Project description:Innate immunity is expected to play a primary role in conferring resistance to novel infectious diseases, but few studies have attempted to examine its role in the evolution of resistance to emerging pathogens in wild vertebrate populations. Here we used experimental infections and cDNA microarrays to examine whether changes in the innate and/or acquired immune responses likely accompanied the emergence of resistance in house finches (Carpodacus mexicanus) in the eastern United States subject to a recent outbreak of conjunctivitis-causing bacterium (Mycoplasma gallisepticum- MG). Three days following experimental infection with MG, we observed differences in the splenic transcriptional responses between House Finches from eastern U.S. populations, with a 12-year history of MG exposure, versus western U.S. populations, with no history of exposure to MG. In particular, western birds down-regulated gene expression, while eastern finches showed no expression change relative to controls. Studies involving poultry have shown that MG can manipulate host immunity, and our observations suggest that pathogen manipulation occurred only in finches from the western populations, outside the range of MG. Fourteen days after infection, eastern finches, but not western finches, up-regulated genes associated with acquired immunity (cell-mediated immunity) relative to controls. These observations suggest population differences in the temporal course of the response to infection with MG, and imply that innate immune processes were targets of selection in response to MG in the eastern U.S. population. Birds were randomly selected to be kept either as controls or infected via ocular inoculation with 20 μl of culture containing 1 x 104 to 1 x 106 color changing units/ml of an early 2007 Auburn MG isolate. All infected birds were inoculated with precisely the same volume of the same culture. Control birds were sham infected using sterile SP4 medium (Whitcomb 1983). Infected birds were euthanized three days (N=6 from Arizona and N=11 from Alabama) and 14 days (N=11 from Arizona and N=12 from Alabama) after treatment. Control birds were euthanized 14 days after sham-inoculation; Control (N=11 birds from Arizona and 9 from Alabama) and infected birds were maintained under identical conditions, but in separate rooms of an aviary. Infected birds were euthanized three days (N=6 from Arizona and N=11 from Alabama) and 14 days (N=11 from Arizona and N=12 from Alabama) after treatment. Control birds were euthanized 14 days after sham-inoculation. We used a common reference design (Yang & Speed 2002), in which we pooled 2 to 6 spleens from birds from the same population in the same treatment to generate enough mRNA for microarray hybridizations and hybridized two pools for each treatment from each population.

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