Development and validation of a respiratory syncytial virus multiplex immunoassay.

PURPOSE: Respiratory syncytial virus (RSV) is one of the leading causes of severe respiratory disease in infants and adults. While vaccines and monoclonal therapeutic antibodies either are or will shortly become available, correlates of protection remain unclear. For this purpose, we developed an RSV multiplex immunoassay that analyses antibody titers toward the post-F, Nucleoprotein, and a diverse mix of G proteins. METHODS: A bead-based multiplex RSV immunoassay was developed, technically validated to standard FDA bioanalytical guidelines, and clinically validated using samples from human challenge studies. RSV antibody titers were then investigated in children aged under 2 and a population-based cohort. RESULTS: Technical and clinical validation showed outstanding performance, while methodological developments enabled identification of the subtype of previous infections through use of the diverse G proteins for approximately 50% of samples. As a proof of concept to show the suitability of the assay in serosurveillance studies, we then evaluated titer decay and age-dependent antibody responses within population cohorts. CONCLUSION: Overall, the developed assay shows robust performance, is scalable, provides additional information on infection subtype, and is therefore ideally suited to be used in future population cohort studies.

Pulmonary Surfactant Proteins Are Inhibited by Immunoglobulin A Autoantibodies in Severe COVID-19.

Rationale: Coronavirus disease 2019 (COVID-19) can lead to acute respiratory distress syndrome with fatal outcomes. Evidence suggests that dysregulated immune responses, including autoimmunity, are key pathogenic factors. Objectives: To assess whether IgA autoantibodies target lung-specific proteins and contribute to disease severity. Methods: We collected 147 blood, 9 lung tissue, and 36 BAL fluid samples from three tertiary hospitals in Switzerland and one in Germany. Severe COVID-19 was defined by the need to administer oxygen. We investigated the presence of IgA autoantibodies and their effects on pulmonary surfactant in COVID-19 using the following methods: immunofluorescence on tissue samples, immunoprecipitations followed by mass spectrometry on BAL fluid samples, enzyme-linked immunosorbent assays on blood samples, and surface tension measurements with medical surfactant. Measurements and Main Results: IgA autoantibodies targeting pulmonary surfactant proteins B and C were elevated in patients with severe COVID-19 but not in patients with influenza or bacterial pneumonia. Notably, pulmonary surfactant failed to reduce surface tension after incubation with either plasma or purified IgA from patients with severe COVID-19. Conclusions: Our data suggest that patients with severe COVID-19 harbor IgA autoantibodies against pulmonary surfactant proteins B and C and that these autoantibodies block the function of lung surfactant, potentially contributing to alveolar collapse and poor oxygenation.

Antibody Binding and Angiotensin-Converting Enzyme 2 Binding Inhibition Is Significantly Reduced for Both the BA.1 and BA.2 Omicron Variants.

BACKGROUND: The rapid emergence of the Omicron variant and its large number of mutations led to its classification as a variant of concern (VOC) by the World Health Organization. Subsequently, Omicron evolved into distinct sublineages (eg, BA.1 and BA.2), which currently represent the majority of global infections. Initial studies of the neutralizing response toward BA.1 in convalescent and vaccinated individuals showed a substantial reduction. METHODS: We assessed antibody (immunoglobulin G [IgG]) binding, ACE2 (angiotensin-converting enzyme 2) binding inhibition, and IgG binding dynamics for the Omicron BA.1 and BA.2 variants compared to a panel of VOCs/variants of interest, in a large cohort (N = 352) of convalescent, vaccinated, and infected and subsequently vaccinated individuals. RESULTS: While Omicron was capable of efficiently binding to ACE2, antibodies elicited by infection or immunization showed reduced binding capacities and ACE2 binding inhibition compared to wild type. Whereas BA.1 exhibited less IgG binding compared to BA.2, BA.2 showed reduced inhibition of ACE2 binding. Among vaccinated samples, antibody binding to Omicron only improved after administration of a third dose. CONCLUSIONS: Omicron BA.1 and BA.2 can still efficiently bind to ACE2, while vaccine/infection-derived antibodies can bind to Omicron. The extent of the mutations within both variants prevents a strong inhibitory binding response. As a result, both Omicron variants are able to evade control by preexisting antibodies.

NeutrobodyPlex-monitoring SARS-CoV-2 neutralizing immune responses using nanobodies.

In light of the COVID-19 pandemic, there is an ongoing need for diagnostic tools to monitor the immune status of large patient cohorts and the effectiveness of vaccination campaigns. Here, we present 11 unique nanobodies (Nbs) specific for the SARS-CoV-2 spike receptor-binding domain (RBD), of which 8 Nbs potently inhibit the interaction of RBD with angiotensin-converting enzyme 2 (ACE2) as the major viral docking site. Following detailed epitope mapping and structural analysis, we select two inhibitory Nbs, one of which binds an epitope inside and one of which binds an epitope outside the RBD:ACE2 interface. Based on these, we generate a biparatopic nanobody (bipNb) with viral neutralization efficacy in the picomolar range. Using bipNb as a surrogate, we establish a competitive multiplex binding assay ("NeutrobodyPlex") for detailed analysis of the presence and performance of neutralizing RBD-binding antibodies in serum of convalescent or vaccinated patients. We demonstrate that NeutrobodyPlex enables high-throughput screening and detailed analysis of neutralizing immune responses in infected or vaccinated individuals, to monitor immune status or to guide vaccine design.

Diminishing Immune Responses against Variants of Concern in Dialysis Patients 4 Months after SARS-CoV-2 mRNA Vaccination.

Patients undergoing chronic hemodialysis were among the first to receive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccinations because of their increased risk for severe coronavirus disease and high case-fatality rates. By using a previously reported cohort from Germany of at-risk hemodialysis patients and healthy donors, where antibody responses were examined 3 weeks after the second vaccination, we assessed systemic cellular and humoral immune responses in serum and saliva 4 months after vaccination with the Pfizer-BioNTech BNT162b2 vaccine using an interferon-γ release assay and multiplex-based IgG measurements. We further compared neutralization capacity of vaccination-induced IgG against 4 SARS-CoV-2 variants of concern (Alpha, Beta, Gamma, and Delta) by angiotensin-converting enzyme 2 receptor-binding domain competition assay. Sixteen weeks after second vaccination, compared with 3 weeks after, cellular and humoral responses against the original SARS-CoV-2 isolate and variants of concern were substantially reduced. Some dialysis patients even had no detectable B- or T-cell responses.

Correction: RNAi-mediated knockdown of daf-12 in the model parasitic nematode Strongyloides ratti.

[This corrects the article DOI: 10.1371/journal.ppat.1007705.].

Rhabditophanes diutinus a parthenogenetic clade IV nematode with dauer larvae.

Comparative studies using non-parasitic model species such as Caenorhabditis elegans, have been very helpful in investigating the basic biology and evolution of parasitic nematodes. However, as phylogenetic distance increases, these comparisons become more difficult, particularly when outside of the nematode clade to which C. elegans belongs (V). One of the reasons C. elegans has nevertheless been used for these comparisons, is that closely related well characterized free-living species that can serve as models for parasites of interest are frequently not available. The Clade IV parasitic nematodes Strongyloides are of great research interest due to their life cycle and other unique biological features, as well as their medical and veterinary importance. Rhabditophanes, a closely related free-living genus, forms part of the Strongyloidoidea nematode superfamily. Rhabditophanes diutinus (= R. sp. KR3021) was included in the recent comparative genomic analysis of the Strongyloididae, providing some insight into the genomic nature of parasitism. However, very little is known about this species, limiting its usefulness as a research model. Here we provide a species description, name the species as R. diutinus and investigate its life cycle and subsequently gene expression in multiple life stages. We identified two previously unreported starvation induced life stages: dauer larvae and arrested J2 (J2A) larvae. The dauer larvae are morphologically similar to and are the same developmental stage as dauers in C. elegans and infective larvae in Strongyloides. As in C. elegans and Strongyloides, dauer formation is inhibited by treatment with dafachronic acid, indicating some genetic control mechanisms are conserved. Similarly, the expression patterns of putative dauer/infective larva control genes resemble each other, in particular between R. diutinus and Strongyloides spp. These findings illustrate and increase the usefulness of R. diutinus as a non-parasitic, easy to work with model species for the Strongyloididae for studying the evolution of parasitism as well as many aspects of the biology of Strongyloides spp, in particular the formation of infective larvae.

Borrelia multiplex: a bead-based multiplex assay for the simultaneous detection of Borrelia specific IgG/IgM class antibodies.

BACKGROUND: Lyme borreliosis (LB) is the most common tick-borne infectious disease in the northern hemisphere. The diagnosis of LB is usually made by clinical symptoms and subsequently supported by serology. In Europe, a two-step testing consisting of an enzyme-linked immunosorbent assay (ELISA) and an immunoblot is recommended. However, due to the low sensitivity of the currently available tests, antibody detection is sometimes inaccurate, especially in the early phase of infection, leading to underdiagnoses. METHODS: To improve upon Borrelia diagnostics, we developed a multiplex Borrelia immunoassay (Borrelia multiplex), which utilizes the new INTELLIFLEX platform, enabling the simultaneous dual detection of IgG and IgM antibodies, saving further time and reducing the biosample material requirement. In order to enable correct classification, the Borrelia multiplex contains eight antigens from the five human pathogenic Borrelia species known in Europe. Six antigens are known to mainly induce an IgG response and two antigens are predominant for an IgM response. RESULTS: To validate the assay, we compared the Borrelia multiplex to a commercial bead-based immunoassay resulting in an overall assay sensitivity of 93.7% (95% CI 84.8-97.5%) and a specificity of 96.5% (95%CI 93.5-98.1%). To confirm the calculated sensitivity and specificity, a comparison with a conventional 2-step diagnostics was performed. With this comparison, we obtained a sensitivity of 95.2% (95% CI 84.2-99.2%) and a specificity of 93.0% (95% CI 90.6-94.7%). CONCLUSION: Borrelia multiplex is a highly reproducible cost- and time-effective assay that enables the profiling of antibodies against several individual antigens simultaneously.

Chemotactic and temperature-dependent responses of the Strongyloidoidea superfamily of nematodes.

Host-seeking behaviour and how a parasite identifies the correct host to infect remains a poorly understood area of parasitology. What is currently known is that host sensation and seeking behaviour is formed from a complex mixture of chemo-, thermo- and mechanosensory behaviours, of which chemosensation is the best studied. Previous studies of olfaction in parasitic nematodes suggested that this behaviour appears to be more closely related to target host and infection mode than phylogeny. However, there has not yet been a study comparing the chemotactic and temperature-dependent behaviours of very closely related parasitic and non-parasitic nematodes. To this end, we examined the temperature-dependent and chemotactic responses of the Strongyloidoidea superfamily of nematodes. We found differences in temperature response between the different species and within infective larvae. Chemotactic responses were highly divergent, with different attraction profiles between all species studied. When examining direct stimulation with fur, we found that it was insufficient to cause an attractive response. Overall, our results support the notion that olfactory sensation is more closely related to lifestyle and host range than phylogeny, and that multiple cues are required to initiate host-seeking behaviour.

RNAi-mediated knockdown of daf-12 in the model parasitic nematode Strongyloides ratti.

The gene daf-12 has long shown to be involved in the dauer pathway in Caenorhabditis elegans (C. elegans). Due to the similarities of the dauer larvae of C. elegans and infective larvae of certain parasitic nematodes such as Strongyloides spp., this gene has also been suspected to be involved in the development of infective larvae. Previous research has shown that the application of dafachronic acid, the steroid hormone ligand of DAF-12 in C. elegans, affects the development of infective larvae and metabolism in Strongyloides. However, a lack of tools for either forward or reverse genetics within Strongyloides has limited studies of gene function within these important parasites. After determining whether Strongyloides had the requisite proteins for RNAi, we developed and report here the first successful RNAi by soaking protocol for Strongyloides ratti (S. ratti) and use this protocol to study the functions of daf-12 within S. ratti. Suppression of daf-12 in S. ratti severely impairs the formation of infective larvae of the direct cycle and redirects development towards the non-infective (non-dauer) free-living life cycle. Further, daf-12(RNAi) S. ratti produce slightly but significantly fewer offspring and these offspring are developmentally delayed or incapable of completing their development to infective larvae (L3i). Whilst the successful daf-12(RNAi) L3i are still able to infect a new host, the resulting infection is less productive and shorter lived. Further, daf-12 knockdown affects metabolism in S. ratti resulting in a shift from aerobic towards anaerobic fat metabolism. Finally, daf-12(RNAi) S. ratti have reduced tolerance of temperature stress.

Optimizing culture conditions for free-living stages of the nematode parasite Strongyloides ratti.

The rat parasitic nematode Strongyloides ratti (S. ratti) has recently emerged as a model system for various aspects of parasite biology and evolution. In addition to parasitic parthenogenetic females, this species can also form facultative free-living generations of sexually reproducing adults. These free-living worms are bacteriovorous and grow very well when cultured in the feces of their host. However, in fecal cultures the worms are rather difficult to find for observation and experimental manipulation. Therefore, it has also been attempted to raise S. ratti on Nematode Growth Media (NGM) plates with Escherichia coli OP50 as food, exactly as described for the model nematode Caenorhabditis elegans. Whilst worms did grow on these plates, their longevity and reproductive output compared to fecal cultures were dramatically reduced. In order to improve the culture success we tested other plates occasionally used for C. elegans and, starting from the best performing one, systematically varied the plate composition, the temperature and the food in order to further optimize the conditions. Here we present a plate culturing protocol for free-living stages of S. ratti with strongly improved reproductive success and longevity.

Characteristics Associated with COVID-19 Breakthrough Infections after Booster Vaccinations in Healthcare Workers: Insights from the TüSeRe:exact Study.

Background: The prevalence of COVID-19 breakthrough infections in healthcare workers (HCWs) remains an issue of concern. This study examines the different characteristics associated with breakthrough infections in HCWs. Methods: From the total participants in the TüSeRe:exact study (n = 1046), we specifically included study participants who had received three vaccinations and were not infected prior to the third vaccination. Participants were invited to complete an online questionnaire, which included inquiries about any breakthrough infections they might have experienced. Univariate Cox regression analysis was used to investigate the association between participant characteristics and breakthrough infections. Results: Among 629 HCWs (497 female and 132 male), 241 (38%) experienced breakthrough infections during the follow-up period. The frequency of breakthrough infections was 39.2% (195/497) among female participants and 34.8% (46/132) among male participants (p = 0.357). The Cox regression model adjusted for age and sex showed that participants with cardiovascular disease (hazard ratio (95%CI) = 0.621 (0.392-0.985); p = 0.043) and those taking antihypertensives (hazard ratio (95%CI) = 0.551 (0.331-0.915); p = 0.021) had a significantly lower hazard ratio for breakthrough infections. The use of analgesics after the first vaccine (hazard ratio (95%CI) = 1.343 (1.025-1.759); p = 0.032) was associated with an increased risk of breakthrough infections. Conclusions: These findings can inform targeted preventive measures and risk management strategies to protect frontline workers and maintain a resilient healthcare system during the ongoing pandemic.

Bridging the gap - estimation of 2022/2023 SARS-CoV-2 healthcare burden in Germany based on multidimensional data from a rapid epidemic panel.

OBJECTIVES: Throughout the SARS-CoV-2 pandemic, Germany like other countries lacked adaptive population-based panels to monitor the spread of epidemic diseases. METHODS: To fill a gap in population-based estimates needed for winter 2022/23 we resampled in the German SARS-CoV-2 cohort study MuSPAD in mid-2022, including characterization of systemic cellular and humoral immune responses by interferon-γ-release assay (IGRA) and CLIA/IVN assay. We were able to confirm categorization of our study population into four groups with differing protection levels against severe COVID-19 courses based on literature synthesis. Using these estimates, we assessed potential healthcare burden for winter 2022/23 in different scenarios with varying assumptions on transmissibility, pathogenicity, new variants, and vaccine booster campaigns in ordinary differential equation models. RESULTS: We included 9921 participants from eight German regions. While 85% of individuals were located in one of the two highest protection categories, hospitalization estimates from scenario modeling were highly dependent on viral variant characteristics ranging from 30-300% compared to the 02/2021 peak. Our results were openly communicated and published to an epidemic panel network and a newly established modeling network. CONCLUSIONS: We demonstrate feasibility of a rapid epidemic panel to provide complex immune protection levels for inclusion in dynamic disease burden modeling scenarios.

Systemic and Mucosal Immunogenicity of Monovalent XBB.1.5-Adapted COVID-19 mRNA Vaccines in Patients with Inflammatory Bowel Disease.

Recently updated COVID-19 mRNA vaccines encode the spike protein of the omicron subvariant XBB.1.5 and are recommended for patients with inflammatory bowel disease (IBD) on immunosuppressive treatment. Nonetheless, their immunogenicity in patients with IBD against rapidly expanding virus variants remains unknown. This prospective multicenter cohort study is the first study to investigate the immunogenicity of XBB.1.5-adapted vaccines in patients with IBD. Systemic and mucosal antibodies targeting the receptor-binding domains (RBDs) of the omicron subvariants XBB.1.5, EG.5.1, and BA.2.86, as well as their neutralization were quantified before and two to four weeks after vaccination with monovalent XBB.1.5-adapted mRNA vaccines. Vaccination increased levels of serum anti-RBD IgG targeting XBB.1.5, EG.5.1, and BA.2.86 (1.9-fold, 1.8-fold, and 2.6-fold, respectively) and enhanced corresponding neutralization responses (2.3-fold, 3.1-fold, and 3.5-fold, respectively). Following vaccination, anti-TNF-treated patients had reduced virus neutralization compared to patients on treatments with other cellular targets. 11.1% and 16.7% of patients lacked EG.5.1 and BA.2.86 neutralization, respectively; all these patients received anti-TNF treatment. At mucosal sites, vaccination induced variant-specific anti-RBD IgG but failed to induce RBD-targeting IgA. Our findings provide a basis for future vaccine recommendations while highlighting the importance of frequent booster vaccine adaptation and the need for mucosal vaccination strategies in patients with IBD.

SARS-CoV-2 specific sIgA in saliva increases after disease-related video stimulation.

Secretory immunoglobulin A (sIgA) in saliva is the most important immunoglobulin fighting pathogens in the respiratory tract and may thus play a role in preventing SARS-CoV-2 infections. To gain a better understanding of the plasticity in the mucosal antibody, we investigated the proactive change in secretion of salivary SARS-CoV-2-specific sIgA in 45 vaccinated and/or previously infected, generally healthy persons (18 to 35 years, 22 women). Participants were exposed to a disease video displaying humans with several respiratory symptoms typical for COVID-19 in realistic situations of increased contagion risk. The disease video triggered an increase in spike-specific sIgA, which was absent after a similar control video with healthy people. The increase further correlated inversely with revulsion and aversive feelings while watching sick people. In contrast, the receptor binding domain-specific sIgA did not increase after the disease video. This may indicate differential roles of the two salivary antibodies in response to predictors of airborne contagion. The observed plasticity of spike-specific salivary antibody release after visual simulation of enhanced contagion risk suggests a role in immune exclusion.

Simultaneous Detection of Different Antibody Classes in a Multiplexed Serological Test.

To monitor the progression of infectious diseases, it is useful to assess immunoreactivity against various antigenic determinants, and measure different antibody isotypes because they appear at different stages of the host immune response. With Lyme borreliosis, the pathogenic agent can be one of the multiple members of the Borrelia species. Therefore, correct sample classification requires evaluating the immunoreactivity against different antigens of different Borrelia species. Additionally, anti-pathogen IgG and IgM responses can have different elicitation time courses during disease progression. Here we demonstrate the development of a two-reporter multiplex immunoassay that has utility in identifying Borrelia-specific immune response in human serum samples by simultaneously evaluating both IgG and IgM immunoreactivity against different bacterial antigens in the same reaction well. This dual-reporter approach retains the analytical performance of single-reporter methods while conserving time and resources and reducing sample size requirements. This assay allows essentially double the serological information to be generated from a blood sample in half the time.

Humoral immune response to SARS-CoV-2 and endemic coronaviruses in urban and indigenous children in Colombia.

BACKGROUND: Although anti-SARS-CoV-2 humoral immune responses and epidemiology have been extensively studied, data gaps remain for certain populations such as indigenous people or children especially in low- and middle-income countries. To address this gap, we evaluated SARS-CoV-2 seroprevalence and humoral immunity towards the parental B.1 strain, local SARS-CoV-2 variants, and endemic coronaviruses in children from Colombia from March to April 2021. METHODS: We performed a cross-sectional seroprevalence study with 80 children from Bogotá and expanded our analysis by comparing results with an independent observational study of 82 children from the Wiwa community living in the north-eastern Colombian territories. Antibody IgG titers towards SARS-CoV-2 and the endemic coronaviruses as well as ACE2 binding inhibition as a proxy for neutralization towards several SARS-CoV-2 variants were analyzed using two multiplex-based immunoassays. RESULTS: While we find seroprevalence estimates of 21.3% in children from Bogotá, seroprevalence is higher with 34.1% in Wiwa children. We observe a robust induction of antibodies towards the surface-exposed spike protein, its S1-, S2- and receptor-binding-subdomains in all SARS-CoV-2 seropositive children. Only nucleocapsid-specific IgG is significantly lower in the indigenous participants. ACE2 binding inhibition is low for all SARS-CoV-2 variants examined. We observe a dominance of NL63 S1 IgG levels in urban and indigenous children which suggests an early exposure to this respiratory virus independent of living conditions and geographic location. SARS-CoV-2 seropositivity does not correlate with antibody levels towards any of the four endemic coronaviruses indicating the absence of cross-protective immunity. CONCLUSIONS: Overall, antibody titers, but in particular ACE2 binding inhibition are low within Colombian samples, requiring further investigation to determine any potential clinical significance.

Our knowledge of SARS-CoV-2, the virus causing COVID-19 remains incomplete for certain populations including indigenous people and younger age groups. Here, we aim to understand the extent to which children from urban and indigenous populations of Colombia were previously infected with SARS-CoV-2 and the related common cold coronaviruses. By measuring antibodies, protective proteins produced by the immune system, we find higher levels of previous SARS-CoV-2 infections in indigenous children of the Wiwa community (34.1%) compared to children from urbanized Bogotá (21.3%). Antibody levels towards the common cold coronaviruses were similar in SARS-CoV-2 infected and uninfected children suggesting immune responses to one coronavirus do not automatically protect against closely-related viruses. Further, we find low levels of protective immunity against SARS-CoV-2 in both populations. This finding warrants further investigation as it relates to reinfection risk and future vaccination strategies in these populations.

STAR SIGN study: Evaluation of COVID-19 vaccine efficacy against the SARS-CoV-2 variants BQ.1.1 and XBB.1.5 in patients with inflammatory bowel disease.

BACKGROUND: Vaccine-elicited immune responses are impaired in patients with inflammatory bowel disease (IBD) treated with anti-TNF biologics. AIMS: To assess vaccination efficacy against the novel omicron sublineages BQ.1.1 and XBB.1.5 in immunosuppressed patients with IBD. METHODS: This prospective multicentre case-control study included 98 biologic-treated patients with IBD and 48 healthy controls. Anti-spike IgG concentrations and surrogate neutralisation against SARS-CoV-2 wild-type, BA.1, BA.5, BQ.1.1, and XBB.1.5 were measured at two different time points (2-16 weeks and 22-40 weeks) following third dose vaccination. Surrogate neutralisation was based on antibody-mediated blockage of ACE2-spike protein-protein interaction. Primary outcome was surrogate neutralisation against tested SARS-CoV-2 sublineages. Secondary outcomes were proportions of participants with insufficient surrogate neutralisation, impact of breakthrough infection, and correlation of surrogate neutralisation with anti-spike IgG concentration. RESULTS: Surrogate neutralisation against all tested sublineages was reduced in patients with IBD who were treated with anti-TNF biologics compared to patients treated with non-anti-TNF biologics and healthy controls (each p ≤ 0.001) at visit 1. Anti-TNF therapy (odds ratio 0.29 [95% CI 0.19-0.46]) and time since vaccination (0.85 [0.72-1.00]) were associated with low, and mRNA-1273 vaccination (1.86 [1.12-3.08]) with high wild-type surrogate neutralisation in a ß-regression model. Accordingly, higher proportions of patients treated with anti-TNF biologics had insufficient surrogate neutralisation against omicron sublineages at visit 1 compared to patients treated with non-anti-TNF biologics and healthy controls (each p ≤ 0.015). Surrogate neutralisation against all tested sublineages decreased over time but was increased by breakthrough infection. Anti-spike IgG concentrations correlated with surrogate neutralisation. CONCLUSIONS: Patients with IBD who are treated with anti-TNF biologics show impaired neutralisation against novel omicron sublineages BQ.1.1 and XBB.1.5 and may benefit from prioritisation for future variant-adapted vaccines.

Strongyloides spp. eliminate male-determining sperm post-meiotically.

If normal male meiosis occurs, it would be expected that 50 % of sperm lack an X chromosome (nullo X) and hence upon fertilisation, result in male progeny. However, for sexual reproduction within the free-living stages of Strongyloides spp. male offspring are absent. We had shown earlier by quantitative whole genome sequencing that within Strongyloides spp., nullo-X sperm are either absent (S. papillosus) or underrepresented (S. ratti) among mature sperm. To investigate how and when this elimination of male-determining sperm occurs, we characterised spermatogenesis and the dynamic localisation of important molecular players such as tubulin, actin and major sperm protein by DIC microscopy, immunohistochemistry, and fluorescent in situ hybridization (FISH) in S. ratti, S. papillosus and Parastrongyloides trichosuri. We found that meiotic divisions in these parasites proceeded as expected for organisms with XO males, resulting in four equally sized spermatocytes, two with and two without an X chromosome. However, mature sperm were found to almost always contain an X chromosome. We also observed structures that contained protein constituents of sperm, such as actin and major sperm protein (MSP) but no DNA. These structures resemble C. elegans residual bodies in appearance and may assume their function. We hypothesize that spermatocytes without an X-chromosome undergo some form of programmed cell death and transform into these residual body-like structures. As in C. elegans, MSP is found in fibrous body-membranous organelles (FB-MOs). Knocking down MSP by RNAi showed that MSP is essential for fertility in S. ratti, as it is in C. elegans.

COVID-19 patient serum less potently inhibits ACE2-RBD binding for various SARS-CoV-2 RBD mutants.

As global vaccination campaigns against SARS-CoV-2 proceed, there is particular interest in the longevity of immune protection, especially with regard to increasingly infectious virus variants. Neutralizing antibodies (Nabs) targeting the receptor binding domain (RBD) of SARS-CoV-2 are promising correlates of protective immunity and have been successfully used for prevention and therapy. As SARS-CoV-2 variants of concern (VOCs) are known to affect binding to the ACE2 receptor and by extension neutralizing activity, we developed a bead-based multiplex ACE2-RBD inhibition assay (RBDCoV-ACE2) as a highly scalable, time-, cost-, and material-saving alternative to infectious live-virus neutralization tests. By mimicking the interaction between ACE2 and the RBD, this serological multiplex assay allows the simultaneous analysis of ACE2 binding inhibition to the RBDs of all SARS-CoV-2 VOCs and variants of interest (VOIs) in a single well. Following validation against a classical virus neutralization test and comparison of performance against a commercially available assay, we analyzed 266 serum samples from 168 COVID-19 patients of varying severity. ACE2 binding inhibition was reduced for ten out of eleven variants examined compared to wild-type, especially for those displaying the E484K mutation such as VOCs beta and gamma. ACE2 binding inhibition, while highly individualistic, positively correlated with IgG levels. ACE2 binding inhibition also correlated with disease severity up to WHO grade 7, after which it reduced.