Defensin driven viral evolution

Abstract

Enteric α-defensins are potent peptide effectors of innate immunity that are abundantly expressed in the small intestine. Certain enteric bacteria and viruses are resistant to defensin-mediated killing and can even appropriate defensins to enhance infection, even though infection by closely related microbes is strongly neutralized by defensins. We therefore hypothesized that enteric α-defensins impose selective pressure during fecal-oral transmission. To test this hypothesis for non-enveloped viruses, we passaged a defensin-sensitive serotype of human adenovirus in the presence of a human defensin. Over many replication cycles, we observed the accumulation of mutations in two external hypervariable loops of the major capsid protein hexon. In contrast, prior studies identified the vertex proteins, fiber and penton base, as important determinants of defensin antiviral activity. Through infection and biochemical assays, we found that although all three capsid proteins serve a critical role in defensin-mediated neutralization, hexon is the primary determinant of enhancement in adenovirus as no virus without homologous HVRs was enhanced. Importantly, we established human enteric α-defensins as mediators of selection during an infection. These results extensively revise our understanding of the interplay between defensins and non-enveloped viruses, providing a rationale for the difference in infection phenotypes of closely related adenoviruses. In addition, they establish the feasibility of defensin-mediated neutralization shaping viral evolution within the gastrointestinal system. We then expanded our studies of defensins as an evolutionary pressure to a different non-enveloped virus, rotavirus. Rotavirus is fecal-orally transmitted, as such virions encounter enteric α-defensins during a natural infection and likely also undergo selective pressure to escape neutralization. However, the interaction between rotavirus and defensins had yet to be studied. Initial experiments established the strong rotavirus enhancing potential of enteric α-defensins. To understand the evolutionary effects of defensins on rotavirus, we then tested the infection levels of rotavirus in the presence of both myeloid and enteric α-defensins from multiple species. Preliminary data focusing on mouse, human, and rhesus rotaviruses and α-defensins identified patterns of enhanced infection in the presence of enteric α-defensins and neutralization in the presence of myeloid α-defensins. These preliminary studies further support the potential of defensin as a selection pressure and provide a new system to understand the interaction between α-defensins and non-enveloped viruses.