title: Effects of carotenoids, immune activation and immune suppression on the intensity of chronic coccidiosis in greenfinches.
abstract: Allocation trade-offs of carotenoids between their use in the immune system and production of integumentary colouration have been suggested as a proximate mechanism maintaining honesty of signal traits. We tested how dietary carotenoid supplementation, immune activation and immune suppression affect intensity of coccidian infection in captive greenfinches Carduelis chloris, a passerine with carotenoid-based plumage. Immune activation with phytohaemagglutinin (PHA) decreased body mass among birds not supplemented with lutein, while among the carotenoid-fed birds, PHA had no effect on mass dynamics. Immune suppression with dexamethasone (DEX) induced loss of body mass and reduced the swelling response to PHA. DEX and PHA increased the concentration of circulating heterophils. Lutein supplementation increased plasma carotenoid levels but had no effect on the swelling response induced by PHA. PHA and DEX treatments did not affect plasma carotenoids. Immune stimulation by PHA suppressed the infection, but only among carotenoid-supplemented birds. Priming of the immune system can thus aid in suppressing chronic infection but only when sufficient amount of carotenoids is available. Our experiment shows the importance of carotenoids in immune response, but also the complicated nature of this impact, which could be the reason for inconsistent results in studies investigating the immunomodulatory effects of carotenoids. The findings about involvement of carotenoids in modulation of an immune response against coccidiosis suggest that carotenoid-based ornaments may honestly signal individuals' ability to manage chronic infections.
authors.affiliation: Department of Zoology, Institute of Ecology and Earth Sciences, Tartu University, Vanemuise 46, 51014 Tartu, Estonia. tuul.sepp@gmail.com
authors.forename: Tuul
authors.initials: T
authors.lastname: Sepp
authors.forename: Ulvi
authors.initials: U
authors.lastname: Karu
authors.forename: Elin
authors.initials: E
authors.lastname: Sild
authors.forename: Marju
authors.initials: M
authors.lastname: Männiste
authors.forename: Peeter
authors.initials: P
authors.lastname: Hõrak
mesh_terms: D000818:Animals; D001715:Bird Diseases / Q000276:immunology* / Q000469:parasitology; D002338:Carotenoids / Q000008:administration & dosage / Q000494:pharmacology / Q000502:physiology*; D002908:Chronic Disease; D003048:Coccidiosis / Q000276:immunology / Q000469:parasitology / Q000662:veterinary*; D003907:Dexamethasone / Q000494:pharmacology; D019587:Dietary Supplements; D046369:Finches / Q000469:parasitology*; D005938:Glucocorticoids / Q000494:pharmacology; D007107:Immune System / Q000187:drug effects / Q000276:immunology*; D007165:Immunosuppression Therapy / Q000662:veterinary; D008297:Male; D008934:Mitogens / Q000494:pharmacology; D010835:Phytohemagglutinins / Q000494:pharmacology
chemical_list: D005938:Glucocorticoids; D008934:Mitogens; D010835:Phytohemagglutinins; D002338:Carotenoids; D003907:Dexamethasone