title: Genotype-specific vs. cross-reactive host immunity against a macroparasite.
abstract: Vertebrate hosts often defend themselves against several co-infecting parasite genotypes simultaneously. This has important implications for the ecological dynamics and the evolution of host defence systems and parasite strategies. For example, it can drive the specificity of the adaptive immune system towards high genotype-specificity or cross-reactivity against several parasite genotypes depending on the sequence and probability of re-infections. However, to date, there is very little evidence on these interactions outside mammalian disease literature. In this study we asked whether genotype-specific or cross-reactive responses dominate in the adaptive immune system of a fish host towards a common macroparasite. In other words, we investigated if the infection success of a parasite genotype is influenced by the immunization genotype. We reciprocally immunized and re-exposed rainbow trout (Oncorhynchus mykiss) to a range of genotypes of the trematode eye fluke Diplostomum pseudospathaceum, and measured infection success of the parasite. We found that the infection success of the parasite genotypes in the re-exposure did not depend on the immunization genotype. While immunization reduced average infection success by 31%, the reduction was not larger against the initial immunization genotype. Our results suggest significant cross-reactivity, which may be advantageous for the host in genetically diverse re-exposures and have significant evolutionary implications for parasite strategies. Overall, our study is among the first to demonstrate cross-reactivity of adaptive immunity against genetically diverse macroparasites with complex life cycles.
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland ; Biodiversity and Conservation Biology, Swiss Federal Research Institute WSL, Birmensdorf, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Rellstab
authors.forename: Anssi
authors.initials: A
authors.lastname: Karvonen
authors.forename: Katja-Riikka
authors.initials: KR
authors.lastname: Louhi
authors.forename: Jukka
authors.initials: J
authors.lastname: Jokela
mesh_terms: D056704:Adaptive Immunity; D000818:Animals; D003429:Cross Reactions; D005393:Fish Diseases / Q000276:immunology / Q000469:parasitology*; D006790:Host-Parasite Interactions / Q000276:immunology*; D008195:Lymnaea; D017686:Oncorhynchus mykiss / Q000276:immunology / Q000469:parasitology*; D014200:Trematoda / Q000502:physiology*; D014201:Trematode Infections / Q000276:immunology* / Q000469:parasitology