Consequences of chronic Interferon-gamma expression on the host

Division Of Basic Sciences - Nci

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Abstract

We are utilizing a mouse model of chronic IFN-gamma expression to determine the biological consequences to the host and the relevance of this phenotype to human disease. We have used a bioinformatics approach to identify conserved regions of the 3' untranslated portion of the interferon-gamma mRNA. It is believed that these conserved regions represent important regulatory elements in the gene structure, as there would be no inherent reason for conservation through evolution unless the non-coding regions of the mRNA provided some evolutionary advantage. Based on this analysis, we targeted a 160-bp region of the murine interferon-gamma 3' untranslated region for deletion as this region is rich in AUUA sequences, and such regions have been previously shown to be important in the regulation of cytokine gene mRNA instability. The knockout (KO) mouse has been successfully created on the C57 BL/6 genetic background and our data indicates that this mouse produces significantly more interferon-gamma at a basal level and upon stimulation as compared to the wild-type mouse. Furthermore, the architecture of lymph nodes, spleen, and thymus is disrupted and the liver exhibits signs of chronic inflammation. T cell homeostasis has been disrupted as increased CD4+ and CD8+ T cells are present and the T reg cells in the mouse have more potent suppressor activity. There is also an increased TH1 response and a decreased TH2 response to antigenic stimulation. The B cell population is also altered and baseline antibody production is skewed. B cells are also observed in the thymus at increased frequency, thus indicating that IFN-gamma may alter B cell trafficking. In addition to the phenotypic consequences, the B cell response to antigen is also disrupted as increased IgM and Ig2a ab responses are seen with a decrease in the IgG1 response. Strong anti-DNA and anti-nuclear antigen antibody responses are also observed suggesting that chronic IFN-gamma expression may play a role in the development of lupus. The female mice also develop primary biliary cholangitis, a disease that has no known etiology. This is the first mouse model to recapitulate the human disease with respect to sex bias as 90% of the human cases are in women. The development of PBC can be transferred into recipient RAG mice by CD4+ T cells. Additionally the mice develop a heart defect that is apparent after exercise and they exhibit high levels of lactic acid in their serum following a brief period of exercise. . Furthermore the mice have proven to be susceptible to melanoma that may be a result of increased levels of IL-27 gene expression that has now been observed. IFN-gamma and IL-27 levels directly correlate and elimination of the IL-27 receptor gene results in improvement of the autoimmune status of the mice. In summary, our approach towards elucidating the multiple mechanisms involved in the biology of interferon-gamma demonstrates the complexity by which interferon-gamma gene expression alters host homeostasis. Thus, we now have developed a mouse model for understanding and elucidating the systems biology effects of long term chronic IFN-gamma gene expression, resulting in chronic inflammation in the host.