Innate immune role of IL-6 in influenza a virus pathogenesis

Abstract

Interleukin-6 (IL-6), a pleiotropic cytokine, is induced by infection of influenza A virus (IAV), where it plays a pivotal role in immune defense and the regulation of inflammation. IAV induces IL-6 transcription upon recognition by pattern recognition receptors, which activate downstream signaling cascades, leading to the activation of transcription factors. Activated transcription factors subsequently regulate the expression of IL-6 in innate immune cells, such as macrophages, dendritic cells, and epithelial cells. IL-6 contributes to antiviral immunity by promoting the recruitment of immune cells to sites of infection and amplifying the inflammatory response. While optimal IL-6 production is essential for effective anti-IAV immunity, excessive IL-6 production can contribute to a dysregulated immune response, leading to a cytokine storm. In this context, IL-6 signaling, in coordination with other proinflammatory cytokines such as TNF-α and IL-1β, not only enhances its own production but can also serve as a key mediator of inflammation. This cascade can result in exaggerated immune responses, causing tissue damage and potentially leading to severe outcomes, including organ failure and death. Understanding the molecular mechanisms underlying cytokine storms presents important therapeutic opportunities. However, the precise pathways responsible for excessive IL-6 production and its dysregulation during IAV infection is not fully understood. This review explores the reported mechanisms regulating IL-6 induction in response to IAV and its innate immune role in IAV pathogenesis, highlighting existing research gaps in understanding IAV-induced IL-6 production and its impact on immune modulation. A deeper understanding of IAV-induced IL-6 production and signaling could inform the development of targeted therapies to more effectively manage influenza.

Keywords: IAV; IL-6; cytokine storm; inflammation; innate immunity.

Figure 1

IAV-induced IL-6 induction mechanism and IL-6 signaling pathways: IL-6 production is initiated by PRRs, such as TLRs and RLRs, which recognize viral PAMPs and DAMPs, leading to the activation of NF-κB signaling and IL-6 expression. The NLRP3 inflammasome further amplifies IL-6 production through IL-1β and IL-18 release. IAV-induced IL-6 modulates immune responses via two distinct signaling pathways: (i) classical signaling, involving membrane-bound IL-6R, and (ii) trans-signaling, mediated by soluble IL-6R. Ligand binding to these receptors activates the JAK-STAT3 pathway, driving downstream gene expression. The coordinated activation of both NF-κB and JAK-STAT3 pathways acts as an inflammation amplifier.