Filamentous bacteriophages: impact on prokaryotic virulence, eukaryotic immunity, and implications for phage therapy.

Filamentous bacteriophages, of the family Inoviridae, are characterized by their reproduction and secretion by their bacterial hosts without killing them. These viruses have evolved mutualistic relationships with their bacterial hosts by impacting bacterial phenotypes in a variety of ways, including biofilm formation, horizontal gene transfer, colonization, and motility. Previous studies have reported that filamentous bacteriophages contain virulence factors that promote the pathogenesis of bacterial infections in animal models and are associated with exacerbating infections in humans. Additionally, these phages have been experimentally used as cloning vectors for DNA sequencing, phage display, and nanotechnological applications. Finally, viromic studies have revealed a substantial presence of filamentous bacteriophages in the human gut. However, their interactions with mammalian cells have not been extensively explored. Here, we review the immunogenicity of filamentous bacteriophages in eukaryotic cells. First, we address how filamentous bacteriophages impact the fitness of their prokaryotic hosts. Then, we review their immunogenicity by focusing on the direct interactions between filamentous bacteriophages and eukaryotic cells that may indicate how these viruses influence various functions. Finally, we provide some thoughts on their impact for use in therapeutics. Through their ubiquitous interactions with prokaryotic and eukaryotic cells, there is still much to be learned about how filamentous bacteriophages affect the biology, pathogenesis, and physiology of the human gut. Unraveling these interactions will provide further evidence as to the importance of the virome to human health.