文摘
Helminth parasites of teleost fish have evolved strategies to evade and manipulate the immune responses of their hosts. Responsiveness of fish host immunity to helminth antigens may therefore vary depending on the degree of host-parasite counter-adaptation. Generalist parasites, infective for a number of host species, might be unable to adapt optimally to the immune system of a certain host species, while specialist parasites might display high levels of adaptation to a particular host species. The degree of adaptations may further differ between sympatric and allopatric host-parasite combinations. Here, we test these hypotheses by in聽vitro exposure of head kidney leukocytes from three-spined sticklebacks (Gasterosteus aculeatus) to antigens from parasites with a broad fish host range (Diplostomum pseudospathaceum, Triaenophorus nodulosus), a specific fish parasite of cyprinids (Ligula intestinalis) and parasites highly specific only to a single fish species as second intermediate host (Schistocephalus pungitii, which does not infect G.聽aculeatus, and Schistocephalus solidus, infecting G.聽aculeatus). In聽vitro responses of stickleback leukocytes to S.聽solidus antigens from six European populations, with S.聽solidus prevalence from <1% to 66% were tested in a fully crossed experimental design. Leukocyte cultures were analysed by means of flow cytometry and a chemiluminescence assay to quantify respiratory burst activity. We detected decreasing magnitudes of in聽vitro responses to antigens from generalist to specialist parasites and among specialists, from parasites that do not infect G.聽aculeatus to a G.聽aculeatus-infecting species. Generalist parasites seem to maintain their ability to infect different host species at the costs of relatively higher immunogenicity compared to specialist parasites. In a comparison of sympatric and allopatric combinations of stickleback leukocytes and antigens from S.聽solidus, magnitudes of in聽vitro responses were dependent on the prevalence of the parasite in the population of origin, rather than on sympatry. Antigens from Norwegian (prevalence 30-50%) and Spanish (40-66%) S.聽solidus induced generally higher in聽vitro responses compared to S.聽solidus from two German (<1%) populations. Likewise, leukocytes from stickleback populations with a high S.聽solidus prevalence showed higher in聽vitro responses to S.聽solidus antigens compared to populations with low S.聽solidus prevalence. This suggests a rather low degree of local adaptation in S.聽solidus populations, which might be due to high gene flow among populations because of their extremely mobile final hosts, fish-eating birds.
