The structure of human CD23 and its interactions with IgE and CD21

The low-affinity immunoglobulin E (IgE) receptor, CD23 (FcɛRII), binds both IgE and CD21 and, through these interactions, regulates the synthesis of IgE, the antibody isotype that mediates the allergic response. We have determined the three-dimensional structure of the C-type lectin domain of CD23 in solution by nuclear magnetic resonance spectroscopy. An analysis of concentration-dependent chemical shift perturbations have allowed us to identify the residues engaged in self-association to the trimeric state, whereas ligand-induced changes have defined the binding sites for IgE and CD21. The results further reveal that CD23 can bind both ligands simultaneously. Despite the C-type lectin domain structure, none of the interactions require calcium. We also find that IgE and CD23 can interact to form high molecular mass multimeric complexes. The interactions that we have described provide a solution to the paradox that CD23 is involved in both up- and down-regulation of IgE and provide a structural basis for the development of inhibitors of allergic disease

Engineering the Fab fragment of the anti-IgE omalizumab to prevent Fab crystallization and permit IgE-Fc complex crystallization

Immunoglobulin E (IgE) plays a central role in the allergic response, in which cross-linking of allergen by Fc[epsilon]RI-bound IgE triggers mast cell and basophil degranulation and the release of inflammatory mediators. The high-affinity interaction between IgE and Fc[epsilon]RI is a long-standing target for therapeutic intervention in allergic disease. Omalizumab is a clinically approved anti-IgE monoclonal antibody that binds to free IgE, also with high affinity, preventing its interaction with Fc[epsilon]RI. All attempts to crystallize the pre-formed complex between the omalizumab Fab and the Fc region of IgE (IgE-Fc), to understand the structural basis for its mechanism of action, surprisingly failed. Instead, the Fab alone selectively crystallized in different crystal forms, but their structures revealed intermolecular Fab/Fab interactions that were clearly strong enough to disrupt the Fab/IgE-Fc complexes. Some of these interactions were common to other Fab crystal structures. Mutations were therefore designed to disrupt two recurring packing interactions observed in the omalizumab Fab crystal structures without interfering with the ability of the omalizumab Fab to recognize IgE-Fc; this led to the successful crystallization and subsequent structure determination of the Fab/IgE-Fc complex. The mutagenesis strategy adopted to achieve this result is applicable to other intractable Fab/antigen complexes or systems in which Fabs are used as crystallization chaperones

Expanding the Anti-Phl p 7 Antibody Toolkit: An Anti-Idiotype Nanobody Inhibitor.

We have previously produced a toolkit of antibodies, comprising recombinant human antibodies of all but one of the human isotypes, directed against the polcalcin family antigen Phl p 7. In this work, we complete the toolkit of human antibody isotypes with the IgD version of the anti-Phl p 7 monoclonal antibody. We also raised a set of nanobodies against the IgD anti-Phl p 7 antibody and identify and characterize one paratope-specific nanobody. This nanobody also binds to the IgE isotype of this antibody, which shares the same idiotype, and orthosterically inhibits the interaction with Phl p 7. The 2.1 Å resolution X-ray crystal structure of the nanobody in complex with the IgD Fab is described

Crystal structures of the human IgD Fab reveal insights into CH1 domain diversity

Antibodies of the IgD isotype remain the least well characterized of the mammalian immunoglobulin isotypes. Here we report three-dimensional structures for the Fab region of IgD, based on four different crystal structures, at resolutions of 1.45–2.75 Å. These IgD Fab crystals provide the first high-resolution views of the unique Cδ1 domain. Structural comparisons identify regions of conformational diversity within the Cδ1 domain, as well as among the homologous domains of Cα1, Cγ1 and Cμ1. The IgD Fab structure also possesses a unique conformation of the upper hinge region, which may contribute to the overall disposition of the very long linker sequence between the Fab and Fc regions found in human IgD. Structural similarities observed between IgD and IgG, and differences with IgA and IgM, are consistent with predicted evolutionary relationships for the mammalian antibody isotypes

Allosteric mechanism of action of the therapeutic anti-IgE antibody omalizumab

Immunoglobulin E and its interactions with receptors FcϵRI and CD23 play a central role in allergic disease. Omalizumab, a clinically approved therapeutic antibody, inhibits the interaction between IgE and FcϵRI, preventing mast cell and basophil activation, and blocks IgE binding to CD23 on B cells and antigen-presenting cells. We solved the crystal structure of the complex between an omalizumab-derived Fab and IgE-Fc, with one Fab bound to each Cϵ3 domain. Free IgE-Fc adopts an acutely bent structure, but in the complex it is only partially bent, with large-scale conformational changes in the Cϵ3 domains that inhibit the interaction with FcϵRI. CD23 binding is inhibited sterically due to overlapping binding sites on each Cϵ3 domain. Studies of omalizumab Fab binding in solution demonstrate the allosteric basis for FcϵRI inhibition and, together with the structure, reveal how omalizumab may accelerate dissociation of receptor-bound IgE from FcϵRI, exploiting the intrinsic flexibility and allosteric potential of IgE

Simple, Fast and Accurate Implementation of the Diffusion Approximation Algorithm for Stochastic Ion Channels with Multiple States

The phenomena that emerge from the interaction of the stochastic opening and closing of ion channels (channel noise) with the non-linear neural dynamics are essential to our understanding of the operation of the nervous system. The effects that channel noise can have on neural dynamics are generally studied using numerical simulations of stochastic models. Algorithms based on discrete Markov Chains (MC) seem to be the most reliable and trustworthy, but even optimized algorithms come with a non-negligible computational cost. Diffusion Approximation (DA) methods use Stochastic Differential Equations (SDE) to approximate the behavior of a number of MCs, considerably speeding up simulation times. However, model comparisons have suggested that DA methods did not lead to the same results as in MC modeling in terms of channel noise statistics and effects on excitability. Recently, it was shown that the difference arose because MCs were modeled with coupled activation subunits, while the DA was modeled using uncoupled activation subunits. Implementations of DA with coupled subunits, in the context of a specific kinetic scheme, yielded similar results to MC. However, it remained unclear how to generalize these implementations to different kinetic schemes, or whether they were faster than MC algorithms. Additionally, a steady state approximation was used for the stochastic terms, which, as we show here, can introduce significant inaccuracies. We derived the SDE explicitly for any given ion channel kinetic scheme. The resulting generic equations were surprisingly simple and interpretable - allowing an easy and efficient DA implementation. The algorithm was tested in a voltage clamp simulation and in two different current clamp simulations, yielding the same results as MC modeling. Also, the simulation efficiency of this DA method demonstrated considerable superiority over MC methods.Comment: 32 text pages, 10 figures, 1 supplementary text + figur

May Measurement Month 2017: an analysis of blood pressure screening results from the United Kingdom and the Republic of Ireland-Europe

Elevated blood pressure (BP), or hypertension, is a growing burden worldwide, leading to over 10 million deaths each year. May Measurement Month (MMM) is a global initiative aimed at raising awareness of high BP and acting as a stimulus to improving screening programmes worldwide. In the United Kingdom (UK) nearly 1 in 5 people, and in the Republic of Ireland (RoI) 3 out of 10, have hypertension, of which a large proportion remains undiagnosed. An opportunistic cross-sectional survey of volunteers aged ≥18 years was carried out in May 2017. Blood pressure measurement, the definition of hypertension and statistical analysis followed a standardized protocol. Screenings sites in hospitals, universities, shopping centres, workplaces, sports clubs, community centres, GP practices, and pharmacies were set up across the UK and RoI as part of this initiative. Seven thousand seven hundred and fourteen individuals were screened during MMM17. After multiple imputation, 3099 (40.3%) had hypertension. Of individuals not receiving antihypertensive medication, 1406 (23.4%) were hypertensive. Of individuals receiving antihypertensive medication, 682 (40.5%) had uncontrolled BP. MMM17 was the largest BP screening campaign ever undertaken in the UK and RoI. These data prove for the first time that a relatively inexpensive, volunteer based, convenience sampling of screening BP in the community identified two out of five individuals as hypertensive, with one in four not receiving treatment. Of major concern is that these data demonstrate that of those individuals receiving treatment, two out of five still did not have controlled BP

May Measurement Month 2019: an analysis of blood pressure screening results from the United Kingdom and Republic of Ireland

In the UK, heart and circulatory diseases account for 29% of all deaths (14% through coronary heart disease and 8% through stroke). In 2015, the prevalence of hypertension was 20% in the UK and 23% in the Republic of Ireland. In 2019, 14% of people registered with a UK general practice had hypertension and yet it was the attributable risk factor for around half of all deaths from coronary heart disease or stroke. We participated in May Measurement Month 2019 to increase awareness of blood pressure (BP) measurement, and to identify the proportion of undiagnosed hypertension and degree of uncontrolled hypertension in the community. The 2019 campaign set up screening sites within the community at places of worship, supermarkets, GP surgeries, workplaces, charity events, community pharmacies, gyms, and various other public places. We screened 10194 participants (mean age 51 ± 18 years, 60% women) and found that 1013 (9.9%) were on antihypertensive treatment, while 3408 (33.4%) had hypertension. Of the 3408 participants with hypertension, only 33.5% were aware of their condition despite 98.8% having previous BP measurements. In those on antihypertensive medication, only 38.2% had controlled BP (<140 and <90 mmHg). Our UK and Republic of Ireland data demonstrate concerning levels of undiagnosed hypertension and sub-optimal BP control in many individuals with a diagnosis. This evidence supports a critical need for better systematic community and primary care screening initiatives

Dose-associated changes in safety and efficacy parameters observed in a 24-week maintenance trial of olanzapine long-acting injection in patients with schizophrenia

<p>Abstract</p> <p>Background</p> <p>In a recently published 24-week maintenance study of olanzapine long-acting injection (LAI) in schizophrenia (Kane et al., 2010), apparent dose-associated changes were noted in both efficacy and safety parameters. To help clinicians balance safety and efficacy when choosing a dose of olanzapine LAI, we further studied these changes.</p> <p>Methods</p> <p>Outpatients with schizophrenia who had maintained stability on open-label oral olanzapine for 4 to 8 weeks were randomly assigned to "low" (150 mg/2 weeks; N = 140), "medium" (405 mg/4 weeks; N = 318), or "high" (300 mg/2 weeks; N = 141) dosages of olanzapine LAI for 24 weeks. Potential relationships between dose and several safety or efficacy measures were examined via regression analysis, the Jonckheere-Terpstra test (continuous data), or the Cochran-Armitage test (categorical data).</p> <p>Results</p> <p>Safety parameters statistically significantly related to dose were mean weight change (low: +0.67 [SD = 4.38], medium: +0.89 [SD = 3.87], high: +1.70 [SD = 4.14] kg, p = .024; effect size [ES] = 0.264 high vs. low dose), mean change in prolactin (low: -5.61 [SD = 12.49], medium: -2.76 [SD = 19.02]), high: +3.58 [SD = 33.78] μg/L, p = .001; ES = 0.410 high vs. low dose), fasting triglycerides change from normal at baseline to high (low: 3.2%, medium: 6.0%, high: 18.9%, p = .001; NNT = 7 high vs. low dose) and fasting high-density lipoprotein cholesterol change from normal at baseline to low (low: 13.8%, medium: 19.6%, high: 30.7%, p = .019; NNT = 6 high vs. low dose). Efficacy measures significantly related to dose included Positive and Negative Syndrome Scale total score mean change (low: +2.66 [SD = 14.95], medium: -0.09 [SD = 13.47], high: -2.19 [SD = 13.11], p <.01; ES = 0.356 high vs. low dose), relapse rate (low: 16%, medium: 10%, high: 5%, p = .003; NNT = 9 high vs. low dose), all-cause discontinuation rate (low: 36%, medium: 30%, high: 24%, p = .037; NNT = 9 high vs. low dose), and rate of discontinuation due to efficacy-related reasons (low: 20%, medium: 14%, high: 6%, p <.001). Time to all-cause discontinuation (p = .035) and time to relapse (p = .005) were also significantly related to dose.</p> <p>Conclusions</p> <p>Analyses of several safety and efficacy parameters revealed significant associations with dose of olanzapine LAI, with the highest dose generally showing greater efficacy as well as greater adverse changes in metabolic safety measures. When considering olanzapine LAI, as with all antipsychotics, it is important to carefully consider the potential benefits and risks for an individual patient.</p> <p>Trial Registration</p> <p>ClinicalTrials.gov: <a href="http://www.clinicaltrials.gov/ct2/show/NCT00088491">NCT00088491</a></p

Structural basis for selective inhibition of immunoglobulin E-receptor interactions by an anti-IgE antibody

Immunoglobulin E (IgE) antibodies play a central role in the allergic response: interaction with FcεRI on mast cells and basophils leads to immediate hypersensitivity reactions upon allergen challenge, while interaction with CD23/FcεRII, expressed on a variety of cells, regulates IgE synthesis among other activities. The receptor-binding IgE-Fc region has recently been found to display remarkable flexibility, from acutely bent to extended conformations, with allosteric communication between the distant FcεRI and CD23 binding sites. We report the structure of an anti-IgE antibody Fab (8D6) bound to IgE-Fc through a mixed protein-carbohydrate epitope, revealing further flexibility and a novel extended conformation with potential relevance to that of membrane-bound IgE in the B cell receptor for antigen. Unlike the earlier, clinically approved anti-IgE antibody omalizumab, 8D6 inhibits binding to FcεRI but not CD23; the structure reveals how this discrimination is achieved through both orthosteric and allosteric mechanisms, supporting therapeutic strategies that retain the benefits of CD23 binding