Dr. Bradley G Magor > Associate Professor
Contact
Room: CW 323A, Biological Sciences
Phone: (780) 492-5956
Fax: (780) 492-9234
Email: bmagor@ualberta.ca
Academic Training
BSc: University of Victoria
MSc: Dalhousie University
PhD: Medical University of South Carolina
PDF: Stanford University
Current Research Interests
My research interests include: 1) studying the functional properties of the immunoglobulin mutating protein AID (activation-induced cytidine deaminase). 2) correlating germinal center cell organization with antibody affinity maturation and susceptibility to autoimmune diseases. 3) understanding how the adaptive immune system developed and evolved in vertebrates. 4) developing the zebrafish as a model system for studying vertebrate immune processes.
Ongoing & Future Lab Projects (background info below):
Somatic Hypermutation & Class Switching in catfish B-cells
Catfish B-cell lines are being used to determine if fish have all or part of the proteins necessary to drive somatic hypermutation and class switch recombination. We previously cloned the gene for the fish AID mutator and established that it could drive hypermutation and class switch recombination in AID knockout mice. The ability to drive class switching is of particular interest because fish B-cells do not undergo class switch recombination. The catfish AID gene, under control of an inducible promoter, has been integrated into the genome of catfish B-cell lines. These cells are being used to characterize the ability of this 'primordial' AID protein to drive hypermutation and class switch recombination in fish cells.
Evolution of cell type specific transcriptional enhancers
The mouse IgH transcriptional enhancer was perhaps the earliest and most thoroughly studied cell-type-specific enhancer. It was determined that to achieve B-cell specific transcriptional activity there needed to be precise spacing and organization of transcription factor binding motifs 10,11 . However we subsequently determined that there was considerable flexibility in how B-cell specific transcriptional activity could be achieved 12,13 . We are presently examining the IgH and AID enhancer function and structure for a number of different species to determine how much plasticity there has been in the organization of these cell type specific enhancers over time. We have also found evidence that the position of the enhancer within the IgH locus has changed over time and that this relocation of the enhancer influenced the evolutionary course of the immunoglobulin gene and antibodies in vertebrates 14 .
Organization of 'Germinal Centres' in fish
In Situ Hybridization (ISH) and Immunocytochemistry techniques are being used to identify the organization of T- and B-cells (including those expressing the AID mutator) in the lymphoid tissues of catfish and zebrafish. These studies complement those being done with transgenic zebrafish.
Transgenic zebrafish to track humoral immune responses
Using transcriptional enhancers and promoters that are specific for fish immunoglobulin and AID genes, we have constructed reporter transgenes. These genes are integrated into the genomes of zebrafish embryo's and can be used to track those cells expressing immunoglobulin and the immunoglobulin mutator AID. These studies explore where, and under what conditions, zebrafish develop humoral immune responses.
Shark monoclonal antibodies
Sharks produce an antibody form that is comprised of only immunoglobulin heavy chain (i.e. there is no light chain). This give the antibody distinct binding characteristics and also means that the entire antibody is encoded by a single gene. This latter trait means that shark antibodies can be easily expressed in a bacteriophage screening system. We are testing different vaccination strategies aimed at developing strong humoral immune responses in nurse sharks. Antibody cDNA's from these sharks are to be used for development of monoclonal antibodies for research purposes.
Fish as a model of human autoimmune disease
In some types of human autoimmune disease there is formation of ectopic germinal centers outside of the secondary lymphoid organs, e.g. in the synovium of arthritic joints. These aberrant germinal centers lack the organization and structure of conventional germinal centers and have been implicated in the propagation and exacerbation of autoimmunity 6,7 . A question we are trying to resolve is whether the poorly structured ‘normal' germinal centers of fishes have similar organization to the ectopic germinal centers of autoimmune diseases. If so, then fish may provide an excellent model for the study of certain human autoimmune diseases. To develop this model system we have studies to determine how prone fish are to developing autoimmune diseases.
Background:
Normal Affinity Maturation in Mammals
Normally activated B-cells can be sequestered from a primary follicle in the spleen, lymph node or GALT, into a secondary follicle that develops into a germinal center. Within the germinal center the B-cells immunoglobulin heavy chain gene (IgH) will undergo class switch recombination and will also accumulate mutations (somatic hypermutations or SH) within the VDJ exon that encodes the antigen binding site. The mutations may destroy or diminish antigen recognition of the antibodies or they may enhance the binding. To prevent escape of B-cells with deleterious mutations, the germinal center B-cells are pre-programmed to undergo apoptosis. The only B-cells that will be given the signal to escape apoptosis are those that are able to compete for binding to the antigen that is held in complex on the surface of follicular dendritic cells (FDCs) at the margins of the germinal center. This process ensures that only B-cells expressing the highest affinity antibodies leave the germinal center and enter the circulation. The ability to ‘select' these high affinity B-cells relies on precise organization of various cell types in and around the germinal center.
Fish and Amphibians have poor affinity maturation
Vaccination of fish and amphibians does not result in a substantial change in the affinity of antibodies to the immunizing agent – i.e. there is poor affinity maturation, though immunological memory does develop. Because the somatic hypermutation machinery does exist even in ‘ancient' vertebrates such as the sharks 1-3 , it is thought that poor affinity maturation in lower vertebrates is due to an inability of hypermutated B-cells to be selected in a germinal center 4,5 . Fish and amphibians do not have the distinct and well structured germinal centers seen in higher vertebrates. We and others have established that fish B-cells have an intact somatic hypermutation system, and we are now looking at how this system is regulated in the apparent absence of germinal centres.
The diminished affinity maturation in fish has obvious negative implications for the aquaculture industry and our ability to protect fish from disease. However these ‘defects' may also make fish ideal model organisms for the study of normal and aberrant affinity maturation in mammals.
Cited references
1. Saunders H.L. and B.G. Magor . (2004). Cloning and expression of the AID gene in the channel catfish. Dev Comp Immunol. 28(7-8):657-63
2. Wakae K, Magor BG, Saunders H , Nagaoka H, Kawamura A, Kinoshita K, Honjo T, and Muramatsu M. (2006) Evolution of class switch recombination function in fish activation- induced cytidine deaminase, AID. Int Immunol. 18(1):41-47
3. Lenardo, M. et al. (1987) Protein-binding sites in Ig gene enhancers determine transcriptional activity and inducibility. Science 236 (4808), 1573-1577
4. Nikolajczyk, B.S. et al. (1996) Precise alignment of sites required for m enhancer activation in B cells. Molecular and Cellular Biology 16 (8), 4544-4554
5. Magor, B.G . et al. (1994) An Ig heavy chain enhancer of the channel catfish Ictalurus punctatus: evolutionary conservation of function but not structure. J Immunol 153 (12), 5556-5563
6. Magor, B.G. et al. (1997) Functional motifs in the IgH enhancer of the channel catfish. Immunogenetics 46 (3), 192-198
7. Ellestad KK and Magor BG . (2005) Evolution of transcriptional enhancers in the immunoglobulin heavy-chain gene: functional characteristics of the zebrafish E m 3' enhancer. Immunogenetics. 57(1-2):129-39
8. Magor, B.G. et al. (1999) Transcriptional enhancers and the evolution of the IgH locus. Immunol Today 20 (1), 13-17
9. Shao CY, Secombes CJ, Porter AJ (2007) Rapid isolation of IgNAR variable single-domain antibody fragments from a sharksynthetic library. Mol Immunol. 44(4):656-65
10. Berek, C. and Schroder, A.E. (1997) A germinal center-like reaction in the nonlymphoid tissue of the synovial membrane. Ann N Y Acad Sci 815, 211-217
11. Stott, D.I. et al. (1998) Antigen-driven clonal proliferation of B cells within the target tissue of an autoimmune disease. The salivary glands of patients with Sjogren's syndrome. J Clin Invest 102 (5), 938-946
12. Diaz, M. et al. (1998) Somatic hypermutation of the new antigen receptor gene (NAR) in the nurse shark does not generate the repertoire: possible role in antigen-driven reactions in the absence of germinal centers. Proc Natl Acad Sci U S A 95 (24), 14343-14348
13. Diaz, M. and Flajnik, M.F. (1998) Evolution of somatic hypermutation and gene conversion in adaptive immunity. Immunol Rev 162, 13-24
14. Diaz, M. et al. (1999) Mutational pattern of the nurse shark antigen receptor gene (NAR) is similar to that of mammalian Ig genes and to spontaneous mutations in evolution: the translesion synthesis model of somatic hypermutation. Int Immunol 11 (5), 825-833
15. Wilson, M. et al. (1997) A novel chimeric Ig heavy chain from a teleost fish shares similarities to IgD. Proc Natl Acad Sci U S A 94 (9), 4593-4597
16. Du Pasquier, L. et al. (1998) Somatic mutation in ectothermic vertebrates: musings on selection and origins. Curr Top Microbiol Immunol 229, 199-216
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Last Modified:2007-03-14 |