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Avian Dis.: Enhanced innate immune responses in a brood parasitic cowbird species: degranulation and oxidative burst.

We examined the relative effectiveness of 2 innate immune responses in 2 species of New World blackbirds (Passeriformes, Icteridae) that differ in resistance to West Nile virus (WNV). We measured degranulation and oxidative burst, 2 fundamental components of phagocytosis, and we predicted that the functional effectiveness of these innate immune responses would correspond to the species' relative resistance to WNV. The brown-headed cowbird (Molothrus ater), an obligate brood parasite, had previously shown greater resistance to infection with WNV, lower viremia and faster recovery when infected, and lower subsequent antibody titers than the red-winged blackbird (Agelaius phoeniceus), a close relative that is not a brood parasite. We found that cowbird leukocytes were significantly more functionally efficient than those of the blackbird leukocytes and 50% more effective at killing the challenge bacteria. These results suggest that further examination of innate immunity in the cowbird may provide insight into adaptations that underlie its greater resistance to WNV. These results support an eco-immunological interpretation that species such as the cowbird, which inhabit ecological niches with heightened exposure to parasites, experience evolutionary selection for more-effective immune responses.

2013;57:285-289.

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Author:Hahn, D.C.; Summers, S.G.; Genovese, K.J.
Publication:Journal of Avian Medicine and Surgery
Article Type:Brief article
Date:Sep 1, 2013
Words:185
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