The parts are greater than the whole: the role of semi-infectious particles in influenza A virus biology

Abstract

The influenza A virus (IAV) genome is incorporated into newly produced virions through a tightly orchestrated process that is one of the best studied examples of genome packaging by a segmented virus. Despite the remarkable selectivity and efficiency of this process, it is clear that the vast majority of IAV virions are unable to express the full set of essential viral gene products and are thus incapable of productive replication in the absence of complementation. Here, we attempt to reconcile the widespread production of these semi-infectious particles (SIPs) with the high efficiency and selectivity of IAV genome packaging. We also cover what is known and what remains unknown about the consequences of SIP production for the replication and evolution of viral populations.

Figure 1:

Heterogeneity in viral genomic content of individual infected cells. Variation in both the genomic content of infecting virions and the effective multiplicity of infection result in heterogeneity in the copy numbers of individual viral gene segments (depicted as colored bars) within individual infected cells. Differences in these infected cell genotypes may result in distinct single cell phenotypes in virus production (indicated by the number of grey virions), host transcriptional responses to infection (indicated by the number of interferon (IFN) symbols), and cell fate (indicated by the number of skulls).