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Title: The role of defensins in controlling Salmonella infection in chickens
Author: Soulier, Annelise
ISNI:       0000 0001 3472 3539
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2007
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Defensins are a family of cysteine-rich vertebrate antimicrobial peptides which can be divided into two main families, a-defensins, found only in mammals, and {J-defensins, identified in all vertebrate species. In chickens, only {J-defensins have been reported, ana are now named avian {J-defensins (AvBD). The project aim was to compare AvBDs mRNA levels in different chicken lines considered as susceptible and resistant to different Salmonella serotypes. Indeed, a previous study showed that a-defensins expressed in Paneth cells were inhibited ~fter Salmonella infection in mice suggesting that the inhibition defensins is a virulence strategy of the intestine pathogen. Therefore, we wished to test the hypothesis that the susceptibility of chicken lines to Salmonella infection correlated with decreased AvBD. transcript levels, as previously shown in mice. To date, thirteen AvBDs have been already described in the literature. Here l describe a novel avian {J-defensin, named AvBD14. The AvBD14 has two exons and one intron and is only expressed at the mRNA level in the skin and spleen. I also propose that two {j-defensins, originally described as gallinacin 1 and 1ex which differ by only three amino acids due to three nucleotide substitutions, actually represent polymorphic variants ofthe same gene, named AvBDl. Because of their differential expression profiles as previously reported, AvBDs 1 and 2, originally isolated from heterophils, and AvBDs 3, 4 and 5, previously described as peptides expressed by epithelial tissues, were chosen to study their expression in a variety of in vitro and in vivo systems. In order to develop new bioreagents, I attempted to express AvBDs using the Baculovirus system. Unfortunately, the specific physicochemical characteristics of these antimicrobial peptides made them difficult to purify and they were, therefore, examined by measuring their mRNA expression levels. In this study, inbred chicken lines 61 and N, previously characterized both for their resistance to systemfc Salmonella disease and their levels of Salmonella colonization, were selected to analyze the expression ofthe AvBD panel chosen. Line 61 and line N chickens are resistant and susceptible to Salmonella serovar Typhimurium colonisation respectively and, interestingly, mRNAs for AvBDs 2, 3 and 5 were undetectable at 7 dpi in the caecal tonsil of line N chickens infected with S. Typhimurium. AvBDl mRNA expression was also down-regulated soon after infection suggesting thatline N susceptibility is a deficiency in innate immunity. In addition, the differential responses of inbred lines to Salmonella serovars indicate the involvement of a common mechanism of resistance. For this purpose, AvBD expression was also analysed in the resistant line, line 61, and the susceptible line, line 72, following infection with different Salmonella serovars. In resistant. and susceptible chickens infected with host-specific or broad host range Salmonella serovars, mRNA level ofAvBDs was differentially expressed, but not inhibited. In conclusion, we have demonstrated .that the level of expression of AvBDs did not detennine the resistance or susceptibility pattern of chicken line 61 and 72 to systemic salmonellosis. However, the expression of several of AvBDs may regulate the resistance of chicken line 61to S.Typhimurium colonisation.
Supervisor: Kaiser, Pete ; Barrow, Paul Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available