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

  • Author / Creator
    Ajamian, Farnam
  • 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.

  • Subjects / Keywords
  • Graduation date
    Spring 2012
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.