Explore the vast range of titles available.

Acute allergic symptoms are caused by allergen-induced crosslinking of allergen-specific immunoglobulin E (IgE) bound to Fc-epsilon receptors on effector cells. Desensitization with allergen-specific immunotherapy (SIT) has been used for over a century, but the dominant protective mechanism remains unclear. One consistent observation is increased allergen-specific IgG, thought to competitively block allergen binding to IgE. Here we show that the blocking potency of the IgG response to Cat-SIT is heterogeneous. Next, using two potent, pre-selected allergen-blocking monoclonal IgG antibodies against the immunodominant cat allergen Fel d 1, we demonstrate that increasing the IgG/IgE ratio reduces the allergic response in mice and in cat-allergic patients: a single dose of blocking IgG reduces clinical symptoms in response to nasal provocation (ANCOVA, p  = 0.0003), with a magnitude observed at day 8 similar to that reported with years of conventional SIT. This study suggests that simply augmenting the blocking IgG/IgE ratio may reverse allergy. Allergen-specific immunotherapy is used to treat patients affected by acute immunoglobulin E (IgE) responses, but the function mechanism is unclear. Here the authors show that the administration of two cat allergen-specific IgGs reduces allergic responses in mouse models and helps ameliorate clinical symptoms in a phase 1b clinical trial.

RasGRP1 and SOS are Ras-specific nucleotide exchange factors that have distinct roles in lymphocyte development. RasGRP1 is important in some cancers and autoimmune diseases but, in contrast to SOS, its regulatory mechanisms are poorly understood. Activating signals lead to the membrane recruitment of RasGRP1 and Ras engagement, but it is unclear how interactions between RasGRP1 and Ras are suppressed in the absence of such signals. We present a crystal structure of a fragment of RasGRP1 in which the Ras-binding site is blocked by an interdomain linker and the membrane-interaction surface of RasGRP1 is hidden within a dimerization interface that may be stabilized by the C-terminal oligomerization domain. NMR data demonstrate that calcium binding to the regulatory module generates substantial conformational changes that are incompatible with the inactive assembly. These features allow RasGRP1 to be maintained in an inactive state that is poised for activation by calcium and membrane-localization signals. Individual cells within the human body must grow, divide or specialize to perform the tasks required of them. The fates of these cells are often directed by proteins in the Ras family, which detect signals from elsewhere in the body and orchestrate responses within each cell. The activities of these proteins must be tightly controlled, because cancers and developmental diseases can result if Ras proteins are not properly regulated. Binding to the small molecule GTP activates Ras and causes conformational changes that allow it to interact with other proteins in various signaling pathways in the cell. GTP is loaded into Ras by proteins called nucleotide exchange factors, which can replace ‘used’ nucleotides with ‘fresh’ ones to activate Ras. These nucleotide exchange factors are also tightly regulated. For example, the genes for many exchange factors are only switched on after particular signals are received, which can restrict their presence to defined times and locations (e.g., cells or tissues). Also, when activating signals are absent, nucleotide exchange factors commonly reside in the cytoplasm, whereas the Ras proteins remain bound to lipid membranes inside the cell. RasGRP1 is a nucleotide exchange factor that controls the development of immune cells, and leukemia and lupus can result if it is not regulated correctly. However, many questions about RasGRP1 remain unanswered, including how it is able to remain inactive, and how it is activated by various different signals. Iwig et al. have now revealed the mechanisms through which RasGRP1 suppresses Ras signaling in immune cells by solving the structures of two fragments of RasGRP1 and then using a combination of structural, biochemical and cell-based methods to explore how it is activated. These analyses revealed that inactive RasGRP1 adopts a conformation in which one of its regulatory elements blocks access to the Ras binding site. Surprisingly, RasGRP1 can form dimers; this hides the portions of the protein that associate with the membrane and thereby keeps RasGRP1 away from Ras. Iwig et al. also found that two signals, calcium ions and a lipid called diacylglycerol, overcome these inhibitory mechanisms by changing the conformation of RasGRP1 and recruiting it to the membrane. These studies provide a framework for understanding how disease-associated mutations in RasGRP1 bypass the regulatory mechanisms that insure proper immune cell development, and will be critical for developing therapeutic agents that inhibit RasGRP1 activity.

Developing B cells show enhanced sensitivity to negatively selecting signals. Weiss and colleagues show that calcium signals arising from activation of the calcium sensor STIM1 lead to activation of Erk and apoptosis via a protein kinase C-δ and the guanine nucleotide-exchange factor RasGRP1-dependent pathway in transitional self-reactive B cells. Clonal deletion of autoreactive B cells is crucial for the prevention of autoimmunity, but the signaling mechanisms that regulate this checkpoint remain undefined. Here we characterize a previously unrecognized Ca 2+ -driven pathway for activation of the kinase Erk, which was proapoptotic and biochemically distinct from Erk activation induced by diacylglycerol (DAG). This pathway required protein kinase C-δ (PKC-δ) and the guanine nucleotide–exchange factor RasGRP and depended on the concentration of the Ca 2+ sensor STIM1, which controls the magnitude of Ca 2+ entry. Developmental regulation of these proteins was associated with selective activation of the pathway in B cells prone to negative selection. This checkpoint was impaired in PKC-δ-deficient mice, which developed B cell autoimmunity. Conversely, overexpression of STIM1 conferred a competitive disadvantage to developing B cells. Our findings establish Ca 2+ -dependent Erk signaling as a critical proapoptotic pathway that mediates the negative selection of B cells.

This study shows that, despite malignant transformation, autoimmune checkpoints are still functional in B-cell leukaemia, with targeted activation of these checkpoints effectively killing patient-derived B-cell leukaemia in a transplant model; the results represent a novel strategy to overcome drug resistance in leukaemia patients. Anticancer action of excess BCR signalling Markus Müschen and colleagues reason that in certain B cell malignancies with constitutive B cell receptor (BCR) signalling — acute lymphoblastic leukaemias carrying BCR–ABL translocations — it may be possible to modify the normal selection process that favours B cells with an intermediate level of BCR signalling to instead drive BCR signalling over a threshold at which malignant B cells fail to survive. They show that this can be achieved by hyperactivation of the kinase SYK, for example, in a mouse model where pharmacological activation of a SYK pathway reduces the growth of patient-derived tumour xenografts. This concept is distinct from approaches to B lymphoma therapies that seek to block BCR signalling, and may be worth exploring in the clinic. B cells are selected for an intermediate level of B-cell antigen receptor (BCR) signalling strength: attenuation below minimum (for example, non-functional BCR) 1 or hyperactivation above maximum (for example, self-reactive BCR) 2 , 3 thresholds of signalling strength causes negative selection. In ∼25% of cases, acute lymphoblastic leukaemia (ALL) cells carry the oncogenic BCR-ABL1 tyrosine kinase (Philadelphia chromosome positive), which mimics constitutively active pre-BCR signalling 4 , 5 . Current therapeutic approaches are largely focused on the development of more potent tyrosine kinase inhibitors to suppress oncogenic signalling below a minimum threshold for survival 6 . We tested the hypothesis that targeted hyperactivation—above a maximum threshold—will engage a deletional checkpoint for removal of self-reactive B cells and selectively kill ALL cells. Here we find, by testing various components of proximal pre-BCR signalling in mouse BCR–ABL1 cells, that an incremental increase of Syk tyrosine kinase activity was required and sufficient to induce cell death. Hyperactive Syk was functionally equivalent to acute activation of a self-reactive BCR on ALL cells. Despite oncogenic transformation, this basic mechanism of negative selection was still functional in ALL cells. Unlike normal pre-B cells, patient-derived ALL cells express the inhibitory receptors PECAM1, CD300A and LAIR1 at high levels. Genetic studies revealed that Pecam1 , Cd300a and Lair1 are critical to calibrate oncogenic signalling strength through recruitment of the inhibitory phosphatases Ptpn6 (ref. 7 ) and Inpp5d (ref. 8 ). Using a novel small-molecule inhibitor of INPP5D (also known as SHIP1) 9 , we demonstrated that pharmacological hyperactivation of SYK and engagement of negative B-cell selection represents a promising new strategy to overcome drug resistance in human ALL.

Missense variants are a major source of human genetic variation. Here we analyze a new mouse missense variant, Rasgrp1Anaef, with an ENU-mutated EF hand in the Rasgrp1 Ras guanine nucleotide exchange factor. Rasgrp1Anaef mice exhibit anti-nuclear autoantibodies and gradually accumulate a CD44hi Helios+ PD-1+ CD4+ T cell population that is dependent on B cells. Despite reduced Rasgrp1-Ras-ERK activation in vitro, thymocyte selection in Rasgrp1Anaef is mostly normal in vivo, although CD44 is overexpressed on naïve thymocytes and T cells in a T-cell-autonomous manner. We identify CD44 expression as a sensitive reporter of tonic mTOR-S6 kinase signaling through a novel mouse strain, chino, with a reduction-of-function mutation in Mtor. Elevated tonic mTOR-S6 signaling occurs in Rasgrp1Anaef naïve CD4+ T cells. CD44 expression, CD4+ T cell subset ratios and serum autoantibodies all returned to normal in Rasgrp1AnaefMtorchino double-mutant mice, demonstrating that increased mTOR activity is essential for the Rasgrp1Anaef T cell dysregulation. Our DNA contains more than three billion nucleotides. Each of these nucleotides can be an A, C, G or T, and groups of three neighboring nucleotides within our DNA are used to represent the 20 amino acids that are used to make proteins. This means that changing just one nucleotide can cause one amino acid to be replaced by a different amino acid in the protein encoded by that stretch of DNA: AAA and AAG code for the amino acid lysine, for example, but AAC and AAT code for asparagine. Known as missense gene variants, these changes can also increase or decrease the expression of the gene. Every person has thousands of missense gene variants, including about 12,000 inherited from their parents. Sometimes these variants have no consequence, but they can be harmful if replacing the correct amino acid with a different amino acid prevents the protein from performing an important task. In particular, missense gene variants in genes that encode immune system proteins are likely to play a role in diseases of the immune system. For example, variants near a gene called Rasgrp1 have been linked to two autoimmune diseases – type 1 diabetes and Graves’ disease—in which the immune system mistakenly attacks the body’s own cells and tissues. Now Daley et al. have shed new light on the mechanism by which a missense gene variant in Rasgrp1 can cause autoimmune diseases. Mice with this mutation show signs of autoimmune disease, but their T cells—white blood cells that have a central role in the immune system – develop normally despite this mutation. Instead, Daley et al. found that a specific type of T cell, called T helper cells, accumulated in large numbers in the mutant mice and stimulated cells of a third type—immune cells called B cells—to produce autoantibodies. The production of autoantibodies is a common feature of autoimmune diseases. Daley et al. traced the origins of the T helper cells to excessive activity on a signaling pathway that involves a protein called mTOR, and went on to show that treatment with the drug rapamycin counteracted the accumulation of the T helper cells and reduced the level of autoimmune activity. In addition to exemplifying how changing just one amino acid change can have a profound effect, the work of Daley et al. is an attractive model for exploring how missense gene variants in people can contribute to autoimmune diseases.

Nature 521, 357–361 (2015); doi:10.1038/nature14231 In Extended Data Fig. 3b of this Letter, 52 flow cytometry dot plots with double stainings for CD19 and ITIM-bearing receptors (PECAM1, LAIR1, CD300A and BTLA) were shown for 13 samples. The CD19-CD300A staining for sample ICN1 was inadvertently replaced with CD19-CD300A staining for sample PDX2.

Clonal deletion of autoreactive B cells is crucial for the prevention of autoimmunity, but the signaling mechanisms that regulate this checkpoint remain undefined. Here we characterize a previously unrecognized Ca(2+)-driven pathway for activation of the kinase Erk, which was proapoptotic and biochemically distinct from Erk activation induced by diacylglycerol (DAG). This pathway required protein kinase C-δ (PKC-δ) and the guanine nucleotide-exchange factor RasGRP and depended on the concentration of the Ca(2+) sensor STIM1, which controls the magnitude of Ca(2+) entry. Developmental regulation of these proteins was associated with selective activation of the pathway in B cells prone to negative selection. This checkpoint was impaired in PKC-δ-deficient mice, which developed B cell autoimmunity. Conversely, overexpression of STIM1 conferred a competitive disadvantage to developing B cells. Our findings establish Ca(2+)-dependent Erk signaling as a critical proapoptotic pathway that mediates the negative selection of B cells.

Clonal deletion of autoreactive B cells is crucial to prevent autoimmunity, but the signaling mechanisms that regulate this checkpoint remain undefined. Here we characterized a previously unrecognized Ca2+-driven Erk activation pathway, which was pro-apoptotic and biochemically distinct from DAG-induced Erk activation. This pathway required PKCδ and RasGRP proteins and depended on Stim1 concentrations, which control the magnitude of Ca2+ entry. Developmental regulation of these proteins was associated with selective activation of the pathway in B cells prone to negative selection. This checkpoint was impaired in PKCδ-deficient mice, which developed B cell autoimmunity. Conversely, Stim1 overexpression conferred a competitive disadvantage to developing B cells. These findings establish Ca2+-dependent Erk signaling as a critical pro-apoptotic pathway that mediates B cell negative selection.