Activation of macrophages by astrovirus through a replication-independent mechanism
Koci, Matthew Damon
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Astroviruses are small, non-enveloped, single stranded RNA viruses known to be one of the leading causes of acute gastroenteritis world wide. Our understanding of astrovirus pathogenesis and disease resolution is limited. This was due to the lack of a small animal model for in depth study of basic astrovirus biology. To increase our understanding of astrovirus disease, we developed a small animal model in young turkeys, infected with turkey astrovirus type-2 (TAstV-2). Through these studies, we described TAstV-2 pathogenesis including viral distribution, kinetics of replication, and cellular histopathology. Additionally, we examined the immune response to primary TAstV-2 infection. These experiments demonstrated that TAstV-2 stimulated avian macrophages (M Ö s) to produce nitric oxide (NO). We hypothesized that TAstV-2 stimulated M Ö production of NO through a replication independent manner. To test this hypothesis we used the well established avian M Ö cell line HD11. These experiments verified that TAstV-2 specifically bound to HD11 cells through an unidentified surface protein, was internalized, and stimulated NO in a replication-independent manner. Additionally, recombinant capsid protein alone is sufficient for NO stimulation suggesting that exposure of M Ö s to astrovirus leads to activation and expression of NO. NO is a known antiviral factor. To determine if NO is involved in primary TAstV-2 clearance or disease, we first asked if NO levels increased during infection. In vivo experiments indicated increased expression of NO in the intestines of TAstV-2 infected embryos but not age-matched controls. Additionally, embryos infected with TAstV-2 in the presence of NO donors had limited viral replication as determined by real time RT-PCR, while the use of NO inhibitors increased the viral titers. These studies suggested that the presence of NO influences viral replication in vivo. These data are the first experimental evidence of an interaction between astroviruses and M Ö s, and suggested that NO and the innate immune response was critical in the control of astrovirus during primary infection.