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Respiratory Syncytial Virus infection biases the immune response in favor of Th2: the role of Indoleamine 2, 3-dioxygenase Open Access


Other title
Indoleamine 2, 3-dioxygenase
Respiratory Syncytial Virus
Type of item
Degree grantor
University of Alberta
Author or creator
Ajamian, Farnam
Supervisor and department
Adamko, Darryl J. (Pediatrics)
Moqbel, Redwan (Department of Immunology, University of Manitoba)
Examining committee member and department
Carina, Majaesic (Pediatrics)
Kane, Kevin (Medical Microbiology & Immunology)
Jacoby, David (Pulmonary and Critical Care Medicine, Oregon Health & Science University)
Thebaud, Bernard (Pediatrics)
Department of Medicine
Experimental Medicine
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Infants that develop severe bronchiolitis due to Respiratory Syncytial Virus (RSV) are at increased risk of developing asthma later in life. To begin my studies in vitro, purified RSV stock was needed. My first study established the critical steps in RSV purification to determine a procedure that ensures the removal of potential contaminating pro-inflammatory mediators in viral preparations. Using polyethylene glycol and ultracentrifugation through various sucrose gradient concentrations, we collected samples at all steps of purification to determine the RSV titer, total protein (µg/mL) and pro-inflammatory cytokines (ELISA). We analyzed the efficacy of each step and determined that, regardless of optimal purification methods employed, CCL5, a bioactive chemokine in allergic inflammation, persisted in virus preparations and co-purified with RSV. This conclusion is important for research on RSV or allergic diseases. In the second part of the study, the basis of the association between RSV and the development of allergic inflammation was investigated. The tryptophan catabolizing enzyme indoleamine 2, 3-dioxygenase (IDO) induces apoptosis of Th1, but not Th2 cells, which may contribute to immune responses associated with allergy and asthma. I hypothesized that RSV induces IDO in human dendritic cells, which results in a Th2-biased immune profile. Human peripheral blood monocytes from healthy adult donors were isolated, differentiated to dendritic cells (moDC), in vitro, and infected with RSV. RSV induced IDO activity and this effect was inhibited by Palivizumab, UV-inactivation and Ribavarin. Inhibition of endosomal TLR function with chloroquine did not block IDO activity. The signal transduction cascade for RSV-induced IDO activity was initiated by intracellular pattern recognition receptors (i.e., RIG-I related) via NF-κB and p38 MAPK pathways. In a transwell system, co-culture of RSV infected moDC with activated T-cells suppressed t-bet (a Th1-associated factor) but not GATA3 (Th2 regulator) expression. Inhibition of IDO activity with the competitive inhibitor, 1-methyl tryptophan, blocked this effect on t-bet expression. In conclusion, this study showed that RSV induced the expression and bioactivity of IDO in moDC, in a virus replication-dependant fashion. My study suggests that RSV has the capacity to play a role in increasing Th2-type response via IDO.
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Citation for previous publication
Ajamian et al.: Respiratory syncytial virus replication induces Indoleamine 2,3-dioxygenase (IDO) activation in human dendritic cells. Allergy, Asthma & Clinical Immunology 2010 6(Suppl 3):P8

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