The role of CD22 and other inhibitory co-receptors in B-cell activation

Egg-driven immunosuppression and granuloma zonation in Peyer's patches of mice with Schistosoma japonicum infection

Egg granulomas caused by Schistosoma japonicum (S. japonicum) are important causes of morbidity and mortality in schistosomiasis. The intestine plays a crucial role in the complete life cycle of S. japonicum; eggs are transported through the intestine and excreted with feces. During this process, the interaction between the eggs and the intestine can trigger a strong intestinal immune system response and cause inflammation. Eggs in the intestine preferentially accumulate in Peyer's patches (PPs). However, the cellular composition of intestinal granulomas and the impacts of egg deposition on the immune function of PPs remain poorly understood. Using a mouse model of S. japonicum infection, we revealed that the deposition of eggs disrupted the structure of PPs, resulting in immunosuppression. We further characterized the cellular composition of intestinal granulomas, revealing a layered distribution of neutrophils, macrophages, T cells, and B cells, with marked neutrophil accumulation. Single-cell RNA sequencing revealed that egg deposition drives B-cell apoptosis, T-cell exhaustion, and activation of fibrotic pathways in myeloid cells, collectively impairing PP function. In conclusion, the layered cellular architecture of intestinal granulomas in PPs suggests a unique immune microenvironment of egg-driven immunosuppression and fibrotic remodeling, and the identification of fibrotic pathways in myeloid cells provides a potential therapeutic target to alleviate fibrosis in patients with S. japonicum infection.

Variable domain glycosylation as a marker and modulator of immune responses: Insights into autoimmunity and B-cell malignancies

Glycosylation of antibodies is essential for shaping immune responses, as it contributes significantly to antibody function and diversity. While immunoglobulin G (IgG) Fc glycosylation is well-characterized, variable domain glycosylation (VDG) introduces an additional and less understood layer of complexity. Notably, VDG is associated with rheumatoid arthritis, where disease-specific IgG autoantibodies abundantly express this modification. Moreover, its presence on these antibodies correlates with disease progression in at-risk individuals and therapeutic outcomes. Emerging evidence links increased VDG levels to other autoimmune diseases and B-cell malignancies, highlighting its potential as both a marker and modulator in disease onset and progression. Importantly, VDG on IgG is now recognized to influence antigen binding, enhance antibody stability, and modulate interactions with the human neonatal Fc receptor. In addition, glycans in the antigen-binding domains of autoreactive B-cell receptors (BCRs) can significantly impact B cell activation. In follicular lymphoma and other B-cell malignancies, the presence of N-glycosylation sites in the immunoglobulin variable domains leads to the introduction of oligomannose glycans, which are postulated to bind to mannose-specific lectins. This interaction might promote antigen-independent activation of BCRs, thereby supporting malignant B cell survival and proliferation. Here, we explore the regulatory pathways of VDG and its functional roles across both physiological and pathological conditions, underscoring its prevalence and significance in various autoimmune diseases and B-cell malignancies. Ultimately, advancing our understanding of the regulatory factors influencing VDG and its functional implications could be highly rewarding for identifying potential therapeutic targets and strategies to prevent and treat autoimmune diseases and B-cell malignancies.

Signaling Activation and Modulation in Extrafollicular B Cell Responses

The differentiation of naive follicular B cells into either the germinal center (GC) or extrafollicular (EF) pathway plays a critical role in shaping the type, affinity, and longevity of effector B cells. This choice also governs the selection and survival of autoreactive B cells, influencing their potential to enter the memory compartment. During the first 2-3 days following antigen encounter, initially activated B cells integrate activating signals from T cells, Toll-like receptors (TLRs), and cytokines, alongside inhibitory signals mediated by inhibitory receptors. This integration modulates the intensity of signaling, particularly of the PI3K/AKT/mTOR pathway, which plays a central role in guiding developmental decisions. These early signaling events determine whether B cells undergo GC maturation or differentiate rapidly into antibody-secreting cells (ASCs) via the EF pathway. Dysregulation of these signaling pathways-whether through excessive activation or defective regulatory mechanisms-can disrupt the balance between GC and EF fates, predisposing individuals to autoimmunity. Accordingly, aberrant PI3K/AKT/mTOR signaling has been implicated in the defective selection of autoreactive B cells, increasing the risk of autoimmune disease. This review focuses on the signaling events in newly activated B cells, with an emphasis on the induction and regulation of the PI3K/AKT/mTOR pathway. It also highlights gaps in our understanding of how alternative B cell fates are regulated. Both the physiological context and the implications of inborn errors of immunity (IEIs) and complex autoimmune conditions will be discussed in this regard.

NCAM1-SHIP2 axis upon recognizing microbes inhibits the expressions of inflammatory factors through P38-H3K4me and P38-NF-κB pathways in oyster

Neural cell adhesion molecule 1 (NCAM1/CD56) as a well-known surface marker for natural killer (NK) cells plays important roles in cell migration, adhesion, and inflammation. In the present study, NCAM1 homolog containingthree immunoglobulin domains, one fibronectin type 3 domain, a transmembrane region and a cytoplasmic tail with two intracellular immunoreceptor tyrosine-based inhibitory motifs (ITIMs) was identified from the Pacific oyster, Crassostrea gigas (defined as CgNCAM1). The mRNA transcripts of CgNCAM1 were highly expressed in haemocytes. The mRNA expressions of CgNCAM1 in haemocytes increased significantly after Vibrio splendidus stimulation. The positive green signals of CgNCAM1 and SH2-containing inositol 5-phosphatase (CgSHIP2) could translocate onto the haemocyte membrane after V. splendidus stimulation. The recombinant extracellular domains of CgNCAM1 exhibited binding activity towards various pathogen-associated molecular patterns (PAMPs) and microbes. Upon binding to its ligands, CgNCAM1 recruited CgSHIP2 to transduce inhibitor signals to reduce the phosphorylation of CgP38. The inhibition of CgP38 reduced the methylation of histone H3K4 and nuclear translocation of NF-κB, which eventually inhibited the mRNA expressions of inflammatory factors (CgIL17-2/3/6 and CgTNF-2) to suppress inflammation. These results suggested that CgNCAM1 could function as an immune checkpoint to sense different PAMPs and microbes and reduce the inflammation through inhibiting P38-epigenetic and P38-NF-κB pathways in oysters.

Well-Paired-Seq2: High-Throughput and High-Sensitivity Strategy for Characterizing Low RNA-Content Cell/Nucleus Transcriptomes

Single-cell RNA sequencing (scRNA-seq) is a transformative technology that unravels the intricate cellular state heterogeneity. However, the Poisson-dependent cell capture and low sensitivity in scRNA-seq methods pose challenges for throughput and samples with a low RNA-content. Herein, to address these challenges, we present Well-Paired-Seq2 (WPS2), harnessing size-exclusion and quasi-static hydrodynamics for efficient cell capture. WPS2 exploits molecular crowding effect, tailing activity enhancement in reverse transcription, and homogeneous enzymatic reaction in the initial bead-based amplification to achieve 3116 genes and 8447 transcripts with an average of ∼20000 reads per cell. WPS2 detected 1420 more genes and 4864 more transcripts than our previous Well-Paired-Seq. It sensitively characterizes transcriptomes of low RNA-content single cells and nuclei, overcoming the Poisson limit for cell and barcoded bead capture. WPS2 also profiles transcriptomes from frozen clinical samples, revealing heterogeneous tumor copy number variations and intercellular crosstalk in clear cell renal cell carcinomas. Additionally, we provide the first single-cell-level characterization of rare metanephric adenoma (MA) and uncover potential specific markers. With the advantages of high sensitivity and high throughput, WPS2 holds promise for diverse basic and clinical research.

What influences the activity of Degrader-Antibody conjugates (DACs)

The targeted protein degradation (TPD) technology employing proteolysis-targeting chimeras (PROTACs) has been widely applied in drug chemistry and chemical biology for the treatment of cancer and other diseases. PROTACs have demonstrated significant advantages in targeting undruggable targets and overcoming drug resistance. However, despite the efficient degradation of targeted proteins achieved by PROTACs, they still face challenges related to selectivity between normal and cancer cells, as well as issues with poor membrane permeability due to their substantial molecular weight. Additionally, the noteworthy toxicity resulting from off-target effects also needs to be addressed. To solve these issues, Degrader-Antibody Conjugates (DACs) have been developed, leveraging the targeting and internalization capabilities of antibodies. In this review, we elucidates the characteristics and distinctions between DACs, and traditional Antibody-drug conjugates (ADCs). Meanwhile, we emphasizes the significance of DACs in facilitating the delivery of PROTACs and delves into the impact of various components on DAC activity. These components include antibody targets, drug-antibody ratio (DAR), linker types, PROTACs targets, PROTACs connections, and E3 ligase ligands. The review also explores the suitability of different targets (antibody targets or PROTACs targets) for DACs, providing insights to guide the design of PROTACs better suited for antibody conjugation.

A photoaffinity glycan-labeling approach to investigate immunoglobulin glycan-binding partners

Glycans play a pivotal role in biology. However, because of the low-affinity of glycan-protein interactions, many interaction pairs remain unknown. Two important glycoproteins involved in B-cell biology are the B-cell receptor and its secreted counterpart, antibodies. It has been indicated that glycans expressed by these B-cell-specific molecules can modulate immune activation via glycan-binding proteins. In several autoimmune diseases, an increased prevalence of variable domain glycosylation of IgG autoantibodies has been observed. Especially, the hallmarking autoantibodies in rheumatoid arthritis, anti-citrullinated protein antibodies, carry a substantial amount of variable domain glycans. The variable domain glycans expressed by these autoantibodies are N-linked, complex-type, and α2-6 sialylated, and B-cell receptors carrying variable domain glycans have been hypothesized to promote selection of autoreactive B cells via interactions with glycan-binding proteins. Here, we use the anti-citrullinated protein antibody response as a prototype to study potential in solution and in situ B-cell receptor-variable domain glycan interactors. We employed SiaDAz, a UV-activatable sialic acid analog carrying a diazirine moiety that can form covalent bonds with proximal glycan-binding proteins. We show, using oligosaccharide engineering, that SiaDAz can be readily incorporated into variable domain glycans of both antibodies and B-cell receptors. Our data show that antibody variable domain glycans are able to interact with inhibitory receptor, CD22. Interestingly, although we did not detect this interaction on the cell surface, we captured CD79 β glycan-B-cell receptor interactions. These results show the utility of combining photoaffinity labeling and oligosaccharide engineering for identifying antibody and B-cell receptor interactions and indicate that variable domain glycans appear not to be lectin cis ligands in our tested conditions.

Emerging phagocytosis checkpoints in cancer immunotherapy

Cancer immunotherapy, mainly including immune checkpoints-targeted therapy and the adoptive transfer of engineered immune cells, has revolutionized the oncology landscape as it utilizes patients' own immune systems in combating the cancer cells. Cancer cells escape immune surveillance by hijacking the corresponding inhibitory pathways via overexpressing checkpoint genes. Phagocytosis checkpoints, such as CD47, CD24, MHC-I, PD-L1, STC-1 and GD2, have emerged as essential checkpoints for cancer immunotherapy by functioning as "don't eat me" signals or interacting with "eat me" signals to suppress immune responses. Phagocytosis checkpoints link innate immunity and adaptive immunity in cancer immunotherapy. Genetic ablation of these phagocytosis checkpoints, as well as blockade of their signaling pathways, robustly augments phagocytosis and reduces tumor size. Among all phagocytosis checkpoints, CD47 is the most thoroughly studied and has emerged as a rising star among targets for cancer treatment. CD47-targeting antibodies and inhibitors have been investigated in various preclinical and clinical trials. However, anemia and thrombocytopenia appear to be formidable challenges since CD47 is ubiquitously expressed on erythrocytes. Here, we review the reported phagocytosis checkpoints by discussing their mechanisms and functions in cancer immunotherapy, highlight clinical progress in targeting these checkpoints and discuss challenges and potential solutions to smooth the way for combination immunotherapeutic strategies that involve both innate and adaptive immune responses.

CD22 Exon 12 Deletion as an Independent Predictor of Poor Treatment Outcomes in B-ALL

We previously reported a splicing defect (CD22ΔE12) associated with the deletion of exon 12 of the inhibitory co-receptor CD22 (Siglec-2) in leukemia cells from patients with CD19+ B-precursor acute lymphoblastic leukemia (B-ALL). CD22ΔE12 causes a truncating frameshift mutation and yields a dysfunctional CD22 protein that lacks most of the cytoplasmic domain required for its inhibitory function, and it is associated with aggressive in vivo growth of human B-ALL cells in mouse xenograft models. Although CD22ΔE12 with selective reduction of CD22 exon 12 (CD22E12) levels was detected in a high percentage of newly diagnosed as well as relapsed B-ALL patients, its clinical significance remains unknown. We hypothesized that B-ALL patients with very low levels of wildtype CD22 would exhibit a more aggressive disease with a worse prognosis because the missing inhibitory function of the truncated CD22 molecules could not be adequately compensated by competing wildtype CD22. Here, we demonstrate that newly diagnosed B-ALL patients with very low levels of residual wildtype CD22 ("CD22E12low"), as measured by RNAseq-based CD22E12 mRNA levels, have significantly worse leukemia-free survival (LFS) as well as overall survival (OS) than other B-ALL patients. CD22E12low status was identified as a poor prognostic indicator in both univariate and multivariate Cox proportional hazards models. CD22E12low status at presentation shows clinical potential as a poor prognostic biomarker that may guide the early allocation of risk-adjusted, patient-tailored treatment regimens and refine risk classification in high-risk B-ALL.

Bispecific Antibody-Based Immune-Cell Engagers and Their Emerging Therapeutic Targets in Cancer Immunotherapy

Cancer is the second leading cause of death worldwide after cardiovascular diseases. Harnessing the power of immune cells is a promising strategy to improve the antitumor effect of cancer immunotherapy. Recent progress in recombinant DNA technology and antibody engineering has ushered in a new era of bispecific antibody (bsAb)-based immune-cell engagers (ICEs), including T- and natural-killer-cell engagers. Since the first approval of blinatumomab by the United States Food and Drug Administration (US FDA), various bsAb-based ICEs have been developed for the effective treatment of patients with cancer. Simultaneously, several potential therapeutic targets of bsAb-based ICEs have been identified in various cancers. Therefore, this review focused on not only highlighting the action mechanism, design and structure, and status of bsAb-based ICEs in clinical development and their approval by the US FDA for human malignancy treatment, but also on summarizing the currently known and emerging therapeutic targets in cancer. This review provides insights into practical considerations for developing next-generation ICEs.

Modulation of CD22 Protein Expression in Childhood Leukemia by Pervasive Splicing Aberrations: Implications for CD22-Directed Immunotherapies

Downregulation of surface epitopes causes postimmunotherapy relapses in B-lymphoblastic leukemia (B-ALL). Here we demonstrate that mRNA encoding CD22 undergoes aberrant splicing in B-ALL. We describe the plasma membrane-bound CD22 Δex5-6 splice isoform, which is resistant to chimeric antigen receptor (CAR) T cells targeting the third immunoglobulin-like domain of CD22. We also describe splice variants skipping the AUG-containing exon 2 and failing to produce any identifiable protein, thereby defining an event that is rate limiting for epitope presentation. Indeed, forcing exon 2 skipping with morpholino oligonucleotides reduced CD22 protein expression and conferred resistance to the CD22-directed antibody-drug conjugate inotuzumab ozogamicin in vitro. Furthermore, among inotuzumab-treated pediatric patients with B-ALL, we identified one nonresponder in whose leukemic blasts Δex2 isoforms comprised the majority of CD22 transcripts. In a second patient, a sharp reduction in CD22 protein levels during relapse was driven entirely by increased CD22 exon 2 skipping. Thus, dysregulated CD22 splicing is a major mechanism of epitope downregulation and ensuing resistance to immunotherapy.

SIGNIFICANCE

The mechanism(s) underlying downregulation of surface CD22 following CD22-directed immunotherapy remains underexplored. Our biochemical and correlative studies demonstrate that in B-ALL, CD22 expression levels are controlled by inclusion/skipping of CD22 exon 2. Thus, aberrant splicing of CD22 is an important driver/biomarker of de novo and acquired resistance to CD22-directed immunotherapies. See related commentary by Bourcier and Abdel-Wahab, p. 87. This article is highlighted in the In This Issue feature, p. 85.

Colorectal Cancer-Associated Immune Exhaustion Involves T and B Lymphocytes and Conventional NK Cells and Correlates With a Shorter Overall Survival

Colorectal cancer (CRC) is one of the most common cancer worldwide, with a growing impact on public health and clinical management. Immunotherapy has shown promise in the treatment of advanced cancers, but needs to be improved for CRC, since only a limited fraction of patients is eligible for treatment, and most of them develop resistance due to progressive immune exhaustion. Here, we identify the transcriptional, molecular, and cellular traits of the immune exhaustion associated with CRC and determine their relationships with the patient's clinic-pathological profile. Bioinformatic analyses of RNA-sequencing data of 594 CRCs from TCGA PanCancer collection, revealed that, in the wide range of immune exhaustion genes, those coding for PD-L1, LAG3 and T-bet were associated (Cramér's V=0.3) with MSI/dMMR tumors and with a shorter overall survival (log-rank test: p=0.0004, p=0.0014 and p=0.0043, respectively), whereas high levels of expression of EOMES, TRAF1, PD-L1, FCRL4, BTLA and SIGLEC6 were associated with a shorter overall survival (log-rank test: p=0.0003, p=0.0188, p=0.0004, p=0.0303, p=0.0052 and p=0.0033, respectively), independently from the molecular subtype of CRC. Expression levels of PD-L1, PD-1, LAG3, EOMES, T-bet, and TIGIT were significantly correlated with each other and associated with genes coding for CD4⁺ and CD8⁺CD3⁺ T cell markers and NKp46⁺CD94⁺EOMES⁺T-bet⁺ cell markers, (OR >1.5, p<0.05), which identify a subset of group 1 innate lymphoid cells, namely conventional (c)NK cells. Expression of TRAF1 and BTLA co-occurred with both T cell markers, CD3γ, CD3δ, CD3ε, CD4, and B cell markers, CD19, CD20 and CD79a (OR >2, p<0.05). Expression of TGFβ1 was associated only with CD4 ⁺ and CD8⁺CD3ε⁺ T cell markers (odds ratio >2, p<0.05). Expression of PD-L2 and IDO1 was associated (OR >1.5, p<0.05) only with cNK cell markers, whereas expression of FCRL4, SIGLEC2 and SIGLEC6 was associated (OR >2.5; p<0.05) with CD19⁺CD20⁺CD79a⁺ B cell markers. Morphometric examination of immunostained CRC tissue sections, obtained from a validation cohort of 53 CRC patients, substantiated the biostatistical findings, showing that the highest percentage of immune exhaustion gene expressing cells were found in tumors from short-term survivors and that functional exhaustion is not confined to T lymphocytes, but also involves B cells, and cNK cells. This concept was strengthened by CYBERSORTx analysis, which revealed the expression of additional immune exhaustion genes, in particular FOXP1, SIRT1, BATF, NR4A1 and TOX, by subpopulations of T, B and NK cells. This study provides novel insight into the immune exhaustion landscape of CRC and emphasizes the need for a customized multi-targeted therapeutic approach to overcome resistance to current immunotherapy.

DCIR and its ligand asialo-biantennary N-glycan regulate DC function and osteoclastogenesis

Dendritic cell immunoreceptor (DCIR) is a C-type lectin receptor with a carbohydrate recognition domain and an immunoreceptor tyrosine-based inhibitory motif. Previously, we showed that Dcir-/- mice spontaneously develop autoimmune enthesitis and sialadenitis, and also develop metabolic bone abnormalities. However, the ligands for DCIR functionality remain to be elucidated. Here we showed that DCIR is expressed on osteoclasts and DCs and binds to an asialo-biantennary N-glycan(s) (NA2) on bone cells and myeloid cells. Osteoclastogenesis was enhanced in Dcir-/- cells, and NA2 inhibited osteoclastogenesis. Neuraminidase treatment, which exposes excess NA2 by removing the terminal sialic acid of N-glycans, suppressed osteoclastogenesis and DC function. Neuraminidase treatment of mice ameliorated collagen-induced arthritis and experimental autoimmune encephalomyelitis in a DCIR-dependent manner, due to suppression of antigen presentation by DCs. These results suggest that DCIR activity is regulated by the modification of the terminal sialylation of biantennary N-glycans, and this interaction is important for the control of both autoimmune and bone metabolic diseases.

Aging Immune System in Acute Ischemic Stroke: A Transcriptomic Analysis

[Figure: see text].

Atypical phenotype and response of B cells in patients with seropositive rheumatoid arthritis

Patients with rheumatoid arthritis (RA) may be classified as seropositive or seronegative according to the presence of autoantibodies. An abnormal B cell phenotype and function could be one of the main components of the immunopathology of seropositive patients; however, there is little information regarding B cell defects in these patients. This study shows a broad characterization of the B cell phenotype and function in patients with seropositive RA. We focused mainly on the evaluation of subsets, the expression of modulatory molecules of cell activation (CD22, FcɣRIIb and FcµR), calcium mobilization, global tyrosine phosphorylation, expression of activation markers, cytokine and immunoglobulin (Ig) production, proliferation and the in-vitro generation of plasma cells. Increased frequency of CD27^- IgM^- IgD^- and CD21^- B cells was observed in patients with seropositive RA compared with healthy donors (HD). Decreased expression of CD22 was primarily found in memory B cells of patients with RA regardless of seropositivity. B cells from seropositive patients exhibited normal proliferation, calcium mobilization kinetics and global tyrosine phosphorylation, but showed an increased frequency of CD86⁺ B cells compared with HD. B cells of seropositive patients secrete less interleukin-10 after in-vitro activation and showed a decreased frequency of plasma cell differentiation and IgM production compared with HD. Our data indicate that patients with seropositive RA have an increased frequency of atypical B cell populations previously associated with chronic activation and antigen exposure. This may result in the observed low responsiveness of these cells in vitro.

Inhibitory Receptor Trap: A Platform for Discovery of Inhibitory Receptors That Utilize Inositol Lipid and Phosphotyrosine Phosphatase Effectors

Among the areas of most impactful recent progress in immunology is the discovery of inhibitory receptors and the subsequent translation of this knowledge to the clinic. Although the original and canonical member of this family is FcγRIIB, more recent studies defined PD1 as an inhibitory receptor that constrains T cell immunity to tumors. These studies led to development of “checkpoint blockade” immunotherapies (CBT) for cancers in which PD1 interactions with its ligand are blocked. Unfortunately, although very effective in some patients, only a small proportion respond to this therapy. This suggests that additional as yet undescribed inhibitory receptors exist, which could be exploited. Here, we describe a new platform, termed inhibitory receptor trap (IRT), for discovery of members of this family. The approach takes advantage of the fact that many of the known inhibitory receptors mediate signaling by phospho-immunoreceptor tyrosine-based inhibition motif (ITIM) mediated recruitment of Src Homology 2 (SH2) domain-containing phosphatases including the SH2 domain-containing inositol phosphatase SHIP1 encoded by the INPP5D gene and the SH2 domain-containing phosphotyrosine phosphatases SHP1 and SHP2 encoded by the PTPN6 and PTPN11 genes respectively. Here, we describe the IRT discovery platform in which the SH2 domains of inhibitory phosphatases are used for affinity-based isolation and subsequent identification of candidate effectors via immunoblotting and high sensitivity liquid chromatography–mass spectrometry. These receptors may represent alternative targets that can be exploited for improved CBT. Salient observations from these studies include the following: SH2 domains derived from the respective phosphatases bind distinct sets of candidates from different cell types. Thus, cells of different identity and different activation states express partially distinct repertoires of up and downstream phosphatase effectors. Phosphorylated PD1 binds not only SHP2 but also SHIP1, thus the latter may be important in its inhibitory function. B cell antigen receptor signaling leads predominantly to CD79 mono-phosphorylation as indicated by much greater binding to LynSH2 than Syk(SH2)₂. This balance of ITAM mono- versus bi-phosphorylation likely tunes signaling by varying activation of inhibitory (Lyn) and stimulatory (Syk) pathways.

N-Glycan Branching Decouples B Cell Innate and Adaptive Immunity to Control Inflammatory Demyelination

B cell depletion potently reduces episodes of inflammatory demyelination in multiple sclerosis (MS), predominantly through loss of innate rather than adaptive immunity. However, molecular mechanisms controlling innate versus adaptive B cell function are poorly understood. N-glycan branching, via interactions with galectins, controls endocytosis and signaling of cell surface receptors to control cell function. Here we report that N-glycan branching in B cells dose dependently reduces pro-inflammatory innate responses by titrating decreases in Toll-like receptor-4 (TLR4) and TLR2 surface expression via endocytosis. In contrast, a minimal level of N-glycan branching maximizes surface retention of the B cell receptor (BCR) and the CD19 co-receptor to promote adaptive immunity. Branched N-glycans inhibit antigen presentation by B cells to reduce T helper cell-17 (TH17)/TH1 differentiation and inflammatory demyelination in mice. Thus, N-glycan branching negatively regulates B cell innate function while promoting/maintaining adaptive immunity via BCR, providing an attractive therapeutic target for MS.

Identification of novel long non-coding RNAs involved in bisphenol A induced immunotoxicity in fish primary macrophages

Bisphenol A (BPA), a well-known environmental endocrine-disrupting chemical (EDC), could pose a great toxicity risk to aquatic organisms. The present study aimed to evaluate the underlying role of long non-coding RNAs (lncRNAs) in BPA-induced immunotoxicity in head kidney (HK) macrophages of the red common carp (Cyprinus carpio), using lncRNA-RNA sequencing (RNA-Seq). In BPA-exposed HK macrophages group, 2,095 and 1,138 differentially expressed mRNAs (DEGs) and lncRNAs (DE-lncRNAs) were obtained, respectively, compared with controls. The qRT-PCR validation results of DEGs and DE-lncRNAs were similar to the RNA-Seq results. The KEGG analysis of DEGs and target genes of DE-lncRNAs have shown that some immune-related signaling pathways, including NF-kappa B, Toll-like receptor, B-cell receptor, Jak-STAT, and Hippo signaling pathways, were severely disrupted by BPA exposure. Moreover, we observed the synergic regulation of some mRNAs involved in immune response such as two hub genes traf6 and mapk1/3 and their upstream lncRNAs in HK macrophages upon the BPA exposure or its analogue bisphenol S (BPS) exposure. This suggested the dysregulation of lncRNAs by BPA or BPS may lead to a change in the expression of hub genes, which affects the cross-talk of various signaling pathways by interaction with other network genes. In conclusion, the present study demonstrates the potential role of lncRNAs in immunotoxicity of bisphenol compounds in red common carp HK macrophages, and our results provide evidence for further exploring lncRNA's role in EDC-induced toxicity in aquatic organisms.

Characterization of Sialic Acid-Binding Immunoglobulin-Type Lectins in Fish Reveals Teleost-Specific Structures and Expression Patterns

The cellular glycocalyx of vertebrates is frequently decorated with sialic acid residues. These sialylated structures are recognized by sialic acid-binding immunoglobulin-type lectins (Siglecs) of immune cells, which modulate their responsiveness. Fifteen Siglecs are known to be expressed in humans, but only four Siglecs are regularly present in fish: Siglec1, CD22, myelin-associated glycoprotein (MAG), and Siglec15. While several studies have dealt with the physiological roles of these four Siglecs in mammals, little is known about Siglecs in fish. In the present manuscript, the expression landscapes of these Siglecs were determined in the two salmonid species Oncorhynchus mykiss and Coregonus maraena and in the percid fish Sander lucioperca. This gene-expression profiling revealed that the expression of MAG is not restricted to neuronal cells but is detectable in all analyzed blood cells, including erythrocytes. The teleostean MAG contains the inhibitory motif ITIM; therefore, an additional immunomodulatory function of MAG is likely to be present in fish. Besides MAG, Siglec1, CD22, and Siglec15 were also expressed in all analyzed blood cell populations. Interestingly, the expression profiles of genes encoding Siglecs and particular associated enzymes changed in a gene- and tissue-specific manner when Coregonus maraena was exposed to handling stress. Thus, the obtained data indicate once more that stress directly affects immune-associated processes.

Updates on CAR T-cell therapy in B-cell malignancies

By increasing disease-free survival and offering the potential for long-term cure, chimeric antigen receptor (CAR) T-cell therapy has dramatically expanded therapeutic options among those with high-risk B-cell malignancies. As CAR T-cell utilization evolves however, novel challenges are generated. These include determining how to optimally integrate CAR T cells into standard of care and overcoming mechanisms of resistance to CAR T-cell therapy, such as evolutionary stress induced on cancer cells leading to immunophenotypic changes that allow leukemia to evade this targeted therapy. Compounding these challenges are the limited ability to determine differences between various CAR T-cell constructs, understanding the generalizability of trial outcomes from multiple sites utilizing unique CAR manufacturing strategies, and comparing distinct criteria for toxicity grading while defining optimal management. Additionally, as understanding of CAR behavior in humans has developed, strategies have appropriately evolved to proactively mitigate toxicities. These challenges offer complimentary insights and guide next steps to enhance the efficacy of this novel therapeutic modality. With a focus on B-cell malignancies as the paradigm for effective CAR T-cell therapy, this review describes advances in the field as well as current challenges and future directions.

The regulators of BCR signaling during B cell activation

B lymphocytes produce antibodies under the stimulation of specific antigens, thereby exerting an immune effect. B cells identify antigens by their surface B cell receptor (BCR), which upon stimulation, directs the cell to activate and differentiate into antibody generating plasma cells. Activation of B cells via their BCRs involves signaling pathways that are tightly controlled by various regulators. In this review, we will discuss three major BCR mediated signaling pathways (the PLC-γ2 pathway, PI3K pathway and MAPK pathway) and related regulators, which were roughly divided into positive, negative and mutual-balanced regulators, and the specific regulators of the specific signaling pathway based on regulatory effects.

Recent BCR stimulation induces a negative autoregulatory loop via FBXO10 mediated degradation of HGAL

Regulating B-cell receptor (BCR) signaling after antigenic stimulation is essential to properly control immune responses. Currently known mechanisms of inhibiting BCR signaling are via co-receptor stimulation and downstream immunoreceptor tyrosine-based inhibition motif (ITIM) phosphorylation. Herein we demonstrate that BCR stimulation induces rapid and reversible palmitoylation of the SCF-FBXO10 ubiquitin E3 ligase. This results in FBXO10 relocation to the cell membrane, where it targets the human germinal center-associated lymphoma (HGAL) protein for ubiquitylation and degradation, leading to decreases in both BCR-induced calcium influx and phosphorylation of proximal BCR effectors. Importantly, FBXO10 recognition and degradation of HGAL is phosphorylation independent and instead relies on a single evolutionarily conserved HGAL amino acid residue (H91) and FBXO10 relocalization to the cytoplasmic membrane. Together our findings demonstrate the first evidence of negative BCR signaling regulation from direct BCR stimulation and define the temporospatial functions of the FBXO10-HGAL axis. FBXO10 is infrequently mutated in DLBCL but some of these mutations deregulate BCR signaling. These observations may have important implications on lymphomagenesis and other immune processes.

Moxetumomab pasudotox for the treatment of hairy cell leukemia

Introduction: Cladribine and pentostatin are the drugs of choice in the treatment of hairy cell leukemia (HCL). Recently, immunotoxin moxetumomab pasudotox has been introduced to improve the prognosis in relapsed and refractory HCL. Areas covered: This review discusses the mechanism of action, safety, and efficacy of moxetumomab pasudotox in HCL patients. A literature review of the MEDLINE database for articles in English concerning immunotoxins, moxetumomab pasudotox, and hairy cell leukemia was conducted via PubMed. Publications from 2000 through December 2018 were scrutinized. The search terms used were immunotoxins and moxetumomab pasudotox in conjunction with hairy cell leukemia. Conference proceedings from the previous five years of the American Society of Hematology, European Hematology Association and American Society of Clinical Oncology were searched manually. Additional relevant publications were obtained by reviewing the references from the chosen articles. Results/conclusion: Moxetumomab pasudotox, a novel recombinant anti-CD22 immunotoxin, was well tolerated and active in the previous phase 1 and 3 studies in patients with HCL. The drug has been approved in 2018 by the FDA for the treatment of patients with relapsed/refractory HCL who had at least two prior systemic therapies including at least one purine nucleoside analog. Expert opinion: The use of moxetumomab pasudotox is a promising new strategy for the treatment of HCL.

Siglecs: A journey through the evolution of sialic acid-binding immunoglobulin-type lectins

Siglecs (sialic acid-binding immunoglobulin-type lectins) are a family of immune regulatory receptors predominantly found on the cells of the hematopoietic system. A V-set Ig-like domain mediates the recognition of different sialylated glycoconjugates, which can lead to the activation or inhibition of the immune response, depending on the involved Siglecs. Siglecs are categorized into two subgroups: one including all CD33-related Siglecs and the other consisting of Siglec-1 (Sialoadhesin), Siglec-2 (CD22), Siglec-4 (myelin-associated glycoprotein, MAG) and Siglec-15. In contrast to the members of the CD33-related Siglecs, which share ∼50-99% sequence identity, Siglecs of the other subgroup show quite low homology (approximately 25-30% sequence identity). Based on the published sequences and functions of Siglecs, we performed phylogenetic analyses and sequence alignments to reveal the conservation of Siglecs throughout evolution. Therefore, we focused on the presence of Siglecs in different classes of vertebrates (fishes, amphibians, birds, reptiles and mammals), offering a bridge between the presence of different Siglecs and the biological situations of the selected animals.

Identification of proteins with the CDw75 epitope in human colorectal cancer

The CDw75 epitope is an α(2,6) sialylated antigen overexpressed in colorectal cancer (CRC), where its expression correlates with the progression of the disease. The CDw75 epitope is located mainly in N-glycoproteins, whose identity remains unknown. The aim of the present study was to identify proteins with the CDw75 epitope as a strategy to deepen the understanding of molecular pathogenesis of CRC and to identify novel biomarkers for this disease. For this purpose, a two-dimensional electrophoresis approach was employed. Protein spots in the gels were matched to the corresponding CDw75 positive spots in the immunoblotted polyvinylidene difluoride membranes, and further identification of the protein species was performed by mass spectrometry. Additionally, one-dimensional western blotting experiments were performed to verify the expression of these candidate proteins in the colorectal tissue and their coincidence in molecular mass with the CDw75-positive bands. The findings of the present study indicate that haptoglobin and the keratins 8 (K8) and 18 (K18) are proteins with the CDw75 epitope in the colorectal tissue from CRC patients and also suggest novel functions and cellular locations for these proteins in the colorectal tissue and in relation to CRC.

Bruton's Tyrosine Kinase, a Component of B Cell Signaling Pathways, Has Multiple Roles in the Pathogenesis of Lupus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the loss of adaptive immune tolerance to nucleic acid-containing antigens. The resulting autoantibodies form immune complexes that promote inflammation and tissue damage. Defining the signals that drive pathogenic autoantibody production is an important step in the development of more targeted therapeutic approaches for lupus, which is currently treated primarily with non-specific immunosuppression. Here, we review the contribution of Bruton’s tyrosine kinase (Btk), a component of B and myeloid cell signaling pathways, to disease in murine lupus models. Both gain- and loss-of-function genetic studies have revealed that Btk plays multiple roles in the production of autoantibodies. These include promoting the activation, plasma cell differentiation, and class switching of autoreactive B cells. Small molecule inhibitors of Btk are effective at reducing autoantibody levels, B cell activation, and kidney damage in several lupus models. These studies suggest that Btk may promote end-organ damage both by facilitating the production of autoantibodies and by mediating the inflammatory response of myeloid cells to these immune complexes. While Btk has not been associated with SLE in GWAS studies, SLE B cells display signaling defects in components both upstream and downstream of Btk consistent with enhanced activation of Btk signaling pathways. Taken together, these observations indicate that limiting Btk activity is critical for maintaining B cell tolerance and preventing the development of autoimmune disease. Btk inhibitors, generally well-tolerated and approved to treat B cell malignancy, may thus be a useful therapeutic approach for SLE.

Besides an ITIM/SHP-1-dependent pathway, CD22 collaborates with Grb2 and plasma membrane calcium-ATPase in an ITIM/SHP-1-independent pathway of attenuation of Ca2+i signal in B cells

CD22 is a surface immunoglobulin implicated in negative regulation of B cell receptor (BCR) signaling; particularly inhibiting intracellular Ca2+ (Ca2+i)signals. Its cytoplasmic tail contains six tyrosine residues (Y773/Y783/Y817/Y828/Y843/Y863, designated Y1~Y6 respectively), including three (Y2/5/6) lying within immunoreceptor tyrosine-based inhibitory motifs (ITIMs) that serve to recruit the protein tyrosine phosphatase SHP-1 after BCR activation-induced phosphorylation. The mechanism of inhibiting Ca2+i by CD22 has been poorly understood. Previous study demonstrated that CD22 associated with plasma membrane calcium-ATPase (PMCA) and enhanced its activity (Chen, J. et al. Nat Immunol 2004;5:651-7). The association is dependent on BCR activation-induced cytoplasmic tyrosine phosphorylation, because CD22 with either all six tyrosines mutated to phenylalanines or cytoplasmic tail truncated loses its ability to associate with PMCA. However, which individual or a group of tyrosine residues determine the association and how CD22 and PMCA interacts, are still unclear. In this study, by using a series of CD22 tyrosine mutants, we found that ITIM Y2/5/6 accounts for 34.3~37.1% Ca2+i inhibition but is irrelevant for CD22/PMCA association. Non-ITIM Y4 and its YEND motif contribute to the remaining 69.4~71.7% Ca2+i inhibition and is the binding site for PMCA-associated Grb2. Grb2, independently of BCR cross-linking, is constitutively associated with and directly binds to PMCA in both chicken and human B cells. Knockout of Grb2 by CRISPR/Cas9 completely disrupted the CD22/PMCA association. Thus, our results demonstrate for the first time that in addition to previously-identified ITIM/SHP-1-dependent pathway, CD22 holds a major pathway of negative regulation of Ca2+i signal, which is ITIM/SHP-1-independent, but Y4/Grb2/PMCA-dependent.

A novel anti-CD22 scFv-apoptin fusion protein induces apoptosis in malignant B-cells

CD22 marker is a highly internalizing antigen which is located on the surface of B-cells and is being used as a promising target for treatment of B cell malignancies. Monoclonal antibodies targeting CD22 have been introduced and some are currently under investigation in clinical trials. Building on the success of antibody drug conjugates, we developed a fusion protein consisting of a novel anti-CD22 scFv and apoptin and tested binding and therapeutic effects in lymphoma cells. The recombinant protein was expressed in E. coli and successfully purified and refolded. In vitro binding analysis by immunofluorescence and flow cytometry demonstrated that the recombinant protein specifically binds to CD22 positive Raji cells but not to CD22 negative Jurkat cells. The cytotoxic properties of scFv–apoptin were assessed by an MTT assay and Annexin V/PI flow cytometry analysis and showed that the recombinant protein induced apoptosis preferentially in Raji cells with no detectable effects in Jurkat cells. Our findings indicated that the recombinant anti-CD22 scFv–apoptin fusion protein could successfully cross the cell membrane and induce apoptosis with high specificity, make it as a promising molecule for immunotherapy of B-cell malignancies.

Molecular basis of human CD22 function and therapeutic targeting

CD22 maintains a baseline level of B-cell inhibition to keep humoral immunity in check. As a B-cell-restricted antigen, CD22 is targeted in therapies against dysregulated B cells that cause autoimmune diseases and blood cancers. Here we report the crystal structure of human CD22 at 2.1 Å resolution, which reveals that specificity for α2-6 sialic acid ligands is dictated by a pre-formed β-hairpin as a unique mode of recognition across sialic acid-binding immunoglobulin-type lectins. The CD22 ectodomain adopts an extended conformation that facilitates concomitant CD22 nanocluster formation on B cells and binding to trans ligands to avert autoimmunity in mammals. We structurally delineate the CD22 site targeted by the therapeutic antibody epratuzumab at 3.1 Å resolution and determine a critical role for CD22 N-linked glycosylation in antibody engagement. Our studies provide molecular insights into mechanisms governing B-cell inhibition and valuable clues for the design of immune modulators in B-cell dysfunction.The B-cell-specific co-receptor CD22 is a therapeutic target for depleting dysregulated B cells. Here the authors structurally characterize the ectodomain of CD22 and present its crystal structure with the bound therapeutic antibody epratuzumab, which gives insights into the mechanism of inhibition of B-cell activation.

Role of Sex Hormone Levels and Psychological Stress in the Pathogenesis of Autoimmune Diseases

The aim of this review article is to assess the connection between psychological stress and sex hormones and their effect on the development of autoimmune diseases. Psychological stress describes what people feel when they are under mental, physical, or emotional pressure. We searched for online articles using MEDLINE®, Embase, Cochrane Library and Google Scholar. Our research yielded a total of 165 articles out of which 30 articles were considered for further perusal. The articles were reviewed from February 2016 to February 2017. Case reports and patients suffering from hematolymphoid malignancies and active infections were excluded from the review. Estrogen and testosterone are potential physiological regulatory factors for the peripheral development of CD4+CD25+ T regulatory cells. Stress at any age leads to the depletion of estrogen and testosterone stores in the body, leading to the loss of expansion of T regulatory cells, making the immature B cells evade the negative selection at the germinal center, or in other words, leading to the loss of central tolerance, a triggering event in autoimmune diseases like systemic lupus erythematosus. Autoimmune diseases in women are most likely due to changes in estrogen levels during mental, physical, pre-menopausal, post-menopausal, and pregnancy-induced stress. We conclude that modulating estrogen in females (pre-menopausal and post-menopausal) and testosterone in males can be used to treat stress-related immune imbalance resulting in autoimmune diseases in both sexes.

Characterization of the Highly Prevalent Regulatory CD24hiCD38hi B-Cell Population in Human Cord Blood

The newborn's immune system must transition from a sterile haploidentical uterus to the world full of antigens. Regulatory B-cells (Breg; broadly defined as CD19⁺CD24^hiCD38^hi) are tolerance promoters in the adult immune system. They can inhibit IFN-γ and IL-17 production by T-cells and are essential in different conditions, including pregnancy. Breg have still not been well characterized in umbilical cord blood, where we hypothesize that they are pivotal in the achievement of tolerance. We studied CD19⁺CD24^hiCD38^hi Breg in healthy umbilical cord blood (hUCB) compared to healthy peripheral adult blood (hAPB). Total numbers of Breg were increased in hUCB compared to hAPB (34.39 vs. 9.49%; p = 0.0002), especially in the marginal zone-like B-cell subset, in which the most marked difference could be observed between hUCB and hAPB (60.80 vs. 4.94%; p = 0.1). CD24^hiCD38^hi subset in hUCB produced IL-10 and inhibited T-cell IFN-γ [1.63 vs. 0.95 stimulation ratio (SR); p = 0.004] and IL-4 (1.63 vs. 1.44 SR; p = 0.39) production. Phenotypically, hUCB Breg cells presented IgM^hiIgD^hiCD5⁺CD10⁺CD27^- markers, similar to those described in hAPB Breg cells, but they showed increased IgM concentration and decreased expression of CD22 and CD73 markers. Our work characterized the frequency, phenotype, and function of Breg in hUCB, which may contribute to understanding of immune tolerance during pregnancy, paving the way to a new approach to immune-related diseases in the fetus and the newborn.

Sialylation of N-glycans: mechanism, cellular compartmentalization and function

Sialylated N-glycans play essential roles in the immune system, pathogen recognition and cancer. This review approaches the sialylation of N-glycans from three perspectives. The first section focuses on the sialyltransferases that add sialic acid to N-glycans. Included in the discussion is a description of these enzymes' glycan acceptors, conserved domain organization and sequences, molecular structure and catalytic mechanism. In addition, we discuss the protein interactions underlying the polysialylation of a select group of adhesion and signaling molecules. In the second section, the biosynthesis of sialic acid, CMP-sialic acid and sialylated N-glycans is discussed, with a special emphasis on the compartmentalization of these processes in the mammalian cell. The sequences and mechanisms maintaining the sialyltransferases and other glycosylation enzymes in the Golgi are also reviewed. In the final section, we have chosen to discuss processes in which sialylated glycans, both N- and O-linked, play a role. The first part of this section focuses on sialic acid-binding proteins including viral hemagglutinins, Siglecs and selectins. In the second half of this section, we comment on the role of sialylated N-glycans in cancer, including the roles of β1-integrin and Fas receptor N-glycan sialylation in cancer cell survival and drug resistance, and the role of these sialylated proteins and polysialic acid in cancer metastasis.

SHP-1 is directly activated by the aryl hydrocarbon receptor and regulates BCL-6 in the presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which is a strong AHR agonist, causes significant suppression of human B cell activation and differentiation. The current studies describe the identification of Src homology phosphatase 1 (SHP-1) encoded by the gene PTPN6 as a putative regulator of TCDD-mediated suppression of B cell activation. Shp-1 was initially identified through a genome-wide analysis of AHR binding in mouse B cells in the presence of TCDD. The binding of AHR to the PTPN6 promoter was further confirmed using electrophoretic mobility shift assays in which, specific binding of AHR was detected at four putative DRE sites within PTPN6 promoter. Time-course measurements performed in human B cells highlighted a significant increase in SHP-1 mRNA and protein levels in the presence of TCDD. The changes in the protein levels of SHP-1 were also observed in a TCDD concentration-dependent manner. The increase in SHP-1 levels was also seen to occur due to a change in early signaling events in the presence of TCDD. We have shown that BCL-6 regulates B cell activation by repressing activation marker CD80 in the presence of TCDD. TCDD-treatment led to a significant increase in the double positive (SHP-1^hi BCL-6^hi) population. Interestingly, treatment of naïve human B cells with SHP-1 inhibitor decreased BCL-6 protein levels suggesting possible regulation of BCL-6 by SHP-1 for the first time. Collectively, these results suggest that SHP-1 is regulated by AHR in the presence of TCDD and may, in part through BCL-6, regulate TCDD-mediated suppression of human B cell activation.

A novel siglec (CgSiglec-1) from the Pacific oyster (Crassostrea gigas) with broad recognition spectrum and inhibitory activity to apoptosis, phagocytosis and cytokine release

Sialic acid binding immunoglobulin-type lectin (siglec) belongs to the immunoglobulin superfamily (IgSF), which acts as regulator involved in glycan recognition and signal transduction in the immune and nervous systems. In the present study, a siglec gene (designated CgSiglec-1) was characterized from the Pacific oyster, Crassostrea gigas. The cDNA of CgSiglec-1 was of 1251 bp encoding a predicted polypeptide of 416 amino acids. CgSiglec-1 was composed of two I-set immunoglobulin (Ig) domains, one transmembrane (TM) domain and two ITIM motifs, sharing a sequence similarity with vertebrate CD22 homologs. The mRNA expression of CgSiglec-1 could be detected in all the selected tissues, with the highest level in hemocytes and labial palps. The confocal analysis revealed that CgSiglec-1 mainly distributed on the cytoplasmic membrane of the oyster hemocytes. In addition, the mRNA transcripts of CgSiglec-1 in hemocytes increased significantly (4.29-fold to that of control group, p < 0.05) after Vibrio splendidus stimulation. The recombinant CgSiglec-1 protein (rCgSiglec-1) could bind to poly sialic acid (pSIAS), lipopolysaccharides (LPS) and peptidoglycan (PGN) in a dose-dependent manner. The blockade of CgSiglec-1 by specific polyclonal antibodies could enhance the LPS-induced cell apoptosis, phagocytosis towards V. splendidus and the release of cytokines, such as CgTNF-1, CgIFNLP and CgIL-17. The results collectively indicated that CgSiglec-1 could act as a bridge molecule between invader recognition and signal transduction cascade, and modulate the immune response by inhibiting various important processes of immunity in oyster.

Novel Targeted Therapy for Precursor B Cell Acute Lymphoblastic Leukemia: anti-CD22 Antibody-MXD3 Antisense Oligonucleotide Conjugate

The exponential rise in molecular and genomic data has generated a vast array of therapeutic targets. Oligonucleotide-based technologies to down regulate these molecular targets have promising therapeutic efficacy. However, there is relatively limited success in translating this into effective in vivo cancer therapeutics. The primary challenge is the lack of effective cancer cell-targeted delivery methods, particularly for a systemic disease such as leukemia. We developed a novel leukemia-targeting compound composed of a monoclonal antibody directly conjugated to an antisense oligonucleotide (ASO). Our compound uses an ASO that specifically targets the transcription factor MAX dimerization protein 3 (MXD3), which was previously identified to be critical for precursor B cell (preB) acute lymphoblastic leukemia (ALL) cell survival. The MXD3 ASO was conjugated to an anti-CD22 antibody (αCD22 Ab) that specifically targets most preB ALL. We demonstrated that the αCD22 Ab-ASO conjugate treatment showed MXD3 protein knockdown and leukemia cell apoptosis in vitro. We also demonstrated that the conjugate treatment showed cytotoxicity in normal B cells, but not in other hematopoietic cells, including hematopoietic stem cells. Furthermore, the conjugate treatment at the lowest dose tested (0.2mg/kg Ab for 6 doses - twice a week for 3 weeks) more than doubled the mouse survival time in both Reh (median survival time 20.5 vs. 42.5 days, p<0.001) and primary preB ALL (median survival time 29.3 vs. 63 days, p<0.001) xenograft models. Our conjugate that uses αCD22 Ab to target the novel molecule MXD3, which is highly expressed in preB ALL cells, appears to be a promising novel therapeutic approach.

Time-Course Study of the Transcriptome of Peripheral Blood Mononuclear Cells (PBMCs) from Sheep Infected with Fasciola hepatica

Fasciola hepatica is a parasitic trematode that infects a wide range of mammalian hosts, including livestock and humans, in temperate and tropical regions globally. This trematode causes the disease fascioliasis, which consists of an acute phase (≤ 12 weeks) during which juvenile parasites migrate through the host liver tissues, and a chronic phase (> 12 weeks) following the establishment of adult parasites in the liver bile ducts. Few studies have explored the progression of the host response over the course of Fasciola infection in the same animals. In this study, we characterized transcriptomic changes in peripheral blood mononuclear cells (PBMCs) collected from sheep at three time points over the first eight weeks of infection relative to uninfected controls. In total, 183 and 76 genes were found to be differentially transcribed at two and eight weeks post-infection respectively. Functional and pathway analysis of differentially transcribed genes revealed changes related to T-cell activation that may underpin a Th2-biased immune response against this parasite. This first insight into the dynamics of host responses during the early stages of infection improves the understanding of the pathogenesis of acute fascioliasis, informs vaccine development and presents a set of PBMC markers with diagnostic potential.

Ectopic expression of a novel CD22 splice-variant regulates survival and proliferation in malignant T cells from cutaneous T cell lymphoma (CTCL) patients

CD22 is a member of the Sialic acid-binding Ig-like lectin (Siglec) family of lectins described to be exclusively present in B lymphocytes and B cell-derived neoplasms. Here, we describe a novel splice form of CD22 (designated CD22∆N), which lacks the N-terminal domain as demonstrated by exon-specific RT-PCR and differential recognition by anti-CD22 antibodies. Importantly, CD22∆N mRNA is expressed in skin lesions from 39 out of 60 patients with cutaneous T cell lymphoma (CTCL), whereas few patients (6 out of 60) expresses full-length, wild type CD22 (CD22wt). In addition, IHC staining of tumor biopsies confirmed the expression of CD22 in CD4+ T cells. Moreover, four out of four malignant T cell lines express CD22: Two cell lines express CD22∆N (MyLa2059 and PB2B) and two express CD22wt (MAC-1 and MAC-2A). siRNA-mediated silencing of CD22 impairs proliferation and survival of malignant T cells, demonstrating a functional role for both CD22∆N and CD22wt in these cells.In conclusion, we provide the first evidence for an ectopic expression of CD22 and a novel splice variant regulating malignant proliferation and survival in CTCL. Analysis of expression and function of CD22 in cutaneous lymphomas may form the basis for development of novel targeted therapies for our patients.

Engagement of CD22 on B cells with the monoclonal antibody epratuzumab stimulates the phosphorylation of upstream inhibitory signals of the B cell receptor

The binding of antigen to the B cell receptor (BCR) results in a cascade of signalling events that ultimately drive B cell activation. Uncontrolled B cell activation is regulated by negative feedback loops that involve inhibitory co-receptors such as CD22 and CD32B that exert their functions following phosphorylation of immunoreceptor tyrosine-based inhibition motifs (ITIMs). The CD22-targeted antibody epratuzumab has previously been shown to inhibit BCR-driven signalling events, but its effects on ITIM phosphorylation of CD22 and CD32B have not been properly evaluated. The present study therefore employed both immunoprecipitation and flow cytometry approaches to elucidate the effects of epratuzumab on direct phosphorylation of key tyrosine (Tyr) residues on both these proteins, using both transformed B cell lines and primary human B cells. Epratuzumab induced the phosphorylation of Tyr(822) on CD22 and enhanced its co-localisation with SHP-1. Additionally, in spite of high basal phosphorylation of other key ITIMs on CD22, in primary human B cells epratuzumab also enhanced phosphorylation of Tyr(807), a residue involved in the recruitment of Grb2. Such initiation events could explain the effects of epratuzumab on downstream signalling in B cells. Finally, we were able to demonstrate that epratuzumab stimulated the phosphorylation of Tyr(292) on the low affinity inhibitory Fc receptor CD32B which would further attenuate BCR-induced signalling. Together, these data demonstrate that engagement of CD22 with epratuzumab leads to the direct phosphorylation of key upstream inhibitory receptors of BCR signalling and may help to explain how this antibody modulates B cell function.

Nanoscale organization and dynamics of the siglec CD22 cooperate with the cytoskeleton in restraining BCR signalling

Receptor organization and dynamics at the cell membrane are important factors of signal transduction regulation. Using super-resolution microscopy and single-particle tracking, we show how the negative coreceptor CD22 works with the cortical cytoskeleton in restraining BCR signalling. In naïve B cells, we found endogenous CD22 to be highly mobile and organized into nanodomains. The landscape of CD22 and its lateral diffusion were perturbed either in the absence of CD45 or when the CD22 lectin domain was mutated. To understand how a relatively low number of CD22 molecules can keep BCR signalling in check, we generated Brownian dynamic simulations and supported them with ex vivo experiments. This combined approach suggests that the inhibitory function of CD22 is influenced by its nanoscale organization and is ensured by its fast diffusion enabling a "global BCR surveillance" at the plasma membrane.

Ikaros limits follicular B cell activation by regulating B cell receptor signaling pathways

The Ikaros transcription factor is essential for early B cell development, but its effect on mature B cells is debated. We show that Ikaros is required to limit the response of naive splenic B cells to B cell receptor signals. Ikaros deficient follicular B cells grow larger and enter cell cycle faster after anti-IgM stimulation. Unstimulated mutant B cells show deregulation of positive and negative regulators of signal transduction at the mRNA level, and constitutive phosphorylation of ERK, p38, SYK, BTK, AKT and LYN. Stimulation results in enhanced and prolonged ERK and p38 phosphorylation, followed by hyper-proliferation. Pharmacological inhibition of ERK and p38 abrogates the increased proliferative response of Ikaros deficient cells. These results suggest that Ikaros functions as a negative regulator of follicular B cell activation.

The Role of the Transcription Factor Ets1 in Lupus and Other Autoimmune Diseases

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by excess B- and T-cell activation, the development of autoantibodies against self-antigens including nuclear antigens, and immune complex deposition in target organs, which triggers an inflammatory response and tissue damage. The genetic and environmental factors that contribute to the development of SLE have been studied extensively in both humans and mouse models of the disease. One of the important genetic contributions to SLE development is an alteration in the expression of the transcription factor Ets1, which regulates the functional differentiation of lymphocytes. Here, we review the genetic, biochemical, and immunological studies that have linked low levels of Ets1 to aberrant lymphocyte differentiation and to the pathogenesis of SLE.

Construction of an immunorelated protein-protein interaction network for clarifying the mechanism of burn

BACKGROUND AND AIM

Severe burn is known to induce a series of pathological responses resulting in increased susceptibility to systemic inflammatory response and multiple organ failure, but the underlying molecular mechanism remains unclear at present. The main aim of this study was to expand our understanding of the events leading to circulating leukocyte response after burn by subjecting the gene expression profiles to a bioinformatic analysis.

MATERIALS AND METHODS

Comprehensive gene expression analysis was performed to identify differentially expressed genes (DEGs) using the expression profile GSE7404 (Mus musculus, circulating leukocyte, 25% of total body surface area (TBSA), full thickness) downloaded from the Gene Expression Omnibus, followed by the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. In addition, a postburn protein-protein interaction (PPI) network was constructed to identify potential biomarkers.

RESULTS

Maximum changes in the gene expression profile were detected 1 day post burn. Separate Gene Ontology (GO) functional enrichment analysis for upregulated and downregulated DEGs revealed significant alterations of genes related to biological process such as "response to stimuli," "metabolic," "cellular and immune system processes," "biological regulation," and "death" in the leukocyte transcriptome after the burn. The KEGG pathway enrichment analysis showed that the upregulated DEGs were significantly enriched in the nodes of immunorelated and signal transduction-related pathways, and the downregulated genes were significantly enriched for the immunorelated pathways. The PPI network and module analysis revealed that, 1 day after the burn, lymphocyte-specific protein tyrosine kinase (Lck) (downregulated), Jun (upregulated), Cd19 (downregulated), Stat1 (downregulated), and Cdk1 (upregulated) were located centrally in both the PPI network and modules.

CONCLUSIONS

Based on an integrated bioinformatic analysis, we concluded that Lck, Jun, Cd19, Stat1, and Cdk1 may be critical 1 day after the burn. These findings expand our understanding of the molecular mechanisms of this important pathological process. Further studies are needed to support our work, focused on identifying candidate biomarkers with sufficient predictive power to act as prognostic and therapeutic biomarkers for burn injury.

Extensive crosslinking of CD22 by epratuzumab triggers BCR signaling and caspase-dependent apoptosis in human lymphoma cells

Epratuzumab has demonstrated therapeutic activity in patients with non-Hodgkin lymphoma, acute lymphoblastic leukemia, systemic lupus erythematosus, and Sjögren's syndrome, but its mechanism of affecting normal and malignant B cells remains incompletely understood. We reported previously that epratuzumab displayed in vitro cytotoxicity to CD22-expressing Burkitt lymphoma cell lines (Daudi and Ramos) only when immobilized on plates or combined with a crosslinking antibody plus a suboptimal amount of anti-IgM (1 μg/mL). Herein, we show that, in the absence of additional anti-IgM ligation, extensive crosslinking of CD22 by plate-immobilized epratuzumab induced intracellular changes in Daudi cells similar to ligating B-cell antigen receptor with a sufficiently high amount of anti-IgM (10 μg/mL). Specifically, either treatment led to phosphorylation of CD22, CD79a and CD79b, along with their translocation to lipid rafts, both of which were essential for effecting caspase-dependent apoptosis. Moreover, such immobilization induced stabilization of F-actin, phosphorylation of Lyn, ERKs and JNKs, generation of reactive oxygen species (ROS), decrease in mitochondria membrane potential (Δψ_m), upregulation of pro-apoptotic Bax, and downregulation of anti-apoptotic Bcl-xl and Mcl-1. The physiological relevance of immobilized epratuzumab was implicated by noting that several of its in vitro effects, including apoptosis, drop in Δψ_m, and generation of ROS, could be observed with soluble epratuzumab in Daudi cells co-cultivated with human umbilical vein endothelial cells. These results suggest that the in vivo mechanism of non-ligand-blocking epratuzumab may, in part, involve the unmasking of CD22 to facilitate the trans-interaction of B cells with vascular endothelium.

MicroRNA-19a and CD22 Comprise a Feedback Loop for B Cell Response in Sepsis

Background

MicroRNA-19a (miR-19a), an oncogenic microRNA, has been recently reported to target CD22 in B cell lymphoma cell lines, but its role in inflammatory response is unclear. CD22 is a negative regulator for BCR signaling, and we hypothesize that miR-19a regulates B cell response by targeting CD22 in sepsis.

Material/Methods

In order to determine whether miR-19a-CD22 pathway was involved in sepsis, and what role it played in the regulatory mechanisms, we detected the levels of miR-19a in B cells obtained from patients with sepsis, and measured the levels of miR-19a and CD22 expression in B cells activated by LPS in vitro. Additionally, we investigated the correlation between miR-19a and CD22, as well as the influence of this pathway on BCR signaling, in transfected B cells.

Results

We found that septic patients displayed up-regulated miR-19a in B cells. In vitro, miR-19a was increased in activated B cells, with CD22 expression initially enhanced but subsequently decreased. Moreover, overexpression of miR-19a resulted in an amplified BCR signaling, while overexpression of CD22 attenuated the effect of miR-19a and increased its expression.

Conclusions

Our study demonstrated that miR-19a and CD22 comprised a feedback loop for B cell response in sepsis, providing a potential therapeutic target to recover the immune homeostasis.

How B cells remember? A sophisticated cytoplasmic tail of mIgG is pivotal for the enhanced transmembrane signaling of IgG-switched memory B cells

Antibody memory is critical for protection against many human infectious diseases and is the basis for nearly all current human vaccines. Isotype switched immunoglobulin (Ig) G-expressing memory B cells are considered as one of the fundaments for the rapid, high affinity and high-titered memory antibody response. The detailed molecular mechanism of the enhanced activation of IgG-switched memory B cells upon BCR engagement with antigens has been an elusive question in immunology. In this review, we tried to discuss all the exciting new advances revealing the molecular mechanisms of the transmembrane signaling through mIgG cytoplasmic tail in IgG-switched memory B cells.