG ODN treatment prior to infection increased resistance to infection and decreased parasitemia in susceptible mouse strains. This increase in resistance coincided with increased trypanosome-specific B and T cell responses, increased type I cytokine production, and changes in trypanosome morphology. Relative resistance to infection was increased in SCID mice, which demonstrates that the innate immune response plays a role in CpG ODN-mediated enhancement of immune responses.; Overall, these results show that the innate immune response is both shaped and enhanced by immunostimulatory DNA. These studies provide a context and framework for analyzing the overall contribution of the innate immune response to relative resistance and trypanosome-specific immune responses. Illuminating the mechanisms by which trypanosomes are eliminated by the immune system is fundamental for understanding resistance to infection and designing immunotherapeutic stratagems.