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Studies on the mechanisms of immune evasion in Trypanosoma carassii infections of the goldfish (Carassius auratus) Open Access


Other title
Trypanosoma carassii
Immune evasion
Type of item
Degree grantor
University of Alberta
Author or creator
Oladiran, Ayoola
Supervisor and department
Belosevic, Mike (Biological Sciences)
Examining committee member and department
Field, Catherine (Agriculture Food and Nutrition Science)
Leys, Sally (Biological Sciences)
Buret, Andre (University of Calgary)
Belosevic, Mike (Biological Sciences)
Stafford, James (Biological Sciences)
Chang, John (Biological Sciences)
Department of Biological Sciences
Physiology and Cell Biology
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Parasites possess variety of mechanisms to modulate or evade host defence systems to maintain chronic infection and ensure their transmission. The protozoan parasite Trypanosoma carassii is infective to a number of freshwater fish species and can cause significant mortality in aquaculture. T. carassii shares similarities with both T. brucei, the causative agent of sleeping sickness and T. cruzi, which causes Chagas’ disease. It is not known how T. carassii escapes host immune responses. My doctoral research focused on the interactions between T. carassii and its fish host with emphasis on the strategies used by the parasite to evade fish immune host defense.. and establish long lasting infections. I identified at the molecular level the key antigens of T. carassii present in excretory/secretory (ES) products and surface protein fractions of the parasite. As a first step toward understanding the importance of select antigens of T. carassii, I produced the recombinant proteins and characterized their roles in immune evasion. Like heat shock protein 70 of other pathogens, I found that T. carassii hsp70 was immunogenic and was present in both ES products and surface protein fraction of the parasite. Recombinant parasite hsp70 significantly increased expression of pro-inflammatory genes and enhanced inflammatory response of goldfish macrophages. In contrast, another parasite surface molecule, glycoprotein 63 (Gp63) down-regulated both pathogen and cytokine-induced inflammatory responses of goldfish monocytes and macrophages. Parasite gp63 was associated with macrophages and appeared to interfere with signalling mechanisms. Since complement-mediated lysis is one of the main host defence responses against trypanosomes, I cloned and characterized parasite surface molecule called calreticulin. Recombinant T. carassii calreticulin bound to first component of complement, C1q, of not only goldfish but also humans. Further, recombinant T. carassii calreticulin inhibited C1q-dependent hemolysis. T. carassii infection of goldfish induced increased expression of pro- and anti-inflammatory cytokines. Increased cytokine mRNA levels were observed during the acute phase of infection, and then they returned to normal levels or were down-regulated during the elimination phase of the infection. These findings demonstrate that parasite surface molecules and those found in ES fraction have the capacity to manipulate host inflammatory and antimicrobial responses, thereby ensuring persistence of T. carassii in its host.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Oladiran A and Belosevic M. 2011. A review: Immune Evasion Strategies of Trypanosomes. Journal of Parasitology in press Oladiran A, Beauparlant D, Belosevic M. The expression analysis of inflammatory and antimicrobial genes in the goldfish (Carassius auratus L.) infected with Trypanosoma carassii. Fish and Shellfish Immunology. 31: 606-613. Oladiran A and Belosevic M. 2010. Trypanosoma carassii calreticulin binds host complement component C1q and inhibits classical complement pathway-mediated lysis. Developmental and Comparative Immunology. 34: 396-405. Oladiran A and Belosevic M. Trypanosoma carassii hsp70 increases expression of inflammatory cytokines and chemokines in macrophages of goldfish (Carassius auratus L). Dev Comp Immunol. 2009. 33: 1128-1136.

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