The emergence of SARS-CoV-2 variants has exacerbated the COVID-19 global health crisis. Thus far, all variants carry mutations in the spike glycoprotein, which is a critical determinant of viral transmission being responsible for attachment, receptor engagement and membrane fusion, and an important target of immunity. Variants frequently bear truncations of flexible loops in the N-terminal domain (NTD) of spike; the functional importance of these modifications has remained poorly characterised. We demonstrate that NTD deletions are important for efficient entry by the Alpha and Omicron variants and that this correlates with spike stability. Phylogenetic analysis reveals extensive NTD loop length polymorphisms across the sarbecoviruses, setting an evolutionary precedent for loop remodelling. Guided by these analyses, we demonstrate that variations in NTD loop length, alone, are sufficient to modulate virus entry. We propose that variations in NTD loop length act to fine-tune spike; this may provide a mechanism for SARS-CoV-2 to navigate a complex selection landscape encompassing optimisation of essential functionality, immunedriven antigenic variation and ongoing adaptation to a new host.

Interferon lambdas (IFNλ) (also known as type III IFNs) are critical cytokines that combat infection predominantly at barrier tissues, such as the lung, liver, and gastrointestinal tract. Humans have four IFNλs (1–4), where IFNλ1–3 show ~80%–95% homology, and IFNλ4 is the most divergent displaying only ~30% sequence identity. Variants in IFNλ4 in humans are associated with the outcome of infection, such as with hepatitis C virus. However, how IFNλ4 variants impact cytokine signalling in other tissues and how well this is conserved is largely unknown. In this study, we address whether differences in antiviral signalling exist between IFNλ4 variants in human hepatocyte and intestinal cells, comparing them to IFNλ3. We demonstrate that compared to IFNλ3, wild-type human IFNλ4 induces a signalling response with distinct magnitudes and kinetics, which is modified by naturally occurring variants P70S and K154E in both cell types. IFNλ4’s distinct antiviral response was more rapid yet transient compared to IFNλ1 and 3. Additionally, divergent antiviral kinetics were also observed using non-human primate IFNλs and cell lines. Furthermore, an IFNλ4-like receptor-interacting interface failed to alter IFNλ1’s kinetics. Together, our data provide further evidence that major functional differences exist within the IFNλ gene family. These results highlight the possible tissue specialisation of IFNλs and encourage further investigation of the divergent, non-redundant activities of IFNλ4 and other IFNλs.

No abstract

Respiratory syncytial virus (RSV) causes severe infections in infants, immunocompromised or elderly individuals resulting in annual epidemics of respiratory disease. Currently, limited clinical RSV surveillance and the lack of predictable RSV seasonal dynamics and limits the public health response. Wastewater-based epidemiology (WBE) has the capacity to determine levels of health-associated biomarkers and has recently been used globally as a key metric in determining prevalence of SARS-CoV-2 in the community. However, the application of genomic WBE for the surveillance of other respiratory viruses is limited. In this study, we present an integrated genomic WBE approach, using RT-qPCR and partial sequencing of the G gene to monitor RSV levels and variants in the community across 2 years encompassing two periods of high RSV clinical positivity in Northern Ireland. We report increasing detection of RSV in wastewater concomitant with increasing numbers of RSV positive clinical cases. Furthermore, analysis of wastewater-derived RSV sequences permitted subtyping, genotyping, and identification of distinct circulating lineages within and between seasons. Altogether, our genomic WBE platform has the potential to complement ongoing global surveillance efforts and aid the management of RSV by informing the timely deployment of pharmaceutical and non-pharmaceutical interventions.

Interferon lambdas (IFNλ) (also known as type III IFNs) are critical cytokines that combat infection predominantly at barrier tissues, such as the lung, liver and gastrointestinal tract. Humans have four IFNλs (1-4) where IFNλ1-3 show ~80-95% homology and IFNλ4 is the most divergent displaying only ~30% sequence identity. Variants in IFNλ4 in humans are associated with the outcome of infection, such as with hepatitis C virus. However, how IFNλ4 variants impact cytokine signalling in other tissues and how well this is conserved is largely unknown. In this study we address whether differences in antiviral signalling exist between IFNλ4 variants in human hepatocyte and intestinal cells, comparing them to IFNλ3. We demonstrate that compared to IFNλ3, wild-type human IFNλ4 induces a signalling response with distinct magnitudes and kinetics, which is modified by naturally-occurring variants P70S and K154E in both cell types. IFNλ4s distinct antiviral response was more rapid yet transient compared to IFNλ1 and 3. Additionally, divergent antiviral kinetics were also observed using non-human primate IFNλs and cell lines. Furthermore, an IFNλ4-like receptor-interacting interface failed to alter IFNλ1s kinetics. Together our data provide further evidence that major functional differences exist within the IFNλ gene family. These results highlight the possible tissue specialisation of IFNλs and encourage further investigation of the divergent, non-redundant activities of IFNλ4 and other IFNλs.