title: Innate immune responses to gut microbiota differ between oceanic and freshwater threespine stickleback populations.
abstract: Animal hosts must co-exist with beneficial microbes while simultaneously being able to mount rapid, non-specific, innate immune responses to pathogenic microbes. How this balance is achieved is not fully understood, and disruption of this relationship can lead to disease. Excessive inflammatory responses to resident microbes are characteristic of certain gastrointestinal pathologies such as inflammatory bowel disease (IBD). The immune dysregulation of IBD has complex genetic underpinnings that cannot be fully recapitulated with single-gene-knockout models. A deeper understanding of the genetic regulation of innate immune responses to resident microbes requires the ability to measure immune responses in the presence and absence of the microbiota using vertebrate models with complex genetic variation. Here, we describe a new gnotobiotic vertebrate model to explore the natural genetic variation that contributes to differences in innate immune responses to microbiota. Threespine stickleback, Gasterosteus aculeatus, has been used to study the developmental genetics of complex traits during the repeated evolution from ancestral oceanic to derived freshwater forms. We established methods to rear germ-free stickleback larvae and gnotobiotic animals monoassociated with single bacterial isolates. We characterized the innate immune response of these fish to resident gut microbes by quantifying the neutrophil cells in conventionally reared monoassociated or germ-free stickleback from both oceanic and freshwater populations grown in a common intermediate salinity environment. We found that oceanic and freshwater fish in the wild and in the laboratory share many intestinal microbial community members. However, oceanic fish mount a strong immune response to residential microbiota, whereas freshwater fish frequently do not. A strong innate immune response was uniformly observed across oceanic families, but this response varied among families of freshwater fish. The gnotobiotic stickleback model that we have developed therefore provides a platform for future studies mapping the natural genetic basis of the variation in immune response to microbes.
authors.affiliation: Biology Department, Institute of Ecology and Evolution, University of Oregon, Eugene, OR 97403, USA Biology Department, Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA kmillig1@uaa.alaska.edu.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Milligan-McClellan
authors.affiliation: Biology Department, Institute of Ecology and Evolution, University of Oregon, Eugene, OR 97403, USA.
authors.forename: Clayton M
authors.initials: CM
authors.lastname: Small
authors.affiliation: Biology Department, Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA.
authors.forename: Erika K
authors.initials: EK
authors.lastname: Mittge
authors.affiliation: Biology Department, Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA.
authors.forename: Meghna
authors.initials: M
authors.lastname: Agarwal
authors.affiliation: Biology Department, Institute of Ecology and Evolution, University of Oregon, Eugene, OR 97403, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Currey
authors.affiliation: Biology Department, Institute of Ecology and Evolution, University of Oregon, Eugene, OR 97403, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: Cresko
authors.affiliation: Biology Department, Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA.
authors.forename: Karen
authors.initials: K
authors.lastname: Guillemin
mesh_terms: D000818:Animals; D005399:Fishes / Q000382:microbiology*; D005618:Fresh Water; D007113:Immunity, Innate; D007422:Intestines / Q000382:microbiology*; D064307:Microbiota; D012623:Seawater
keywords: Animal model; Fish; Germ-free; Gnotobiotic; Neutrophils; Stickleback