Biology subjects

Schwemmle, M.

Publications and source records attributed to Schwemmle, M..

12 recordsLinked to original sources

bioRxiv2026

Bat-borne influenza A H9N2 virus shows species-specific replication and transmission

Bat-borne H9N2 IAV (bat H9N2), initially detected in bat feces in Egypt in 2017, has recently attracted attention because of its unexpected pre-pandemic properties, including airborne transmission between ferrets and efficient replication in human lung explant cultures. However, its host range and potential reservoir hosts remain poorly defined, particularly with respect to additional bat hosts and mammalian or avian mixing-vessel species. Here, we compare the susceptibility of two pteropodid bat species, Rousettus aegyptiacus and Eidolon helvum, and additionally assessed pigs and quails following intranasal inoculation with bat H9N2. Juvenile R. aegyptiacus showed only low-level viral replication and shedding, largely restricted to the upper respiratory tract, and did not show transmission to contact bats. In contrast, both juvenile and adult E. helvum, despite showing no clinical signs, showed high-level viral replication and shedding in the upper respiratory tract, with efficient and early transmission to contact bats. Viral RNA was most abundant in the respiratory turbinates, the nasopharyngeal meatus and the tracheal epithelium, where it was associated with moderate to severe necrotizing rhinitis and tracheitis. The lower respiratory tract was less involved, with viral RNA confined to scattered bronchioles and associated with focal necrotizing bronchiolitis. Other organs, including the gastrointestinal tract, lacked histologic lesions and viral RNA labeling. In pigs and quails, intranasal inoculation did not result in detectable replication, transmission, or seroconversion. Our findings demonstrate marked differences in the susceptibility to bat H9N2 between the two fruit bat species tested and identify E. helvum as a highly susceptible host capable of rapid and efficient transmission. Conversely, pigs and quails were not susceptible, suggesting that additional viral adaptations may be required to allow for a productive infection in these species.

microbiology↗

bioRxiv2026

MHC-II acts as a fusion-triggering receptor for bat influenza virus

Influenza A virus hemagglutinin is a prototypical class I viral fusion protein that binds sialylated glycans and is activated by low pH in endosomes. In contrast, bat-derived IAV subtypes H17N10 and H18N11 use major histocompatibility complex class II (MHC-II) as an entry receptor, but how this receptor contributes to membrane fusion remains unknown. We find that MHC-II-dependent hemagglutinin subtypes H17, H18, and H19 possess an increased negative net charge relative to canonical HAs. Using cryo-electron tomography, we demonstrate that H18N11 morphology remains stable and H18 is in prefusion conformation at strongly acidic pH. Remarkably, H18 undergoes fusion-relevant conformational changes only when both MHC-II binding and low pH are present. By reconstitution of H18N11 fusion with liposomes and purified MHC-II, we show that receptor engagement is required to trigger the fusion activity of H18. These findings identify MHC-II as a receptor that directly triggers membrane fusion and reveal a previously unrecognized receptor-dependent mechanism of influenza virus entry. SignificanceBat-derived influenza A viruses (IAV) challenged established paradigms because they use major histocompatibility complex class II (MHC-II) molecules instead of sialylated glycans for cell entry. Recent studies suggest that MHC-II usage extends beyond bats, with avian, swine, and human strains showing dual receptor specificity. However, how MHC-II contributes to membrane fusion has remained unclear. We show that, unlike conventional HAs that are activated by acidity alone, the H18 fusion protein requires receptor engagement and low pH to undergo fusion-relevant conformational changes leading to membrane fusion. Hence, we reveal a novel receptor-dependent mechanism of membrane fusion for the MHC-II dependent entry of H18N11.

microbiology↗

bioRxiv2024

The bat Influenza A virus subtype H18N11 induces nanoscale MHCII clustering upon host cell attachment

Prior to the discovery of the bat influenza A virus (IAV) subtypes H17N10 and H18N11, it was believed that all IAVs bind via the viral hemagglutinin (HA) to sialic acid residues to mediate attachment and subsequent viral entry. Both HA subtypes, H17 and H18, however, do not bind to sialic acids but instead engage a proteinaceous receptor: major histocompatibility complex class II (MHCII). The mechanistic details of this hitherto unknown protein-mediated entry are not understood. Since conventional IAVs require attachment to clusters of sialylated glycans to overcome the low affinity of the HA-sialic acid interaction, we hypothesized that bat HA would likewise interact with multiple MHCII molecules. Here, we used photoactivated localization microscopy (PALM) on fixed and live cells expressing MHCII fused to appropriate fluorescent reporters. We show that bat IAV particles attach to pre-existing MHCII clusters present on susceptible cells and that the local HA-MHCII interaction results in an increased cluster size. To measure the impact of viral attachment on the dynamics of MHCII, we utilized an experimental setup designated "inverse infection" where intact viral particles were immobilized on coverslips before live MHCII-expressing cells were seeded on top. Recording the trajectories of single MHCII molecules, this approach revealed that the mobility of MHCII was indeed slowed down in viral proximity leading to a local enrichment of MHCII molecules beneath the viral particle. Taken together, these data suggest that attachment of viral particles leads to clustering of MHCII, a process similar to the MHCII dynamics observed during the formation of an immunological synapse.

microbiology↗

bioRxiv2023

IFN-lambda is protective against lethal oral Toxoplasma gondii infection

Interferons are essential for innate and adaptive immune responses against a wide variety of pathogens. Interferon lambda (IFN-{lambda}) protects mucosal barriers during pathogen exposure. The intestinal epithelium is the first contact site for Toxoplasma gondii (T. gondii) with its hosts and the first defense line that limits parasite infection. Knowledge of very early T. gondii infection events in the gut tissue is limited and a possible contribution of IFN-{lambda} has not been investigated so far. Here, we demonstrate with systemic interferon lambda receptor (IFNLR1) and conditional (Villin-Cre) knockout mouse models and bone marrow chimeras of oral T. gondii infection and mouse intestinal organoids a significant impact of IFN-{lambda} signaling in intestinal epithelial cells and neutrophils to T. gondii control in the gastrointestinal tract. Our results expand the repertoire of interferons that contribute to the control of T. gondii and may lead to novel therapeutic approaches against this world-wide zoonotic pathogen.

immunology↗

bioRxiv2022

Cold-passaged isolates and bat-swine influenza A chimeric viruses as modified live-attenuated vaccines against influenza A viruses in pigs

Swine influenza A virus (swIAV) infections in pig populations cause considerable morbidity and economic losses. Frequent reverse zoonotic incursions of human IAV boost reassortment opportunities with authentic porcine and avian-like IAV in swine herds potentially enhancing zoonotic and even pre-pandemic potential. Vaccination using adjuvanted inactivated full virus vaccines is frequently used in attempting control of swIAV infections. Accelerated antigenic drift of swIAV in large swine holdings and interference of maternal antibodies with vaccine in piglets can compromise these efforts. Potentially more efficacious modified live-attenuated vaccines (MLVs) bear the risk of reversion of MLV to virulence. Here we evaluated new MLV candidates based on cold-passaged swIAV or on reassortment-incompetent bat-IAV-swIAV chimeric viruses. Serial cold-passaging of various swIAV subtypes did not yield unambiguously temperature-sensitive mutants although safety studies in mice and pigs suggested some degree of attenuation. Chimeric bat-swIAV expressing the hemagglutinin and neuraminidase of an avian-like H1N1, in contrast, proved to be safe in mice and pigs, and a single nasal inoculation induced protective immunity against homologous challenge in pigs. Reassortant-incompetent chimeric bat-swIAV vaccines could aid in reducing the amount of swIAV circulating in pig populations, thereby increasing animal welfare, limiting economic losses and lowering the risk of zoonotic swIAV transmission.

microbiology↗

bioRxiv2022

Impaired immune response drives age-dependent severity of COVID-19

SARS-CoV-2 is a highly contagious respiratory virus and the causative agent for COVID-19. The severity of disease varies from mildly symptomatic to lethal and shows an extraordinary correlation with increasing age, which represents the major risk factor for severe COVID-191. However, the precise pathomechanisms leading to aggravated disease in the elderly are currently unknown. Delayed and insufficient antiviral immune responses early after infection as well as dysregulated and overshooting immunopathological processes late during disease were suggested as possible mechanisms. Here we show that the age-dependent increase of COVID-19 severity is caused by the disruption of a timely and well-coordinated innate and adaptive immune response due to impaired interferon (IFN) responses. To overcome the limitations of mechanistic studies in humans, we generated a mouse model for severe COVID-19 and compared the kinetics of the immune responses in adult and aged mice at different time points after infection. Aggravated disease in aged mice was characterized by a diminished IFN-{gamma} response and excessive virus replication. Accordingly, adult IFN-{gamma} receptor-deficient mice phenocopied the age-related disease severity and supplementation of IFN-{gamma} reversed the increased disease susceptibility of aged mice. Mimicking impaired type I IFN immunity in adult and aged mice, a second major risk factor for severe COVID-192-4, we found that therapeutic treatment with IFN-{lambda} in adult and a combinatorial treatment with IFN-{gamma} and IFN-{lambda} in aged Ifnar1-/-mice was highly efficient in protecting against severe disease. Our findings provide an explanation for the age-dependent disease severity of COVID-19 and clarify the nonredundant antiviral functions of type I, II and III IFNs during SARS-CoV-2 infection in an age-dependent manner. Based on our data, we suggest that highly vulnerable individuals combining both risk factors, advanced age and an impaired type I IFN immunity, may greatly benefit from immunotherapy combining IFN-{gamma} and IFN-{lambda}.

immunology↗

bioRxiv2021

A broadly neutralizing biparatopic Nanobody protects mice from lethal challenge with SARS-CoV-2 variants of concern

The ongoing COVID-19 pandemic and the frequent emergence of new SARS-CoV-2 variants of concern (VOCs), requires continued development of fast and effective therapeutics. Recently, we identified high-affinity neutralizing nanobodies (Nb) specific for the receptor-binding domain (RBD) of SARS-CoV-2, which are now being used as biparatopic Nbs (bipNbs) to investigate their potential as future drug candidates. Following detailed in vitro characterization, we chose NM1267 as the most promising candidate showing high affinity binding to several recently described SARS-CoV-2 VOCs and strong neutralizing capacity against a patient isolate of B.1.351 (Beta). To assess if bipNb NM1267 confers protection against SARS-CoV-2 infection in vivo, human ACE2 transgenic mice were treated by intranasal route before infection with a lethal dose of SARS-CoV-2. NM1267-treated mice showed significantly reduced disease progression, increased survival rates and secreted less infectious virus via their nostrils. Histopathological analyses and in situ hybridization further revealed a drastically reduced viral load and inflammatory response in lungs of NM1267-treated mice. These data suggest, that bipNb NM1267 is a broadly active and easily applicable drug candidate against a variety of emerging SARS-CoV-2 VOCs.

biochemistry↗

bioRxiv2021

Engineered chimeric T cell receptor fusion construct (TRuC)-expressing T cells prevent translational shutdown in SARS-CoV-2-infected cells

SARS-CoV-2, the causative agent of Covid-19, is known to evade the immune system by several mechanisms. This includes the shutdown of the host cellular protein synthesis, which abrogates the induction of antiviral interferon responses. The virus initiates the infection of susceptible cells by binding with its spike protein (S) to the host angiotensin-converting enzyme 2 (ACE2). Here we applied the T cell receptor fusion construct (TRuC) technology to engineer T cells against such infected cells. In our TRuCs an S-binding domain is fused to the CD3{varepsilon} component of the T cell receptor (TCR) complex, enabling recognition of S-containing cells in an HLA independent manner. This domain either consists of the S-binding part of ACE2 or a single-chain variable fragment of an anti-S antibody. We show that the TRuC T cells are activated by and kill cells that express S of SARS-CoV-2 and its alpha (B.1.1.7) and beta (B.1.351) variants at the cell surface. Treatment of SARS-CoV-2 infected cells with our engineered T cells did not lead to massive cytotoxicity towards the infected cells, but resulted in a complete rescue of the translational shutdown despite ongoing viral replication. Our data show that engineered TRuC T cell products might be used against SARS-CoV-2 by exposing infected cells to the host innate immune system.

bioengineering↗

bioRxiv2021

Enhanced FcγRIII/CD16 activation by discrete ligands as independent correlates of disease severity in COVID-19 patients

A dysregulated immune response with high levels of SARS-CoV-2 specific IgG antibodies characterizes patients with severe or critical COVID-19. Although a robust IgG response is traditionally considered to be protective, excessive triggering of activating Fc-gamma-receptors (Fc{gamma}Rs) could be detrimental and cause immunopathology. Here, we document that patients who develop soluble circulating IgG immune complexes (sICs) during infection are subject to enhanced immunopathology driven by Fc{gamma}R activation. Utilizing cell-based reporter systems we provide evidence that sICs are predominantly formed prior to a specific humoral response against SARS-CoV-2. sIC formation, together with increased afucosylation of SARS-CoV-2 specific IgG eventually leads to an enhanced CD16 (Fc{gamma}RIII) activation of immune cells reaching activation levels comparable active systemic lupus erythematosus (SLE) disease. Our data suggest a vicious cycle of escalating immunopathology driven by an early formation of sICs in predisposed patients. These findings reconcile the seemingly paradoxical findings of high antiviral IgG responses and systemic immune dysregulation in severe COVID-19. Clinical implicationsThe identification of sICs as drivers of an escalating immunopathology in predisposed patients opens new avenues regarding intervention strategies to alleviate critical COVID-19 progression. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=78 SRC="FIGDIR/small/449893v4_ufig1.gif" ALT="Figure 1"> View larger version (17K): org.highwire.dtl.DTLVardef@b4616corg.highwire.dtl.DTLVardef@682d1aorg.highwire.dtl.DTLVardef@16946cborg.highwire.dtl.DTLVardef@a6ef7d_HPS_FORMAT_FIGEXP M_FIG C_FIG A vicious cycle of immunopathology in COVID-19 patients is driven by soluble multimeric immune complexes (sICs). SARS-CoV-2 infection triggers sIC formation in prone individuals. Activation of Fc{gamma}RIII/CD16 expressing immune cells by sICs precedes a humoral response to SARS-CoV2 infection. sICs and infection add to IgG afucosylation, further enhancing Fc{gamma}RIII/CD16 activation by opsonized targets. High inflammation induces further sIC mediated immune cell activation ultimately leading to an escalating immunopathology.

immunology↗

bioRxiv2021

Genome-Wide CRISPR Screening Identifies BRD9 as a Druggable Component of Interferon-Stimulated Gene Expression and Antiviral Activity

Transient interferon (IFN) induction of IFN-stimulated genes (ISGs) creates a formidable protective antiviral state. However, loss of appropriate control mechanisms can result in constitutive pathogenic ISG upregulation. Here, we used genome-wide loss-of-function screening to establish genes critical for IFN signaling, identifying all expected members of the JAK-STAT pathway and the previously unappreciated bromodomain-containing protein 9 (BRD9), a defining subunit of non-canonical BAF (ncBAF) chromatin remodeling complexes. Genetic knock-out or small-molecule mediated degradation of BRD9 limited IFN-induced expression of a subset of ISGs in multiple cell-types, and prevented IFN from exerting full antiviral activity against several RNA and DNA viruses. Mechanistically, BRD9 acts at the level of ISG transcription, exhibits a proximal association with STAT2 following IFN stimulation, and relies on its intact acetyl-binding bromodomain and unique ncBAF scaffolding function for activity. Given its druggability, BRD9 may be an attractive target for dampening constitutive ISG expression under certain pathogenic autoinflammatory conditions.

immunology↗

bioRxiv2020

Ex vivo detection of SARS-CoV-2-specific CD8+ T cells: rapid induction, prolonged contraction, and formation of functional memory

CD8+ T cells are critical for the elimination and long-lasting protection of many viral infections, but their role in the current SARS-CoV-2 pandemic is unclear. Emerging data indicates that SARS-CoV-2-specific CD8+ T cells are detectable in the majority of individuals recovering from SARS-CoV-2 infection. However, optimal virus-specific epitopes, the role of pre-existing heterologous immunity as well as their kinetics and differentiation program during disease control have not been defined in detail. Here, we show that both pre-existing and newly induced SARS-CoV-2-specific CD8+ T-cell responses are potentially important determinants of immune protection in mild SARS-CoV-2 infection. In particular, our results can be summarized as follows: First, immunodominant SARS-CoV-2-specific CD8+ T-cell epitopes are targeted in the majority of individuals with convalescent SARS-CoV-2 infection. Second, MHC class I tetramer analyses revealed the emergence of phenotypically diverse and functionally competent pre-existing and newly induced SARS-CoV-2-specific memory CD8+ T cells that showed similar characteristics compared to influenza-specific CD8+ T cells. Third, SARS-CoV-2-specific CD8+ T-cell responses are more robustly detectable than antibodies against the SARS-CoV-2-spike protein. This was confirmed in a longitudinal analysis of acute-resolving infection that demonstrated rapid induction of the SARS-CoV-2-specific CD8+ T cells within a week followed by a prolonged contraction phase that outlasted the waning humoral immune response indicating that CD8+ T-cell responses might serve as a more precise correlate of antiviral immunity than antibody measurements after convalescence. Collectively, these data provide new insights into the fine specificity, heterogeneity, and dynamics of SARS-CoV-2-specific memory CD8+ T cells, potentially informing the rational development of a protective vaccine against SARS-CoV-2.

immunology↗

bioRxiv2018

The bat influenza H17N10 can be neutralized by broadly-neutralizing monoclonal antibodies and its neuraminidase can facilitate viral egress.

The diversity of subtypes within the Influenza A virus genus has recently expanded with the identification of H17N10 and H18N11 from bats. In order to further study the tropism and zoonotic potential of these viruses, we have successfully produced lentiviral pseudotypes bearing both haemagglutinin H17 and neuraminidase N10. These pseudotypes were shown to be efficiently neutralized by the broadly-neutralizing monoclonal antibodies CR9114 and FI6. Our studies also confirm previous reports that H17 does not use sialic acid as its cellular receptor, as pseudotypes bearing the H17 envelope glycoprotein are released into the cell supernatant in the absence of NA. However, we demonstrate that N10 facilitates heterosubtypic (H5 and H7) influenza HA-bearing pseudotype release in the absence of another source of NA, significantly increasing luciferase pseudotype production titres. Despite this, N10 shows no activity in the enzyme-linked lectin assay used for traditional sialidases. These findings suggest that this protein plays an important role in viral egress, but is perhaps involved in further accessory roles in the bat influenza lifecycle that are yet to be discovered. Thus we show the lentiviral pseudotype system is a useful research tool, and amenable for investigation of bat influenza tropism, restriction and sero-epidemiology, without the constraints or safety issues with producing a replication-competent virus, to which the human population is naive.\n\nSignificance statementInfluenza virus is responsible for mortality and morbidity across the globe; human populations are constantly at risk of newly emerging strains from the aquatic bird reservoir which harbors most of the subtypes of influenza A (H1-H16). Recently identified subtypes (H17N10, H18N11) from bats have broadened the reservoir from which potential pandemic strains of influenza can emerge. To evaluate the potential for these novel subtypes to cross over into human populations, their ability to establish an infection, in addition to the extent of cross-reactive immunity established by human seasonal strains needs to be investigated. This study highlights a novel platform for the study of the bat H17 and N10 envelope glycoproteins, using a lentiviral pseudotype system. Following the generation of this pseudotype it was employed in cell entry and microneutralization assays. These showed that two well-characterised monoclonal antibodies (mAb) which target avian and human influenza subtypes will also neutralize H17. Furthermore the data presented in this study show a novel aspect of the N10 glycoprotein in its ability to facilitate the budding of pseudotypes bearing different influenza HAs.

microbiology↗