The role of defensins and C-X-C chemokines in mammalian innate immunity

• Main Author: Rehaume, Linda Marie
• Language: English
• Published: University of British Columbia 2010
• Online Access: http://hdl.handle.net/2429/29909

In humans, defensins constitute the largest group of host defence peptides that are evolutionarily conserved components of innate immunity. Defensins share many structural and functional characteristics with C-X-C chemokines, including a C-X-C amino acid motif, net positive charge, disulphide bonding, three-dimensional shape and chemokine activity. Deficiencies in α-defensins and C-X-C chemokines have been correlated with susceptibility to infection and chronic inflammatory diseases. However the genetics and diversity of defensins and mechanisms underlying these disorders were not well understood. This thesis comprises three separate but overlapping approaches to address these issues. The genomic content of murine α-defensins within the reference C57BL/6J strain was characterized. Novel α-defensin (11) and defensin-related cryptdin (3) genes were found, as were gene duplications and differences in genomic content between strains of mice. A next-generation sequencing method was developed for the quantitative analysis of α-defensin and defensin-related cryptdin gene expression. The α-defensin DEFA1 induced interleukin (IL) 8 and IL10 release from human PBMCs. The mechanism(s) of action of defensins, which appears to involve induction of chemokines and anti-inflammatory cytokines, needs further elucidation in vivo. Consequently, novel murine models of inflammation and immunosuppression were developed. The IL8 and Il10 genes were separately cloned, behind an intestine-specific promoter, into eukaryotic expression vectors, which were used to transfect murine embryonic stem cells. Correct targeting was confirmed for both constructs and germline transmission achieved for the IL8 mice. Conditional homozygous mice were generated, which, upon breeding with Cre-expressing mice, will express IL8, a C-X-C chemokine, in an intestinal-specific manner. This will enable analyses of effects of chemokine overexpression on intestinal infection, and on peptide efficacy in the resolution of infection. In other studies to address innate immune mechanisms, the transcriptional profiles of patients susceptible to Salmonella and mycobacterial infections due to immunodeficiencies in IL12- and interferon-γ-mediated immunity were generated. These data indicated that the chemokines CXCL9 and CXCL10 might mediate immunity to Mycobacteria whereas additional defects in TLR4 responses appeared to underlie susceptibility to Salmonella. The data presented here strengthen our understanding of the murine defensin repertoire and provide tools that enable sophisticated systems level studies of in vivo function.