Plexin B2 and Semaphorin 4C Guide T Cell Recruitment and Function in the Germinal Center

Characterization of runs of homozygosity islands in American mink using whole-genome sequencing data

The genome-wide analysis of runs of homozygosity (ROH) islands can be an effective strategy for identifying shared variants within a population and uncovering important genomic regions related to complex traits. The current study performed ROH analysis to characterize the genome-wide patterns of homozygosity, identify ROH islands and annotated genes within these candidate regions using whole-genome sequencing data from 100 American mink (Neogale vison). After sequence processing, variants were called using GATK and Samtools pipelines. Subsequent to quality control, 8,373,854 bi-allelic variants identified by both pipelines remained for further analysis. A total of 34,652 ROH segments were identified in all individuals, among which shorter segments (0.3-1 Mb) were abundant throughout the genome, approximately accounting for 84.39% of all ROH. Within these segments, we identified 63 ROH islands housing 156 annotated genes. The genes located in ROH islands were associated with fur quality (EDNRA, FGF2, FOXA2 and SLC24A4), body size/weight (MYLK4, PRIM2, FABP2, EYS and PHF3), immune capacity (IL2, IL21, PTP4A1, SEMA4C, JAK2, CCNA2 and TNIP3) and reproduction (ADAD1, KHDRBS2, INSL6, PGRMC2 and HSPA4L). Furthermore, Gene Ontology and KEGG pathway enrichment analyses revealed 56 and 9 significant terms (FDR-corrected p-value < 0.05), respectively, among which cGMP-PKG signalling pathway, regulation of actin cytoskeleton, and calcium signalling pathway were highlighted due to their functional roles in growth and fur characteristics. This is the first study to present ROH islands in American mink. The candidate genes from ROH islands and functional enrichment analysis suggest possible signatures of selection in response to the mink breeding targets, such as increased body length, reproductive performance and fur quality. These findings contribute to our understanding of genetic characteristics, and provide complementary information to assist with implementation of breeding strategies for genetic improvement in American mink.

Multiphoton fluorescence microscopy for in vivo imaging

Multiphoton fluorescence microscopy (MPFM) has been a game-changer for optical imaging, particularly for studying biological tissues deep within living organisms. MPFM overcomes the strong scattering of light in heterogeneous tissue by utilizing nonlinear excitation that confines fluorescence emission mostly to the microscope focal volume. This enables high-resolution imaging deep within intact tissue and has opened new avenues for structural and functional studies. MPFM has found widespread applications and has led to numerous scientific discoveries and insights into complex biological processes. Today, MPFM is an indispensable tool in many research communities. Its versatility and effectiveness make it a go-to technique for researchers investigating biological phenomena at the cellular and subcellular levels in their native environments. In this Review, the principles, implementations, capabilities, and limitations of MPFM are presented. Three application areas of MPFM, neuroscience, cancer biology, and immunology, are reviewed in detail and serve as examples for applying MPFM to biological research.

Serum Proteomics Distinguish Subtypes of NMO Spectrum Disorder and MOG Antibody-Associated Disease and Highlight Effects of B-Cell Depletion

BACKGROUND AND OBJECTIVES

AQP4 antibody-positive NMOSD (AQP4-NMOSD), MOG antibody-associated disease (MOGAD), and seronegative NMOSD (SN-NMOSD) are neuroautoimmune conditions that have overlapping clinical manifestations. Yet, important differences exist in these diseases, particularly in B-cell depletion (BCD) efficacy. Yet, the biology driving these differences remains unclear. Our study aims to clarify biological pathways distinguishing these diseases beyond autoantibodies and investigate variable BCD effects through proteomic comparisons.

METHODS

In a retrospective study, 1,463 serum proteins were measured in 53 AQP4-NMOSD, 25 MOGAD, 18 SN-NMOSD, and 49 healthy individuals. To identify disease subtype-associated signatures, we examined serum proteins in patients without anti-CD20 B-cell depletion (NoBCD). We then assessed the effect of BCD treatment within each subtype by comparing proteins between BCD-treated and NoBCD-treated patients.

RESULTS

In NoBCD-treated patients, serum profiles distinguished the 3 diseases. AQP4-NMOSD showed elevated type I interferon-induced chemokines (CXCL9 and CXCL10) and TFH chemokine (CXCL13). MOGAD exhibited increased cytotoxic T-cell proteases (granzyme B and granzyme H), while SN-NMOSD displayed elevated Wnt inhibitory factor 1, a marker for nerve injury. Across all subtypes, BCD-treated patients showed reduction of B-cell-associated proteins. In AQP4-NMOSD, BCD led to a decrease in several inflammatory pathways, including IL-17 signaling, cytokine storm, and macrophage activation. By contrast, BCD elevated these pathways in patients with MOGAD. BCD had no effect on these pathways in SN-NMOSD.

DISCUSSION

Proteomic profiles show unique biological pathways that distinguish AQP4-NMOSD, MOGAD, or SN-NMOSD. Furthermore, BCD uniquely affects inflammatory pathways in each disease type, providing an explanation for the disparate therapeutic response in AQP4-NMOSD and MOGAD.

Plexin B2 tissue expression and related gene polymorphisms in psoriasis and their relation to NB-UVB and Acitretin therapy

Psoriasis is a chronic, immune-mediated, hyperproliferative skin disease. Etiopathogenesis of psoriasis is not well understood. Plexin B2 was found to have effects on CD100-mediated T-cell morphology and expressed in the immune system. It may play a role in the pathogenesis of psoriasis. To assess the tissue level of plexin-B2 and plexin B2 related gene polymorphism which is signal regulatory protein gamma (SIRPγ-rs71212732) in psoriatic patients before and after NB-UVB, acitretin therapy alone or in combination and to detect correlation between level of tissue plexin B2 and disease severity and improvement. This single blinded randomized controlled trial was carried on 50 psoriatic patients and 50 healthy controls. Psoriasis Area and Severity Index score (PASI) was used to evaluate the disease severity. Tissue plexin-b2 level was measured using ELISA and SIRPγ-rs71212732 (T\C) was assessed using TaqMan™ assays and real-time PCR. A significant lower tissue plexin-B2 level was observed in control group (2.9 ± 0.6 pg/g) than cases (25.8 ± 2.8, pg/g) (p < 0.001). Also, a significantly higher tissue plexin-B2 level was observed in sever psoriasis (32.7 ± 3.8 pg/ml) in than moderate psoriasis (13.6 ± 2.1 pg/ml, p = 0.001). Tissue plexin B2 was positively correlated with diseases severity. Significantly higher (TC& TT) genotypes and mutant (C) allele among patients compared to the controls, p < 0.001 for all. Tissue plexin-b2 level was high in psoriasis vulgaris with positive correlation with disease severity and decreased after treatment. This may indicate a role of plexin-b2 in psoriasis vulgaris pathogenesis.

The role of semaphorins in allergic diseases

Semaphorins were originally identified as guidance molecules in neural development. However, accumulating evidence indicates that 'immune semaphorins' are critically involved in regulating immune cell activation, differentiation, mobility and migration. Semaphorins are also intimately associated with the pathogenesis of allergic diseases including asthma, allergic rhinitis, atopic dermatitis, allergic conjunctivitis, and eosinophilic chronic rhinosinusitis. Interestingly, reflecting their function in positive or negative regulation of immune cells, levels of some semaphorins are increased while others are decreased in patients with allergic diseases. This review presents the pathogenic functions of immune semaphorins in allergic inflammation and discusses the potential use of these molecules as therapeutic targets for allergic diseases.

Expression analysis, clinical significance and potential function of PLXNB2 in acute myeloid leukaemia

BACKGROUND

The overall survival (OS) rate of adult patients suffering from acute myeloid leukaemia (AML) remains unsatisfactory at less than 40%. Current risk stratification systems fail to provide accurate guidelines for precise treatment. Novel biomarkers for predicting prognosis are urgently needed. Plexin B2 (PLXNB2), a functional receptor of angiogenin (ANG), has been found to be aberrantly expressed in multitudinous tumours. We detected overexpression of PLXNB2 mRNA in AML via transcriptome microarray analysis. This study aims to explore the potential role of PLXNB2 as a biomarker of prognosis and a prospective target of AML.

METHODS

qRT‒PCR was conducted to verify the expression of PLXNB2 mRNA in bone marrow mononuclear cells from AML patients. Immunohistochemical and immunofluorescence staining were performed and confirmed increased expression of PLXNB2 protein in AML bone marrow tissues. Data on PLXNB2 expression, prognosis and clinical features were accessed from multiple bioinformatic databases, including The Cancer Genome Atlas (TCGA). Genes coexpressed and correlated with PLXNB2 were identified and analysed in the TCGA AML cohort. Metascape was applied for functional and pathway enrichment analysis of genes related to PLXNB2. Small molecular agents and traditional Chinese medicines potentially targeting genes related to PLXNB2 were screened via the Connectivity Map, TCMSP and HIT databases.

RESULTS

PLXNB2 mRNA and protein levels are higher in AML samples than in normal controls. Overexpression of PLXNB2 is associated with worse OS in AML. Patients with high PLXNB2 expression might benefit more from haematopoietic stem cell transplantation (HSCT) (indicated by prolonged OS) than those with only chemotherapy treatment. Differentially expressed genes between the high and low PLXNB2 expression groups were overlapped with PLXNB2-coexpressed genes, and genes that overlapped were enriched in immune functions, endothelial cell regulation and cell interaction gene sets, indicating the potential function of PLXNB2 in AML. A total of 36 hub genes were identified from the differentially expressed genes, and MRC1, IL10, CD163 and CCL22 had significant prognostic value for AML. Analysis of the connectivity map and traditional agents revealed that honokiol, morphines, triptolide and paeoniflorin could be potential treatment regimens.

CONCLUSIONS

The overexpression of PLXNB2 is an adverse prognostic factor in adult AML patients and could be used as a potential biomarker. PLXNB2 might exert an oncogenic role by modulating immune functions, endothelial cell functions and cell interactions. AML patients with high PLXNB2 expression could benefit more from HSCT.

Cleavage of semaphorin 4 C interferes with the neuroprotective effect of the semaphorin 4 C/Plexin B2 pathway on experimental intracerebral hemorrhage in rats

Semaphorin 4 C (SEMA4C) and its cognate receptor Plexin B2 are important regulators of axon guidance and are involved in many neurological diseases, in which SEMA4C acts not only as a ligand ("forward" mode) but also as a signaling receptor ("reverse" mode). However, the role of SEMA4C/Plexin B2 in intracerebral hemorrhage (ICH) remains unclear. In this study, ICH in adult male Sprague-Dawley rats was induced by autologous blood injection in the right basal ganglia. In vitro, cultured primary neurons were subjected to OxyHb to imitate ICH injury. Recombinant SEMA4C (rSEMA4C) and overexpressing lentiviruses encoding full-length SEMA4C or secretory SEMA4C (sSEMA4C) were administered to rats by intraventricular injection. First, we found that elevated levels of sSEMA4C in the cerebrospinal fluid (CSF) of clinical patients were associated with poor prognosis. Both SEMA4C and sSEMA4C were increased in brain tissue around the hematoma after ICH in rats. Overexpression of SEMA4C attenuated neuronal apoptosis, neurosis, and neurologic impairment after ICH. However, treatment with rSEMA4C or sSEMA4C overexpression exacerbated neuronal injury. In addition, when treated with SEMA4C overexpression, the forward mode downstream protein RhoA and the reverse mode downstream ID1/3 transcriptional factors of SEMA4C/Plexin B2 signaling were all activated. Nevertheless, when exposed to rSEMA4C or sSEMA4C overexpression, only the forward mode was activated. Thus, sSEMA4C may be a novel molecular biomarker to predict the prognosis of patients with ICH, and the prevention of SEMA4C cleavage is expected to be a promising therapeutic target.

Glial receptor PLXNB2 regulates schizophrenia-related stress perception via the amygdala

Stress is a trigger for the development of psychiatric disorders. However, how stress trait differs in schizophrenia patients is still unclear. Stress also induces and exacerbates immune activation in psychiatric disorders. Plexins (Plxn) and its ligands semaphorins (Sema) are important cellular receptors with plural functions in both the brain and the immune system. Recently, the role of Plxn/Sema in regulation of neuroinflammation was also noticed. Here, when investigating immune mechanisms underlying stress susceptibility in schizophrenia, we discovered the role of Plxnb2 in stress response. Patients of first-episode schizophrenia (FES) with high stress (FES-hs, n=51) and low stress (FES-ls, n=50) perception and healthy controls (HCs) (n=49) were first recruited for neuroimaging and blood bulk RNA sequencing (RNA-seq). A mouse model of chronic unpredictable stress (CUS) and intra-amygdaloid functional blocking of Plxnb2 were further explored to depict target gene functions. Compared to HCs, FES-hs patients had bigger caudate and thalamus (FDR=0.02&0.001, respectively) whereas FES-ls patients had smaller amygdala (FDR=0.002). Blood RNA-seq showed differentially expressed PLXNB2 and its ligands among patient groups and HCs (FDR<0.05~0.01). Amygdaloid size and PLXNB2 level were both negatively correlated with stress perception (p<0.01&0.05, respectively), which fully mediated the amygdaloid positive association with PLXNB2 expression (β=0.9318, 95% CI: 0.058~1.886) in FES-hs patients. In mice, Plxnb2 was enriched in astrocytes and microglia and CUS reduced its expression in astrocytes (p<0.05). Inhibition of amygdaloid Plxnb2 by its functional blocking monoclonal antibody (mAb)-102 induced mice anxiety (p<0.05), amygdaloid enlargement (p<0.05), and microglial ramification (p<0.001) compared to saline. These data suggest that PLXNB2 regulates amygdala-dependent stress responses.

Muscone Can Improve Spinal Cord Injury by Activating the Angiogenin/Plexin-B2 Axis

Spinal cord injury (SCI) is a devastating neurological disorder that usually damages sensorimotor and autonomic functions. Signaling pathways can play a key role in the repair process of SCI. The plexin-B2 acts as a receptor for angiogenin and mediates ribosomal RNA transcription, influencing cell survival and proliferation. Protein kinase B serine/threonine kinase interacts with angiogenin to form a positive feedback effect. Brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor can induce angiogenin nuclear translocation. Moreover, the BDNF can promote the secretion of angiogenin. Interestingly, all of them can activate the angiogenin/plexin-B2 axis. Muscone has anti-inflammatory and proliferative features as it can inhibit nuclear transcription factor kappa-B (NF-κB) and activate the angiogenin/plexin-B2 axis, thus being significant agent in the SCI repair process. Herein, we review the potential mechanism of angiogenin/plexin-B2 axis activation and the role of muscone in SCI treatment. Muscone may attenuate inflammatory responses and promote neuronal regeneration after SCI.

T Cell Help in the Autoreactive Germinal Center

The germinal center serves as a site of B cell selection and affinity maturation, critical processes for productive adaptive immunity. In autoimmune disease tolerance is broken in the germinal center reaction, leading to production of autoreactive B cells that may propagate disease. Follicular T cells are crucial regulators of this process, providing signals necessary for B cell survival in the germinal center. Here we review the emerging roles of follicular T cells in the autoreactive germinal center. Recent advances in immunological techniques have allowed study of the gene expression profiles and repertoire of follicular T cells at unprecedented resolution. These studies provide insight into the potential role follicular T cells play in preventing or facilitating germinal center loss of tolerance. Improved understanding of the mechanisms of T cell help in autoreactive germinal centers provides novel therapeutic targets for diseases of germinal center dysfunction.

Plexin-B2 and Semaphorins Do Not Drive Rhabdomyosarcoma Proliferation or Migration

Rhabdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma for which subsets of patients have longstanding unmet clinical needs. For example, children with alveolar rhabdomyosarcoma and metastases at diagnosis will experience only 8% disease-free 5-year survival for nonlocalized unresectable recurrent disease. Hence, development of novel therapeutic strategies is urgently needed to improve outcomes. The Plexin-Semaphorin pathway is largely unexplored for sarcoma research. However, emerging interest in the Plexin-Semaphorin signaling axis in pediatric sarcomas has led to phase I cooperative group dose-finding clinical trials, now completed (NCT03320330). In this study, we specifically investigated the protein expression of transmembrane receptor Plexin-B2 and its cognate SEMA4C ligands in clinical RMS tumors and cell models. By RNA interferences, we assessed the role of Plexin-B2 in cell growth and cell migration ability in selected alveolar and embryonal RMS cell model systems. Our results affirmed expression of Plexin-B2 across human samples, while also dissecting expression of the different protein subunits of Plexin-B2 along with the assessment of preferred Semaphorin ligands of Plexin-B2. Plexin-B2 knockdown had positive or negative effects on cell growth, which varied by cell model system. Migration assayed after Plexin-B2 knockdown revealed selective cell line specific migration inhibition, which was independent of Plexin-B2 expression level. Overall, these findings are suggestive of context-specific and possibly patient-specific (stochastic) role of Plexin-B2 and SEMA4 ligands in RMS.

Identifying Function Determining Residues in Neuroimmune Semaphorin 4A

Semaphorin 4A (Sema4A) exerts a stabilizing effect on human Treg cells in PBMC and CD4+ T cell cultures by engaging Plexin B1. Sema4A deficient mice display enhanced allergic airway inflammation accompanied by fewer Treg cells, while Sema4D deficient mice displayed reduced inflammation and increased Treg cell numbers even though both Sema4 subfamily members engage Plexin B1. The main objectives of this study were: 1. To compare the in vitro effects of Sema4A and Sema4D proteins on human Treg cells; and 2. To identify function-determining residues in Sema4A critical for binding to Plexin B1 based on Sema4D homology modeling. We report here that Sema4A and Sema4D display opposite effects on human Treg cells in in vitro PBMC cultures; Sema4D inhibited the CD4+CD25+Foxp3+ cell numbers and CD25/Foxp3 expression. Sema4A and Sema4D competitively bind to Plexin B1 in vitro and hence may be doing so in vivo as well. Bayesian Partitioning with Pattern Selection (BPPS) partitioned 4505 Sema domains from diverse organisms into subgroups based on distinguishing sequence patterns that are likely responsible for functional differences. BPPS groups Sema3 and Sema4 into one family and further separates Sema4A and Sema4D into distinct subfamilies. Residues distinctive of the Sema3,4 family and of Sema4A (and by homology of Sema4D) tend to cluster around the Plexin B1 binding site. This suggests that the residues both common to and distinctive of Sema4A and Sema4D may mediate binding to Plexin B1, with subfamily residues mediating functional specificity. We mutated the Sema4A-specific residues M198 and F223 to alanine; notably, F223 in Sema4A corresponds to alanine in Sema4D. Mutant proteins were assayed for Plexin B1-binding and Treg stimulation activities. The F223A mutant was unable to stimulate Treg stability in in vitro PBMC cultures despite binding Plexin B1 with an affinity similar to the WT protein. This research is a first step in generating potent mutant Sema4A molecules with stimulatory function for Treg cells with a view to designing immunotherapeutics for asthma.

In Vivo Migration and Tfh Cell Interactions

Follicular T-helper cells play a key role in orchestrating the germinal center response. Cellular dynamics revealed by intravital imaging have helped deepen our understanding of how follicular T-helper cells develop and function in vivo. Here we describe routine methods to image T-cell dynamics during germinal center responses. Methods for quantitative analysis of imaging data are detailed using published examples.

Potential Immune Biomarker Candidates and Immune Subtypes of Lung Adenocarcinoma for Developing mRNA Vaccines

mRNA vaccines against cancer have advantages in safety, improved therapeutic efficacy, and large-scale production. Therefore, our purpose is to identify immune biomarkers and to analyze immune status for developing mRNA vaccines and selecting appropriate patients for vaccination. We downloaded clinical information and RNA-seq data of 494 LUAD patients from TCGA. LUAD mutational information was hierarchically clustered by NMF package (Version 0.23.0). DeconstructSigs package (Version 1.8.0) and NMF consistency clustering were used to identify mutation signatures. Maftools package (Version 2.6.05) was used to select LUAD-related immune biomarkers. TIMER was used to discuss the correlation between genetic mutations and cellular components. Unsupervised clustering Pam method was used to identify LUAD immune subtypes. Log-rank test and univariate/multivariate cox regression were used to predict the prognosis of immune subtypes. Dimensionality reduction analysis was dedicated to the description of LUAD immune landscape. LUAD patients are classified into four signatures: T >C, APOBEC mutation, age, and tobacco. Then, GPRIN1, MYRF, PLXNB2, SLC9A4, TRIM29, UBA6, and XDH are potential LUAD-related immune biomarker candidates to activate the immune response. Next, we clustered five LUAD-related immune subtypes (IS1–IS5) by prognostic prediction. IS3 showed prolonged survival. The reliability of our five immune subtypes was validated by Thorsson’s results. IS2 and IS4 patients had high tumor mutation burden and large number of somatic mutations. Besides, we identified that immune subtypes of cold immunity (patients with IS2 and IS4) are ideal mRNA vaccination recipients. Finally, LUAD immune landscape revealed immune cells and prognostic conditions, which provides important information to select patients for vaccination. GPRIN1, MYRF, PLXNB2, SLC9A4, TRIM29, UBA6, and XDH are potential LUAD-related immune biomarker candidates to activate the immune response. Patients with IS2 and IS4 might potentially be immunization-sensitive patients for vaccination.

The spatio-temporal control of effector T cell migration

Effector T cells leave the lymph nodes armed with specialized functional attributes. Their antigenic targets may be located anywhere in the body, posing the ultimate challenge: how to efficiently identify the target tissue, navigate through a complex tissue matrix and, ultimately, locate the immunological insult. Recent advances in real-time in situ imaging of effector T cell migratory behaviour have revealed a great degree of mechanistic plasticity that enables effector T cells to push and squeeze their way through inflamed tissues. This process is shaped by an array of 'stop' and 'go' guidance signals including target antigens, chemokines, integrin ligands and the mechanical cues of the inflamed microenvironment. Effector T cells must sense and interpret these competing signals to correctly position themselves to mediate their effector functions for complete and durable responses in infectious disease and malignancy. Tuning T cell migration therapeutically will require a new understanding of this complex decision-making process.

Acquisition of optimal TFH cell function is defined by specific molecular, positional, and TCR dynamic signatures

The development of follicular helper CD4 T (TFH) cells is a dynamic process resulting in a heterogenous pool of TFH subsets. However, the cellular and molecular determinants of this heterogeneity and the possible mechanistic links between them is not clear. We found that human TFH differentiation is associated with significant changes in phenotypic, chemokine, functional, metabolic and transcriptional profile. Furthermore, this differentiation was associated with distinct positioning to follicular proliferating B cells. Single-cell T cell receptor (TCR) clonotype analysis indicated the transitioning toward PD-1^hiCD57^hi phenotype. Furthermore, the differentiation of TFH cells was associated with significant reduction in TCR level and drastic changes in immunological synapse formation. TFH synapse lacks a tight cSMAC (central supra molecular activation Cluster) but displays the TCR in peripheral microclusters, which are potentially advantageous in the ability of germinal center (GC) B cells to receive necessary help. Our data reveal significant aspects of human TFH heterogeneity and suggest that the PD-1^hiCD57^hi TFH cells, in particular, are endowed with distinctive programming and spatial positioning for optimal GC B cell help.

Semaphorin 4D as a guidance molecule in the immune system

Semaphorin 4D (Sema4D) is a classic member of the semaphorin family involved in axonal guidance processes. The key effects of Sema4D in neurons are mediated by high affinity plexin receptors and are associated with cytoskeleton rearrangement, leading to growth cone collapse or regulation of cell migration. Along with this, the semaphorin is widely represented in the immune system and has a pronounced immunoregulatory activity. The involvement of Sema4D in the control of immune cell migration was shown almost twenty years ago, in one of the first studies of semaphorin. The emergence of such work was quite predictable, since the most well-known effects of Sema4D outside the immune system were associated precisely with the control of cell motility. However, after identification of CD72 as a specific Sema4D receptor in the immune system, studies of the immunoregulatory activity of semaphorin focused on its CD72-dependent effects unrelated to cytoskeleton rearrangement, and this trend continues up to now. Nevertheless, a number of recent studies demonstrating the presence of plexin receptors for Sema4D in the immune system forces us to return to the question of whether this semaphorin can play its classic role of a guidance molecule in relation to immune cells too. The review discusses Sema4D involvement in the control of immune cell migration, as well as the mechanisms of these effects and their potential contribution to the development and function of immune system.

Stepwise Tfh cell differentiation revisited: new advances and long-standing questions

T follicular helper (Tfh) cells play an essential role in germinal center formation and the generation of high-affinity antibodies. Studies have proposed that Tfh cell differentiation is a multi-step process. However, it is still not fully understood how a subset of activated CD4⁺ T cells begin to express CXCR5 during the early stage of the response and, shortly after, how some CXCR5⁺ precursor Tfh (pre-Tfh) cells enter B cell follicles and differentiate further into germinal center Tfh (GC-Tfh) cells while others have a different fate. In this mini-review, we summarize the recent advances surrounding these two aspects of Tfh cell differentiation and discuss related long-standing questions, including Tfh memory.

A Two-Step Process of Effector Programming Governs CD4+ T Cell Fate Determination Induced by Antigenic Activation in the Steady State

Various processes induce and maintain immune tolerance, but effector T cells still arise under minimal perturbations of homeostasis through unclear mechanisms. We report that, contrary to the model postulating primarily tolerogenic mechanisms initiated under homeostatic conditions, effector programming is an integral part of T cell fate determination induced by antigenic activation in the steady state. This effector programming depends on a two-step process starting with induction of effector precursors that express Hopx and are imprinted with multiple instructions for their subsequent terminal effector differentiation. Such molecular circuits advancing specific terminal effector differentiation upon re-stimulation include programmed expression of interferon-γ, whose production then promotes expression of T-bet in the precursors. We further show that effector programming coincides with regulatory conversion among T cells sharing the same antigen specificity. However, conventional type 2 dendritic cells (cDC2) and T cell functions of mammalian target of rapamycin complex 1 (mTORC1) increase effector precursor induction while decreasing the proportion of T cells that can become peripheral Foxp3⁺ regulatory T (pTreg) cells.

The mechanisms in the steady state that govern the formation of effector T cells with potentially autoimmune functions remain unclear. Opejin et al. reveal a two-step process starting with induction of effector precursors that express Hopx and are imprinted with multiple instructions for their subsequent terminal effector differentiation.

Sema4D Aggravated LPS-Induced Injury via Activation of the MAPK Signaling Pathway in ATDC5 Chondrocytes

Osteoarthritis (OA) is the most common chronic degenerative joint disease, and it remains the main cause of chronic disability in elderly individuals. Sema4D (semaphorin 4D) is involved in the immune system and related to bone injury, osteoporosis, osteoblast differentiation, and rheumatoid arthritis. However, the role of Sema4D in OA remains unclear. Hence, the LPS-stimulated chondrocyte cell injury model was constructed in this study to investigate the role of Sema4D in OA development. The results showed that Sema4D was increased in LPS-treated ATDC5 cells, and the knockdown of Sema4D suppressed the decline of cell viability, the increase of cell apoptosis, and the increase of IL-6, IL-1β, and TNF-α secretion in ATDC5 cells induced by LPS. Meanwhile, Sema4D overexpression aggravated the cell injury triggered by LPS, and inhibiting Plexin B1 partly abolished the effect of Sema4D overexpression on LPS-induced chondrocyte injury. Furthermore, silencing of Sema4D blocked the activation of the MAPK pathway in LPS-stimulated ATDC5 cells. Enhanced Sema4D promoted the activation of the MAPK pathway in LPS-stimulated ATDC5 cells. What is more, inhibiting the MAPK signaling pathway abolished the promoting effect of Sema4D overexpression on LPS-induced chondrocyte injury. Therefore, our study suggested that the knockdown of Sema4D protects ATDC5 cells against LPS-induced injury through inactivation of the MAPK signaling pathway via interacting with Plexin B1.

Semaphorin 4A, 4C, and 4D: Function comparison in the autoimmunity, allergy, and cancer

Semaphorins are a group of proteins that are divided into eight subclasses and identified by a conserved Sema domain on their carboxyl terminus. Sema4A, 4C, and 4D are the members of the fourth class of semaphorin family, which are known as membrane semaphorins; however, these molecules can be altered to soluble semaphorins by proteolytic cleavage. Semaphorins have various roles in the immune, nervous, and metabolic systems. In the immune system, these molecules contribute to the formation of cellular, humoral, and innate immune responses, such as inflammation, leukocyte migration, immunological synapse formation, and germinal center events. Given the diverse roles of semaphorins in the immune system, in this review, we have tried to give a comprehensive look at the role of these molecules in autoimmunity, allergy, and cancer. Sema4D and 4A seem to play a critical role in the pathogenesis of some autoimmune diseases, such as multiple sclerosis. In contrast, it has been shown that Sema4A and 4C have beneficial effects on allergies, and their absence can exacerbate the severity of the disease. In the case of cancer, an increase in all three of these molecules has been reported. Sema4D and 4C can contribute to tumor progression in human patients or experimental models, while the role of Sema4A has not yet been fully understood. In conclusion, semaphorins seem to be a favorable therapeutic target for autoimmune diseases and allergies. However, in cancer, studies have not yet been able to identify the exact role of semaphorins, and further studies are needed.

Plexin-B2 in psoriasis; a clinical and immunohistochemical study

Psoriasis is an inflammatory, immune-mediated disease. Plexins are transmembrane proteins that are involved in immune system regulation and inflammation. This work aimed to investigate the immunohistochemical expression of Plexin-B2 in plaque psoriasis in both lesional and perilesional skin. This case-control study included 30 patients with psoriasis vulgaris in comparison with 20 age- and sex-matched apparently healthy persons. We used the Psoriasis Area and Severity Index (PASI) score to evaluate psoriasis severity. Biopsies from 30 lesional, 30 perilesional, and 20 control-skin patients were subjected to histopathological and immunohistochemical evaluations of Plexin-B2. There was significant stepwise overexpression of Plexin-B2 in proliferating keratinocytes from controls (66 ± 31.02) to perilesional (116 ± 41.95) and lesional (159.7 ± 63.05) skin (P < .001). Also, Plexin-B2 showed significant overexpression in dermal inflammatory cells of lesional psoriatic skin (153.67 ± 72.71) when compared to controls skin (25.71 ± 11.34) (P < .001). There was a significant positive correlation between Plexin-B2 expression and psoriasis severity (r = 0.557; P < .001). Plexin-B2 could promote skin inflammation, as well as keratinocyte proliferation in psoriasis vulgaris; therefore, it may be used as a targeted therapy for psoriasis treatment.

Negative regulation of dendritic cell activation in psoriasis mediated via CD100-plexin-B2

Psoriasis is a chronic inflammatory skin disease in which dendritic cells (DCs) play a pivotal role by inducing Th1/Th17 immune responses; however, the regulation of DC activation in psoriasis remains largely unknown. Previously we found that the level of soluble CD100 was increased in sera of psoriasis patients, and CD100 promoted the activation of inflammasome in keratinocytes. In the present study, CD100 knockout mice were utilized for generation of imiquimod (IMQ)-induced psoriatic dermatitis, with the result that skin inflammation in the early, but not late, phase of the psoriatic dermatitis was significantly exacerbated compared to that in wild-type controls. This was attributed mainly to the deficiency of CD100 in hematopoietic cells. Bone marrow-derived DCs, but not T cells or keratinocytes, from CD100 knockout mice produced significantly increased levels of IL-1β, IL-36, and IL-23 upon stimulation with IMQ in a plexin-B2-dependent manner. Moreover, the surface level of plexin-B2 on DCs of psoriasis patients was lower than that of healthy individuals, and CD100 attenuated IMQ-induced production of IL-1β and IL-36 from monocyte-derived DCs of psoriasis patients. Our results uncovered a negative regulatory mechanism for DCs activation in psoriasis, which was mediated via CD100-plexin-B2 in a cell type- and receptor-specific manner. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

T cell interactions with B cells during germinal center formation, a three-step model

Establishment of effective immunity against invading microbes depends on continuous generation of antibodies that facilitate pathogen clearance. Long-lived plasma cells with the capacity to produce high affinity antibodies evolve in germinal centers (GCs), where B cells undergo somatic hypermutation and are subjected to affinity-based selection. Here, we focus on the cellular interactions that take place early in the antibody immune response during GC colonization. Clones bearing B-cell receptors with different affinities and specificities compete for entry to the GC, at the boundary between the B-cell and T-cell zones in lymphoid organs. During this process, B cells compete for interactions with T follicular helper cells, which provide selection signals required for differentiation into GC cells and antibody secreting cells. These cellular engagements are long-lasting and depend on activation of adhesion molecules that support persistent interactions and promote transmission of signals between the cells. Here, we discuss how interactions between cognate T and B cells are primarily maintained by three types of molecular interactions: homophilic signaling lymphocytic activation molecule (SLAM) interactions, T-cell receptor: peptide-loaded major histocompatibility class II (pMHCII), and LFA-1:ICAMs. These essential components support a three-step process that controls clonal selection for entry into the antibody affinity maturation response in the GC, and establishment of long-lasting antibody-mediated immunity.

T follicular helper cell heterogeneity: Time, space, and function

T follicular helper (Tfh) cells play a crucial role in orchestrating the humoral arm of adaptive immune responses. Mature Tfh cells localize to follicles in secondary lymphoid organs (SLOs) where they provide help to B cells in germinal centers (GCs) to facilitate immunoglobulin affinity maturation, class-switch recombination, and generation of long-lived plasma cells and memory B cells. Beyond the canonical GC Tfh cells, it has been increasingly appreciated that the Tfh phenotype is highly diverse and dynamic. As naive CD4⁺ T cells progressively differentiate into Tfh cells, they migrate through a variety of microanatomical locations to obtain signals from other cell types, which in turn alters their phenotypic and functional profiles. We herein review the heterogeneity of Tfh cells marked by the dynamic phenotypic changes accompanying their developmental program. Focusing on the various locations where Tfh and Tfh-like cells are found, we highlight their diverse states of differentiation. Recognition of Tfh cell heterogeneity has important implications for understanding the nature of T helper cell identity specification, especially the plasticity of the Tfh cells and their ontogeny as related to conventional T helper subsets.

G-protein coupled receptors and ligands that organize humoral immune responses

B-cell responses are dynamic processes that depend on multiple types of interactions. Rare antigen-specific B cells must encounter antigen and specialized systems are needed-unique to each lymphoid tissue type-to ensure this happens efficiently. Lymphoid tissue barrier cells act to ensure that pathogens, while being permitted entry for B-cell recognition, are blocked from replication or dissemination. T follicular helper (Tfh) cells often need to be primed by dendritic cells before supporting B-cell responses. For most responses, antigen-specific helper T cells and B cells need to interact, first to initiate clonal expansion and the plasmablast response, and later to support the germinal center (GC) response. Newly formed plasma cells need to travel to supportive niches. GC B cells must become confined to the follicle center, organize into dark and light zones, and interact with Tfh cells. Memory B cells need to be positioned for rapid responses following reinfection. Each of these events requires the actions of multiple G-protein coupled receptors (GPCRs) and their ligands, including chemokines and lipid mediators. This review will focus on the guidance cue code underlying B-cell immunity, with an emphasis on findings from our laboratory and on newer advances in related areas. We will discuss our recent identification of geranylgeranyl-glutathione as a ligand for P2RY8. Our goal is to provide the reader with a focused knowledge about the GPCRs guiding B-cell responses and how they might be therapeutic targets, while also providing examples of how multiple types of GPCRs can cooperate or act iteratively to control cell behavior.

The AKT kinase signaling network is rewired by PTEN to control proximal BCR signaling in germinal center B cells

Compared to naïve B cells (NBCs), both B cell antigen receptor (BCR) and CD40 signaling are rewired in germinal center (GC) B cells (GCBCs) to optimize selection for high-affinity B cells. The mechanism for BCR reprogramming in GCBCs remains unknown. We describe a GC-specific, AKT kinase-driven negative feedback loop that attenuates BCR signaling. A mass spectrometry proteomic approach revealed that AKT activity was retargeted in GCBCs compared to NBCs. Retargeting was linked to differential AKT T308 and S473 phosphorylation, in turn due to GC-specific upregulation of phosphoinositide-dependent protein kinase PDK1 and the phosphatase PTEN, which retuned phosphatidylinositol-3-OH kinase (PI3K) signals. In GCBCs, AKT preferentially targeted CSK, SHP-1 and HPK1, which are negative regulators of BCR signaling. Phosphorylation results in markedly increased enzymatic activity of these proteins, creating a negative-feedback loop that dampens upstream BCR signaling. Inhibiting AKT substantially enhanced activation of BCR proximal kinase LYN as well as downstream BCR signaling molecules in GCBCs, establishing the relevance of this pathway.

B Cell Responses: Cell Interaction Dynamics and Decisions

B cells and the antibodies they produce have a deeply penetrating influence on human physiology. Here, we review current understanding of how B cell responses are initiated; the different paths to generate short- and long-lived plasma cells, germinal center cells, and memory cells; and how each path impacts antibody diversity, selectivity, and affinity. We discuss how basic research is informing efforts to generate vaccines that induce broadly neutralizing antibodies against viral pathogens, revealing the special features associated with allergen-reactive IgE responses and uncovering the antibody-independent mechanisms by which B cells contribute to health and disease.

Pivotal role for αV integrins in sustained Tfh support of the germinal center response for long-lived plasma cell generation

CD4+ follicular helper T cells (Tfh) are essential for germinal center (GC) reactions in the lymph node that generate high-affinity, long-lived plasma cells (LLPCs). Temporal GC analysis suggests B memory cells (Bmem) are generated early, while LLPCs are generated late in the GC reaction. Distinct roles for Tfh at these temporally different stages are not yet clear. Tfh entry into the GC is highly dynamic and the signals that maintain Tfh within the GC for support of late LLPC production are poorly understood. The GC is marked by inflammation-induced presentation of specific ECM components. To determine if T cell recognition of these ECM components played a role in Tfh support of the GC, we immunized mice with a T cell-restricted deletion of the ECM-binding integrin α_V (α_V-CD4 cKO). T cell integrin α_V deletion led to a striking defect in the number and size of the GCs following immunization with OVA protein in complete Freund's adjuvant. The GC defect was not due to integrin α_V deficiency impeding Tfh generation or follicle entry or the ability of α_V-CD4 cKO Tfh to contact and support B cell activation. Instead, integrin α_V was essential for T cell-intrinsic accumulation within the GC. Altered Tfh positioning resulted in lower-affinity antibodies and a dramatic loss of LLPCs. Influenza A infection revealed that α_V integrin was not required for Tfh support of Bmem but was essential for Tfh support of LLPCs. We highlight an α_V integrin-ECM-guided mechanism of Tfh GC accumulation that selectively impacts GC output of LLPCs but not Bmem.

Toward the Existence of a Sympathetic Neuroplasticity Adaptive Mechanism Influencing the Immune Response. A Hypothetical View-Part I

The nervous system exerts a profound influence on the function of the immune system (IS), mainly through the sympathetic arm of the autonomic nervous system. In fact, the sympathetic nervous system richly innervates secondary lymphoid organs (SLOs) such as the spleen and lymph nodes. For decades, different research groups working in the field have consistently reported changes in the sympathetic innervation of the SLOs during the activation of the IS, which are characterized by a decreased noradrenergic activity and retraction of these fibers. Most of these groups interpreted these changes as a pathological phenomenon, referred to as "damage" or "injury" of the noradrenergic fibers. Some of them postulated that this "injury" was probably due to toxic effects of released endogenous mediators. Others, working on animal models of chronic stimulation of the IS, linked it to the very chronic nature of processes. Unlike these views, this first part of the present work reviews evidence which supports the hypothesis of a specific adaptive mechanism of neural plasticity from sympathetic fibers innervating SLOs, encompassing structural and functional changes of noradrenergic nerves. This plasticity mechanism would involve segmental retraction and degeneration of these fibers during the activation of the IS with subsequent regeneration once the steady state is recovered. The candidate molecules likely to mediate this phenomenon are also here introduced. The second part will extend this view as to the potential changes in sympathetic innervation likely to occur in inflamed non-lymphoid peripheral tissues and its possible immunological implications.

Synaptic Interactions in Germinal Centers

The germinal center (GC) is a complex, highly dynamic microanatomical niche that allows the generation of high-affinity antibody-producing plasma cells and memory B cells. These cells constitute the basis of long-lived highly protective antibody responses. For affinity maturation to occur, B cells undergo multiple rounds of proliferation and mutation of the genes that encode the immunoglobulin V region followed by selection by specialized T cells called follicular helper T (T_FH) cells. In order to achieve this result, the GC requires spatially and temporally coordinated interactions between the different cell types, including B and T lymphocytes and follicular dendritic cells. Cognate interactions between T_FH and GC B cells resemble cellular connections and synaptic communication within the nervous system, which allow signals to be transduced rapidly and effectively across the synaptic cleft. Such immunological synapses are particularly critical in the GC where the speed of T–B cell interactions is faster and their duration shorter than at other sites. In addition, the antigen-based specificity of cognate interactions in GCs is critical for affinity-based selection in which B cells compete for T cell help so that rapid modulation of the signaling threshold determines the outcome of the interaction. In the context of GCs, which contain large numbers of cells in a highly compacted structure, focused delivery of signals across the interacting cells becomes particularly important. Promiscuous or bystander delivery of positive selection signals could potentially lead to the appearance of long-lived self-reactive B cell clones. Cytokines, cytotoxic granules, and more recently neurotransmitters have been shown to be transferred from T_FH to B cells upon cognate interactions. This review describes the current knowledge on immunological synapses occurring during GC responses including the type of granules, their content, and function in T_FH-mediated help to B cells.

Low expression of Mda-7/IL-24 and high expression of C-myb in tumour tissues are predictors of poor prognosis for Burkitt lymphoma patients

Objectives Burkitt lymphoma is one of the most common types of haematopoietic malignancy in children and adolescents. Mda-7/IL-24 had been identified as a differentiation inducer of Burkitt lymphoma cells. Previous studies have revealed that knockdown of C-myb can also lead to the terminal differentiation of Burkitt lymphoma cells. The aim of the present study was to investigate the correlation between the expression of Mda-7/IL-24 and C-myb, as well as their prognostic significance, for Burkitt lymphoma patients. Methods The tumour tissues were collected from 59 cases of Burkitt lymphoma patients and detected with Western blotting and immunohistochemistry. Results The results showed that the expression of Mda-7/IL-24 was lower, whereas the expression of C-myb was higher in Burkitt lymphoma tissues compared to specimens of normal lymph node tissues. Furthermore, C-myb expression was negatively correlated with Mda-7/IL-24 expression at the protein level in Burkitt lymphoma tissues and cell lines. Both the expression of Mda-7/IL-24 and C-myb in Burkitt lymphoma tissues was associated with some clinicopathological parameters, such as clinical stage, infiltration in the bone marrow, Ki67 and overall survival rates. Conclusion These results indicated that low expression of Mda-7/IL-24 along with high expression of C-myb are predictors for poor prognosis of Burkitt lymphoma patients; this outcome suggests that Mda-7/IL-24 and C-myb might be potential targets for clinical treatment of Burkitt lymphoma.

ABBREVIATIONS

Mda-7/IL-24: melanoma differentiation associated gene7/interleukin 24; FCM: flow cytometry; Ecog: Eastern Cooperative Oncology Group; IPI: International lymphoma prognosis index.

Association between biomechanical alterations and migratory ability of semaphorin-3A-treated thymocytes

BACKGROUND

Class 3 semaphorins are soluble proteins involved in cell adhesion and migration. Semaphorin-3A (Sema3A) was initially shown to be involved in neuronal guidance, and it has also been reported to be associated with immune disorders. Both Sema3A and its receptors are expressed by most immune cells, including monocytes, macrophages, and lymphocytes, and these proteins regulate cell function. Here, we studied the correlation between Sema3A-induced changes in biophysical parameters of thymocytes, and the subsequent repercussions on cell function.

METHODS

Thymocytes from mice were treated in vitro with Sema3A for 30min. Scanning electron microscopy was performed to assess cell morphology. Atomic force microscopy was performed to further evaluate cell morphology, membrane roughness, and elasticity. Flow cytometry and/or fluorescence microscopy were performed to assess the F-actin cytoskeleton and ROCK2. Cell adhesion to a bovine serum albumin substrate and transwell migration assays were used to assess cell migration.

RESULTS

Sema3A induced filopodia formation in thymocytes, increased membrane stiffness and roughness, and caused a cortical distribution of the cytoskeleton without changes in F-actin levels. Sema3A-treated thymocytes showed reduced substrate adhesion and migratory ability, without changes in cell viability. In addition, Sema3A was able to down-regulate ROCK2.

CONCLUSIONS

Sema3A promotes cytoskeletal rearrangement, leading to membrane modifications, including increased stiffness and roughness. This effect in turn affects the adhesion and migration of thymocytes, possibly due to a reduction in ROCK2 expression.

GENERAL SIGNIFICANCE

Sema3A treatment impairs thymocyte migration due to biomechanical alterations in cell membranes.

CD100-Plexin-B2 Promotes the Inflammation in Psoriasis by Activating NF-κB and the Inflammasome in Keratinocytes

PlxnB2 and its ligand, CD100, were originally identified as axon-guidance molecules that function during neuronal development; however, studies also showed that CD100-plexins participate in various immune responses. In this study, we found that the expression of PlxnB2 on keratinocytes was specifically increased in lesional skin of psoriasis patients but not atopic dermatitis. Levels of soluble CD100 and membrane-bound CD100 were elevated in sera of psoriasis patients and on keratinocytes of psoriatic skin, respectively. By binding to PlxnB2, soluble CD100 promoted the production of CXCL-1, CCL-20, IL-1β, and IL-18 by keratinocytes and activated the NLRP3 inflammasome. Moreover, CD100-PlxnB2 stimulated the NF-κB signaling pathway in keratinocytes through activation of small GTPase RhoA and Rac1. Our data showed that cooperation of CD100 and PlxnB2 promoted the inflammatory responses in keratinocytes by activating NF-κB and the NLRP3 inflammasome and participated in the pathogenesis of psoriasis. CD100/PlxnB2 might be a potential therapeutic target for psoriasis.