Biology subjects

de Haan, C. A. M.

Publications and source records attributed to de Haan, C. A. M..

8 recordsLinked to original sources

bioRxiv2026

Spike and host glycan determinants of HKU1 airway tropism

Human coronavirus HKU1 comprises two distinct serotypes, A and B, whose spike proteins are substantially divergent. Here, we show that spikes from both serotypes preferentially bind 9-O-acetylated 2,8-linked disialosides. Cryo-electron microscopy of the B-type N5 spike reveals a conserved extended binding site in domain S1A that accommodates both the terminal and penultimate sialic acid residues, with interactions involving the penultimate residue substantially enhancing binding. Spike N-glycan processing modulates affinity and linkage selectivity; glycans flanking the binding pocket offer a plausible structural basis for these effects. In contrast to the HKU1-A spike, which adopts open S1B-up conformations upon ligand binding, the N5 apo structure showed that the ligand-binding site was already formed and the e1 relay element register-shifted in most protomers. Nevertheless, we detected neither spontaneous opening nor a transition to an S1B-up state following ligand binding. These findings, obtained with a minimally modified ectodomain, differ from recent reports of ligand-independent opening. Molecular dynamics simulations indicated that membrane-embedded GT3, but not GD3, presents its glycan chain in a geometry compatible with S1A-mediated engagement. Concordantly, in human nasal epithelial cultures cell surface GT3-like O-acetylated trisialoside glycotopes were detected in ciliated cells, linking their cell-type-specific presentation to HKU1 tropism.

microbiology↗

bioRxiv2026

Infection drives localised and individualised antibody repertoires, whereas immunisation promotes repertoire convergence in pig

Respiratory viruses elicit mucosal and systemic immunity, yet how tissue compartmentalisation and exposure route shape B cell repertoires remain unclear. Using the pig model, we characterised antibody repertoires in bronchoalveolar lavage, tracheobronchial lymph nodes, spleen, and blood following intranasal infection with pandemic influenza virus (pH1N1) or porcine respiratory coronavirus (PRCV), and after intramuscular PRCV immunisation. Infection induced highly compartmentalised responses, with antigen-associated clones enriched in lung, lymph nodes and spleen but with limited presentation in blood. These clones were largely private, indicating individualised responses, and displayed tissue-specific diversity. The similar tissue distributions between pH1N1 and PRCV infections suggest a conserved spatial organisation, although differential lymph node involvement indicates pathogen-specific effects. In contrast, intramuscular immunisation generated more convergent, public repertoires in blood, characterised by reduced clonal size diversity. Monoclonal antibody analysis revealed functional heterogeneity and limited overlap with bulk repertoires. Together, these findings show that despite stable germline usage, functional antibody responses are shaped by the route of antigen exposure, clonal selection, and host specific factors, resulting in distinct repertoire architectures between infection and immunisation. Author summaryRespiratory viruses such as influenza and coronaviruses infect the airways and lungs, where they trigger immune responses that help the body fight infection. Most studies of immunity rely on blood, although many immune cells function in tissues like the lungs. Therefore, we may be missing important parts of the immune response. We used pigs, a large animal model that closely resembles humans in respiratory biology and is naturally infected with influenzas and coronaviruses, to investigate how immune responses are shaped by infection compared with intramuscular vaccination. We examined B cells in lungs, nearby lymph nodes, spleen, and blood after infection with influenza or a porcine coronavirus and compared these with responses after vaccination. We found that infection generates distinct, individual immune responses in the lung and lymphoid organs. Vaccination by injection led to more similar responses across animals, mostly in the blood. This suggests the way the immune system encounters an antigen influences the response generated. We also showed that antibodies with similar binding properties can behave very differently in their ability to neutralise viruses. Our findings show that infection and vaccination shape immunity in fundamentally different ways, with important implications for designing vaccines that better protect against respiratory diseases.

immunology↗

bioRxiv2025

The gH/gL/gO Complex of Elephant Endotheliotropic Herpesvirus 1A Functions as a Receptor Binding Complex

Elephant endotheliotropic herpesvirus (EEHV) causes a fatal haemorrhagic disease in young elephants and represents a major threat to the survival of these endangered species. Despite its clinical importance, the mechanisms of EEHV entry and host cell recognition remain poorly understood. Here, we show that the EEHV1A homolog of the Betaherpesvirus glycoprotein O (gO) assembles with glycoproteins H and L (gH/gL) to form a heterotrimeric complex analogous to the human cytomegalovirus (HCMV) gH/gL/gO trimer. Using single-particle cryo-electron microscopy, we determined the structure of the EEHV1A gH/gL/gO complex at 3.2 [A] resolution, revealing a conserved overall architecture but distinct gO topology and disulfide arrangement. The EEHV1A trimer, but not gH/gL alone, bound primary elephant endothelial cells, monocytes, and lymphocytes, indicating that gH/gL/gO serves as the receptor-binding complex of EEHV1A. This binding was specifically blocked by sera from naturally infected elephants, confirming its antigenic relevance. Finally, negative-stain electron microscopy polyclonal epitope mapping of gH/gL/gO-Fab complexes identified a Fab population that bound gO near the apex of the gH/gL/gO trimer, suggesting that these antibodies may interfere with gH/gL/gO-receptor interactions. Together, these findings define the molecular architecture and receptor-binding properties of the EEHV1A gH/gL/gO complex and provide a structural framework for the development of vaccines and antibody-based interventions against EEHV-associated disease.

microbiology↗

bioRxiv2025

Structural basis for postfusion-specific binding to Respiratory Syncytial Virus F protein by the canonical antigenic site I antibody 131-2a

The Respiratory Syncytial Virus (RSV) Fusion (F) protein is a major target of antiviral antibodies following natural infection or vaccination and responsible for mediating fusion between the viral envelope and the host membrane. The fusion process is driven by a large-scale conformational change in F, switching irreversibly from the metastable prefusion state to the stable postfusion conformation. Previous research has identified six distinct antigenic sites in RSV-F, termed sites O, I, II, III, IV, and V. Of these, only antigenic site I is fully specific to the postfusion conformation of F. A monoclonal antibody 131-2a that specifically targets postfusion F has been widely used as a research tool to probe for postfusion F and to define antigenic site I in serological studies, yet its sequence and precise epitope have remained unknown. Here we use mass spectrometry-based de novo sequencing of 131-2a to reverse engineer a recombinant product and study the epitope to define antigenic site I with molecular detail, revealing the structural basis for the antibodys specificity towards postfusion RSV-F.

immunology↗

bioRxiv2024

A Spike Trimer Dimer-Inducing Nanobody with Anti-Sarbecovirus Activity

The continued emergence and zoonotic threat posed by coronaviruses highlight the urgent need for effective antiviral strategies with broad reactivity to counter new emerging strains. Nanobodies (or single-domain antibodies) are promising alternatives to traditional monoclonal antibodies, due to their small size, cost-effectiveness and ease of bioengineering. Here, we describe 7F, a llama-derived nanobody, targeting the spike receptor binding domain of sarbecoviruses and SARS-like coronaviruses. 7F demonstrates potent neutralization against SARS-CoV-2 and cross-neutralizing activity against SARS-CoV and SARS-like CoV WIV16 pseudoviruses. Structural analysis reveals 7Fs ability to induce the formation of spike trimer dimers by engaging with two SARS-CoV-2 spike RBDs, targeting the highly conserved class IV region. Bivalent 7F constructs substantially enhance neutralization potency and breadth, up to more recent SARS-CoV-2 variants of concern. Furthermore, we demonstrate the therapeutic potential of 7F against SARS-CoV-2 in the fully differentiated 3D tissue cultures mirroring the epithelium of the human airway ex vivo. The broad sarbecovirus activity and distinctive structural features of 7F underscore its potential as promising antiviral against emerging and evolving sarbecoviruses.

microbiology↗

bioRxiv2023

Low gH/gL (sub)species-specific antibody levels indicate elephants at risk of fatal elephant endotheliotropic herpesvirus hemorrhagic disease

Elephant endotheliotropic herpesviruses (EEHVs), of which seven species and multiple subspecies are currently distinguished, naturally infect either Asian (Elephas maximus) or African elephants (Loxodonta species). While all adult elephants are latently infected with at least one EEHV (sub)species, EEHV infections in young elephants may lead to acute, fatal hemorrhagic disease (EEHV-HD). The disease is primarily observed in calves with low to non-detectable EEHV-specific antibodies, suggesting it is the result of an uncontrolled primary infection. Yet, young elephants showing high antibody levels in serological assays based on EEHV(1A) gB, which detect antibodies against multiple EEHV (sub)species, are not necessarily protected against EEHV-HD. To better determine which animals are at risk of EEHV-HD, we developed gB and gH/gL ELISAs for all Asian elephant EEHV (sub)species and assessed their specificity using 396 sera from 164 Asian elephants kept in Europeans zoos. Antibody levels measured against gB of different EEHV (sub)species correlated strongly with one another, indicating gB-specific antibodies are highly cross-reactive. In contrast, antibody responses towards gH/gL of different EEHV (sub)species were far less correlated and could be used to distinguish between infections with different (sub)species. Subsequently, antibody responses in sera of 23 EEHV-HD fatalities were analyzed. Whereas high antibody levels against gB could be detected in sera of multiple EEHV-HD fatalities, all fatalities had low antibody levels against gH/gL of the EEHV (sub)species they succumbed to. Overall, our data indicate that (sub)species-specific gH/gL ELISAs may be used to identify animals at risk of developing EEHV-HD upon infection with a particular EEHV (sub)species.

microbiology↗

bioRxiv2020

Elephant endotheliotropic herpesvirus is omnipresent in elephants in European zoos and an Asian elephant range country

Elephant endotheliotropic herpesviruses (EEHVs) are a group of evolutionary divergent herpesviruses that may cause acute, often lethal, hemorrhagic disease (EEHV-HD) in young elephants. Although EEHV was first discovered over 20 years ago, its prevalence in different elephant populations is still largely unknown, partially due to the lack of readily available, sensitive serological assays. In order to improve diagnostic tools for the detection of EEHV infections and to obtain insight in its spread among elephants, we developed novel ELISAs focusing on EEHV1A gB and gH/gL as antigens. Performance of the ELISAs was assessed using sera taken from 41 European zoo elephants and 69 semi-captive elephants from Laos, one of the Asian elephant range countries. Sera from all (sub)adult animals tested ([≥]5 years of age) showed high reactivity with both gB and gH/gL, whereas reactivity towards the antigens was generally lower for sera of juvenile animals (1 > 5 years). Only one (juvenile) animal, which was sampled directly after succumbing to EEHV-HD, was found to be seronegative for EEHV. The two other EEHV-HD cases tested showed low antibody levels, suggesting that all three cases died upon a primary EEHV infection. Direct comparison with another EEHV-specific ELISA previously used in two large serosurveys, showed that EEHV prevalence was underestimated before, likely due to aberrant folding of the antigen used. In conclusion, our study suggests that essentially all (semi-)captive (sub)adult elephants in European zoos and in Laos carry EEHV, and that young elephants with low antibody levels are at risk of dying from EEHV-HD. ImportanceOver the last 30 years, nearly 20% of all Asian elephants born in Western zoos succumbed to acute hemorrhagic disease caused by elephant endotheliotropic herpesvirus (EEHV-HD). Yet, the prevalence of EEHV in captive and wild elephant populations is still largely unknown, mainly due to the lack of readily available, sensitive serological assays. For this study two highly sensitive EEHV-specific ELISAs were developed. Using these assays, it was shown that nearly all elephants tested were seropositive for EEHV, with highest antibody levels detected in (sub)adult elephants. In contrast, antibody levels in EEHV-HD cases were very low or non-detectable. Lack of antibodies may thus be a risk factor for developing severe disease. As the novel ELISAs are low-tech in nature, these assays may easily be disseminated to local laboratories in zoos and elephant range countries in order to determine EEHV serostatus of individual animals or complete herds and (wild) populations.

microbiology↗

bioRxiv2019

NK cell activation by RSV-specific antibodies is decreased in infants with severe respiratory infections and correlates with Fc-glycosylation

BackgroundRespiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract infections in infants and there is no vaccine available. In early life, the most important contributors to protection against infectious diseases are the innate immune system and maternal antibodies. However, the mechanisms by which antibodies can protect against RSV disease are incompletely understood, as both antibody levels and neutralization capacity correlate poorly with protection. We therefore asked whether antibody-mediated natural killer (NK) cell activation correlates with RSV disease.\n\nMethodsWe performed an observational case-control study including infants hospitalized for RSV infection (n=43, cases), hernia surgery (n=16, controls), or RSV-negative viral respiratory tract infections (n=18, controls). First, we determined RSV antigen-specific antibody levels in infant plasma using a multiplex immunoassay. Subsequently, we measured the capacity of these antibodies to activate NK cells. Finally, we assessed Fc-glycosylation of the RSV-specific antibodies by mass spectrometry.\n\nResultsWe found that RSV-specific maternal antibodies potently activate NK cells in vitro. While the concentrations of RSV-specific antibodies did not differ between cases and controls, antibodies from infants hospitalized for severe lower respiratory tract infections (RSV and/or other) induced significantly less NK cell interferon gamma production than those from uninfected controls. Furthermore, NK cell activation correlated with Fc-fucosylation of RSV-specific antibodies, but their glycosylation status did not significantly differ between cases and controls.\n\nConclusionsOur results suggest that Fc-dependent antibody function and quality, exemplified by NK cell activation and glycosylation, contribute to protection against severe RSV disease and warrant further studies to evaluate the potential of harnessing these activities to develop an effective vaccine.

immunology↗