Interferons (IFN) are crucial for the innate immune response. Slightly more than two decades ago, a new type of IFN was discovered: the lambda IFN (type III IFN). Like other IFN, the type III IFN display antiviral activity against a wide variety of infections, they induce expression of antiviral, interferon-stimulated genes (MX1, OAS, IFITM1), and they have immuno-modulatory activities that shape adaptive immune responses. Unlike other IFN, the type III IFN signal through distinct receptors is limited to a few cell types, primarily mucosal epithelial cells. As a consequence of their greater and more durable production in nasal and respiratory tissues, they can determine the outcome of respiratory infections. This review is focused on the role of IFN-λ in the pathogenesis of respiratory viral infections, with influenza as a prime example. The influenza virus is a major public health problem, causing up to half a million lethal infections annually. Moreover, the virus has been the cause of four pandemics over the last century. Although IFN-λ are increasingly being tested in antiviral therapy, they can have a negative influence on epithelial tissue recovery and increase the risk of secondary bacterial infections. Therefore, IFN-λ expression deserves increased scrutiny as a key factor in the host immune response to infection.

Background: Exosomes are involved in intercellular communication and can transfer regulatory molecules between cells. Consequently, they can participate in host immune response regulation. For the influenza A virus (IAV), there is very limited information on changes in exosome composition during cell infection shedding light on the potential role of these extracellular membrane vesicles. Thus, the aim of our work was to study changes in exosomal composition following IAV infection of cells, as well as to evaluate their effect on uninfected cells. Methods: To characterize changes in the composition of cellular miRNAs and mRNAs of exosomes during IAV infection of A549 cells, NGS was used, as well as PCR to identify viral genes. Naïve A549 cells were stimulated with infected-cell-secreted exosomes for studying their activity. Changes in the expression of genes associated with the cell’s immune response were shown using PCR. The effect of exosomes on IAV replication was shown in MDCK cells using In-Cell ELISA and PCR of the supernatants. Results: A change in the miRNA composition (miR-21-3p, miR-26a-5p, miR-23a-5p, miR-548c-5p) and mRNA composition (RPL13A, MKNK2, TRIB3) of exosomes under the influence of the IAV was shown. Many RNAs were involved in the regulation of the immune response of the cell, mainly by suppressing it. After exosome stimulation of naïve cells, a significant decrease in the expression of genes involved in the immune response was shown (RIG1, IFIT1, MDA5, COX2, NFκB, AnxA1, PKR, IL6, IL18). When infecting MDCK cells, a significant decrease in nucleoprotein levels was observed in the presence of exosomes secreted by mock-infected cells. Viral levels in supernatants also decreased. Conclusions: Exosomes secreted by IAV-infected cells could reduce the immune response of neighboring intact cells, leading to more effective IAV replication. This may be associated both with regulatory functions of cellular miRNAs and mRNAs carried by exosomes, or with the presence of viral mRNAs encoding proteins with an immunosuppressive function.

Type III interferons (lambda IFNs) are a quite new, small family of three closely related cytokines with interferon-like activity. Attention to IFN-λ is mainly focused on direct antiviral activity in which, as with IFN-α, viral genome replication is inhibited without the participation of immune system cells. The heterodimeric receptor for lambda interferons is exposed mainly on epithelial cells, which limits its possible action on other cells, thus reducing the likelihood of developing undesirable side effects compared to type I IFN. In this study, we examined the antiviral potential of exogenous human IFN-λ1 in cellular models of viral infection. To study the protective effects of IFN-λ1, three administration schemes were used: ‘preventive’ (pretreatment); ‘preventive/therapeutic’ (pre/post); and ‘therapeutic’ (post). Three IFN-λ1 concentrations (from 10 to 500 ng/mL) were used. We have shown that human IFN-λ1 restricts SARS-CoV-2 replication in Vero cells with all three treatment schemes. In addition, we have shown a decrease in the viral loads of CHIKV and IVA with the ‘preventive’ and ‘preventive/therapeutic’ regimes. No significant antiviral effect of IFN-λ1 against AdV was detected. Our study highlights the potential for using IFN-λ as a broad-spectrum therapeutic agent against respiratory RNA viruses.

In this study, we developed a novel, multiplex qPCR assay for simultaneous detection of RIG-1, MDA5, and IFIT-1 at the mRNA level. The assay was validated in A549 cells transfected with in vitro transcribed RNAs. Both exogenous RNA-GFP and self-amplifying (saRNA-GFP) induced significant expression of RIG-1, MDA5, IFIT-1, as well as type I and III interferons. In contrast, native RNA from intact A549 cells did not upregulate expression of these genes. Next, we evaluated RIG-1, MDA5, and IFIT-1 mRNA levels in the white blood cells of patients with influenza A virus (H3N2) or SARS-CoV-2. In acute phase (about 4 days after disease onset) both viruses induced these genes expression. Clinical observations of SARS-CoV-2 typically describe a two-step disease progression, starting with a mild-to-moderate presentation followed by a secondary respiratory worsening 9 to 12 days after the first onset of symptoms. It revealed that the expression of RIG-1, MDA5, and MxA was not increased after 2 and 3 weeks from the onset the disease, while for IFIT-1 it was observed the second peak at 21 day post infection. It is well known that RIG-1, MDA5, and IFIT-1 expression is induced by the action of interferons. Due to the ability of SOCS-1 to inhibit interferon-dependent signaling, and the distinct antagonism of SARS-CoV-2 in relation to interferon-stimulated genes expression, we assessed SOCS-1 mRNA levels in white blood cells. SARS-CoV-2 patients had increased SOCS-1 expression, while the influenza-infected group did not differ from heathy donors. Moreover, SOCS-1 mRNA expression remained stably elevated during the course of the disease. It can be assumed that augmented SOCS-1 expression is one of multiple mechanisms that allow SARS-CoV-2 to escape from the interferon-mediated immune response. Our results implicate SOCS-1 involvement in the pathogenesis of SARS-CoV-2.

Respiratory syncytial virus (RSV) is known to cause annual epidemics of respiratory infections; however, the lack of specific treatment options for this disease poses a challenge. In light of this, there has been a concerted effort to identify small molecules that can effectively combat RSV. This article focuses on the mechanism of action of compound K142, which was identified as a primary screening leader in the earlier stages of the project. The research conducted demonstrates that K142 significantly reduces the intensity of virus penetration into the cells, as well as the formation of syncytia from infected cells. These findings show that the compound’s interaction with the surface proteins of RSV is a key factor in its antiviral activity. Furthermore, pharmacological modeling supports that K142 effectively interacts with the F-protein. However, in vivo studies have shown only weak antiviral activity against RSV infection, with a slight decrease in viral load observed in lung tissues. As a result, there is a need to enhance the bioavailability or antiviral properties of this compound. Based on these findings, we hypothesize that further modifications of the compound under study could potentially increase its antiviral activity.