Murine Type III interferons are functionally redundant and correlate with bacterial burden during influenza/bacterial super-infection

Type III interferon, age and IFNL gene single nucleotide polymorphisms determine the characteristics of H1N1 influenza infection

Background

Host factors, such as innate immune response, genetic polymorphisms, age, and body weight are important determinants of susceptibility, severity, and responsiveness to treatment of influenza disease. However, the molecular mechanisms underlying these clinical associations remain poorly characterized, particularly regarding IFN-λ-mediated antiviral responses.

Methods

Wild-type mice and IL-28B-/- mice were used to systematically investigate the antiviral and anti-inflammatory functions of IL-29 or IL-28, respectively. Plaque assay and DNA genotyping were conducted to determine the correlations between IFN-λ polymorphisms and H1N1 infection outcomes. ELISA, Real-time PCR and luciferase reporter assays were carried out to explore the mechanism.

Results

IFN-λ plays an important antiviral and immunoprotective role in H1N1 infection. Specifically, IL-29 and IL-28 exhibit important dual antiviral and anti-inflammaroty roles. Age factor also affects H1N1 clearance and therapeutic responsiveness. Human alveolar epithelial cells (AECs) from young donors support higher H1N1 replication and weak response to antiviral treatment with IL-29. Rs12979860 (IL-28 C/T), rs8099917 (IL-28 T/G) and rs30461 (IL-29 A/G), the three identified single nucleotide polymorphisms (SNPs) in IFNL genes, are also associated with H1N1 outcomes. AECs from rs12979860TT and rs8099917GG donors exhibit higher H1N1 replication and nonresponsiveness to IL-29 antiviral therapy. AECs from rs12979860 TT donors also produce lower levels of IFN and exhibit inhibited promoter activity of IL-29 in response to H1N1 infection. In addition, increased allele frequencies of rs12979860 T and rs8099917 G were associated with higher BMI, another important factor influencing H1N1 susceptibility.

Conclusions

This is the first study to comprehensively explore the impact of host factors, especially IFN-λ polymorphisms, on H1N1 virus infection. Further elucidation of the underlying mechanisms may help to develop novel prevention and treatment strategies for influenza virus infection.

Context-specific anti-inflammatory roles of type III interferon signaling in the lung in nonviral injuries

Type III interferons (λ1, λ2, and λ3) are potent antiviral cytokines in the lung. However, their roles in nonviral lung injuries are less well understood. This study investigates the activation of type III interferon signaling in three distinct models of lung injuries caused by diverse stimuli: the bacterial pathogen Pseudomonas aeruginosa, bacterial endotoxin LPS, and the chemotherapeutic agent bleomycin. Our data show that, despite inducing a potent inflammatory response, Pseudomonas and LPS did not increase IFNλ secretion. In contrast, bleomycin instillation increased secretion of IFNλ in the airways at both early and late time points. Consistent with limited secretion, type III interferon signaling had a minimal role in the host response to both Pseudomonas and LPS, as measured by pathogen burden, inflammatory response, and lung injury. Conversely, a deficiency in type III interferon signaling led to increased inflammatory signaling and elevated acute lung injury in the bleomycin model on day 3. This elevated early injury resulted in impaired recovery in IFNLR1 knockout mice, as evidenced by their recovery from bleomycin-induced weight loss. Taken together, these data suggest a context-specific activation of type III interferon signaling, where it plays an anti-inflammatory role in the lung.

Roles and Effects of Interferon Lambda Signaling in the Context of Bacterial Infections

Type III interferon, or interferon lambda (IFNλ), was discovered 20 years ago and has been studied primarily for its role in combatting viral infections. However, it is also induced in response to certain bacterial infections but its roles and effects in this context are relatively poorly understood. In this mini review, we discuss the roles of IFNλ signaling in bacterial infections, highlighting its deleterious or protective effects for different infections. We also discuss a couple of recent studies showing that some bacteria possess defense mechanisms against the effects of IFNλ. We hope that this review will spur further investigation into the roles of IFNλ in the context of bacterial infections and will promote considerations of its therapeutic potential for these infections.

IFNλ: balancing the light and dark side in pulmonary infection

Interferon (IFN) represents a well-known component of antiviral immunity that has been studied extensively for its mechanisms of action and therapeutic potential when antiviral treatment options are limited. Specifically in the respiratory tract, IFNs are induced directly on viral recognition to limit the spread and transmission of the virus. Recent focus has been on the IFNλ family, which has become an exciting focus in recent years for its potent antiviral and anti-inflammatory activities against viruses infecting barrier sites, including the respiratory tract. However, insights into the interplay between IFNλs and other pulmonary infections are more limited and suggest a more complex role, potentially detrimental, than what was seen during viral infections. Here, we review the role of IFNλs in pulmonary infections, including viral, bacterial, fungal, and multi-pathogen super-infections, and how this may impact future work in the field.

Heterotypic Influenza Infections Mitigate Susceptibility to Secondary Bacterial Infection

Influenza-associated bacterial superinfections have devastating impacts on the lung and can result in increased risk of mortality. New strains of influenza circulate throughout the population yearly, promoting the establishment of immune memory. Nearly all individuals have some degree of influenza memory before adulthood. Due to this, we sought to understand the role of immune memory during bacterial superinfections. An influenza heterotypic immunity model was established using influenza A/Puerto Rico/8/34 and influenza A/X31. We report in this article that influenza-experienced mice are more resistant to secondary bacterial infection with methicillin-resistant Staphylococcus aureus as determined by wasting, bacterial burden, pulmonary inflammation, and lung leak, despite significant ongoing lung remodeling. Multidimensional flow cytometry and lung transcriptomics revealed significant alterations in the lung environment in influenza-experienced mice compared with naive animals. These include changes in the lung monocyte and T cell compartments, characterized by increased expansion of influenza tetramer-specific CD8+ T cells. The protection that was seen in the memory-experienced mouse model is associated with the reduction in inflammatory mechanisms, making the lung less susceptible to damage and subsequent bacterial colonization. These findings provide insight into how influenza heterotypic immunity reshapes the lung environment and the immune response to a rechallenge event, which is highly relevant to the context of human infection.