Recognition of membrane ligands by lymphocytes.

Recognition of membrane-bound ligands is a fundamental event that determines the fate of lymphocytes during immune responses. Extensive studies have been performed in order to understand the recognition of soluble ligands, however very little is known of the parameters that determine the interaction of membrane-bound ligand/receptors. In my PhD thesis 1 have studied how lymphocytes interact with membrane-bound ligands. I initially characterise how B cells recognise membrane-ligands by expressing CFP-tagged antigens on the surface of target cells. To further dissect this process, I have set-up a system of artificial lipid bilayers that allows a quantitative analysis. Fluorescently labelled antigen molecules of varying affinities are displayed at a range of densities on glass-supported bilayers. The interaction of transgenic B cells with them can then be followed by different microscopy techniques in real time. 1 have described a dynamic cellular response in the early stages of the recognition process in which B cells spread and contract on the antigen bearing membranes to collect the bound molecules in a central cluster to later extract it. This response is triggered by signals delivered through the BCR and is an active process guided by actin polymerisation. The extent of the spreading response is dependent on both the antigen density and its affinity for the BCR and it determines the amount of antigen accumulated. I have also set-up a technique to analyse at the molecular level the differential dynamics of reorganisation of key co-receptor molecules involved in triggering B cell activation. Finally, I extended the bilayers system to characterise the interaction of human NK T cells with a set of specific ligands of different affinities for the T cell receptor (TCR). I have determined the thresholds for the formation of the immunological synapse. In summary, 1 have characterised the early events triggered upon membrane-antigen recognition and elucidated a novel mechanism by which B cells are able to gather antigen and therefore perform their biological function

Daughter B cells are not created equal: Asymmetric segregation of antigen during B cell division

Comment on: Thaunat O, et al. Science 2012; 335:475-9

Actualización en el diagnóstico, tratamiento y pronóstico de osteosíntesis imperfecta.

The "glass eye disease", scientifically known as osteogenesis imperfecta, is a genetic disorder that affects the production of collagen in bones, leading to a significant susceptibility to fractures and bone weakness. Even though there have been advances in understanding how the disease develops, the diversity in its clinical and genetic manifestations continues to be an obstacle in medicine. The purpose of this review is to provide a more comprehensive and contemporary analysis on how it's diagnosed, the alternatives for its management, and what can be expected in the long term for those affected. Genetic sequencing has emerged as a more accurate diagnostic tool, while treatment approaches have evolved towards a multidisciplinary approach involving physiotherapy, orthopedic surgery, and pharmacological therapy with bisphosphonates to enhance bone density. The prognosis for these patients has improved, although quality of life can still be compromised, especially in severe cases. Recent advancements in genetic diagnosis and molecular therapies have revolutionized the treatment approach, offering renewed hope for patients. However, there remains an urgent need for further research and development of safer and more effective therapies to enhance well-being and survival rates among these patients.La "enfermedad del ojo de cristal", científicamente llamada osteogénesis imperfecta, es un desorden genético que afecta la fabricación de colágeno en los huesos, llevando a una significativa susceptibilidad a fracturas y debilidad ósea. Aunque ha habido avances en el conocimiento de cómo se desarrolla la enfermedad, la variedad en sus manifestaciones clínicas y genéticas continúa siendo un obstáculo en la medicina. Esta revisión tiene como propósito brindar un análisis más exhaustivo y contemporáneo sobre cómo se diagnostica, las alternativas para su manejo y qué se puede esperar a largo plazo para las personas afectadas. Se evidencio que el uso de la secuenciación genética, está permitiendo un diagnóstico más certero, además, el tratamiento ha evolucionado hacia un enfoque multidisciplinar que incluye fisioterapia, cirugía ortopédica y terapia farmacológica con bifosfonatos para aumentar la densidad ósea. El pronóstico de estos pacientes ha mejorado, aunque el nivel de vida puede verse perjudica, sobre todo en los casos más graves. Los recientes avances en el diagnóstico genético y las terapias a nivel molecular han cambiado por completo la forma de tratar, dando nuevas esperanzas a los pacientes. A pesar de estos avances, sigue existiendo una necesidad urgente de investigar y desarrollar terapias nuevas, más seguras y eficaces, con el propósito de aumentar el bienestar y las tasas de supervivencia de estos pacientes

Affinity measured by microcluster

Like T cell activation, B cell activation is driven by aggregation of B cell receptors (BCRs) into microclusters. New work suggests that the early dynamics of BCR mobility and microcluster formation “translate” BCR affinity for antigen into B cell responsiveness

CD98hc facilitates B cell proliferation and adaptive humoral immunity.

The proliferation of antigen-specific lymphocytes and resulting clonal expansion are essential for adaptive immunity. We report here that B cell-specific deletion of the heavy chain of CD98 (CD98hc) resulted in lower antibody responses due to total suppression of B cell proliferation and subsequent plasma cell formation. Deletion of CD98hc did not impair early B cell activation but did inhibit later activation of the mitogen-activated protein kinase Erk1/2 and downregulation of the cell cycle inhibitor p27. Reconstitution of CD98hc-deficient B cells with CD98hc mutants showed that the integrin-binding domain of CD98hc was required for B cell proliferation but that the amino acid-transport function of CD98hc was dispensable for this. Thus, CD98hc supports integrin-dependent rapid proliferation of B cells. We propose that the advantage of adaptive immunity favored the appearance of CD98hc in vertebrates

Visualizing B cell capture of cognate antigen from follicular dendritic cells

The prominent display of opsonized antigen by follicular dendritic cells (FDCs) has long favored the view that they serve as antigen-presenting cells for B cells. Surprisingly, however, although B cell capture of antigen from macrophages and dendritic cells has been visualized, acquisition from FDCs has not been directly observed. Using two-photon microscopy, we visualized B cell capture of cognate antigen from FDCs. B cell CXCR5 expression was required, and encounter with FDC-associated antigen could be detected for >1 wk after immunization. B cell–FDC contact times were often brief but occasionally persisted for >30 min, and B cells sometimes acquired antigen together with FDC surface proteins. These observations establish that FDCs can serve as sites of B cell antigen capture, with their prolonged display time ensuring that even rare B cells have the chance of antigen encounter, and they suggest possible information transfer from antigen-presenting cell to B cell

Dynamic cortical actin remodeling by ERM proteins controls BCR microcluster organization and integrity

By dynamically remodeling the cortical actin network, ezrin and moesin control BCR microcluster formation, organization, and integrity

Antigen affinity discrimination is an intrinsic function of the B cell receptor

Antibody affinity maturation, a hallmark of adaptive immune responses, results from the selection of B cells expressing somatically hypermutated B cell receptors (BCRs) with increased affinity for antigens. Despite the central role of affinity maturation in antibody responses, the molecular mechanisms by which the increased affinity of a B cell for antigen is translated into a selective advantage for that B cell in immune responses is incompletely understood. We use high resolution live-cell imaging to provide evidence that the earliest BCR-intrinsic events that follow within seconds of BCR–antigen binding are highly sensitive to the affinity of the BCR for antigen. High affinity BCRs readily form oligomers and the resulting microclusters grow rapidly, resulting in enhanced recruitment of Syk kinase and calcium fluxes. Thus, B cells are able to read the affinity of antigen by BCR-intrinsic mechanisms during the earliest phases of BCR clustering, leading to the initiation of B cell responses

Monovalent engagement of the BCR activates ovalbumin-specific transnuclear B cells

Valency requirements for B cell activation upon antigen encounter are poorly understood. OB1 transnuclear B cells express an IgG1 B cell receptor (BCR) specific for ovalbumin (OVA), the epitope of which can be mimicked using short synthetic peptides to allow antigen-specific engagement of the BCR. By altering length and valency of epitope-bearing synthetic peptides, we examined the properties of ligands required for optimal OB1 B cell activation. Monovalent engagement of the BCR with an epitope-bearing 17-mer synthetic peptide readily activated OB1 B cells. Dimers of the minimal peptide epitope oriented in an N to N configuration were more stimulatory than their C to C counterparts. Although shorter length correlated with less activation, a monomeric 8-mer peptide epitope behaved as a weak agonist that blocked responses to cell-bound peptide antigen, a blockade which could not be reversed by CD40 ligation. The 8-mer not only delivered a suboptimal signal, which blocked subsequent responses to OVA, anti-IgG, and anti-kappa, but also competed for binding with OVA. Our results show that fine-tuning of BCR-ligand recognition can lead to B cell nonresponsiveness, activation, or inhibition