Influenza A Virus interactions with complement factor H

Abstract

Influenza A virus (IAV) is a major causative agent of respiratory tract infection in humans. Human IAVs cause seasonal epidemics, whilst avian IAV strains sporadically cross the host range barrier leading to zoonotic infections. The complement system is a component of the innate immune system that acts to remove pathogens including IAVs. Many bacterial pathogens and several viral pathogens have been reported to actively target components of the complement activation pathway as a defensive strategy. The aim of this project is to understand if there is an interaction between IAV and co-factor H, a critical inhibitor of the complement system and what effect any interaction may have on influenza replication. Using purified human co-factor H protein and purified human (H1N1 and H3N2) and avian (H9N2 and H5N3) IAVs we have demonstrated using ELISA assays that an interaction does occur between co-factor H and all the IAV strains tested. Far western blot analysis suggests that the interaction is with the viral Hemagglutinin (HA), which is responsible for attachment and entry of IAV to cells. Interestingly the interaction has divergent effects on the replication of the IAV strains; enhancing human H1N1 replication and restricting H3N2 replication in A549 and THP-1 cells whilst having no effect on the replication of avian H5N3 or H9N2 viruses. Understanding IAV interaction with the complement pathway could enhance our ability to produce effective vaccines.