Expression data of Brain CD45+ cells from WT and STI knockout mice after WNV infection

West Nile virus (WNV) is the most important cause of endemic encephalitis in the USA. Strikingly, only a small percentage of patients develop clinical disease and of these patients, approximately 1 out of 150 patients develops encephalitis. The basis for this great variability in disease outcome is unknown, but may be related to the innate immune response. Innate immune responses, critical for control of WNV infection, are initiated by signaling through pathogen recognition receptors (PRR) such as RIG-I and MDA5. IPS-1 is a key adaptor in generating a PRR-dependent interferon response.. Here we show that IPS-1 deficiency in hematopoietic cells resulted in increased mortality and delayed WNV clearance from the brain. In IPS-1-/- mice, a dysregulated immune response was detected, characterized by a massive influx of macrophages and virus-specific T cells into the infected brain. These T cells were multifunctional and were able to lyse peptide-pulsed target cells in vitro. However, virus-specific T cells in the infected IPS-1-/- brain exhibited lower functional avidity than those in C57BL/6 brains, possibly contributing to less efficient virus clearance. The presence of virus-specific memory T cells was also not protective. We also show that macrophages were increased in numbers in the IPS-1-/- brain. Both macrophages and microglia exhibited an activated phenotype. Microarray analyses showed the preferential upregulation of genes associated with leukocyte activation and inflammation. Together, these results demonstrate the critical role that hematopoietic cell expression of Type 1 interferon and other IPS-1-dependent molecules have in WNV clearance and in regulating the inflammatory response.

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Zhao J, Vijay R, Zhao J, Gale M Jr, Diamond MS, Perlman S