Role of eosinophils in respiratory syncytial virus infection
Creators: name: Townsend, Dijana
Publisher: name: The Australian National University
Year: 2014

description: Eosinophils recruited to the lungs, in response to respiratory syncytial virus (RSV) infection, have been associated with, the pathophysiological sequel of infection and more recently, with accelerated virus clearance. Heparan sulfates (HS), on the cell surface, are utilised by RSV to initiate infection, making HS a potential therapeutics target. As there is no effective RSV vaccine currently available, controlling RSV has remained a formidable challenge. The aims of this thesis were to investigate: (1) in vitro RSV effect on eosinophil morphology and eosinophil antiviral activity against RSV; (2) in vivo eosinophil antiviral activity expressed by four distinct mouse models following RSV infection and re-infection; and (3) the efficacy of HS mimetics treatment on RSV infection in vitro and in vivo. Firstly, transmission electron microscopy analysis, major basic protein and eosinophil peroxidase assays, eosinophil chemotaxis and RSV kinetics assays were used to examine aim 1. In vitro findings indicated human RSV pathogen inability to infect murine eosinophils however; eosinophil exposure to RSV antigen or RSV infected HEp-2 supernatant resulted in eosinophil activation, degranulation and chemotaxis. Secondly, four genetically modified BALB/s strains were infected and re-infected. Analysis of bronchoalveolar lavage (BALF), blood and lung histology was used to elucidate aim 2. These in vivo results revealed significant eosinophil mediated reduction in viral load following RSV primary infection of IL-5 Tg and IL-5 Tg Rag 2-/- BALB/c. However, following the RSV re-infection, eosinophils in addition to NK cells and type 2 innate lymphoid cells (ILC) were unable to provide the same antiviral protection in both, Rag 2-/- and IL-5 Tg Rag 2-/- BALB/c mice. Results of CD4+ cell adoptive transfer demonstrated a significant reduction of viral load recovered from IL-5 Tg Rag 2-/- BALB/c mice re-infected with RSV. Lastly, the antiviral potential of 53 HS mimetics was tested in vitro under four clinically relevant conditions. Following the in vitro findings, six HS mimetics were tested in vivo as a post RSV infection treatment and as a prophylactic treatment of RSV infection. Results revealed the first HS mimetic study examining and reporting on 53 HS mimetics RSV antiviral activity in vitro followed by HS mimetics effect on viral load reduction in vivo. Moreover, HS 228 was found to be the best performing compound, both, as post RSV infection HS treatment and prophylactic treatment of RSV infection, while reducing RSV disease pathology in vivo. Taken together, the findings of this thesis identify that RSV induced eosinophil activation results in targeted eosinophil response in vitro and in vivo; however, that eosinophil recruitment and activation following RSV re-infection appears to be dependent on stimulation by RSV-specific memory Th2 cells and/or sufficient cellular response involving NK cells and/or type 2 ILCs. In addition, exhaustive HS mimetics analysis has resulted in a comprehensive list of potential antiviral compounds that could be targeted for RSV therapeutic development. Furthermore, HS mimetics tested were found to activate an immune response even in the absence of viral infection, suggesting their potential in pre-emptive immune activation and modulation.