Control of influenza A virus infection by gamma interferon-inducible mediators

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Influenza A virus is a cause of morbidity and mortality worldwide. Due to antigenic shift and drift of the virus, including the emergence of pandemic strains, humans are often challenged with strains different from those to which they have been exposed by vaccination or prior infection. This has historically resulted in very serious increases in illness and death. The most severe pandemic of influenza A virus that has occurred in modern times was the worldwide pandemic of 1918-1920 when over 20 million deaths occurred. Development of new interventive strategies to combat virus-related illness therefore remains critical to complement the present vaccine approach. For this, a clear understanding of the host's response to influenza virus infection is essential. For its part, the immune system has at its disposal several strategies to combat influenza A virus. How the immune system deals with the virus is controlled by a complex network of interactions involving cells, cell surface molecules, soluble mediators termed cytokines and chemokines. One cytokine, interferon-gamma, seems to be a key player in the body s ability to get rid of the virus. Here, we are trying to understand how interferon-gamma does this. We believe that this cytokine causes specific immune cells to produce other molecules, such as indolamine 2,3-deoxygenase (IDO) and chemokines, and that it is these molecules that control virus growth. We do not know whether these molecules stop virus growth directly or by creating the right conditions for this. We are interested in understanding the sequence of events that is started by interferon-gamma and ends in the clearance of virus from the lungs. To study the immune response to influenza virus, we use a mouse model that reproduces most features of the human disease. By understanding the events that lead to effective virus clearance in this disease, it may be possible to design new ways in which to combat this problematic infection in humans.