Neopterin and 7,8-dihydroneopterin in T-cell regulation

Research project P 14154 Neopterin and 7,8-dihydroneopterin in human T-cell regulation Dietmar FUCHS 24.01.2000 The pteridines neopterin and 7,8-dihydroneopterin are synthesized in large amounts by human macrophages/monocytes during activated cell-mediated immune response. The major trigger thereby is interferon- (IFN-), a cytokine released by activated type 1 T-helper (Th1) cells. Neopterin concentrations in blo od and urine are known to be elevated in a large variety of human diseases, including infections caused by viruses (e.g. HIV), or by intracellular bacteria (such as tuberculosis). Elevated neopterin concentrations were also observed in autoimmune diseases, including rheumatoid arthritis and systemic lupus erythernatosus (SLE), and often correlate very closely with disease progression, e.g., in HIV infection and SLE. Neopterin consequently serves as a sensitive laboratory diagnostic tool in monitoring disease activity in many patients. Recent studies performed in cell culture models showed that neopterin and 7,8-dihydroneopterin are likely to be involved in regulatory processes in eukaryotic cells. In the human lymphocytic cell line JURKAT 7,8-dihydroneoptedn activated the signal transduction factors NF-1cB and AP-1, and in various cell lines the pteridine was able to onset programmed cell death (apoptosis). Another study showed that 7,8-dihydroneopterin can enhance gene expression of the HIVA promoter in JURKAT cells. The ability of neopterin-derivatives to interfere with the cellular redox balance seems to be crucial in these processes. The aim of this project is to further study the biochemical and regulatory functions of neopterin and 7,8-dihydroneopterin. The presence of neopterinderivatives in various disorders and their ability to interfere with redox-sensitive signaling pathways and to mediate apoptosis is becoming more relevant as the pathology of many diseases today is known to be associated with oxidative stress and enhanced apoptotic cell death. The effects of neopterin and 7,84hydroneopterin on freshly isolated human T cells from healthy donors and from patients with SLE shall be assayed. Thereby special attention will be drawn on interactions between the pteridines and the cytokine network. These investigations are inevitable to interpret results obtained in cell culture models and to elucidate the role of the production of neopterin and 7,8-dihydroneopterin inhuman immune activation.

Neopterin derivatives are produced by macrophages and dendritic cells in response to the Th-1 type cytokine interferon- during cell-mediated immune activation. The role of neopterin as a immune activation marker is well established in a large variety of diseases, including human immunodeficiency virus infection, or autoimmune diseases such as systemic lupus erythematosus. Recent studies demonstrated that neopterin derivatives display specific biochemical functions. Neopterin derivatives activate intracellular transcription factors, modulate gene expression, or induce apoptosis in different cell lines. The scope of this project was to study the biochemical relevance of neopterin derivatives in primary cultures of human T cells to further investigate and underline a possible significance in vivo. 7,8-Dihydroneopterin, but not neopterin, was found to potently induce apoptosis in peripheral blood T cells. In comparison to T lymphoblastic cell lines, freshly isolated T cells reacted more sensitively to the pteridine. Evidence has accumulated that oxidative stress might play a role in the ability of 7,8- dihydroneopterin to induce apoptosis and oxygen radical formation in aqueous solutions of 7,8-dihydroneopterin. In agreement, in our co-incubation experiments antioxidants significantly reduced apoptosis induced by 7,8- dihydroneopterin in T lymphocytes. In parallel experiments, T cells were isolated from patients with systemic lupus erythematosus. Although immunological activation markers were relatively low in the group of patients tested, cells showed significantly lower rates of apoptotic cells in response to 7,8-dihydroneopterin after 24 hours incubation compared to T cells from healthy blood donors. Results suggest that 7,8-dihydroneopterin specifically attacks normal T cells and thereby contributes to the accumulation of autoreactive T cell clones in systemic lupus erythematosus. In addition, the modulatory effect of neopterin derivatives on the production of cytokines was studied. In contrast to earlier investigation performed in cell lines, neither neopterin nor 7,8-dihydroneopterin influenced cytokine production in T cells. But 5,6,7,8-tetrahydroneopterin completely blocked mitogen-induced cytokine production in primary cultures of T lymphocytes. In conclusion, within this project we could verify that neopterin derivatives modulate human T cell function and could thereby represent a tool for monocytes or dendritic cells to regulate T cell response. Further, neopterin derivatives might play a crucial role in chronic inflammation by contributing to the development of immunodeficiency.