Biphasic RLR–IFN-β Response Controls the Balance between Antiviral Immunity and Cell Damage

Abstract

In RNA virus–infected cells, retinoic acid–inducible gene-I–like receptors (RLRs) sense foreign RNAs and activate signaling cascades to produce IFN-α/β. However, not every infected cell produces IFN-α/β that exhibits cellular heterogeneity in antiviral immune responses. Using the IFN-β–GFP reporter system, we observed bimodal IFN-β production in the uniformly stimulated cell population with intracellular dsRNA. Mathematical simulation proposed the strength of autocrine loop via RLR as one of the contributing factor for biphasic IFN-β expression. Bimodal IFN-β production with intracellular dsRNA was disturbed by blockage of IFN-α/β secretion or by silencing of the IFN-α/β receptor. Amplification of RLRs was critical in the generation of bimodality of IFN-β production, because IFN-βhigh population expressed more RLRs than IFN-βlow population. In addition, bimodality in IFN-β production results in biphasic cellular response against infection, because IFN-βhigh population was more prone to apoptosis than IFN-βlow population. These results suggest that RLR-mediated biphasic cellular response may act to restrict the number of cells expressing IFN-β and undergoing apoptosis in the infected population.

Single-cell analysis of early antiviral gene expression reveals a determinant of stochasticIFNB1expression

“…We treated previously described clonal HepG2 cells 29 with IFN-β and imaged RIG-I and housekeeping gene ALAS 30 mRNA at various time points. Unstimulated cells displayed basal level of RIG-I mRNA, 27 transcripts per cell on average.…”

Regulation of type I interferon responses

“…Even in populations of nearly identical cells, not all cells that are infected by a virus or exposed to microbial products produce type I IFNs and express ISGs 65–67 . The stochastic nature of ISG expression seems to be related to bimodal induction of STAT2 and IRF7, which can drive high amounts of ISG transcription in a particular subset of cells, whereas other cells express much lower amounts of ISG transcripts.…”

Fluorescence-Activated Cell Sorting-Based Analysis Reveals an Asymmetric Induction of Interferon-Stimulated Genes in Response to Seasonal Influenza A Virus

“…One important challenge that needs to be considered to overcome this limitation is the considerable variation among cells in their capability to respond to biological stimuli (33), which also includes IFN and ISG expression. In fact, only a fraction of cells stimulated with a RIG-I ligand upregulate IFN gene transcription due to stochastic events (34)(35)(36), and cells within one culture differ widely in the minimal type I IFN concentration required to upregulate ISGs (37). This suggests that it is important to determine the activation and execution of the antiviral IFN response at the level of single cells.…”