The structural basis of Salmonella A2B5 toxin neutralization by antibodies targeting the glycan-receptor binding subunits.

Many bacterial pathogens secrete A(2)B5 toxins comprising two functionally distinct yet complementary "A" and "B" subunits to benefit the pathogens during infection. The lectin-like pentameric B subunits recognize specific sets of host glycans to deliver the toxin into target host cells. Here, we offer the molecular mechanism by which neutralizing antibodies, which have the potential to bind to all glycan-receptor binding sites and thus completely inhibit toxin binding to host cells, are inhibited from exerting this action. Cryogenic electron microscopy (cryo-EM)-based analyses indicate that the skewed positioning of the toxin A subunit(s) toward one side of the toxin B pentamer inhibited neutralizing antibody binding to the laterally located epitopes, rendering some glycan-receptor binding sites that remained available for the toxin binding and endocytosis process, which is strikingly different from the counterpart antibodies recognizing the far side-located epitopes. These results highlight additional features of the toxin-antibody interactions and offer important insights into anti-toxin strategies.

Mechanisms of typhoid toxin neutralization by antibodies targeting glycan receptor binding and nuclease subunits.

Nearly all clinical isolates of Salmonella Typhi, the cause of typhoid fever, are antibiotic resistant. All S. Typhi isolates secrete an A2B5 exotoxin called typhoid toxin to benefit the pathogen during infection. Here, we demonstrate that antibiotic-resistant S. Typhi secretes typhoid toxin continuously during infection regardless of antibiotic treatment. We characterize typhoid toxin antibodies targeting glycan-receptor-binding PltB or nuclease CdtB, which neutralize typhoid toxin in vitro and in vivo, as demonstrated by using typhoid toxin secreted by antibiotic-resistant S. Typhi during human cell infection and lethal dose typhoid toxin challenge to mice. TyTx11 generated in this study neutralizes typhoid toxin effectively, comparable to TyTx4 that binds to all PltB subunits available per holotoxin. Cryoelectron microscopy explains that the binding of TyTx11 to CdtB makes this subunit inactive through CdtB catalytic-site conformational change. The identified toxin-neutralizing epitopes are conserved across all S. Typhi clinical isolates, offering critical insights into typhoid toxin-neutralizing strategies.

Chromatin accessibility of circulating CD8+ T cells predicts treatment response to PD-1 blockade in patients with gastric cancer.

Although tumor genomic profiling has identified small subsets of gastric cancer (GC) patients with clinical benefit from anti-PD-1 treatment, not all responses can be explained by tumor sequencing alone. We investigate epigenetic elements responsible for the differential response to anti-PD-1 therapy by quantitatively assessing the genome-wide chromatin accessibility of circulating CD8+ T cells in patients' peripheral blood. Using an assay for transposase-accessible chromatin using sequencing (ATAC-seq), we identify unique open regions of chromatin that significantly distinguish anti-PD-1 therapy responders from non-responders. GC patients with high chromatin openness of circulating CD8+ T cells are significantly enriched in the responder group. Concordantly, patients with high chromatin openness at specific genomic positions of their circulating CD8+ T cells demonstrate significantly better survival than those with closed chromatin. Here we reveal that epigenetic characteristics of baseline CD8+ T cells can be used to identify metastatic GC patients who may benefit from anti-PD-1 therapy.

Immune Cell-Stromal Circuitry in Lupus Photosensitivity.

Photosensitivity is a sensitivity to UV radiation (UVR) commonly found in systemic lupus erythematosus (SLE) patients who have cutaneous disease. Upon even ambient UVR exposure, patients can develop inflammatory skin lesions that can reduce the quality of life. Additionally, UVR-exposed skin lesions can be associated with systemic disease flares marked by rising autoantibody titers and worsening kidney disease. Why SLE patients are photosensitive and how skin sensitivity leads to systemic disease flares are not well understood, and treatment options are limited. In recent years, the importance of immune cell-stromal interactions in tissue function and maintenance is being increasingly recognized. In this review, we discuss SLE as an anatomic circuit and review recent findings in the pathogenesis of photosensitivity with a focus on immune cell-stromal circuitry in tissue health and disease.

IL-7Rαlow CD8+ T Cells from Healthy Individuals Are Anergic with Defective Glycolysis.

Effector memory (EM) CD8+ T cells expressing lower levels of IL-7R α (IL-7Rαlow) from healthy individuals are partly compromised in vitro, but the identity of these cells has remained unclear. In this study, we demonstrate that human IL-7Rαlow EM CD8+ T cells are naturally occurring anergic cells in vivo and impaired in proliferation and IL-2 production but competent in IFN-γ and TNF-α production, a state that can be restored by IL-2 stimulation. IL-7Rαlow EM CD8+ T cells show decreased expression of GATA3 and c-MYC and are defective in metabolic reprogramming toward glycolysis, a process required for the proliferation of T cells. However, IL-7Rαlow EM CD8+ T cells can proliferate with TCR stimulation in the presence of IL-2 and IL-15, suggesting that these cells can be restored to normality or increased activity by inflammatory conditions and may serve as a reservoir for functional immunity.

Salmonella Typhoid Toxin PltB Subunit and Its Non-typhoidal Salmonella Ortholog Confer Differential Host Adaptation and Virulence.

Typhoidal and non-typhoidal Salmonelleae (NTS) cause typhoid fever and gastroenteritis, respectively, in humans. Salmonella typhoid toxin contributes to typhoid disease progression and chronic infection, but little is known about the role of its NTS ortholog. We found that typhoid toxin and its NTS ortholog induce different clinical presentations. The PltB subunit of each toxin exhibits different glycan-binding preferences that correlate with glycan expression profiles of host cells targeted by each bacterium at the primary infection or intoxication sites. Through co-crystal structures of PltB subunits bound to specific glycan receptor moieties, we show that they induce markedly different glycan-binding preferences and virulence outcomes. Furthermore, immunization with the NTS S. Javiana or its toxin offers cross-reactive protection against lethal-dose typhoid toxin challenge. Cumulatively, these results offer insights into the evolution of host adaptations in Salmonella AB toxins, their cell and tissue tropisms, and the design for improved typhoid vaccines and therapeutics.

Analysis of Immune Cell Repopulation After Anti-thymocyte Globulin Administration for Steroid-Resistant T-cell-mediated Rejection.

BACKGROUND: Anti-thymocyte globulin (ATG) is a treatment option for steroid-resistant T-cell-mediated rejection after kidney transplantation. However, the extent to which immune-cell subsets can repopulate the peripheral blood is unknown. METHODS: Six patients with steroid-resistant T-cell-mediated rejection were recruited and underwent analysis of their immune cells for 1 year after ATG administration. Multicolor flow cytometric analysis was used to evaluate the proportions of T cells, B cells, natural killer cells, and monocytes. RESULTS: T-cell repopulation from 24% to 75% occurred in the treatment group. The major repopulated cells were effector memory CD8+ T cells followed by effector memory CD4+ T cells. The population of effector memory CD8+ T cells with low expression of interleukin-7 receptor α increased over time. The population of regulatory T cells (eg, CD8+CD28-CD56+ T cells and CD4+CD25bright T cells) increased after ATG administration. However, the populations of other immune-cell subsets, including B cells, natural killer cells, and monocytes, were not significantly altered by ATG. CONCLUSIONS: Our findings on immune cell repopulation after ATG administration will enable future studies aiming to unravel the steroid-resistance mechanism underlying T-cell-mediated rejection.

The role of 9-O-acetylated glycan receptor moieties in the typhoid toxin binding and intoxication.

Typhoid toxin is an A2B5 toxin secreted from Salmonella Typhi-infected cells during human infection and is suggested to contribute to typhoid disease progression and the establishment of chronic infection. To deliver the enzymatic 'A' subunits of the toxin to the site of action in host cells, the receptor-binding 'B' subunit PltB binds to the trisaccharide glycan receptor moieties terminated in N-acetylneuraminic acid (Neu5Ac) that is α2-3 or α2-6 linked to the underlying disaccharide, galactose (Gal) and N-acetylglucosamine (GlcNAc). Neu5Ac is present in both unmodified and modified forms, with 9-O-acetylated Neu5Ac being the most common modification in humans. Here we show that host cells associated with typhoid toxin-mediated clinical signs express both unmodified and 9-O-acetylated glycan receptor moieties. We found that PltB binds to 9-O-acetylated α2-3 glycan receptor moieties with a markedly increased affinity, while the binding affinity to 9-O-acetylated α2-6 glycans is only slightly higher, as compared to the affinities of PltB to the unmodified counterparts, respectively. We also present X-ray co-crystal structures of PltB bound to related glycan moieties, which supports the different effects of 9-O-acetylated α2-3 and α2-6 glycan receptor moieties on the toxin binding. Lastly, we demonstrate that the cells exclusively expressing unmodified glycan receptor moieties are less susceptible to typhoid toxin than the cells expressing 9-O-acetylated counterparts, although typhoid toxin intoxicates both cells. These results reveal a fine-tuning mechanism of a bacterial toxin that exploits specific chemical modifications of its glycan receptor moieties for virulence and provide useful insights into the development of therapeutics against typhoid fever.

Impacts of GFP-FoxP3+ regulatory T cells on lupus hallmarks differ by genetic background and type of GFP knock-in.

FoxP3 reporter mice expressing green fluorescence protein (GFP) have been used as a very convenient tool to investigate the impact of regulatory T (Treg) cells on pathogenesis in autoimmune diseases. Here, we found that GFP-FoxP3+ knock-in (KI) mice showed alterations in the production of anti-nuclear autoantibodies (ANAs) and nephritis with different extent, depending on the presence or absence of lupus susceptibility gene locus 1 (Sle1) and KI method: contrasting with B6.Sle1.fGFP-FoxP3 mice, expressing GFP via N-terminal insertion, B6.Sle1.iGFP-FoxP3, expressing GFP via bicistronic internal ribosome entry site-driven promotion, exhibited significantly lower penetrance of serum ANA, comparing to control B6.Sle1 mice. Moreover, B6.Sle1.GFP-FoxP3+ mice reduced the Sle1-induced splenomegaly and B-cell expansion independently of the KI method employed, mainly by reducing the numbers of transitional 1 (T1) B cells and CD21-CD23- B cells, including plasmablasts and plasma cells. The absolute numbers of both splenic CD4+ T cells and Treg cells from B6.Sle1.GFP-FoxP3 KI mice were significantly reduced but their proportion was not changed, compared to B6.Sle1 mice. Although the glomerular basement membranes were thickened in both B6.Sle1 and B6.Sle1.iGFP-FoxP3 mice, they were thinner in B6.Sle1.fGFP-FoxP3 mice. The latter mice expressed more nephrophilic autoantibodies and deposited more complement component 3 in glomeruli compared to B6.iGFP-FoxP3 mice. FoxP3+ Treg cells may modulate B-cell tolerance in lupus-prone B6.Sle1 mice, presumably by modulating pathogenic, nephrophilic autoantibody production and nephritis.

Interleukin-7 Contributes to the Invasiveness of Prostate Cancer Cells by Promoting Epithelial-Mesenchymal Transition.

Precise mechanisms underlying interleukin-7 (IL-7)-mediated tumor invasion remain unclear. Thus, we investigated the role of IL-7 in tumor invasiveness using metastatic prostate cancer PC-3 cell line derivatives, and assessed the potential of IL-7 as a clinical target using a Janus kinase (JAK) inhibitor and an IL-7-blocking antibody. We found that IL-7 stimulated wound-healing migration and invasion of PC-3 cells, increased phosphorylation of signal transducer and activator of transcription 5, Akt, and extracellular signal-regulated kinase. On the other hand, a JAK inhibitor and an IL-7-blocking antibody decreased the invasiveness of PC-3 cells. IL-7 increased tumor sphere formation and expression of epithelial-mesenchymal transition (EMT) markers. Importantly, lentiviral delivery of IL-7Rα to PC-3 cells significantly increased bone metastasis in an experimental murine metastasis model compared to controls. The gene expression profile of human prostate cancer cells from The Cancer Genome Atlas revealed that EMT pathways are strongly associated with prostate cancers that highly express both IL-7 and IL-7Rα. Collectively, these data suggest that IL-7 and/or IL-7Rα are promising targets of inhibiting tumor metastasis.

Corrigendum: Interleukin-7 Induces Osteoclast Formation via STAT5, Independent of Receptor Activator of NF-kappaB Ligand.

[This corrects the article on p. 1376 in vol. 8, PMID: 29104576.].

Interleukin-7 Induces Osteoclast Formation via STAT5, Independent of Receptor Activator of NF-kappaB Ligand.

Interleukin-7 (IL-7), which is required for the development and survival of T cells in the thymus and periphery, plays a role in joint destruction. However, it remains unclear how IL-7 affects osteoclast formation. Thus, we investigated the mechanism by which IL-7 induced osteoclast formation through IL-7 receptor α (IL-7Rα) in osteoclast precursors. We cultured peripheral blood mononuclear cells or synovial fluid mononuclear cells with IL-7 in the presence or absence of an appropriate inhibitor to analyze osteoclast formation. We also constructed IL-7Rα-expressing RAW264.7 cells to uncover the mechanism(s) by which IL-7 induced osteoclast formation differed from that of receptor activator of nuclear factor κB ligand (RANKL). We found that IL-7 induced osteoclast formation of human monocytes from peripheral blood or synovial fluid in a RANKL-independent and a signal transducer and activator of transcription 5 (STAT5)-dependent manner. IL-7-induced osteoclasts had unique characteristics, such as small, multinucleated tartrate-resistant acid phosphatase positive cells and no alterations even when RANKL was added after IL-7 pretreatment. RAW264.7 cells, if overexpressing IL-7Rα, also were able to differentiate into osteoclasts by IL-7 through a STAT5 signaling pathway. Furthermore, IL-7-induced osteoclast formation was repressed by inhibitors of the IL-7R signaling molecules Janus kinase and STAT5. Our findings demonstrate that IL-7 is a truly osteoclastogenic factor, which may induce osteoclast formation via activation of STAT5, independent of RANKL. We also suggest the possibility that an IL-7R pathway blocker could alleviate joint damage by inhibiting osteoclast formation, especially in inflammatory conditions.

Differentially Expressed Potassium Channels Are Associated with Function of Human Effector Memory CD8+ T Cells.

The voltage-gated potassium channel, Kv1.3, and the Ca2+-activated potassium channel, KCa3.1, regulate membrane potentials in T cells, thereby controlling T cell activation and cytokine production. However, little is known about the expression and function of potassium channels in human effector memory (EM) CD8+ T cells that can be further divided into functionally distinct subsets based on the expression of the interleukin (IL)-7 receptor alpha (IL-7Rα) chain. Herein, we investigated the functional expression and roles of Kv1.3 and KCa3.1 in EM CD8+ T cells that express high or low levels of the IL-7 receptor alpha chain (IL-7Rαhigh and IL-7Rαlow, respectively). In contrast to the significant activity of Kv1.3 and KCa3.1 in IL-7Rαhigh EM CD8+ T cells, IL-7Rαlow EM CD8+ T cells showed lower expression of Kv1.3 and insignificant expression of KCa3.1. Kv1.3 was involved in the modulation of cell proliferation and IL-2 production, whereas KCa3.1 affected the motility of EM CD8+ T cells. The lower motility of IL-7Rαlow EM CD8+ T cells was demonstrated using transendothelial migration and motility assays with intercellular adhesion molecule 1- and/or chemokine stromal cell-derived factor-1α-coated surfaces. Consistent with the lower migration property, IL-7Rαlow EM CD8+ T cells were found less frequently in human skin. Stimulating IL-7Rαlow EM CD8+ T cells with IL-2 or IL-15 increased their motility and recovery of KCa3.1 activity. Our findings demonstrate that Kv1.3 and KCa3.1 are differentially involved in the functions of EM CD8+ T cells. The weak expression of potassium channels in IL-7Rαlow EM CD8+ T cells can be revived by stimulation with IL-2 or IL-15, which restores the associated functions. This study suggests that IL-7Rαhigh EM CD8+ T cells with functional potassium channels may serve as a reservoir for effector CD8+ T cells during peripheral inflammation.

Modulation of gut microbiota and delayed immunosenescence as a result of syringaresinol consumption in middle-aged mice.

Age-associated immunological dysfunction (immunosenescence) is closely linked to perturbation of the gut microbiota. Here, we investigated whether syringaresinol (SYR), a polyphenolic lignan, modulates immune aging and the gut microbiota associated with this effect in middle-aged mice. Compared with age-matched control mice, SYR treatment delayed immunosenescence by enhancing the numbers of total CD3+ T cells and naïve T cells. SYR treatment induced the expression of Bim as well as activation of FOXO3 in Foxp3+ regulatory T cells (Tregs). Furthermore, SYR treatment significantly enhanced the Firmicutes/Bacteroidetes ratio compared with that in age-matched controls by increasing beneficial bacteria, Lactobacillus and Bifidobacterium, while reducing the opportunistic pathogenic genus, Akkermansia. In addition, SYR treatment reduced the serum level of lipopolysaccharide-binding protein, an inflammatory marker, and enhanced humoral immunity against influenza vaccination to the level of young control mice. Taken together, these findings suggest that SYR may rejuvenate the immune system through modulation of gut integrity and microbiota diversity as well as composition in middle-aged mice, which may delay the immunosenescence associated with aging.

CD4+ FOXP3+ Regulatory T Cells Exhibit Impaired Ability to Suppress Effector T Cell Proliferation in Patients with Turner Syndrome.

OBJECTIVE: We investigated whether the frequency, phenotype, and suppressive function of CD4+ FOXP3+ regulatory T cells (Tregs) are altered in young TS patients with the 45,X karyotype compared to age-matched controls. DESIGN AND METHODS: Peripheral blood mononuclear cells from young TS patients (n = 24, 17.4-35.9 years) and healthy controls (n = 16) were stained with various Treg markers to characterize their phenotypes. Based on the presence of thyroid autoimmunity, patients were categorized into TS (-) (n = 7) and TS (+) (n = 17). Tregs sorted for CD4+ CD25bright were co-cultured with autologous CD4+ CD25- target cells in the presence of anti-CD3 and -CD28 antibodies to assess their suppressive function. RESULTS: Despite a lower frequency of CD4+ T cells in the TS (-) and TS (+) patients (mean 30.8% and 31.7%, vs. 41.2%; P = 0.003 and P < 0.001, respectively), both groups exhibited a higher frequency of FOXP3+ Tregs among CD4+ T cells compared with controls (means 1.99% and 2.05%, vs. 1.33%; P = 0.029 and P = 0.004, respectively). There were no differences in the expression of CTLA-4 and the frequency of Tregs expressing CXCR3+, and CCR4+ CCR6+ among the three groups. However, the ability of Tregs to suppress the in vitro proliferation of autologous CD4+ CD25- T cells was significantly impaired in the TS (-) and TS (+) patients compared to controls (P = 0.003 and P = 0.041). Meanwhile, both the TS (-) and TS (+) groups had lower frequencies of naïve cells (P = 0.001 for both) but higher frequencies of effector memory cells (P = 0.004 and P = 0.002) than did the healthy control group. CONCLUSIONS: The Tregs of the TS patients could not efficiently suppress the proliferation of autologous effector T cells, despite their increased frequency in peripheral CD4+ T cells.

Autoregulatory function of interleukin-10-producing pre-naïve B cells is defective in systemic lupus erythematosus.

INTRODUCTION: Pre-naïve B cells represent an intermediate stage in human B-cell development with some functions of mature cells, but their involvement in immune responses is unknown. The aim of this study was to determine the functional role of normal pre-naïve B cells during immune responses and possible abnormalities in systemic lupus erythematosus (SLE) that might contribute to disease pathogenesis. METHODS: Pre-naïve, naïve, and memory B cells from healthy individuals and SLE patients were stimulated through CD40 and were analyzed for interleukin-10 (IL-10) production and co-stimulatory molecule expression and their regulation of T-cell activation. Autoreactivity of antibodies produced by pre-naïve B cells was tested by measuring immunoglobulin M (IgM) autoantibodies in culture supernatants after differentiation. RESULTS: CD40-stimulated pre-naïve B cells produce larger amounts of IL-10 but did not suppress CD4(+) T-cell cytokine production. Activated pre-naïve B cells demonstrated IL-10-mediated ineffective promotion of CD4(+) T-cell proliferation and induction of CD4(+)FoxP3(+) T cells and IL-10 independent impairment of co-stimulatory molecule expression and tumor necrosis factor-alpha (TNF-α) and IL-6 production. IgM antibodies produced by differentiated pre-naïve B cells were reactive to single-stranded deoxyribonucleic acid. SLE pre-naïve B cells were defective in producing IL-10, and co-stimulatory molecule expression was enhanced, resulting in promotion of robust CD4(+) T-cell proliferation. CONCLUSIONS: There is an inherent and IL-10-mediated mechanism that limits the capacity of normal pre-naïve B cells from participating in cellular immune response, but these cells can differentiate into autoantibody-secreting plasma cells. In SLE, defects in IL-10 secretion permit pre-naïve B cells to promote CD4(+) T-cell activation and may thereby enhance the development of autoimmunity.

Plasma neutrophil gelatinase-associated lipocalin predicts acute pyelonephritis in children with urinary tract infections.

BACKGROUND: The identification of acute pyelonephritis (APN) is still a challenge. METHODS: Patients admitted for their first urinary tract infection (UTI) were enrolled. Plasma neutrophil gelatinase-associated lipocalin (NGAL) levels were measured at admittance and after treatment. Laboratory, clinical, and imaging results were compared between children with and without APN. RESULTS: A total of 123 patients were enrolled (53 APN and 70 lower UTI). After adjusting for age and gender, plasma NGAL levels were higher in the APN group than in the lower UTI group (233 (129-496) ng/ml vs. 71 (50.8-110) ng/ml, P < 0.001). NGAL levels were correlated with the serum levels of leukocytes, C-reactive protein, and creatinine, as well as fever duration (P < 0.05). Multivariable analysis revealed that log-transformed plasma NGAL was an independent predictor of APN (P < 0.05). Receiver operating curve analysis showed a good diagnostic profile of NGAL for identifying APN (area under the curve 0.864) with a best cut-off value of 102.5 ng/ml. The NGAL levels in both two groups decreased after treatment compared to levels before treatment (P < 0.001). CONCLUSION: Plasma NGAL can be a sensitive predictor for identifying APN and monitoring the treatment response of pediatric UTI.

Peripheral immature B cells: modulators of autoimmunity.

B cells play an essential role in humoral immunity by producing antigen-specific antibodies. However, B cells also participate in cellular immune responses by presenting antigens, providing costimulation, and producing cytokines to activate and expand effectors and memory T cell populations. Recent identification of antibody-independent functions of B cells has reawakened interest in the many roles of B cells in normal immune responses as well as in autoimmune diseases. B cells interact with other immunocompetent cells during a tightly regulated immune activation process, acting as both effector and regulator. If this balance between effector and regulatory B cell functions is disrupted, harmful effects of immune activation such as autoimmunity can occur. In this review, we will discuss the role of human peripheral immature B cells in normal immune responses as a modulator of autoimmunity. We will also discuss abnormalities of these cells in pathogenesis of systemic autoimmunity with particular focus on systemic lupus erythematosus pathogenesis.

Anti-asthmatic activities of an ethanol extract of Aster yomena in an ovalbumin-induced murine asthma model.

Aster yomena is used in traditional remedies to treat cough, asthma and insect bites; however, its therapeutic mechanism is not completely understood. To elucidate the anti-asthmatic effect of A. yomena, we investigated the anti-asthmatic characteristics of an alcohol extract of A. yomena in an ovalbumin (OVA)-induced murine asthma model. In this study, we showed that A. yomena extract inhibited the overall pathophysiological features of asthma by suppressing Th2 responses and enzymes associated with the production of inflammatory mediators. This suppression resulted in decreased Th2 type cytokines and eosinophils in the bronchoalveolar lavage fluid and OVA-specific IgE in serum. Additionally, A. yomena extract significantly decreased airway hyperresponsiveness and abrogated the histopathological changes in the lungs, which reached normal levels in the OVA-challenged mice treated with A. yomena extract. These findings suggest that A. yomena could be a promising natural agent for treating bronchial asthma in humans.