Rhinovirus is one of the most common viral infections in humans. It causes approximately half of all colds and is often asymptomatic. However, it frequently triggers exacerbations of asthma and chronic obstructive pulmonary disease, as well as severe wheezing in children and smokers. The course of infection varies, largely depending on host factors.
The primary site of rhinovirus replication is the respiratory epithelium. In addition to serving as a physical barrier, it participates in innate immune signaling. Epithelial cells recognize viral RNA and initiate an interferon (IFN) response, activating IRF3, leading to production of type I and III IFNs and induction of interferon-stimulated genes (ISGs). These signals spread to neighboring cells and restrict viral replication.
If the IFN response is impaired, viral replication increases, and the risk of severe disease rises. Several studies have also shown that pretreatment of respiratory epithelium with exogenous recombinant IFN reduces or blocks viral replication.
To investigate these mechanisms, researchers from Yale School of Medicine conducted experiments using cultured human nasal epithelial cells. In this model, cells form a mucosal-like structure that supports viral replication. The IFN response was experimentally suppressed to observe infection dynamics.
Results showed that a normal IFN response effectively controls rhinovirus replication. When IFN signaling is impaired, a different program is activated – a strong inflammatory response driven by NF-κB, NLRP1, and IL-1 receptor signaling, leading to increased production of IL-1β and other pro-inflammatory molecules, as well as enhanced mucus secretion.
Blocking the NLRP1–IL-1 pathway reduced inflammation, suggesting potential therapeutic strategies.
Suppression of the IFN Response Increases Viral Load and Cell Death
Type III interferon (IFN-III) is the dominant interferon produced by nasal epithelial cells during rhinovirus infection. Under normal conditions, viral replication peaks on day 2 and then declines.
Suppression of IFN signaling with BX795, an IRF3 inhibitor, led to a sharp increase in viral replication, viral particle release, and cell death. Similarly, ruxolitinib – a JAK1 inhibitor – enhanced viral replication by blocking IFN signaling.
In the nasal mucosa, rhinovirus primarily infects ciliated cells, with less than 2% of cells infected. Suppression of the IFN response dramatically changes this pattern – more than 30% of cells become infected, including not only ciliated but also basal and secretory cells.
Conversely, pretreatment with recombinant IFN-λ1 suppressed viral replication.
IFN Response Induces ISG Expression in Infected and Neighboring Cells
During rhinovirus infection, ISGs are activated in nearly all epithelial cells despite infection of fewer than 2% of cells. Early ISG responses include antiviral effectors, viral sensors, positive regulators such as STAT1, and chemokines such as CXCL10 and CXCL11.
Basal cells produce chemokines that recruit T cells, consistent with their position near the underlying tissue where leukocytes are recruited.
After the peak of viral replication (days 2–5), nasal epithelial cells exhibit increased expression of late ISGs involved in antigen presentation and antiviral defense. At the same time, production of pro-inflammatory chemokines (CXCL1, CXCL8) and secreted proteins (LCN2, SLPI) increases in basal and secretory cells.
The early phase of infection is characterized by IRF- and STAT1-driven programs, while later stages involve reduced activity of these pathways and activation of cell cycle and antioxidant programs, reflecting resolution of the antiviral state.
IFN Suppression Shifts the Epithelium Toward Inflammation and Hypersecretion
Blocking IFN signaling completely inhibits ISG activation and shifts epithelial responses toward a strong inflammatory program: increased production of chemokines that recruit neutrophils and other myeloid cells, elevated IL-1α/β, and increased secretion of mucins and antimicrobial proteins, accompanied by increased mucus viscosity and impaired ciliary function.
NF-κB Regulates Both Inflammatory and Antiviral Responses
NF-κB blockade increases rhinovirus replication by approximately 10-fold – similar to IFN suppression. At the same time, NF-κB inhibition eliminates the exaggerated inflammatory response caused by IFN suppression, including IL-1β secretion and expression of mucins and antimicrobial proteins.
However, NF-κB inhibition also reduces IFN-λ1 production and ISG expression. Thus, NF-κB regulates both inflammatory and interferon responses in the nasal epithelium during rhinovirus infection.
NF-κB Maintains Epithelial Integrity
When NF-κB is inhibited, both antiviral and inflammatory responses are suppressed, disrupting epithelial function and activating pathways associated with epithelial damage, similar to those observed in chronic respiratory diseases.
Cell differentiation is also impaired – cells become less specialized and function less effectively.
These findings indicate that NF-κB helps maintain epithelial integrity during infection, preventing damage and loss of differentiation.
NLRP1 Inflammasome Amplifies Inflammation
Rhinovirus infection induces IL-1β secretion via activation of the NLRP1 inflammasome, triggered by the viral 3C protease.
Blocking NLRP1, caspase-1, or IL-1 receptor reduces IL-1β production, while inhibition of the viral 3C protease (rupintrivir) suppresses inflammation more effectively than inhibitors of viral replication. Genetic deletion of NLRP1 also reduces production of pro-inflammatory cytokines and chemokines.
Conclusion
IRF and NF-κB signaling pathways regulate the type III interferon response – the primary defense of the nasal epithelium against rhinovirus. At the same time, NF-κB, together with IL-1 and NLRP1, controls the pro-inflammatory response.
IL-1 and NLRP1 can therefore be considered potential targets for reducing excessive inflammation in rhinovirus infection.
