Abstract
Early events in retrovirus transmission are determined by interactions between incoming viruses and frontline cells near entry sites. Despite their importance for retroviral pathogenesis, very little is known about these events. We developed a bioluminescence imaging (BLI)-guided multiscale imaging approach to study these events in vivo. Engineered murine leukemia reporter viruses allowed us to monitor individual stages of retrovirus life cycle including virus particle flow, virus entry into cells, infection and spread for retroorbital, subcutaneous, and oral routes. BLI permitted temporal tracking of orally administered retroviruses along the gastrointestinal tract as they traversed the lumen through Peyer's patches to reach the draining mesenteric sac. Importantly, capture and acquisition of lymph-, blood-, and milk-borne retroviruses spanning three routes was promoted by a common host factor, the I-type lectin CD169, expressed on sentinel macrophages. These results highlight how retroviruses co-opt the immune surveillance function of tissue-resident sentinel macrophages for establishing infection.
Highlights
Retroviruses cause cancer and immunodeficiencies (Blattner, 1999)
We established a bioluminescence imaging (BLI)-directed approach for studying individual stages of retroviral infection in vivo by strategically inserting reporters into unique sites in the murine leukemia virus (MLV) genome (Figure 1A)
To monitor virus entry into the cytoplasm of cells, we fused firefly luciferase (Fluc) to the C-terminus of MLV Gag (MLV Gag-Fluc EnvWT) and exploited the ATP-dependence of Fluc activity, which is restricted to the host cell cytoplasm in vivo
Summary
Retroviruses cause cancer and immunodeficiencies (Blattner, 1999). Once retroviruses establish viral reservoirs, it is difficult to eliminate infection as retroviral genomes are permanently integrated into host DNA. We implemented BLI by developing a series of MLV-based reporter viruses to enable observation of specific stages of the retrovirus life cycle in vivo, including viral particle flow, entry into the cytoplasm, first infection events, and spread. We first validated this system by testing its ability to uncover new insights into previously studied subcutaneous and intravenous transmission routes (Sewald et al, 2015; Uchil et al, 2019b; Pi et al, 2019). Understanding these events will inform design of improved prophylactic strategies that target prevention of virus acquisition and establishment of infection
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