Host influence on cell tropism and immune response to MERS-CoV

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Zoonotic viruses, such as Middle East respiratory syndrome coronavirus (MERS-CoV) can cause severe pathology in humans, but in reservoir hosts, little to no evidence of disease may be present. In camels, which serve as a amplifying host, a primarily upper respiratory tract infection has been experimentally observed with little pathology and no longer term consequences, despite high levels of virus shedding. In humans, and nonhuman primate and mouse animal models, mild to severe disease is served, with virus primarily targeting the lower respiratory tract for replication. Understanding how a virus interacts with different hosts, where there is significant differences in viral replication, shedding and ultimately disease can provide many insights into beneficial and detrimental virus-host interactions. My lab is in the process of establishing a surrogate animal model for camels, using alpacas, to allow us to study virus replication, shedding, transmission, tissue tropism and pathogenesis to compare and contrast reservoir and disease models. Preliminary data indicates that alpacas and camels are comparable models. As a comparator, we will use transgenic mice that express human dipeptidyl peptidase 4 (hDPP4), the receptor for MERS-COV. This model recapitulates severe disease comparable to that observed in humans. Studying the virus interplay with the host in both these two widely different models will allow us to dissect out mechanisms of how virus spread, cellular tropism and the host response varies in different model systems. This will help us to understand the mechanisms that both the virus and the host use to influence virus replication and tropism - which ultimately determines whether infection results in a relatively reservoir-like state suitable for transmitting the virus on to new hosts or disease-like state that results in significant illness and/or death. First we will define the cellular tropism of MERS-CoV in the mouse and alpaca models, determining receptor distribution and quantifying virus output in primary cell cultures of respiratory tract tissues. In vitro findings will be confirmed in the animal model. As all MERS-CoV viruses to date have been passaged in monkey cells, we will generate a camelid-adapted virus in a camel cells line, with subsequent genomic and growth kinetic characterization to determine effects on tropism and pathogenesis. Next, we will determine differences in immune cell recruitment and activity in respiratory tract tissues in both animal models using cell type specific gene markers, determining levels of inflammatory cytokines and identifying what cells are recruited to sites of infection. Last, we will determine the mechanism of virus spread in respiratory tissues. The kinetics of infection under different conditions that favour either release and diffusion or cell-to-cell spread with determine if virus spread in the lung is primarily cell-to-cell.