Lyn kinase controls basophil GATA-3 transcription factor expression and induction of Th2 cell differentiation

Characterization of Freshly Isolated Human Peripheral Blood B Cells, Monocytes, CD4+ and CD8+ T Cells, and Skin Mast Cells by Quantitative Transcriptomics

Quantitative transcriptomics offers a new way to obtain a detailed picture of freshly isolated cells. By direct isolation, the cells are unaffected by in vitro culture, and the isolation at cold temperatures maintains the cells relatively unaltered in phenotype by avoiding activation through receptor cross-linking or plastic adherence. Simultaneous analysis of several cell types provides the opportunity to obtain detailed pictures of transcriptomic differences between them. Here, we present such an analysis focusing on four human blood cell populations and compare those to isolated human skin mast cells. Pure CD19+ peripheral blood B cells, CD14+ monocytes, and CD4+ and CD8+ T cells were obtained by fluorescence-activated cell sorting, and KIT+ human connective tissue mast cells (MCs) were purified by MACS sorting from healthy skin. Detailed information concerning expression levels of the different granule proteases, protease inhibitors, Fc receptors, other receptors, transcription factors, cell signaling components, cytoskeletal proteins, and many other protein families relevant to the functions of these cells were obtained and comprehensively discussed. The MC granule proteases were found exclusively in the MC samples, and the T-cell granzymes in the T cells, of which several were present in both CD4+ and CD8+ T cells. High levels of CD4 were also observed in MCs and monocytes. We found a large variation between the different cell populations in the expression of Fc receptors, as well as for lipid mediators, proteoglycan synthesis enzymes, cytokines, cytokine receptors, and transcription factors. This detailed quantitative comparative analysis of more than 780 proteins of importance for the function of these populations can now serve as a good reference material for research into how these entities shape the role of these cells in immunity and tissue homeostasis.

MultiSC: a deep learning pipeline for analyzing multiomics single-cell data

Single-cell technologies enable researchers to investigate cell functions at an individual cell level and study cellular processes with higher resolution. Several multi-omics single-cell sequencing techniques have been developed to explore various aspects of cellular behavior. Using NEAT-seq as an example, this method simultaneously obtains three kinds of omics data for each cell: gene expression, chromatin accessibility, and protein expression of transcription factors (TFs). Consequently, NEAT-seq offers a more comprehensive understanding of cellular activities in multiple modalities. However, there is a lack of tools available for effectively integrating the three types of omics data. To address this gap, we propose a novel pipeline called MultiSC for the analysis of MULTIomic Single-Cell data. Our pipeline leverages a multimodal constraint autoencoder (single-cell hierarchical constraint autoencoder) to integrate the multi-omics data during the clustering process and a matrix factorization-based model (scMF) to predict target genes regulated by a TF. Moreover, we utilize multivariate linear regression models to predict gene regulatory networks from the multi-omics data. Additional functionalities, including differential expression, mediation analysis, and causal inference, are also incorporated into the MultiSC pipeline. Extensive experiments were conducted to evaluate the performance of MultiSC. The results demonstrate that our pipeline enables researchers to gain a comprehensive view of cell activities and gene regulatory networks by fully leveraging the potential of multiomics single-cell data. By employing MultiSC, researchers can effectively integrate and analyze diverse omics data types, enhancing their understanding of cellular processes.

Based on Weighted Gene Co-Expression Network Analysis Reveals the Hub Immune Infiltration-Related Genes Associated with Ulcerative Colitis

Purpose

Immune infiltration plays a pivotal role in the pathogenesis of mucosal damage in ulcerative colitis (UC). The objective of this study was to systematically analyze and identify genetic characteristics associated with immune infiltration in UC.

Patients and Methods

Gene expression data from three independent datasets obtained from the Gene Expression Omnibus (GEO) were utilized. By employing the ssGSEA and CIBERSORT algorithms, we estimated the extent of immune cell infiltration in UC samples. Subsequently, Weighted Correlation Network Analysis (WGCNA) was performed to identify gene modules exhibiting significant associations with immune infiltration, and further identification of hub genes associated with immune infiltration was accomplished using least absolute shrinkage and selection operator (LASSO) regression analysis. The relationship between the identified hub genes and clinical information was subsequently investigated.

Results

Our findings revealed significant activation of both innate and adaptive immune cells in UC. Notably, the expression levels of CD44, IL1B, LYN, and ITGA5 displayed strong correlations with immune cell infiltration within the mucosa of UC patients. Immunohistochemical analysis confirmed the significant upregulation of CD44, LYN, and ITGA5 in UC samples, and their expression levels were found to be significantly associated with common inflammatory markers, including the systemic immune inflammation indices, C-reactive protein, and erythrocyte sedimentation rate.

Conclusion

CD44, LYN, and ITGA5 are involved in the immune infiltration pathogenesis of UC and may be potential therapeutic targets for UC.

Anti-dsDNA IgE induces IL-4 production from basophils, potentially involved in B-cell differentiation in systemic lupus erythematosus

OBJECTIVES

Recently, the involvement of basophils and IgE-type autoantibodies in the pathogenesis of SLE has been elucidated using mouse models; however, few studies have been conducted in humans. In this study, the role of basophils and anti-double-stranded DNA (dsDNA) IgE in SLE was examined using human samples.

METHODS

The correlation between disease activity and serum levels of anti-dsDNA IgE in SLE was evaluated using enzyme-linked immunosorbent assay. Cytokines produced by IgE-stimulated basophils from healthy subjects were assessed using RNA sequences. The interaction of basophils and B cells to promote B cell differentiation was investigated using a co-culture system. The ability of basophils from patients with SLE with anti-dsDNA IgE to create cytokines that may be involved in B cell differentiation in response to dsDNA was examined using real-time PCR.

RESULTS

Anti-dsDNA IgE levels in the serum of patients with SLE correlated with disease activity. Healthy donor basophils produced IL-3, IL-4 and TGF-β1 after anti-IgE stimulation. Co-culture of B cells with anti-IgE-stimulated basophils increased plasmablasts which were cancelled by neutralizing IL-4. After encountering the antigen, basophils released IL-4 more quickly than follicular helper T cells. Basophils isolated from patients with anti-dsDNA IgE promoted IL-4 expression by adding dsDNA.

CONCLUSIONS

These results suggest that basophils contribute to the pathogenesis of SLE by promoting B cell differentiation via dsDNA-specific IgE in patients similar to the process described in mouse models.

Antibody-mediated regulation of basophils: emerging views and clinical implications

An increasing number of human diseases, including allergies, infections, inflammation, and cancer, involve roles for basophils. Traditionally viewed as the rarest leukocytes that are present only in the circulation, basophils have recently emerged as important players in systemic as well as tissue-specific immune responses. Their functions are regulated by immunoglobulins (Igs), and this enables basophils to integrate diverse adaptive and innate immunity signals. IgE is well known to regulate basophil responses in the context of type 2 immunity and allergic inflammation; however, growing evidence shows that IgG, IgA, and IgD also shape specific aspects of basophil functions relevant to many human diseases. We discuss recent mechanistic advances underpinning antibody-mediated basophil responses and propose strategies for the treatment of basophil-associated disorders.

Basophils control T cell priming through soluble mediators rather than antigen presentation

Basophils play an important role in the development of type 2 immunity and have been linked to protective immunity against parasites but also inflammatory responses in allergic diseases. While typically classified as degranulating effector cells, different modes of cellular activation have been identified, which together with the observation that different populations of basophils exist in the context of disease suggest a multifunctional role. In this review we aim to highlight the role of basophils play in antigen presentation of type 2 immunity and focus on the contribution basophils play in the context of antigen presentation and T cell priming. We will discuss evidence suggesting that basophils perform a direct role in antigen presentation and relate it to findings that indicate cellular cooperation with professional antigen-presenting cells, such as dendritic cells. We will also highlight tissue-specific differences in basophil phenotypes that might lead to distinct roles in cellular cooperation and how these distinct interactions might influence immunological and clinical outcomes of disease. This review thus aims to consolidate the seemingly conflicting literature on the involvement of basophils in antigen presentation and tries to find a resolution to the discussion whether basophils influence antigen presentation through direct or indirect mechanisms.

Analysis of Peripheral Blood Basophils in Pediatric Systemic Lupus Erythematosus

Basophils are the least abundant circulating leukocytes, and their immunological role has not yet been completely elucidated. There is evidence supporting their immunomodulatory role in several pathological settings; recently, studies in both experimental models and humans suggested that basophil homeostasis may be altered in systemic lupus erythematosus (SLE). Here, we first assessed circulating basophils in children affected with pediatric SLE (pSLE). In this cross-sectional study, circulating basophils were enumerated by fluorescence-based flow cytometry analysis in children affected with pSLE, in addition to children suffering from juvenile idiopathic arthritis (JIA) or non-inflammatory/non-rheumatic conditions. This study included 52 pediatric patients distributed in these three groups. We observed a statistically significant reduction of peripherally circulating basophils in children with pSLE compared to the other two groups of patients. This preliminary study is consistent with the available studies in adult patients with SLE showing a reduced number of circulating basophils. However, further research is needed to draw final conclusions on basophils' homeostasis in pSLE, in addition to their correlation with the disease activity and concomitant therapies.

Mast Cell and Basophil Granule Proteases - In Vivo Targets and Function

Proteases are stored in very large amounts within abundant cytoplasmic granules of mast cells (MCs), and in lower amounts in basophils. These proteases are stored in their active form in complex with negatively charged proteoglycans, such as heparin and chondroitin sulfate, ready for rapid release upon MC and basophil activation. The absolute majority of these proteases belong to the large family of chymotrypsin related serine proteases. Three such enzymes are found in human MCs, a chymotryptic enzyme, the chymase, a tryptic enzyme, the tryptase and cathepsin G. Cathepsin G has in primates both chymase and tryptase activity. MCs also express a MC specific exopeptidase, carboxypeptidase A3 (CPA3). The targets and thereby the functions of these enzymes have for many years been the major question of the field. However, the fact that some of these enzymes have a relatively broad specificity has made it difficult to obtain reliable information about the biologically most important targets for these enzymes. Under optimal conditions they may cleave a relatively large number of potential targets. Three of these enzymes, the chymase, the tryptase and CPA3, have been shown to inactivate several venoms from snakes, scorpions, bees and Gila monster. The chymase has also been shown to cleave several connective tissue components and thereby to be an important player in connective tissue homeostasis. This enzyme can also generate angiotensin II (Ang II) by cleavage of Ang I and have thereby a role in blood pressure regulation. It also display anticoagulant activity by cleaving fibrinogen and thrombin. A regulatory function on excessive TH2 immunity has also been observed for both the chymase and the tryptase by cleavage of a highly selective set of cytokines and chemokines. The chymase also appear to have a protective role against ectoparasites such as ticks, mosquitos and leeches by the cleavage of their anticoagulant proteins. We here review the data that has accumulated concerning the potential in vivo functions of these enzymes and we discuss how this information sheds new light on the role of MCs and basophils in health and disease.

CT-M8 Mice: A New Mouse Model Demonstrates That Basophils Have a Nonredundant Role in Lupus-Like Disease Development

Tissue-specific mouse models are essential tools to decipher the role of each cell compartment and/or their expressed genes in the pathophysiology of diseases. Here, we describe a new knock-in mouse model allowing expression of both the fluorescent protein tdTomato and the CRE recombinase selectively in the basophil compartment under the control of the Mcpt8 gene. These “CT-M8” mice did not show any abnormalities in their peripheral distribution of major immune cell populations nor their basophil function. CT-M8 mice allowed the identification of basophils by immunofluorescence and flow cytometry and basophil-specific Cre-mediated floxed gene deletion. Breeding of our CT-M8 mice with the ROSA26^{flox-stop-DTA} mice led to the generation of basophil-deficient mice with no detectable abnormalities in other cell compartments. These mice were then used to document basophil involvement in systemic lupus erythematosus (SLE) pathophysiology since we previously reported by transient depletion of these cells during the course of an ongoing disease that they support and amplify autoantibody production in two distinct lupus-like mouse models (Lyn^−/− and pristane-induced). Here, constitutive basophil deficiency prevented pristane-induced lupus-like disease development by limiting autoantibody titers and renal damages. Therefore, basophils have a nonredundant role in pristane-induced lupus-like disease and are involved in both its induction and amplification. This CT-M8 new mouse model will allow us to finely decipher the role of basophils and their expressed genes in health and disease.

[Basophils and IgE in autoimmunity: Mechanisms and therapeutic targets]

Understanding the pathophysiology of antibody-driven autoimmune diseases (AAID) represents a major challenge for the biomedical community to develop innovative therapeutic strategies that are still lacking to control these diseases. If the reason why AAID are developing still needs to be defined, loss of tolerance to self-antigens leads to the development of an autoimmune chain reaction in some individuals. However, autoreactive antibodies are present in a large proportion of the general population without any associated pathological condition. The amplification of autoantibody production, circulating immune complex formation and innate immune system activation leading to this amplification are some central phenomena in AAID pathophysiology. In this review, we summarize the contribution of type 2 immunity, basophils and IgE in the initiation of some amplification loops that are pathogenic in some AAID, including systemic lupus erythematosus and mixed connective tissue disease.

AMG853, A Bispecific Prostaglandin D2 Receptor 1 and 2 Antagonist, Dampens Basophil Activation and Related Lupus-Like Nephritis Activity in Lyn-Deficient Mice

Systemic lupus erythematosus is a complex autoimmune disease during which patients develop autoantibodies raised against nuclear antigens. During the course of the disease, by accumulating in secondary lymphoid organs (SLOs), basophils support autoreactive plasma cells to amplify autoantibody production. We have recently shown that murine lupus-like disease could be controlled by 10 days of oral treatment with a combination of prostaglandin D₂ (PGD₂) receptor (PTGDR) antagonists through the inhibition of basophil activation and recruitment to SLOs. Importantly, inhibiting solely PTGDR-1 or PTGDR-2 was ineffective, and the development of lupus-like disease could only be dampened by using antagonists for both PTGDR-1 and PTGDR-2. Here, we aimed at establishing a proof of concept that a clinically relevant bispecific antagonist of PTGDR-1 and PTGDR-2 could be efficient to treat murine lupus-like nephritis. Diseased Lyn-deficient female mice received treatment with AMG853 (vidupiprant, a bispecific PTGDR-1/PTGDR-2 antagonist) for 10 days. This led to the dampening of basophil activation and recruitment in SLOs and was associated with a decrease in plasmablast expansion and immunoglobulin E (IgE) production. Ten days of treatment with AMG853 was consequently sufficient in reducing the dsDNA-specific IgG titers, circulating immune complex glomerular deposition, and renal inflammation, which are hallmarks of lupus-like disease. Thus, bispecific PTGDR-1 and PTGDR-2 antagonists, such as AMG853, are a promising class of drugs for the treatment or prevention of organ damage in systemic lupus erythematosus.

Propolis suppresses cytokine production in activated basophils and basophil-mediated skin and intestinal allergic inflammation in mice

BACKGROUND

Propolis is a resinous mixture produced by honey bees that contains cinnamic acid derivatives and flavonoids. Although propolis has been reported to inhibit mast cell functions and mast cell-dependent allergic responses, the effect of propolis on basophil biology remains unknown. This study aimed to investigate the inhibitory effect of propolis on FcεRI-mediated basophil activation.

METHODS

To determine the inhibitory effect of propolis on basophil activation in vitro, cytokine production and FcεRI signal transduction were analyzed by ELISA and western blotting, respectively. To investigate the inhibitory effect of propolis in vivo, IgE-CAI and a food allergy mouse model were employed.

RESULTS

Propolis treatment resulted in the suppression of IgE/antigen-induced production of IL-4, IL-6 and IL-13 in basophils. Phosphorylation of FcεRI signaling molecules Lyn, Akt and ERK was inhibited in basophils treated with propolis. While propolis did not affect the basophil population in the treated mice, propolis did inhibit IgE-CAI. Finally, ovalbumin-induced intestinal anaphylaxis, which involves basophils and basophil-derived IL-4, was attenuated in mice prophylactically treated with propolis.

CONCLUSIONS

Taken together, these results demonstrate the ability of propolis to suppress IgE-dependent basophil activation and basophil-dependent allergic inflammation. Therefore, prophylactic treatment with propolis may be useful for protection against food allergic reactions in sensitive individuals.

Comparative Analysis of Global Proteome and Lysine Acetylome Between Naive CD4+ T Cells and CD4+ T Follicular Helper Cells

As a subgroup of CD4⁺ T helper cells, follicular helper T (Tfh) cells provide help to germinal center B cells and mediate the development of long-lived humoral immunity. Dysregulation of Tfh cells is associated with several major autoimmune diseases. Although recent studies showed that Tfh cell differentiation is controlled by the transcription factor Bcl6, cytokines, and cell-cell signals, limited information is available on the proteome and post-translational modifications (PTMs) of proteins in human Tfh cells. In the present study, we investigated quantitative proteome and acetylome in human naive CD4⁺ T cells and in vitro induced Tfh (iTfh) cells using the tandem mass tag (TMT) labeling technique, antibody-based affinity enrichment, and high-resolution liquid chromatography-mass spectrometry (LC-MS)/mass spectrometry (MS) analysis. In total, we identified 802 upregulated proteins and 598 downregulated proteins at the threshold of 1.5-fold in iTfh cells compared to naive CD4⁺ T cells. With the aid of intensive bioinformatics, the biological process, the cellular compartment, the molecular function, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, and protein–protein interaction of these differentially expressed proteins were revealed. Moreover, the acetylome data showed that 22 lysine (K) acetylated proteins are upregulated and 26 K acetylated proteins are downregulated in iTfh cells compared to the naive CD4⁺ T cells, among which 11 differentially acetylated K residues in core histones were identified, indicating that protein acetylation and epigenetic mechanism are involved in regulating Tfh cell differentiation. The study provides some important clues for investigating T cell activation and Tfh cell differentiation.

IgE in the Pathogenesis of SLE: From Pathogenic Role to Therapeutic Target

Systemic lupus erythematosus (SLE) is a multifactorial chronic autoimmune disease, marked by the presence of autoantibodies to nuclear antigens belonging to different isotype classes. For several years, IgE antibodies have been incriminated in the development of allergic diseases and parasitic infections and different anti-IgE therapies have been developed to encounter the pathogenic role of IgE in these pathologies. Recently, multiple studies showed the presence of elevated total IgE levels and demonstrated a pathogenic role of autoreactive IgE in SLE. This review aims to summarize the findings incriminating IgE and autoreactive IgE in the pathophysiology of SLE, to describe their functional outcomes on their targeted cells as well as to discuss different IgE-related therapeutic modalities that emerged and that may be beneficial for SLE patient care.

Basophils and Systemic Lupus Erythematosus in Murine Models and Human Patients

Basophils are the rarest cell population in the blood. Even though basophils are known to participate in some allergic reactions and immune responses to parasitic infections, their immunological role is still largely elusive. Recent evidence has suggested that in some murine models of systemic lupus erythematosus and lupus-like nephritis, basophils may also be implicated in autoimmunity processes by promoting autoantibody production and tissue injury. We conducted a systematic search to collect the available evidence on basophils' potential immunomodulatory role in autoimmunity and, particularly, systemic lupus erythematosus. We identified several articles investigating basophils' role in murine models of lupus (n = 3) and in patients affected with systemic lupus erythematosus (n = 8). Even though the alteration of the "adaptive" immune response is considered the main immunopathological event in systemic lupus erythematosus, the contribution from the mechanisms of "innate" immunity and, particularly, basophils may be relevant as well, by modulating the activation, polarization, and survival of lymphocytes.

IgE Autoreactivity in Atopic Dermatitis: Paving the Road for Autoimmune Diseases?

Atopic dermatitis (AD) is a common skin disease affecting 20% of the population beginning usually before one year of age. It is associated with the emergence of allergen-specific IgE, but also with autoreactive IgE, whose function remain elusive. This review discusses current knowledge relevant to the mechanisms, which leads to the secretion of autoreactive IgE and to the potential function of these antibodies in AD. Multiple autoantigens have been described to elicit an IgE-dependent response in this context. This IgE autoimmunity starts in infancy and is associated with disease severity. Furthermore, the overall prevalence of autoreactive IgE to multiple auto-antigens is high in AD patients. IgE-antigen complexes can promote a facilitated antigen presentation, a skewing of the adaptive response toward type 2 immunity, and a chronic skin barrier dysfunction and inflammation in patients or AD models. In AD, skin barrier defects and the atopic immune environment facilitate allergen sensitization and the development of other IgE-mediated allergic diseases in a process called the atopic march. AD is also associated epidemiologically with several autoimmune diseases showing autoreactive IgE secretion. Thus, a potential outcome of IgE autoreactivity in AD could be the development of further autoimmune diseases.

Dasatinib Inhibits Lyn and Fyn Src-Family Kinases in Mast Cells to Suppress Type I Hypersensitivity in Mice

Mast cells (MCs) are systemically distributed and secrete several allergic mediators such as histamine and leukotrienes to cause type I hypersensitivity. Dasatinib is a type of anti-cancer agent and it has also been reported to inhibit human basophils. However, dasatinib has not been reported for its inhibitory effects on MCs or type I hypersensitivity in mice. In this study, we examined the inhibitory effect of dasatinib on MCs and MC-mediated allergic response in vitro and in vivo. in vitro, dasatinib inhibited the degranulation of MCs by antigen stimulation in a dose-dependent manner (IC50, ~34 nM for RBL-2H3 cells; ~52 nM for BMMCs) without any cytotoxicity. It also suppressed the secretion of inflammatory cytokines IL-4 and TNF-α by antigen stimulation. Furthermore, dasatinib inhibited MC-mediated passive cutaneous anaphylaxis (PCA) in mice (ED50, ~29 mg/kg). Notably, dasatinib significantly suppressed the degranulation of MCs in the ear tissue. As the mechanism of its effect, dasatinib inhibited the activation of Syk and Syk-mediated downstream signaling proteins, LAT, PLCγ1, and three typical MAP kinases (Erk1/2, JNK, and p38), which are essential for the activation of MCs. Interestingly, in vitro tyrosine kinase assay, dasatinib directly inhibited the activities of Lyn and Fyn, the upstream tyrosine kinases of Syk in MCs. Taken together, dasatinib suppresses MCs and PCA in vitro and in vivo through the inhibition of Lyn and Fyn Src-family kinases. Therefore, we suggest the possibility of repositioning the anti-cancer drug dasatinib as a treatment for various MC-mediated type I hypersensitive diseases.

Paradigm Shifts in Mast Cell and Basophil Biology and Function: An Emerging View of Immune Regulation in Health and Disease

The physiological role of the mast cell and basophil has for many years remained enigmatic. In this chapter, we briefly summarize some of the more recent studies that shed new light on the role of mast cells and basophils in health and disease. What we gain from these studies is a new appreciation for mast cells and basophils as sentinels in host defense and a further understanding that dysregulation of mast cell and basophil function can be a component of various diseases other than allergies. Perhaps the most important insight reaped from this work is the increasing awareness that mast cells and basophils can function as immunoregulatory cells that modulate the immune response in health and disease. Collectively, the recent knowledge provides new challenges and opportunities toward the development of novel therapeutic strategies to augment host protection and modify disease through manipulation of mast cell and basophil function.

S1P₄ Regulates Passive Systemic Anaphylaxis in Mice but Is Dispensable for Canonical IgE-Mediated Responses in Mast Cells

Mast cells are key players in the development of inflammatory allergic reactions. Cross-linking of the high-affinity receptor for IgE (FcεRI) on mast cells leads to the generation and secretion of the sphingolipid mediator, sphingosine-1-phosphate (S1P) which is able, in turn, to transactivate its receptors on mast cells. Previous reports have identified the expression of two of the five receptors for S1P on mast cells, S1P₁ and S1P₂, with functions in FcεRI-mediated chemotaxis and degranulation, respectively. Here, we show that cultured mouse mast cells also express abundant message for S1P₄. Genetic deletion of S1pr4 did not affect the differentiation of bone marrow progenitors into mast cells or the proliferation of mast cells in culture. A comprehensive characterization of IgE-mediated responses in S1P₄-deficient bone marrow-derived and peritoneal mouse mast cells indicated that this receptor is dispensable for mast cell degranulation, cytokine/chemokine production and FcεRI-mediated chemotaxis in vitro. However, interleukin-33 (IL-33)-mediated enhancement of IgE-induced degranulation was reduced in S1P₄-deficient peritoneal mast cells, revealing a potential negative regulatory role for S1P₄ in an IL-33-rich environment. Surprisingly, genetic deletion of S1pr4 resulted in exacerbation of passive systemic anaphylaxis to IgE/anti-IgE in mice, a phenotype likely related to mast cell-extrinsic influences, such as the high circulating levels of IgE in these mice which increases FcεRI expression and consequently the extent of the response to FcεRI engagement. Thus, we provide evidence that S1P₄ modulates anaphylaxis in an unexpected manner that does not involve regulation of mast cell responsiveness to IgE stimulation.

Prostaglandin D2 amplifies lupus disease through basophil accumulation in lymphoid organs

In systemic lupus erythematosus (SLE), autoantibody production can lead to kidney damage and failure, known as lupus nephritis. Basophils amplify the synthesis of autoantibodies by accumulating in secondary lymphoid organs. Here, we show a role for prostaglandin D2 (PGD2) in the pathophysiology of SLE. Patients with SLE have increased expression of PGD2 receptors (PTGDR) on blood basophils and increased concentration of PGD2 metabolites in plasma. Through an autocrine mechanism dependent on both PTGDRs, PGD2 induces the externalization of CXCR4 on basophils, both in humans and mice, driving accumulation in secondary lymphoid organs. Although PGD2 can accelerate basophil-dependent disease, antagonizing PTGDRs in mice reduces lupus-like disease in spontaneous and induced mouse models. Our study identifies the PGD2/PTGDR axis as a ready-to-use therapeutic modality in SLE.

IgE in lupus pathogenesis: Friends or foes?

Systemic lupus erythematosus (SLE) is a complex autoimmune disease involving multiple immunological pathways. Recently, several studies have suggested an implication of Immunoglobulin E (IgE) in the pathophysiology of SLE. In the Lyn^-/- and FcγIIB^-/-.Yaa lupus mouse models, autoreactive IgE activate basophils, and promote a Th2 environment with, subsequently, production of autoantibodies by plasma cells. Autoreactive IgE has been also shown to play a role in the activation of human plasmacytoid dendritic cells (pDCs), in synergy with IgG, which results in an increase of interferon-alpha (IFN-α) production. In contrast, a protective effect of total non-autoreactive IgE has also been suggested, through a decreased ability of FcεRI-triggered pDCs to secrete IFN-α. This review summarizes in a comprehensive manner the emerging recent literature in the field, and propose new concepts to reconcile the observations.

Basophils contribute to pristane-induced Lupus-like nephritis model

Lupus nephritis (LN), one of the most severe outcomes of systemic lupus erythematosus (SLE), is initiated by glomerular deposition of immune-complexes leading to an inflammatory response and kidney failure. Autoantibodies to nuclear antigens and autoreactive B and T cells are central in SLE pathogenesis. Immune mechanisms amplifying this autoantibody production drive flares of the disease. We previously showed that basophils were contributing to LN development in a spontaneous lupus-like mouse model (constitutive Lyn -/- mice) and in SLE subjects through their activation and migration to secondary lymphoid organs (SLOs) where they amplify autoantibody production. In order to study the basophil-specific mechanisms by which these cells contribute to LN development, we needed to validate their involvement in a genetically independent SLE-like mouse model. Pristane, when injected to non-lupus-prone mouse strains, induces a LN-like disease. In this inducible model, basophils were activated and accumulated in SLOs to promote autoantibody production. Basophil depletion by two distinct approaches dampened LN-like disease, demonstrating their contribution to the pristane-induced LN model. These results enable further studies to decipher molecular mechanisms by which basophils contribute to lupus progression.

New insights into the immunopathogenesis of systemic lupus erythematosus

The aetiology of systemic lupus erythematosus (SLE) is multifactorial, and includes contributions from the environment, stochastic factors, and genetic susceptibility. Great gains have been made in understanding SLE through the use of genetic variant identification, mouse models, gene expression studies, and epigenetic analyses. Collectively, these studies support the concept that defective clearance of immune complexes and biological waste (such as apoptotic cells), neutrophil extracellular traps, nucleic acid sensing, lymphocyte signalling, and interferon production pathways are all central to loss of tolerance and tissue damage. Increased understanding of the pathogenesis of SLE is driving a renewed interest in targeted therapy, and researchers are now on the verge of developing targeted immunotherapy directed at treating either specific organ system involvement or specific subsets of patients with SLE. Accordingly, this Review places these insights within the context of our current understanding of the pathogenesis of SLE and highlights pathways that are ripe for therapeutic targeting.

Basophil-derived IL-4 plays versatile roles in immunity

Recent studies demonstrated that basophils play crucial and non-redundant roles in the immune system, in spite of the fact that they are the rarest granulocytes and represent less than 1 % of peripheral blood leukocytes. In response to various stimuli, basophils release effector molecules stored in their cytoplasmic granules, including chemical mediators and proteases, and also secrete cytokines and chemokines. In this review, we will focus on the physiological and pathological roles of basophil-derived IL-4. Basophils can readily produce large quantities of IL-4 and are therefore the important source of IL-4. Basophil-derived IL-4 has been shown to regulate other immune cells, including T cells, B cells, group 2 innate lymphoid cells, monocytes, and macrophages. It also acts on non-hematopoietic cells such as fibroblasts and endothelial cells. Those cells stimulated with basophil-derived IL-4 contribute to the positive or negative regulation of a variety of immune responses in health and disease, including protection against parasitic and bacterial infections, allergy, and autoimmune diseases. Thus, basophil-derived IL-4 plays versatile roles in immunity.

Airway inflammation in asthma: key players beyond the Th2 pathway

PURPOSE OF REVIEW

The Th2 pathway starts with the binding of IL-4 to the IL-4 receptor followed by the phosphorylation of signal transducer and activator of transcription 6 and the activation of GATA3. The most important question relates to the sources of IL-4 and IL-4 related inflammation. Which cells other than Th2 cells are responsible for airway inflammation in asthma?

RECENT FINDINGS

Accumulating data indicate that basophils contribute to endothelium-related IL-4-dependent inflammation. There is also a dendritic cell-related alternative for the induction of Th2 cells via Notch signalling. GATA3 deoxyribozyme improves asthma that is not clearly related to T-cells. The innate immune response in allergy is linked to mast cells, basophils, and the innate lymphoid cell type 2 (ILC2). ILC2s respond to IL-25, IL-33, thymic stromal lymphopoietin, and leukotrienes by producing IL-4, IL-5, and IL-13. In addition to all this inflammatory-cell-driven asthma, increasing evidence has emerged relating to smooth muscle cell activation, the endothelial and epithelial barrier functions, and improvements in the barrier function. The elevation of intracellular cyclic adenosine monophosphate because of the use of phosphodiesterase inhibitors adds to the prevention of epithelial-endothelial leakage, supports airway smooth muscle relaxation, and is immunosuppressive.

CONCLUSION AND SUMMARY

IL-4 is the predominant Th2 cell cytokine. Many more cells, including eosinophils, basophils, mast cells, and ILC2, contribute to the production of IL-4 in the airways. Epithelial cells and endothelial cells lose barrier function in the context of allergic airway inflammation, and this could be at least partially remedied by increasing the intracellular cyclic adenosine monophosphate levels through phosphodiesterase inhibition.

A reverse-engineering approach to dissect post-translational modulators of transcription factor's activity from transcriptional data

Background

Transcription factors (TFs) act downstream of the major signalling pathways functioning as master regulators of cell fate. Their activity is tightly regulated at the transcriptional, post-transcriptional and post-translational level. Proteins modifying TF activity are not easily identified by experimental high-throughput methods.

Results

We developed a computational strategy, called Differential Multi-Information (DMI), to infer post-translational modulators of a transcription factor from a compendium of gene expression profiles (GEPs). DMI is built on the hypothesis that the modulator of a TF (i.e. kinase/phosphatases), when expressed in the cell, will cause the TF target genes to be co-expressed. On the contrary, when the modulator is not expressed, the TF will be inactive resulting in a loss of co-regulation across its target genes. DMI detects the occurrence of changes in target gene co-regulation for each candidate modulator, using a measure called Multi-Information. We validated the DMI approach on a compendium of 5,372 GEPs showing its predictive ability in correctly identifying kinases regulating the activity of 14 different transcription factors.

Conclusions

DMI can be used in combination with experimental approaches as high-throughput screening to efficiently improve both pathway and target discovery. An on-line web-tool enabling the user to use DMI to identify post-transcriptional modulators of a transcription factor of interest che be found at http://dmi.tigem.it.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-015-0700-3) contains supplementary material, which is available to authorized users.

IL-3 contributes to development of lupus nephritis in MRL/lpr mice

MRL/lpr mice develop a spontaneous autoimmune disease that closely resembles human systemic lupus erythematosus (SLE) with DNA autoantibodies, hypergammaglobulinemia, immune complex glomerulonephritis, and systemic vasculitis. Little is known about the role of IL-3 in SLE. In order to study this we analyzed the expression of IL-3 in murine lupus and determined whether blockade of IL-3 with a monoclonal antibody or injection of recombinant IL-3 affects lupus nephritis in MRL/lpr mice. During disease progression IL-3 levels were increased in the plasma and in the supernatant of cultured splenocytes from MRL/lpr mice. Administration of IL-3 aggravated the disease with significantly higher renal activity scores, more renal fibrosis, and more glomerular leukocyte infiltration and IgG deposition. Blockade of IL-3 significantly improved acute and chronic kidney damage, reduced the glomerular infiltration of leukocytes and the glomerular deposition of IgG, and decreased the development of renal fibrosis. Furthermore, DNA autoantibody production, proteinuria, and serum creatinine levels were significantly lower in the anti-IL-3 group. Thus, IL-3 plays an important role in the pathogenesis of SLE and the progression of lupus nephritis. Hence, blockade of IL-3 may represent a new strategy for treatment of lupus nephritis.

Paradigm shifts in mast cell and basophil biology and function: an emerging view of immune regulation in health and disease

The physiological role of the mast cell and basophil has for many years remained enigmatic. In this chapter we briefly summarize some of the more recent studies that shed new light on the role of mast cells and basophils in health and disease. What we gain from these studies is a new appreciation for mast cells and basophils as sentinels in host defense and a further understanding that dysregulation of mast cell and basophil function can be a component of various diseases other than allergies. Perhaps, the most important insight reaped from this work is the increasing awareness that mast cells and basophils can function as immunoregulatory cells that modulate the immune response in health and disease. Collectively, the recent knowledge provides new challenges and opportunities towards the development of novel therapeutic strategies to augment host protection and modify disease through manipulation of mast cell and basophil function.

Role of basophils in rheumatoid arthritis (Review)

The T helper (Th)1/Th2 imbalance plays a crucial role in the development of rheumatoid arthritis (RA). It is well known that basophils can affect the Th1/Th2 balance by enhancing the Th2 response, while impairing the Th1 response, which is known to be involved in the development of a number of diseases. However, limited information is available with regard to the role of basophils in RA. Decreased levels of circulating basophils and a dominant Th1 response have been reported in adult patients with RA, while children with juvenile RA have been largely found to have increased levels of circulating basophils and a dominant Th2 response. Furthermore, the circulating basophils in the two conditions have an activated phenotype and are associated with disease activity. In addition, a longitudinal study found the Th2 response was dominant in the early stages of RA, while the Th1 response was dominant in long-term chronic RA. These observations indicate that basophils may be involved in the development of RA by affecting the Th1/Th2 balance, particularly in the early stages of RA. Therefore, targeting basophils may be a novel therapeutic strategy for the treatment of RA; however, further investigation is required.

Role of basophils in the pathogenesis of minimal change nephrotic syndrome: A literature review

A number of studies have verified that minimal change nephrotic syndrome (MCNS) may result from the dysfunction of T cells and B cells, although the precise mechanisms are yet to be elucidated. It is widely recognized that MCNS is a T helper (Th)2-dominant glomerular disease caused by an imbalanced Th1/Th2 immune response. Increased levels of the Th2 cytokines, interleukin (IL)-4 and IL-13, have been demonstrated to be closely associated with disease activity. In addition, basophils can affect the Th1/Th2 balance by enhancing the Th2 response and impairing the Th1 response, which are then involved in the development of numerous diseases. However, whether basophils are vital in the pathogenesis of MCNS remains unknown. Frequent positivity of the human basophil degranulation test in patients with MCNS has been observed. Thus, basophils should be analyzed in order to determine their role in the pathogenesis of MCNS.

The deleterious role of basophils in systemic lupus erythematosus

Systemic lupus erythematosus is a complex autoimmune disease of multifactorial origins. All compartments of the immune system appear to be affected, at least in some way, and to contribute to disease pathogenesis. Because of an escape from negative selection autoreactive T and B cells accumulate in SLE patients leading to the production of autoantibodies mainly raised against nuclear components and their subsequent deposition into target organs. We recently showed that basophils, in an IgE and IL-4 dependent manner, contribute to SLE pathogenesis by amplifying autoantibody production. Here, we summarize what we have learned about the deleterious role of basophils in lupus both in a mouse model and in SLE patients. We discuss which possible pathways could be involved in basophil activation and recruitment to secondary lymphoid organs during SLE, and how basophils may amplify autoantibody production.

A critical role for Lyn kinase in strengthening endothelial integrity and barrier function

The Src family kinases (SFKs) c-Src and Yes mediate vascular leakage in response to various stimuli including lipopolysaccharide (LPS) and vascular endothelial growth factor (VEGF). Here, we define an opposing function of another SFK, Lyn, which in contrast to other SFKs, strengthens endothelial junctions and thereby restrains the increase in vascular permeability. Mice lacking Lyn displayed increased mortality in LPS-induced endotoxemia and increased vascular permeability in response to LPS or VEGF challenge compared with wild-type littermates. Lyn knockout mice repopulated with wild-type bone marrow-derived cells have higher vascular permeability than wild-type mice, suggesting a role of endothelial Lyn in the maintenance of the vascular barrier. Small interfering RNA-mediated down-regulation of Lyn disrupted endothelial barrier integrity, whereas expression of a constitutively active mutant of Lyn enhanced the barrier. However, down-regulation of Lyn did not affect LPS-induced endothelial permeability. We demonstrate that Lyn association with focal adhesion kinase (FAK) and phosphorylation of FAK at tyrosine residues 576/577 and 925 were required for Lyn-dependent stabilization of endothelial adherens junctions. Thus, in contrast to c-Src and Yes, which increase vascular permeability in response to stimuli, Lyn stabilizes endothelial junctions through phosphorylation of FAK. Therefore, therapeutics activating Lyn kinase may strengthen the endothelial barrier junction and hence have anti-inflammatory potential.

Sphingosine-1-phosphate can promote mast cell hyper-reactivity through regulation of contactin-4 expression

Both genes and the environment are determinants in the susceptibility to allergies and may alter the severity of the disease. We explored whether an increase in the levels of the lipid mediator S1P in vivo, a condition found during allergic asthma, could affect the sensitivity or the response of MCs to IgE/Ag and the onset of allergic disease. We found that increasing S1P levels by genetic deletion of S1P lyase, the enzyme catabolizing S1P, led to elevated activity of circulating tryptase. Accordingly, MCs of S1P lyase-deficient mice were mostly degranulated in the tissues and showed enhanced calcium levels, degranulation, and cytokine production in response to IgE/Ag in vitro. Th 1-skewed mice (C57BL/6) had lower levels of S1P in circulation and histamine responses than did Th 2-skewed (129/Sv) mice. However, when S1P levels were increased by pharmacologic inhibition of S1P lyase, the C57BL/6 mice showed increased histamine release into the circulation and anaphylactic responses similar to those in the 129/Sv mice. Culturing of MCs in the presence of S1P enhanced their degranulation responses, and when the S1P-treated MCs were used to reconstitute MC-deficient (Kit(W-sh)) mice, they caused enhanced anaphylaxis. Gene expression arrays in S1P lyase-deficient MCs and MCs treated with S1P continuously revealed increased expression of numerous genes, including the adhesion molecule CNTN4,which contributed to the enhanced responses. Our findings argue that dysregulation in the metabolism of S1P is a contributing factor in modulating MC responsiveness and the allergic response.

Protective and pathological roles of mast cells and basophils

Mast cells and basophils are potent effector cells of the innate immune system, and they have both beneficial and detrimental functions for the host. They are mainly implicated in pro-inflammatory responses to allergens but can also contribute to protection against pathogens. Although both cell types were identified more than 130 years ago by Paul Ehrlich, their in vivo functions remain poorly understood. The precursor cell populations that give rise to mast cells and basophils have recently been characterized and isolated. Furthermore, new genetically modified mouse strains have been developed, which enable more specific targeting of mast cells and basophils. Such advances offer new opportunities to uncover the true in vivo activities of these cells and to revisit their previously proposed effector functions.

Usage of sphingosine kinase isoforms in mast cells is species and/or cell type determined

FcεRI engagement in mast cells (MCs) induces the activation of two distinct sphingosine kinase isoforms (SphK1 and SphK2) to produce sphingosine-1-phosphate, a mediator essential for MC responses. Whereas embryonic-derived SphK2-null MCs showed impaired responses to Ag, RNA silencing studies on other MC types indicated a dominant role for SphK1. Given the known functional heterogeneity of MCs, we explored whether the reported differences in SphK1 or SphK2 usage could be reflective of phenotypic differences between MC populations. Using lentiviral-based short hairpin RNA to silence SphK1 or SphK2, we found that SphK2 is required for murine MC degranulation, calcium mobilization, and cytokine and leukotriene production, irrespective of the tissue from which the MC progenitors were derived, the stage of MC granule maturity, or the conditions used for differentiation. This finding was consistent with the lack of a full allergic response in SphK2-null mice challenged to undergo passive cutaneous anaphylaxis. A redundant role for both SphKs was uncovered, however, in chemotaxis toward Ag in all MC types tested and in TNF-α production in certain MC types. In contrast, human MC responses were dependent only on SphK1, associating with a more robust expression of this isoform and a more varied representation of SphK variants relative to murine MCs. The findings show that the function of SphK1 and SphK2 can be interchangeable in MCs; however, an important determinant of SphK isoform usage is the species of origin and an influencing factor, the tissue from which MCs may be derived and/or their differentiation state.

Interrogation of sphingosine-1-phosphate receptor 2 function in vivo reveals a prominent role in the recovery from IgE and IgG-mediated anaphylaxis with minimal effect on its onset

Autocrine stimulation of S1PR2, a receptor for the lipid mediator sphingosine-1-phosphate (S1P), has been implicated in mast cell degranulation to IgE/antigen (Ag) although, paradoxically, its ligand cannot trigger substantial degranulation. Additionally, the in vivo role of S1PR2 in the overall allergic responses is unclear since S1PR2 was reported to be required for the onset of systemic anaphylaxis by IgE/Ag but, in apparent contradiction, also for the recovery from histamine-induced anaphylaxis in a mast cell independent manner. Here, we sought to clarify the role of S1PR2 in mast cell degranulation and in IgE and IgG-mediated anaphylaxis. Lack of S1PR2 reduced IgE/Ag-induced degranulation in in vitro experiments with mucosal mast cells, but had no effect on connective tissue type mast cells. This latter response correlated with a lack of involvement of S1PR2 in the onset of non-lethal IgE/Ag-mediated systemic and cutaneous anaphylaxis. However, S1pr2(-/-) mice were slow to recover (or did not recover) from FcɛRI-mediated anaphylaxis, an outcome that mirrored their known impairment in histamine clearance due to defective vascular tone. A minor role for S1PR2 in mast cell degranulation was uncovered upon engagement of low affinity receptors for IgG and in the onset of IgG-mediated anaphylaxis. Our findings show that S1PR2 is dispensable for initiating IgE/Ag-mediated connective tissue mast cell degranulation and anaphylaxis, but it is required for normal recovery from anaphylaxis.

Basophil modulation by cytokine instruction

Basophils have recently been recognized as critical effector cells in allergic reactions and protective immunity against helminths. Precise characterization of basophil biology could help to develop specific therapies that interfere with differentiation, tissue recruitment, or induction of effector functions and thereby ameliorate allergic disorders. The development, homeostasis, and effector functions of basophils are tightly regulated by extrinsic signals and in particular by cytokines. IL-3, GM-CSF, and thymic stromal lymphopoietin activate the STAT5 pathway that promotes proliferation, activation, and cytokine secretion but also induces a negative feedback loop via Pim-1 and SOCS proteins. Basophils further express receptors for IL-18 and IL-33, which are associated with the signaling adaptor MyD88 and activate the NF-κB and MAP kinase pathways. This review focuses on positive and negative regulation of basophils by these cytokines.

Human cord blood derived immature basophils show dual characteristics, expressing both basophil and eosinophil associated proteins

Basophils are blood cells of low abundance associated with allergy, inflammation and parasite infections. To study the transcriptome of mature circulating basophils cells were purified from buffy coats by density gradient centrifugations and two-step magnetic cell sorting. However, after extensive analysis the cells were found to be transcriptionally inactive and almost completely lack functional mRNA. In order to obtain transcriptionally active immature basophils for analysis of their transcriptome, umbilical cord blood cells were therefore cultured in the presence of interleukin (IL)-3 for 9 days and basophils were enriched by removing non-basophils using magnetic cell sorting. The majority of purified cells demonstrated typical metachromatic staining with Alcian blue dye (95%) and expression of surface markers FcεRI and CD203c, indicating a pure population of cells with basophil-like phenotype. mRNA was extracted from these cells and used to construct a cDNA library with approximately 600 000 independent clones. This library served as tool to determine the mRNA frequencies for a number of hematopoietic marker proteins. It was shown that these cells express basophil/mast cell-specific transcripts, i.e. β-tryptase, serglycin and FcεRI α-chain, to a relatively low degree. In contrast, the library contained a high number of several eosinophil-associated transcripts such as: major basic protein (MBP), charcot leyden crystal (CLC), eosinophil cationic protein (ECP), eosinophil derived neurotoxin (EDN) and eosinophil peroxidase (EPO). Out of these transcripts, MBP and EPO were the most frequently observed, representing 8% and 3.2% of the total mRNA pool, respectively. Moreover, in a proteome analysis of cultured basophils we identified MBP and EPO as the two most prominent protein bands, suggesting a good correlation between protein and mRNA analyses of these cells. The mixed phenotype observed for these cells strengthens the conclusion that eosinophils and basophils are closely linked during human hematopoietic development. The dual phenotype also indicates that other cytokines than IL-3 or cell surface interactions are needed to obtain the full basophil specific phenotype in vivo.

Optimizing the GATA-3 position weight matrix to improve the identification of novel binding sites

BACKGROUND

The identifying of binding sites for transcription factors is a key component of gene regulatory network analysis. This is often done using position-weight matrices (PWMs). Because of the importance of in silico mapping of tentative binding sites, we previously developed an approach for PWM optimization that substantially improves the accuracy of such mapping.

RESULTS

The present work implements the optimization algorithm applied to the existing PWM for GATA-3 transcription factor and builds a new di-nucleotide PWM. The existing available PWM is based on experimental data adopted from Jaspar. The optimized PWM substantially improves the sensitivity and specificity of the TF mapping compared to the conventional applications. The refined PWM also facilitates in silico identification of novel binding sites that are supported by experimental data. We also describe uncommon positioning of binding motifs for several T-cell lineage specific factors in human promoters.

CONCLUSION

Our proposed di-nucleotide PWM approach outperforms the conventional mono-nucleotide PWM approach with respect to GATA-3. Therefore our new di-nucleotide PWM provides new insight into plausible transcriptional regulatory interactions in human promoters.

Loss of STAT6 promotes autoimmune disease and atopy on a susceptible genetic background

Atopy and autoimmunity are usually considered opposed immunological manifestations. Lyn(-/-) mice develop lupus-like autoimmune disease yet have coexistent intrinsic allergic traits and are prone to severe, persistent asthma induced exogenously. Recently it has been proposed that the Th2 environment and IgE auto-Abs promotes autoimmune disease in Lyn(-/-) mice. To examine this apparent contradiction, we derived Lyn(-/-) mice with a null mutation in STAT6, a regulator of Th2 immunity that integrates signaling from the IL-4/IL-13 receptor complex. Atopy and spontaneous peritoneal eosinophilia, characteristic of Lyn(-/-) mice, were lost in young Lyn(-/-)STAT6(-/-) mice; however, autoimmune disease was markedly exacerbated. At a time-point where Lyn(-/-) mice showed only mild autoimmune disease, Lyn(-/-)STAT6(-/-) mice had maximal titres of IgG and IgA auto-Abs, impaired renal function, myeloid expansion and a highly activated T cell compartment. Remarkably, low level IgE auto-Abs but not IgG1 auto-Abs were a feature of some aged Lyn(-/-)STAT6(-/-) mice. Furthermore, aged Lyn(-/-)STAT6(-/-) mice showed dramatically increased levels of serum IgE but minimal IgG1, suggesting that class-switching to IgE can occur in the absence of an IgG1 intermediate. The results show that Lyn-deficient mice can overcome the effects of disabling Th2 immunity, highlighting the importance of Lyn in controlling Th2 responses. Our data also indicates that, under certain conditions, STAT6-independent factors can promote IgE class-switching. This work has important clinical implications as many experimental therapies designed for the treatment of asthma or atopy are based on targeting the STAT6 axis, which could potentially reveal life endangering autoimmunity or promote atopy in susceptible individuals.

Functions of the Lyn tyrosine kinase in health and disease

Src family kinases such as Lyn are important signaling intermediaries, relaying and modulating different inputs to regulate various outputs, such as proliferation, differentiation, apoptosis, migration and metabolism. Intriguingly, Lyn can mediate both positive and negative signaling processes within the same or different cellular contexts. This duality is exemplified by the B-cell defect in Lyn-/- mice in which Lyn is essential for negative regulation of the B-cell receptor; conversely, B-cells expressing a dominant active mutant of Lyn (Lynup/up) have elevated activities of positive regulators of the B-cell receptor due to this hyperactive kinase. Lyn has well-established functions in most haematopoietic cells, viz. progenitors via influencing c-kit signaling, through to mature cell receptor/integrin signaling, e.g. erythrocytes, platelets, mast cells and macrophages. Consequently, there is an important role for this kinase in regulating hematopoietic abnormalities. Lyn is an important regulator of autoimmune diseases such as asthma and psoriasis, due to its profound ability to influence immune cell signaling. Lyn has also been found to be important for maintaining the leukemic phenotype of many different liquid cancers including acute myeloid leukaemia (AML), chronic myeloid leukaemia (CML) and B-cell lymphocytic leukaemia (BCLL). Lyn is also expressed in some solid tumors and here too it is establishing itself as a potential therapeutic target for prostate, glioblastoma, colon and more aggressive subtypes of breast cancer. LAY To relay information, a cell uses enzymes that put molecular markers on specific proteins so they interact with other proteins or move to specific parts of the cell to have particular functions. A protein called Lyn is one of these enzymes that regulate information transfer within cells to modulate cell growth, survival and movement. Depending on which type of cell and the source of the information input, Lyn can positively or negatively regulate the information output. This ability of Lyn to be able to both turn on and turn off the relay of information inside cells makes it difficult to fully understand its precise function in each specific circumstance. Lyn has important functions for cells involved in blood development, including different while blood cells as well as red blood cells, and in particular for the immune cells that produce antibodies (B-cells), as exemplified by the major B-cell abnormalities that mice with mutations in the Lyn gene display. Certain types of leukaemia and lymphoma appear to have too much Lyn activity that in part causes the characteristics of these diseases, suggesting it may be a good target to develop new anti-leukaemia drugs. Furthermore, some specific types, and even specific subtypes, of solid cancers, e.g. prostate, brain and breast cancer can also have abnormal regulation of Lyn. Consequently, targeting this protein in these cancers could also prove to be beneficial.