Head Domain Research Articles

Detrital zircon U-Pb + Hf data supports 2.1 Ga extensional and 2.0 Ga syn-orogenic basin in southwest Rae Province during early Nuna assembly

This study examines the Paleoproterozoic history of supracrustal rocks in the western Canadian Shield to better inform the tectonic history of northern Laurentia. Samples for detrital zircon U-Pb geochronology and Hf isotopes were collected from the western Rae Province, Taltson magmatic zone, and the Great Slave Lake shear zone in order to assess depositional ages, provenance and geodynamic significance of the detrital systems. Samples from the western Rae Province were sourced locally and deposited after 2.1 Ga in a broadly extensional regime, based on widespread source terrane ages and few data near the maximum depositional age as well as coeval regional mafic magmatism and absence of coeval metamorphism. By contrast, the Taltson samples were deposited after 2.0 Ga, have a significant 2.2 to 2.0 Ga detrital source of relatively juvenile material, have young zircon that overlap in age with the Taltson and Thelon orogens, and yield a significant fraction of the dates that are close to the maximum depositional age. These Taltson samples were also derived from western Rae Province sources or Buffalo Head and Chinchaga domain sources and are interpreted to have formed in a contractional or collisional regime coeval with Taltson-Thelon orogeny. The 2.2 to 2.0 Ga detritus was likely derived from reworked ca. 2.3 Ga juvenile source. A sample from the Great Slave Lake shear zone was deposited after 2.0 Ga in a contractional/collisional regime and was sourced from Slave Province crust and Taltson-Thelon plutons. Our data support extension along the western Rae Province margin at ca. 2.1 Ga and distinct histories of the Rae and Slave Provinces prior to their collision at ca. 1.95 Ga. Before 2.1 Ga, the Rae Province may have been attached to the Slave, North China, Bastar, Dharwar, or Sinhghbum cratons.

Noise-based correction for electrical impedance tomography

Objective. Noisy measurements frequently cause noisy and inaccurate images in impedance imaging. No post-processing technique exists to calculate the propagation of measurement noise and use this to suppress noise in the image. The objectives of this work were (1) to develop a post-processing method for noise-based correction (NBC) in impedance tomography, (2) to test whether NBC improves image quality in electrical impedance tomography (EIT), (3) to determine whether it is preferable to use correlated or uncorrelated noise for NBC, (4) to test whether NBC works with in vivo data and (5) to test whether NBC is stable across model and perturbation geometries. Approach. EIT was performed in silico in a 2D homogeneous circular domain and an anatomically realistic, heterogeneous 3D human head domain for four perturbations and 25 noise levels in each case. This was validated by performing EIT for four perturbations in a circular, saline tank in 2D as well as a human head-shaped saline tank with a realistic skull-like layer in 3D. Images were assessed on the error in the weighted spatial variance (WSV) with respect to the true, target image. The effect of NBC was also tested for in vivo EIT data of lung ventilation in a human thorax and cortical activity in a rat brain. Main results. On visual inspection, NBC maintained or increased image quality for all perturbations and noise levels in 2D and 3D, both experimentally and in silico. Analysis of the WSV showed that NBC significantly improved the WSV in nearly all cases. When the WSV was inferior with NBC, this was either visually imperceptible or a transformation between noisy reconstructions. For in vivo data, NBC improved image quality in all cases and preserved the expected shape of the reconstructed perturbation. Significance. In practice, uncorrelated NBC performed better than correlated NBC and is recommended as a general-use post-processing technique in EIT.

Human neutralizing antibodies target a conserved lateral patch on H7N9 hemagglutinin head

Avian influenza A virus H7N9 causes severe human infections with >30% fatality. Currently, there is no H7N9-specific prevention or treatment for humans. Here, from a 2013 H7N9 convalescent case in Hong Kong, we isolate four hemagglutinin (HA)-reactive monoclonal antibodies (mAbs), with three directed to the globular head domain (HA1) and one to the stalk domain (HA2). Two clonally related HA1-directed mAbs, H7.HK1 and H7.HK2, potently neutralize H7N9 and protect female mice from lethal H7N9/AH1 challenge. Cryo-EM structures reveal that H7.HK1 and H7.HK2 bind to a β14-centered surface and disrupt the 220-loop that makes hydrophobic contacts with sialic acid on an adjacent protomer, thereby blocking viral entry. Sequence analysis indicates the lateral patch targeted by H7.HK1 and H7.HK2 to be conserved among influenza subtypes. Both H7.HK1 and H7.HK2 retain HA1 binding and neutralization capacity to later H7N9 isolates from 2016–2017, consistent with structural data showing that the antigenic mutations during this timeframe occur at their epitope peripheries. The HA2-directed mAb H7.HK4 lacks neutralizing activity but when used in combination with H7.HK2 moderately augments female mouse protection. Overall, our data reveal antibodies to a conserved lateral HA1 supersite that confer neutralization, and when combined with a HA2-directed non-neutralizing mAb, augment protection.

Are the Head and Tail Domains of Intermediate Filaments Really Unstructured Regions?

Intermediate filaments (IFs) are integral components of the cytoskeleton which provide cells with tissue-specific mechanical properties and are involved in a plethora of cellular processes. Unfortunately, due to their intricate architecture, the 3D structure of the complete molecule of IFs has remained unresolved. Even though most of the rod domain structure has been revealed by means of crystallographic analyses, the flanked head and tail domains are still mostly unknown. Only recently have studies shed light on head or tail domains of IFs, revealing certainsecondary structures and conformational changes during IF assembly. Thus, a deeper understanding of their structure could provide insights into their function.

A Luciferase Immunosorbent Assay Based on Attachment Glycoprotein for the Rapid and Easy Detection of Nipah Virus IgG Antibodies.

Nipah virus (NiV) is a virulent zoonotic disease whose natural host is the fruit bat (Pteropus medius), which can coexist with and transmit the virus. Due to its high pathogenicity, wide host range, and pandemic potential, establishing a sensitive, specific, and rapid diagnostic method for NiV is key to preventing and controlling its spread and any outbreaks. Here, we established a luciferase immunosorbent assay (LISA) based on the NiV attachment glycoprotein (G) to detect NiV-specific immunoglobulin G by expressing a fusion protein of nanoluciferase (NanoLuc) and the target antigen. Sensitivity analysis was performed and compared to an indirect enzyme-linked immunosorbent assay (ELISA), and specificity and cross-reactivity assessments were performed using NiV-positive horse serum and Ebola virus-, Crimean-Congo hemorrhagic fever virus-, and West Nile virus-positive horse sera. The optimal structural domain for NiV detection was located within amino acids 176-602 of the NiV G protein head domain. Moreover, the LISA showed at least fourfold more sensitivity than the indirect ELISA, and the cross-reactivity results suggested that the LISA had good specificity and was capable of detecting NiV-specific immunoglobulin G in both mouse and horse serum. In conclusion, the establishment of a rapid, simple NiV LISA using the G protein head domain provides a resource for NiV monitoring.

Are the class 18 myosins Myo18A and Myo18B specialist sarcomeric proteins?

Initially, the two members of class 18 myosins, Myo18A and Myo18B, appeared to exhibit highly divergent functions, complicating the assignment of class-specific functions. However, the identification of a striated muscle-specific isoform of Myo18A, Myo18Aγ, suggests that class 18 myosins may have evolved to complement the functions of conventional class 2 myosins in sarcomeres. Indeed, both genes, Myo18a and Myo18b, are predominantly expressed in the heart and somites, precursors of skeletal muscle, of developing mouse embryos. Genetic deletion of either gene in mice is embryonic lethal and is associated with the disorganization of cardiac sarcomeres. Moreover, Myo18Aγ and Myo18B localize to sarcomeric A-bands, albeit the motor (head) domains of these unconventional myosins have been both deduced and biochemically demonstrated to exhibit negligible ATPase activity, a hallmark of motor proteins. Instead, Myo18Aγ and Myo18B presumably coassemble with thick filaments and provide structural integrity and/or internal resistance through interactions with F-actin and/or other proteins. In addition, Myo18Aγ and Myo18B may play distinct roles in the assembly of myofibrils, which may arise from actin stress fibers containing the α-isoform of Myo18A, Myo18Aα. The β-isoform of Myo18A, Myo18Aβ, is similar to Myo18Aα, except that it lacks the N-terminal extension, and may serve as a negative regulator through heterodimerization with either Myo18Aα or Myo18Aγ. In this review, we contend that Myo18Aγ and Myo18B are essential for myofibril structure and function in striated muscle cells, while α- and β-isoforms of Myo18A play diverse roles in nonmuscle cells.

Genomic characterization of Influenza A (H1N1)pdm09 and SARS-CoV-2 from Influenza Like Illness (ILI) and Severe Acute Respiratory Illness (SARI) cases reported between July–December, 2022

Influenza Like Illness (ILI) and Severe Acute Respiratory Infection (SARI) cases are more prone to Influenza and SARS-CoV-2 infection. Accordingly, we genetically characterized Influenza and SARS-CoV-2 in 633 ILI and SARI cases by rRT-PCR and WGS. ILI and SARI cases showed H1N1pdm09 prevalence of 20.9% and 23.2% respectively. 135 (21.3%) H1N1pdm09 and 23 (3.6%) H3N2 and 5 coinfection (0.78%) of H1N1pdm09 and SARS-CoV-2 were detected. Phylogenetic analysis revealed H1N1pdm09 resemblance to clade 6B.1A.5a.2 and their genetic relatedness to InfA/Perth/34/2020, InfA/Victoria/88/2020 and InfA/Victoria/2570/2019. Pan 24 HA and 26 NA nonsynonymous mutations and novel HA (G6D, Y7F, Y78H, P212L, G339R, T508K and S523T) and NA (S229A) mutations were observed. S74R, N129D, N156K, S162N, K163Q and S164T alter HA Cb and Sa antibody recognizing site. Similarly, M19T, V13T substitution and multiple mutations in transmembrane and NA head domain drive antigenic drift. SARS-CoV-2 strains genetically characterized to Omicron BA.2.75 lineage containing thirty nonsynonymous spike mutations exhibited enhanced virulence and transmission rates. Coinfection although detected very minimal, the mutational changes in H1N1pdm09 and SARS-CoV-2 virus infected individuals could alter antibody receptor binding sites, allowing the viruses to escape immune response resulting in better adaptability and transmission. Thus continuous genomic surveillance is required to tackle any future outbreak.

Vaccination with antigenically complex hemagglutinin mixtures confers broad protection from influenza disease.

Current seasonal influenza virus vaccines induce responses primarily against immunodominant but highly plastic epitopes in the globular head of the hemagglutinin (HA) glycoprotein. Because of viral antigenic drift at these sites, vaccines need to be updated and readministered annually. To increase the breadth of influenza vaccine-mediated protection, we developed an antigenically complex mixture of recombinant HAs designed to redirect immune responses to more conserved domains of the protein. Vaccine-induced antibodies were disproportionally redistributed to the more conserved stalk of the HA without hindering, and in some cases improving, antibody responses against the head domain. These improved responses led to increased protection against homologous and heterologous viral challenges in both mice and ferrets compared with conventional vaccine approaches. Thus, antigenically complex protein mixtures can at least partially overcome HA head domain antigenic immunodominance and may represent a step toward a more universal influenza vaccine.

Mesenchymal Stem Cells improve phenotype of induced pluripotent stem cell (iPSC)-derived cardiomyocytes in Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a clinically and anatomically severe form of congenital heart disease (CHD). We previously demonstrated that genetic variants in the alpha myosin heavy chain (MYH6) gene are significantly associated with HLHS as well as poor outcomes in patients. Additionally, induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) carrying an MYH6-R443P head domain variant demonstrated an impaired CM phenotype including dysmorphic sarcomere structure, altered contractility, and upregulated MYH7 expression. Mesenchymal stem cells (MSCs) and their secretome are currently being explored as a potential therapeutic for cardiac injury. In this study, a possible treatment strategy for iPSC-CMs with a MYH6 tail domain variant was examined through investigation of co-culturing umbilical cord tissue derived MSCs from a healthy newborn. iPSC-CMs from an unaffected family member were included as a normal control to compare cellular RNA and protein changes observed in the MYH6-E1584K line. The MYH6-E1584K variant line demonstrated significant upregulation of sarcomere, calcium channel, and inflammation/immune related gene expression in both mRNA and protein levels. Co-culturing with MSCs rescued expression of several genes and was confirmed through label free proteomic analysis. Co-culturing iPSC-CMs with MSCs also significantly improved contraction (contraction maximum displacement and velocity) in MYH6-E1584K iPSC-CMs. Finally, measurements of microRNA, cytokines, and exosomes secreted into cultured media indicated significant changes. This study suggests that MSC secreted factors improve CM expression and function and may elucidate a new mechanistic target for patients with HLHS. AHW/HHI Innovation Pilot Award. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Contributions of the individual domains of αIIbβ3 integrin to its extension: Insights from multiscale modeling.

The platelet integrin αIIbβ3 undergoes long-range conformational transitions between bent and extended conformations to regulate platelet aggregation during hemostasis and thrombosis. However, how exactly αIIbβ3 transitions between conformations remains largely elusive. Here, we studied how transitions across bent and extended-closed conformations of αIIbβ3 integrin are regulated by effective interactions between its functional domains. We first carried out μs-long equilibrium molecular dynamics (MD) simulations of full-length αIIbβ3 integrins in bent and intermediate conformations, the latter characterized by an extended headpiece and closed legs. Then, we built heterogeneous elastic network models, perturbed inter-domain interactions, and evaluated their relative contributions to the energy barriers between conformations. Results showed that integrin extension emerges from: (i) changes in interfaces between functional domains; (ii) allosteric coupling of the head and upper leg domains with flexible lower leg domains. Collectively, these results provide new insights into integrin conformational activation based on short- and long-range interactions between its functional domains and highlight the importance of the lower legs in the regulation of integrin allostery.

Spectroscopic analysis of the bacterially expressed head domain of rotavirus VP6.

The rotavirus capsid protein VP6 forms the middle of three protein layers and is responsible for many critical steps in the viral life cycle. VP6 as a structural protein can be used in various applications including as a subunit vaccine component. The head domain of VP6 (VP6H) contains key sequences that allow the protein to trimerize and that represent epitopes that are recognized by human antibodies in the viral particle. The domain is rich in β-sheet secondary structures. Here, VP6H was solubilised from bacterial inclusion bodies and purified using a single affinity chromatography step. Spectral (far-UV circular dichroism and intrinsic tryptophan fluorescence) analysis revealed that the purified domain had native-like secondary and tertiary structures. The domain could maintain structure up to 44°C during thermal denaturation following which structural changes result in an intermediate forming and finally irreversible aggregation and denaturation. The chemical denaturation with urea and guanidinium hydrochloride produces intermediates that represent a loss in the cooperativity. The VP6H domain is stable and can fold to produce its native structure in the absence of the VP6 base domain but cannot be defined as an independent folding unit.

Vimentin filaments integrate low-complexity domains in a complex helical structure

Intermediate filaments (IFs) are integral components of the cytoskeleton. They provide cells with tissue-specific mechanical properties and are involved in numerous cellular processes. Due to their intricate architecture, a 3D structure of IFs has remained elusive. Here we use cryo-focused ion-beam milling, cryo-electron microscopy and tomography to obtain a 3D structure of vimentin IFs (VIFs). VIFs assemble into a modular, intertwined and flexible helical structure of 40 α-helices in cross-section, organized into five protofibrils. Surprisingly, the intrinsically disordered head domains form a fiber in the lumen of VIFs, while the intrinsically disordered tails form lateral connections between the protofibrils. Our findings demonstrate how protein domains of low sequence complexity can complement well-folded protein domains to construct a biopolymer with striking mechanical strength and stretchability.

The immunodominance of antigenic site Sb on the H1 influenza virus hemagglutinin increases with high immunoglobulin titers of the cohorts and with young age, but not sex

The head domain of the hemagglutinin of influenza viruses plays a dominant role in the antibody response due to the presence of immunodominant antigenic sites that are the main targets of host neutralizing antibodies. For the H1 hemagglutinin, five major antigenic sites defined as Sa, Sb, Ca1, Ca2, and Cb have been described. Although previous studies have focused on defining the hierarchy of the antigenic sites of the hemagglutinin in different human cohorts, it is still unclear if the immunodominance profile of the antigenic sites might change with the antibody levels of individuals or if other demographic factors (such as exposure history, sex, or age) could also influence the importance of the antigenic sites. The major antigenic sites of influenza viruses hemagglutinins are responsible for eliciting most of the hemagglutination inhibition antibodies in the host. To determine the antibody prevalence towards each major antigenic site, we evaluated the hemagglutination inhibition against a panel of mutant H1 viruses, each one lacking one of the “classic” antigenic sites. Our results showed that the individuals from the Stop Flu NYU cohort had an immunodominant response towards the sites Sb and Ca2 of H1 hemagglutinin. A simple logistic regression analysis of the immunodominance profiles and the hemagglutination inhibition titers displayed by each donor revealed that individuals with high hemagglutination inhibition titers against the wild-type influenza virus exhibited higher probabilities of displaying an immunodominance profile dominated by Sb, followed by Ca2 (Sb > Ca2 profile), while individuals with low hemagglutination inhibition titers presented a higher chance of displaying an immunodominance profile in which Sb and Ca2 presented the same level of immunodominance (Sb = Ca2 profile). Finally, while age exhibited an influence on the immunodominance of the antigenic sites, biological sex was not related to displaying a specific immunodominance profile.

Post-translational modifications of vertebrate striated muscle myosin heavy chains.

Post-translational modifications (PTMs) play a crucial role in regulating the function of many sarcomeric proteins, including myosin. Myosins comprise a family of motor proteins that play fundamental roles in cell motility in general and muscle contraction in particular. A myosin molecule consists of two myosin heavy chains (MyHCs) and two pairs of myosin light chains (MLCs); two MLCs are associated with the neck region of each MyHC's N-terminal head domain, while the two MyHC C-terminal tails form a coiled-coil that polymerizes with other MyHCs to form the thick filament backbone. Myosin undergoes extensive PTMs, and dysregulation of these PTMs may lead to abnormal muscle function and contribute to the development of myopathies and cardiovascular disorders. Recent studies have uncovered the significance of PTMs in regulating MyHC function and showed how these PTMs may provide additional modulation of contractile processes. Here, we discuss MyHC PTMs that have been biochemically and/or functionally studied in mammals' and rodents' striated muscle. We have identified hotspots or specific regions in three isoforms of myosin (MYH2, MYH6, and MYH7) where the prevalence of PTMs is more frequent and could potentially play a significant role in fine-tuning the activity of these proteins.

Unraveling Desmin's Head Domain Structure and Function.

Understanding the structure and function of intermediate filaments (IFs) is necessary in order to explain why more than 70 related IF genes have evolved in vertebrates while maintaining such dramatically tissue-specific expression. Desmin is a member of the large multigene family of IF proteins and is specifically expressed in myocytes. In an effort to elucidate its muscle-specific behavior, we have used a yeast two-hybrid system in order to identify desmin's head binding partners. We described a mitochondrial and a lysosomal protein, NADH ubiquinone oxidoreductase core subunit S2 (NDUFS2), and saposin D, respectively, as direct desmin binding partners. In silico analysis indicated that both interactions at the atomic level occur in a very similar way, by the formation of a three-helix bundle with hydrophobic interactions in the interdomain space and hydrogen bonds at R16 and S32 of the desmin head domain. The interactions, confirmed also by GST pull-down assays, indicating the necessity of the desmin head domain and, furthermore, point out its role in function of mitochondria and lysosomes, organelles which are disrupted in myopathies due to desmin head domain mutations.

Left-right Myosin-Is, Myosin1C, and Myosin1D exhibit distinct single molecule behaviors on the plasma membrane of Drosophila macrophages.

Left-right (LR) asymmetry is crucial for animal development, particularly in Drosophila where LR-asymmetric morphogenesis of organs hinges on cellular-level chirality, termed cell chirality. In this species, two class I myosins, Myosin1D (Myo1D), and Myosin1C (Myo1C), respectively determine dextral (wild type) and sinistral (mirror image) cell chirality. Previous studies demonstrated Myo1D's ability to propel F-actin in leftward circles during in vitro gliding assays, suggesting its mechanochemical role in defining dextral chirality. Conversely, Myo1C propels F-actin without exhibiting LR-directional preference in this assay, suggesting at other properties governing sinistral chirality. Given the interaction of Myo1D and Myo1C with the membrane, we hypothesized that differences in their membrane behaviors might be critical in dictating their dextral or sinistral activities. In this study, employing single-molecule imaging analyses, we investigated the dynamic behaviors of Myo1D and Myo1C on the plasma membrane. Our findings revealed that Myo1C exhibits a significantly greater proportion of slow-diffusing population compared to Myo1D. Importantly, this characteristic was contingent upon both head and tail domains of Myo1C. The distinct diffusion patterns of Myo1D and Myo1C did not exert mutual influence on each other. This divergence in membrane diffusion between Myo1D and Myo1C may be crucial for dictating cell and organ chirality.

Protective human monoclonal antibodies target conserved sites of vulnerability on the underside of influenza virus neuraminidase

Continuously evolving influenza viruses cause seasonal epidemics and pose global pandemic threats. Although viral neuraminidase (NA) is an effective drug and vaccine target, our understanding of the NA antigenic landscape still remains incomplete. Here, we describe NA-specific human antibodies that target the underside of the NA globular head domain, inhibit viral propagation of a wide range of human H3N2, swine-origin variant H3N2, and H2N2 viruses, and confer both pre- and post-exposure protection against lethalH3N2 infection in mice. Cryo-EM structures of two such antibodies in complex with NA reveal non-overlapping epitopes covering the underside of the NA head. These sites are highly conserved among N2 NAs yet inaccessible unless the NA head tilts or dissociates. Our findings help guide the development of effective countermeasures against ever-changing influenza viruses by identifying hidden conserved sites of vulnerability on the NA underside.

Influenza A virus hemagglutinin: from classical fusion inhibitors to proteolysis targeting chimera-based strategies in antiviral drug discovery

The influenza virus glycoprotein hemagglutinin (HA) participates in critical steps of the attachment of viral particles to the host cell membrane receptor and membrane fusion. Due to its crucial involvement in the initial phases of influenza A infections, HA emerges as a promising target in the search of novel drug-like candidates. Given its pivotal role in the early stages of influenza A infections, intense drug discovery efforts have been undertaken to target HA in the past decades. Drug discovery studies mainly rely on preventing the recognition of sialic acid units by the receptor binding site in the globular head (GH) domain, or the conformational rearrangement required for the fusion of viral and cell membranes. In this work, the aim is to summarize the progress made in HA-targeted development of small molecule fusion inhibitors. To this end, attention will primarily be focused on the analysis of the X-ray crystallographic structures of HA bound to fusion inhibitors. Furthermore, this study also aims to highlight the efforts made in exploiting the structural information in conjunction with molecular modeling techniques to discern the mechanism of action of the fusion inhibitors and to assist the design and interpretation of structure-activity relationships of novel lead compounds will be highlighted. The final section will be dedicated to elucidating novel and promising antiviral strategies proceeding from the transformation of known small molecule antivirals in proteolysis targeting chimera (PROTAC)-based targeted protein degradation. This knowledge will be valuable to assist the exploitation of classical and novel antiviral structure-based strategies, together with a deeper understanding of the mechanism of action and minimization of the impact of drug resistance.

Immunogenicity of chimeric hemagglutinins delivered by an orf virus vector platform against swine influenza virus.

Orf virus (ORFV) is a large DNA virus that can harbor and efficiently deliver viral antigens in swine. Here we used ORFV as a vector platform to deliver chimeric hemagglutinins (HA) of Influenza A virus of swine (IAV-S). Vaccine development against IAV-S faces limitations posed by strain-specific immunity and the antigenic diversity of the IAV-S strains circulating in the field. A promising alternative aiming at re-directing immune responses on conserved epitopes of the stalk segment of the hemagglutinin (HA2) has recently emerged. Sequential immunization with chimeric HAs comprising the same stalk but distinct exotic head domains can potentially induce cross-reactive immune responses against conserved epitopes of the HA2 while breaking the immunodominance of the head domain (HA1). Here, we generated two recombinant ORFVs expressing chimeric HAs encoding the stalk region of a contemporary H1N1 IAV-S strain and exotic heads derived from either H6 or H8 subtypes, ORFVΔ121cH6/1 and ORFVΔ121cH8/1, respectively. The resulting recombinant viruses were able to express the heterologous protein in vitro. Further, the immunogenicity and cross-protection of these vaccine candidates were assessed in swine after sequential intramuscular immunization with OV-cH6/1 and OV-cH8/1, and subsequent challenge with divergent IAV-S strains. Humoral responses showed that vaccinated piglets presented increasing IgG responses in sera. Additionally, cross-reactive IgG and IgA antibody responses elicited by immunization were detected in sera and bronchoalveolar lavage (BAL), respectively, by ELISA against different viral clades and a diverse range of contemporary H1N1 IAV-S strains, indicating induction of humoral and mucosal immunity in vaccinated animals. Importantly, viral shedding was reduced in nasal swabs from vaccinated piglets after intranasal challenge with either Oh07 (gamma clade) or Ca09 (npdm clade) IAV-S strains. These results demonstrated the efficiency of ORFV-based vectors in delivering chimeric IAV-S HA-based vaccine candidates and underline the potential use of chimeric-HAs for prevention and control of influenza in swine.

Trypanosoma brucei Invariant Surface Glycoprotein 75 Is an Immunoglobulin Fc Receptor Inhibiting Complement Activation and Antibody-Mediated Cellular Phagocytosis.

Various subspecies of the unicellular parasite Trypanosoma brucei cause sleeping sickness, a neglected tropical disease affecting millions of individuals and domestic animals. Immune evasion mechanisms play a pivotal role in parasite survival within the host and enable the parasite to establish a chronic infection. In particular, the rapid switching of variant surface glycoproteins covering a large proportion of the parasite's surface enables the parasite to avoid clearance by the adaptive immune system of the host. In this article, we present the crystal structure and discover an immune-evasive function of the extracellular region of the T. brucei invariant surface gp75 (ISG75). Structural analysis determined that the ISG75 ectodomain is organized as a globular head domain and a long slender coiled-coil domain. Subsequent ligand screening and binding analysis determined that the head domain of ISG75 confers interaction with the Fc region of all subclasses of human IgG. Importantly, the ISG75-IgG interaction strongly inhibits both activation of the classical complement pathway and Ab-dependent cellular phagocytosis by competing with C1q and host cell FcγR CD32. Our data reveal a novel immune evasion mechanism of T. brucei, with ISG75 able to inactivate the activities of Abs recognizing the parasite surface proteins.