Nucleic acids, oxidation, and anti-microbial peptides

Autoimmune reactivity to antigens that are associated with nucleic acids is a hallmark of autoimmune disorders such as systemic lupus erythematosus (SLE), systemic sclerosis, primary Sjögrens syndrome, polymyositis/dermatomyositis, or rheumatoid arthritis (RA). In the last years it has become evident that the selection of these autoantigens for immune attack is based on their intrinsic ability to activate nucleic acid-binding receptor systems such as Toll-like receptors (TLR). Whereas there is ample evidence of an important role of activation of the innate immune system by nucleic acids in disease pathogenesis, especially in SLE, many issues remain unanswered. The aim of this project is to shed light on three areas in question, i.e. 1.) the nature of the involved antigen-presenting cells (APC), 2.) the mechanism of the uptake of nucleic acids in these APCs, and 3.) the influence of reactive oxygen species (ROS), and to elucidate a possible connection between these three pathways. 1.) Using a state-of-the-art panel of in vitro technology, the APCs responsible for rendering lymphocytes capable of inducing lupus or arthritis will be characterized functionally and phenotypically. For analysis of the pathophysiological role of certain subsets of APCs, cellular transfer experiments into several nave autoimmune- prone mice and rat strains will be performed. 2.) Recent data indicate an intriguing connection between oxidative burst and innate immune reactivity towards nucleic acids. The aim of this part of the project is to shed further light on the association between these mechanisms and to elucidate an eventual link to impaired phagocytosis due to lack of ROS. 3.) Especially in lupus, exposure to endogenous nucleic acids in the context of a defective waste disposal system or excessive and prolonged cell death has been assumed to contribute importantly to disease development and maintenance. However, nucleic acids are normally rapidly degraded by ubiquitous nucleases in vivo and it has been debated how they can reach the nucleic acid-sensing TLRs residing in endosomal compartments. In the light of recent data revealing the nucleic acid-shuttling properties of host-derived anti-microbial peptides (AMP) in the context of psoriasis it will be highly interesting if expression of AMPs also has an influence on lupus and arthritis. This will be done by analysing expression of AMPs in mouse and rat models and in peripheral blood from SLE and RA patients and by inhibition experiments employing anti-AMP antibodies or siRNA. If successful, integration and combination of the concepts of TLRs, oxidative burst and anti-microbial peptides within this project will advance the understanding of the pathogenesis of autoimmune diseases and may contribute to the development of a novel, tailored concept of therapy.

Summary for public relations work Rheumatic autoimmune diseases such as rheumatoid arthritis (RA) and Systemic Lupus Erythematosus (SLE) affect the quality of life and life expectancy of the patients and also have a profound economic impact due to expenditures for health care and lost wages. A hallmark of the above mentioned diseases is the reactivity of the immune system against the bodys own nucleic acids (DNA and RNA). The aim of this project was to shed light on three areas in question, i.e. 1.) the nature of the involved cells, 2.) the mechanism of the uptake of nucleic acids in these cells, and 3.) the influence of oxidation, and to elucidate a possible connection between these three areas. In the first part of the project a rat arthritis model (pristane-induced arthritis) was used to show that nucleic acids activate cells of the so-called innate immune system, in particular so-called macrophages. Subsequently, these macrophages activate so-called T cells and render them arthritogenic. Anti-microbial peptides (AMPs) and nucleic acids are able to form ionic complexes. The formation of these complexes leads to an enhanced uptake into the cells. In the second part of this project the role of AMPs for the development and the activity diseases of arthritis was analysed. We could show that there is a strong reactivity against AMPs (particular against cathelicidins) in animal models of arthritis and lupus and in human individuals with SLE. On the other hand, a mouse strain that does not have cathelicidins is not protected against arthritis and lupus. It is therefore currently not clear, if the reactivity against AMPs is directly involved in the development of rheumatic diseases. Recent data indicate an intriguing connection between oxidative burst and innate immune reactivity towards nucleic acids. The aim of the second part of the project was to shed further light on the association between these mechanisms and to elucidate an eventual link to impaired phagocytosis due to lack of oxidation. We were able to demonstrate that the oxidative burst can eventually protect mice from the development of lupus. In this project, a connection between abnormal uptake of nucleic acids, oxidative burst and anti-microbial peptides was elucidated. The gained results advance the understanding of the pathogenesis of autoimmune diseases and may contribute to the development of novel, tailored concepts of therapy.