The complement system is a critical part of innate immune responses that most animal viruses encounterduring natural infections. While it is clear that complement (C') is an important factor in neutralization ofsome RNA viruses, very few mechanistic details are known about how C' regulates paramyxovirusinfections. Here, we seek to fill gaps in understanding of interactions of complement (C') with the emerginghighly pathogenic paramyxovirus Nipah virus (NiV). This project emerged from our recent published finding that: 1) complement is activated in vitro bypseudotypes containing the NiV F and G glycoproteins, but importantly, unlike any other paramyxovirus wehave tested so far this does not result in neutralization. Our preliminary data also demonstrate that: 2) thecellular C' inhibitor Factor I protease associates with the NiV F but not HN protein and 3) Factor I associatedwith NiV pseudotypes can inactivate C3b by cleavage into iC3b. The novelty of the second and thirdfindings is that no other pathogen has been reported so far to recruit Factor I as a mechanism to evadecomplement. In addition, support for our hypothesis would show a new function for the paramyxovirus Fprotein in evading innate immunity.
In Aim 1, we will use biochemical approaches to test the hypothesis that functional human Factor Iinteracts specifically with the NiV F protein. Work in Aim 2 will involve studies with live NiV infection underBiosafety Level 4 (BSL4) conditions. We will determine the extent to which live NiV activates C' in vitro andthe capacity of C' to neutralize NiV infectivity. In addition to recruitment of soluble Factor I, we hypothesizethat NiV also captures cell surface inhibitors of C' such as CD46 and CD55. This will be tested using liveNiV infection of tissue culture cells that express varying levels of inhibitors. This pilot project seeks to extend our novel findings from studies with NiV pseudotypes into live NiVunder BSL-4 conditions, and to gain further supporting data for a novel mechanism of C' evasion. Both arenecessary steps to establish a secure foundation for more mechanistic detailed studies with live virus andinto experiments in animal models.
There is intense interest in mechanisms that modulate the interplay between viruses and the host innateimmune system. The role of complement in neutralizing emerging paramyxoviruses such as Nipah virusand how these viruses counteract complement pathways are unknown. To our knowledge; our novelfinding on how Nipah virus evades neutralization has not been described for any other pathogen.Insights into inhibition of complement will have implications for virus pathogenesis and rationalapproaches to vaccine development.
Johnson, John B; Borisevich, Viktoriya; Rockx, Barry et al. (2015) A novel factor I activity in Nipah virus inhibits human complement pathways through cleavage of C3b. J Virol 89:989-98 |
Mayer, Anne E; Parks, Griffith D (2014) An AGM model for changes in complement during pregnancy: neutralization of influenza virus by serum is diminished in late third trimester. PLoS One 9:e112749 |
Parks, Griffith D; Alexander-Miller, Martha A (2013) Paramyxovirus activation and inhibition of innate immune responses. J Mol Biol 425:4872-92 |