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The ultimate strategy for control of viral infections is to develop genetically resistant animals. Resistance to respiratory illness following infectious bronchitis virus (IBV) infection of chicks can be correlated with genetic relatedness in the B complex. Similar to high path avian influenza virus, IBV a non-zoonotic pathogen, causes a systemic infection. Our overall aim is to determine mechanisms that promote B haplotype resistance to viral respiratory disease. <P> Objective 1 is to characterize the pathogenesis in chicks with B haplotypes expressing extreme clinical illness following IBV infection and to further identify the impact of viral pathotypes, with markedly different capacities to cause respiratory or kidney disease, on these host responses. Pathogenesis will be determined by clinical illness, viral load and histopathology. <P>Objective 2 will identify differences in innate and adaptive immunity that correspond with extreme B haplotype responses to IBV infection. B lymphocyte production of specific antibody will be quantified from extreme haplotypes using antibody ELISA and ELISPOT assays. IBV specific CD8+ T lymphocytes responses will be examined after stimulation by target cells infected with IBV. The early observed differences in clincial illness following IBV infection suggests that innate immunity plays a critical role. Monocytes and NK cells will be the focus of innate immunity which will be examined at the functional level, and by evaluating mRNA expression of the individual cell populations. Microarray analyses of NK cells will provide insight into mechanisms that result in specific transcript changes in expression mediate variation across B haplotypes.
NON-TECHNICAL SUMMARY: The ultimate strategy for control of viral infections is to develop animals that are resistant to disease. Our studies will identify factors that make chickens resistant to disease caused by infectious bronchitis virus (IBV). IBV causes a disease similar to the (high pathogenic) serious form of avian influenza. However, IBV only infects birds and therefore, it not a threat to research personnel or the community. Our previous studies have shown that the illness caused by IBV differs in severity depending on the genetics of the birds that were being used for study. These studies will be very comprehensive in that we will evaluate the critical components of the immune system that are involved in controlling viral disease. Therefore, we will not only identify birds with the genetic background to resist disease caused by a respiratory virus, but we will identify specific components of the immune system that are responsible for the resistance. Ultimately, birds could be selected that are resistant to viral infections.
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APPROACH: While the mechanisms responsible for differences in virally induced clinical illness of defined B lines are not known (19), Fulton et al. (20) showed haplotype relationships that correspond to the haplotype responses to IBV. We will use our collective expertises to examine pathogenesis of, and innate and adaptive immunity to IBV infection, and thus elucidate factors that are direct or indirect consequences of expression of B complex genes. The specific aims are to compare: 1. Pathogenesis of distinct strains of IBV in B haplotype defined chickens. A. The pathogenesis of distinct IBV strains in B2/B2, B12/B12 and B8/B8 haplotype lines. The histopathology, viral load, and degree of clinical illness will be evaluated in these lines using 3 distinct viral pathotypes; Wolgemuth (severely nephropathogenic, moderately pneumopathogenic strain), Gray (moderate peumopathogenic, moderate nepthropathogenic), and Mass41 (severe pneumopathogenic, non-nephropathogenic). B. Identify dominance in the B haplotype lines that are more resistant to IBV infection. Using the viral strain that detected the greatest extreme in pathogenesis above, the B15, and B21 homozygous lines will additionally be evaluated as they have been shown to differ with IBV infection and heterozygous matings, such as B2/B12, B8/B2, and/or B8/B12, will be infected to determine the dominance of resistance phenotypes. 2. Compare the immune responses of contrasting haplotype lines to a selected viral strain. A. Compare the innate immune responses. Functional assays will be used to characterize and compare target cell activation of NK cells and poly I:C activation of macrophages. mRNA expressions of genes will be compared to identify molecules and pathways responding to infection. B. Compare the adaptive immune responses. The induction of IBV specific antibody responses and B lymphocytes, in antigen secreting cell assays, will be compared. CD8+ T cell responses, shown to be responsible for the initial elimination of virus, will be compared using ex vivo induction with APC and using adoptive transfer of CD8+ T cells. Overall hypotheses are: 1) Resistance or susceptibility to IBV infection is genetically linked indirectly, if not directly, through the MHC to induce vigorous innate immune responses that translate into a more effective adaptive immunity. 2) Adaptive immunity is also genetically linked either directly or indirectly to the MHC, even in the absence of vigorous innate immunity.