Gut Microbiota-Induced Immunoglobulin G Controls Systemic Infection by Symbiotic Bacteria and Pathogens.

The gut microbiota is compartmentalized in the intestinal lumen and induces local immune responses, but it remains unknown whether the gut microbiota can induce systemic response and contribute to systemic immunity. We report that selective gut symbiotic gram-negative bacteria were able to disseminate systemically to induce immunoglobulin G (IgG) response, which primarily targeted gram-negative bacterial antigens and conferred protection against systemic infections by E. coli and Salmonella by directly coating bacteria to promote killing by phagocytes. T cells and Toll-like receptor 4 on B cells were important in the generation of microbiota-specific IgG. We identified murein lipoprotein (MLP), a highly conserved gram-negative outer membrane protein, as a major antigen that induced systemic IgG homeostatically in both mice and humans. Administration of anti-MLP IgG conferred crucial protection against systemic Salmonella infection. Thus, our findings reveal an important function for the gut microbiota in combating systemic infection through the induction of protective IgG.

Effect of Donor Age on Endocrine Function of and Immune Response to Ovarian Grafts.

Premature loss of ovarian function (POI) is associated with numerous negative side effects, including vasomotor symptoms, sleep and mood disturbances, disrupted urinary function, and increased risks for osteoporosis and heart disease. Hormone replacement therapy (HRT), the standard of care for POI, delivers only a subset of ovarian hormones and fails to mimic the monthly cyclicity and daily pulsatility characteristic of healthy ovarian tissue in reproductive-aged individuals whose ovarian tissue contains thousands of ovarian follicles. Ovarian tissue allografts have the potential to serve as an alternative, cell-based HRT, capable of producing the full panel of ovarian hormones at physiologically relevant doses and intervals. However, the risks associated with systemic immune suppression (IS) required to prevent allograft rejection outweigh the potential benefits of comprehensive and dynamic hormone therapy. This work investigates whether the age of ovarian tissue donor animals affects the function of, and immune response to, subcutaneous ovarian grafts. We performed syngeneic and semi-allogeneic ovarian transplants using tissue from mice aged 6-8 (D7) or 20-22 (D21) days and evaluated ovarian endocrine function and immune response in a mouse model of POI. Our results revealed that tissue derived from D7 donors, containing an ample and homogeneous primordial follicle reserve, was more effective in fully restoring hypothalamic-pituitary-ovarian feedback. In contrast, tissue derived from D21 donors elicited anti-donor antibodies with higher avidity compared to tissue from younger donors, suggesting that greater immunogenicity may be a trade-off of using mature donors. This work contributes to our understanding of the criteria donor tissue must meet to effectively function as a cell-based HRT and explores the importance of donor age as a factor in ovarian allograft rejection.

The five dimensions of B cell tolerance.

B cell tolerance has been generally understood to be an acquired property of the immune system that governs antibody specificity in ways that avoid auto-toxicity. As useful as this understanding has proved, it fails to fully explain the existence of auto-reactive specificities in healthy individuals and contribution these may have to health. Mechanisms underlying B cell tolerance are considered to select a clonal repertoire that generates a collection of antibodies that do not bind self, ie tolerance operates more or less in three dimensions that largely spare autologous cells and antigens. Yet, most B lymphocytes in humans and probably in other vertebrates are auto-reactive and absence of these auto-reactive B cells is associated with disease. We suggest that auto-reactivity can be embodied by extending the concept of tolerance by two further dimensions, one of time and circumstance and one that allows healthy cells to actively resist injury. In this novel concept, macromolecular recognition by the B cell receptor leading to deletion, anergy, receptor editing or B cell activation is extended by taking account of the time of development of normal immune responses (4th dimension) and the accommodation (or tolerance) of normal cells to bound antibody, activation of complement, and interaction with inflammatory cells (fifth dimension). We discuss how these dimensions contribute to understanding B cell biology in health or disease.

Indoleamine 2,3-Dioxygenase 1, Increased in Human Gastric Pre-Neoplasia, Promotes Inflammation and Metaplasia in Mice and Is Associated With Type II Hypersensitivity/Autoimmunity.

BACKGROUND & AIMS: Chronic gastrointestinal inflammation increases the risk of cancer by mechanisms that are not well understood. Indoleamine-2,3-dioxygenase 1 (IDO1) is a heme-binding enzyme that regulates the immune response via catabolization and regulation of tryptophan availability for immune cell uptake. IDO1 expression is increased during the transition from chronic inflammation to gastric metaplasia. We investigated whether IDO1 contributes to the inflammatory response that mediates loss of parietal cells leading to metaplasia. METHODS: Chronic gastric inflammation was induced in Ido1-/- and CB57BL/6 (control) mice by gavage with Helicobacter felis or overexpression of interferon gamma in gastric parietal cells. We also performed studies in Jh-/- mice, which are devoid of B cells. Gastric tissues were collected and analyzed by flow cytometry, immunostaining, and real-time quantitative polymerase chain reaction. Plasma samples were analyzed by enzyme-linked immunosorbent assay. Gastric tissues were obtained from 20 patients with gastric metaplasia and 20 patients without gastric metaplasia (controls) and analyzed by real-time quantitative polymerase chain reaction; gastric tissue arrays were analyzed by immunohistochemistry. We collected genetic information on gastric cancers from The Cancer Genome Atlas database. RESULTS: H felis gavage induced significantly lower levels of pseudopyloric metaplasia in Ido1-/- mice, which had lower frequencies of gastric B cells, than in control mice. Blood plasma from H felis-infected control mice had increased levels of autoantibodies against parietal cells, compared to uninfected control mice, but this increase was lower in Ido1-/- mice. Chronically inflamed stomachs of Ido1-/- mice had significantly lower frequencies of natural killer cells in contact with parietal cells, compared with stomachs of control mice. Jh-/- mice had lower levels of pseudopyloric metaplasia than control mice in response to H felis infection. Human gastric pre-neoplasia and carcinoma specimens had increased levels of IDO1 messenger RNA compared with control gastric tissues, and IDO1 protein colocalized with B cells. Co-clustering of IDO1 messenger RNA with B-cell markers was corroborated by The Cancer Genome Atlas database. CONCLUSIONS: IDO1 mediates gastric metaplasia by regulating the B-cell compartment. This process appears to be associated with type II hypersensitivity/autoimmunity. The role of autoimmunity in the progression of pseudopyloric metaplasia warrants further investigation.

Toward a solution for cardiac failure in the newborn.

The newborn infant with severe cardiac failure owed to congenital structural heart disease or cardiomyopathy poses a daunting therapeutic challenge. The ideal solution for both might be cardiac transplantation if availability of hearts was not limiting and if tolerance could be induced, obviating toxicity of immunosuppressive therapy. If one could safely and effectively exploit neonatal tolerance for successful xenotransplantation of the heart, the challenge of severe cardiac failure in the newborn infant might be met. We discuss the need, the potential for applying neonatal tolerance in the setting of xenotransplantation and the possibility that other approaches to this problem might emerge.

Accommodation in ABO-incompatible organ transplants.

Accommodation refers to a condition in which a transplant (or any tissue) appears to resist immune-mediated injury and loss of function. Accommodation was discovered and has been explored most thoroughly in ABO-incompatible kidney transplantation. In this setting, kidney transplants bearing blood group A or B antigens often are found to function normally in recipients who lack and hence produce antibodies directed against the corresponding antigens. Whether accommodation is owed to changes in anti-blood group antibodies, changes in antigen or a change in the response of the transplant to antibody binding are critically reviewed and a new working model that allows for the kinetics of development of accommodation is put forth. Regardless of how accommodation develops, observations on the fate of ABO-incompatible transplants offer lessons applicable more broadly in transplantation and in other fields.

Host conditioning and rejection monitoring in hepatocyte transplantation in humans.

BACKGROUND & AIMS: Hepatocyte transplantation partially corrects genetic disorders and has been associated anecdotally with reversal of acute liver failure. Monitoring for graft function and rejection has been difficult, and has contributed to limited graft survival. Here we aimed to use preparative liver-directed radiation therapy, and continuous monitoring for possible rejection in an attempt to overcome these limitations. METHODS: Preparative hepatic irradiation was examined in non-human primates as a strategy to improve engraftment of donor hepatocytes, and was then applied in human subjects. T cell immune monitoring was also examined in human subjects to assess adequacy of immunosuppression. RESULTS: Porcine hepatocyte transplants engrafted and expanded to comprise up to 15% of irradiated segments in immunosuppressed monkeys preconditioned with 10Gy liver-directed irradiation. Two patients with urea cycle deficiencies had early graft loss following hepatocyte transplantation; retrospective immune monitoring suggested the need for additional immunosuppression. Preparative radiation, anti-lymphocyte induction, and frequent immune monitoring were instituted for hepatocyte transplantation in a 27year old female with classical phenylketonuria. Post-transplant liver biopsies demonstrated multiple small clusters of transplanted cells, multiple mitoses, and Ki67+ hepatocytes. Mean peripheral blood phenylalanine (PHE) level fell from pre-transplant levels of 1343±48µM (normal 30-119µM) to 854±25µM (treatment goal ≤360µM) after transplant (36% decrease; p<0.0001), despite transplantation of only half the target number of donor hepatocytes. PHE levels remained below 900µM during supervised follow-up, but graft loss occurred after follow-up became inconsistent. CONCLUSIONS: Radiation preconditioning and serial rejection risk assessment may produce better engraftment and long-term survival of transplanted hepatocytes. Hepatocyte xenografts engraft for a period of months in non-human primates and may provide effective therapy for patients with acute liver failure. LAY SUMMARY: Hepatocyte transplantation can potentially be used to treat genetic liver disorders but its application in clinical practice has been impeded by inefficient hepatocyte engraftment and the inability to monitor rejection of transplanted liver cells. In this study, we first show in non-human primates that pretreatment of the host liver with radiation improves the engraftment of transplanted liver cells. We then used this knowledge in a series of clinical hepatocyte transplants in patients with genetic liver disorders to show that radiation pretreatment and rejection risk monitoring are safe and, if optimized, could improve engraftment and long-term survival of transplanted hepatocytes in patients.

TAK1 maintains the survival of immunoglobulin λ-chain-positive B cells.

TAK1 (MAP3K7) mediation of the IκB kinase (IKK) complex-nuclear factor-κB (NF-κB) pathway is crucial for the activation of immune response and to perpetuate inflammation. Although progress has been made to understand TAK1 function in the B-cell receptor (BCR) signaling, the physiological roles of TAK1 in B-cell development, particularly in the bone marrow (BM), remain elusive. Previous studies suggested that the IKK complex is required for the development of immunoglobulin light chain λ-positive B cells, but not for receptor editing. In contrast, NF-κB activity is suggested to be involved in the regulation of receptor editing. Thus, NF-κB signaling in early B-cell development is yet to be fully characterized. Therefore, we addressed the role of TAK1 in early B-cell development. TAK1-deficient mice showed significant reduction of BM Igλ-positive B-cell numbers without any alteration in the BCR editing. Furthermore, the expression of survival factor Bcl-2 was reduced in TAK1-deficient BM B cells as assessed by microarray and quantitative PCR analyses. Ex vivo over-expression of exogenous Bcl-2 enhanced the survival of TAK1-deficient Igλ-positive B cells. TAK1-IKK-NF-κB signaling contributes to the survival of λ-chain-positive B cells through NF-κB-dependent anti-apoptotic Bcl-2 expression.

Accommodation and related conditions in vascularized composite allografts.

PURPOSE OF REVIEW: The outcome of vascularized composite allografts (VCA) often appear unrelated to the presence of donor-specific antibodies (DSA) in blood of the recipient or deposition of complement in the graft. The attenuation of injury and the absence of rejection in other types of grafts despite manifest donor-specific immunity have been explained by accommodation (acquired resistance to immune-mediated injury), adaptation (loss of graft antigen) and/or enhancement (antibody-mediated antigen blockade). Whether and how accommodation, adaptation and/or enhancement impact on the outcome of VCA is unknown. Here we consider how recent observations concerning accommodation in organ transplants might advance understanding and resolve uncertainties about the clinical course of VCA. RECENT FINDINGS: Investigation of the mechanisms through which kidney allografts avert antibody-mediated injury and rejection provide insights potentially applicable to VCA. Interaction of DSA can facilitate replacement of donor by recipient endothelial cells, modulate or decrease synthesis of antigen, mobilize antigen that in turn blocks further immune recognition and limit the amount of bound antibody, allowing accommodation to ensue. These processes also can explain the apparent dissociation between the presence and levels of DSA in blood, deposition of C4d in grafts and antibody-mediated rejection. Over time the processes might also explain the inception of chronic graft changes. SUMMARY: The disrupted tissue in VCA and potential for repopulation by endothelial cells of the recipient establish conditions that potentially decrease susceptibility to acute antibody-mediated rejection. These conditions include clonal suppression of donor-specific B cells, and adaptation, enhancement and accommodation. This setting also potentially highlights heretofore unrecognized interactions between these 'protective' processes.

Cell Fusion Connects Oncogenesis with Tumor Evolution.

Cell fusion likely drives tumor evolution by undermining chromosomal and DNA stability and/or by generating phenotypic diversity; however, whether a cell fusion event can initiate malignancy and direct tumor evolution is unknown. We report that a fusion event involving normal, nontransformed, cytogenetically stable epithelial cells can initiate chromosomal instability, DNA damage, cell transformation, and malignancy. Clonal analysis of fused cells reveals that the karyotypic and phenotypic potential of tumors formed by cell fusion is established immediately or within a few cell divisions after the fusion event, without further ongoing genetic and phenotypic plasticity, and that subsequent evolution of such tumors reflects selection from the initial diverse population rather than ongoing plasticity of the progeny. Thus, one cell fusion event can both initiate malignancy and fuel evolution of the tumor that ensues.

Cell Fusion in the War on Cancer: A Perspective on the Inception of Malignancy.

Cell fusion occurs in development and in physiology and rarely in those settings is it associated with malignancy. However, deliberate fusion of cells and possibly untoward fusion of cells not suitably poised can eventuate in aneuploidy, DNA damage and malignant transformation. How often cell fusion may initiate malignancy is unknown. However, cell fusion could explain the high frequency of cancers in tissues with low underlying rates of cell proliferation and mutation. On the other hand, cell fusion might also engage innate and adaptive immune surveillance, thus helping to eliminate or retard malignancies. Here we consider whether and how cell fusion might weigh on the overall burden of cancer in modern societies.

IgM in the kidney: a multiple personality disorder.

IgM in the blood of normal individuals consists mainly of 'natural' polyreactive antibodies. Natural IgM is thought to provide an initial defense against infection and to promote the healing of wounded cells. Yet, as Panzer and colleagues show, these benefits can be eclipsed when the IgM binds to damaged cells of the glomerulus, activating complement. IgM in glomeruli thus signifies cellular damage and may warn that the pace of that damage exceeds the capacity for repair.

Efficacy of plasmapheresis on donor-specific antibody reduction by HLA specificity in post-kidney transplant recipients.

BACKGROUND: Donor-specific antibodies (DSAs) to HLA antigens can cause acute antibody-mediated rejection (AMR) after kidney transplantation (Txp). Therapeutic plasma exchange (TPE) has been used for AMR treatment; however, DSA reduction rates are inconsistent. We investigated DSA reduction rates by HLA specificity and clinical outcome. STUDY DESIGN AND METHODS: Sixty-four courses of TPE for 56 kidney Txp recipients with high DSA were investigated. Dates of TPE procedures and Txp, patients' age, sex, race, creatinine (Cr), and mean fluorescent intensity (MFI) of DSA were retrieved. MFI reduction rate after one to three TPE and four to six TPE procedures were calculated by HLA DSA specificity in each patient, and the mean reduction rates were compared. The relationship of TPE treatment, MFI or Cr improvement rate, and graft age was also investigated. RESULTS: Patients received a mean 6.0 TPE procedures. Most received intravenous immunoglobulin after TPE and immunosuppressives. Forty-two cases (65.6%) had DSA to HLA Class I and 54 cases (84.4%) to Class II, including 32 cases (50.0%) to both. Mean MFI reduction rates after one to three TPE and four to six TPE procedures were 25.7 and 37.1% in HLA Class I, 25.1 and 34.2% in Class II, and 14.3 and 19.9% in DR51-53. The mean Cr improvements at the end of TPE and 3 and 6 months after TPE were 3.41, -0.37, and -0.72%, respectively. CONCLUSION: Six TPE procedures decreased DSA more than three TPE procedures, but reduction rate was lower by the second three TPE procedures than the first three TPE procedures. Although the mean Cr improvement was minimal, the treatment has good potential to stop further deterioration of kidney function. Better Cr improvement rate is correlated with the graft age.

The paradoxical functions of B cells and antibodies in transplantation.

Scarcely anyone would dispute that donor-specific B cells and the Abs that they produce can cause rejection of transplants. Less clear and more controversial, however, is the possibility that donor-specific B cells and the Abs that they produce are one or more means by which transplants can be protected from injury. In this article, we review and discuss this possibility and consider how less well-known functions of B cells and Abs might impact on the design of therapeutics and the management of transplant recipients.

Heparan Sulfate Proteoglycan Metabolism and the Fate of Grafted Tissues.

Tissue and organ transplants between genetically distinct individuals are always or nearly always rejected. The universality and speed of transplant rejection distinguishes this immune response from all others. Although this distinction is incompletely understood, some efforts to shed light on transplant rejection have revealed broader insights, including a relationship between activation of complement in grafted tissues, the metabolism of heparan sulfate proteoglycan and the nature of immune and inflammatory responses that ensue. Complement activation on cell surfaces, especially on endothelial cell surfaces, causes the shedding heparan sulfate, an acidic saccharide, from the cell surface and neighboring extracellular matrix. Solubilized in this way, heparan sulfate can activate leukocytes via toll like receptor-4, triggering inflammatory responses and activating dendritic cells, which migrate to regional lymphoid organs where they spark and to some extent govern cellular immune responses. In this way local ischemia, tissue injury and infection, exert systemic impact on immunity. Whether or in what circumstances this series of events explains the distinct characteristics of the immune response to transplants is still unclear but the events offer insight into the inception of immunity under the sub-optimal conditions accompanying infection and mechanisms by which infection and tissue injury engender systemic inflammation.

Reduced BAFF-R and increased TACI expression in common variable immunodeficiency.

PURPOSE: B-cell survival and differentiation critically depend on the interaction of BAFF-R and TACI with their ligands, BAFF and APRIL. Mature B-cell defects lead to Common Variable Immunodeficiency (CVID), which is associated with elevated serum levels of BAFF and APRIL. Nevertheless, BAFF-R and TACI expression in CVID and their relationship with ligand availability remain poorly understood. METHODS AND RESULTS: We found that BAFF-R expression was dramatically reduced on B cells of CVID patients, relative to controls. BAFF-R levels inversely correlated with serum BAFF concentration both in CVID and healthy subjects. We also found that recombinant BAFF stimulation reduced BAFF-R expression on B cells without decreasing transcript levels. On the other hand, CVID subjects had increased TACI expression on B cells in direct association with serum BAFF but not APRIL levels. Moreover, splenomegaly was associated with higher TACI expression, suggesting that perturbations of TACI function may underlie lymphoproliferation in CVID. CONCLUSIONS: Our results indicate that availability of BAFF determines BAFF-R and TACI expression on B cells, and that BAFF-R expression is controlled by BAFF binding. Identification of the factors governing BAFF-R and TACI is crucial to understanding CVID pathogenesis, and B-cell biology in general, as well as to explore their potential as therapeutic targets.

Antigen-Clustered Nanovaccine Achieves Long-Term Tumor Remission by Promoting B/CD 4 T Cell Crosstalk.

Current cancer vaccines using T cell epitopes activate antitumor T cell immunity through dendritic cell/macrophage-mediated antigen presentation, but they lack the ability to promote B/CD4 T cell crosstalk, limiting their anticancer efficacy. We developed antigen-clustered nanovaccine (ACNVax) to achieve long-term tumor remission by promoting B/CD4 T cell crosstalk. The topographic features of ACNVax were achieved using an iron nanoparticle core attached with an optimal number of gold nanoparticles, where the clusters of HER2 B/CD4 T cell epitopes were conjugated on the gold surface with an optimal intercluster distance of 5-10 nm. ACNVax effectively trafficked to lymph nodes and cross-linked with BCR, which are essential for stimulating B cell antigen presentation-mediated B/CD4 T cell crosstalk in vitro and in vivo. ACNVax, combined with anti-PD-1, achieved long-term tumor remission (>200 days) with 80% complete response in mice with HER2+ breast cancer. ACNVax not only remodeled the tumor immune microenvironment but also induced a long-term immune memory, as evidenced by complete rejection of tumor rechallenge and a high level of antigen-specific memory B, CD4, and CD8 cells in mice (>200 days). This study provides a cancer vaccine design strategy, using B/CD4 T cell epitopes in an antigen clustered topography, to achieve long-term durable anticancer efficacy through promoting B/CD4 T cell crosstalk.

Affinity maturation of antibodies requires integrity of the adult thymus.

The generation of B-cell responses to proteins requires a functional thymus to produce CD4(+) T cells which helps in the activation and differentiation of B cells. Because the mature T-cell repertoire has abundant cells with the helper phenotype, one might predict that in mature individuals, the generation of B-cell memory would proceed independently of the thymus. Contrary to that prediction, we show here that the removal of the thymus after the establishment of the T-cell compartment or sham surgery without removal of the thymus impairs the affinity maturation of antibodies. Because removal or manipulation of the thymus did not decrease the frequency of mutation of the Ig variable heavy chain exons encoding antigen-specific antibodies, we conclude that the thymus controls affinity maturation of antibodies in the mature individual by facilitating the selection of B cells with high-affinity antibodies.

TACI deficiency impairs sustained Blimp-1 expression in B cells decreasing long-lived plasma cells in the bone marrow.

Deficiencies in transmembrane activator and CAML interactor (TACI) result in common variable immune deficiency, a syndrome marked by recurrent infections with encapsulated microorganisms, impaired production of antibodies, and lymphoproliferation. How TACI promotes antibody production and inhibits lymphoproliferation is not understood. To answer this question, we studied the generation of immunity to protein antigens in both TACI-deficient and TACI-proficient mice. We show that TACI promotes sustained Blimp-1 expression by B cells responding to antigen, which in turn limits B-cell clonal expansion and facilitates differentiation of long-lived antibody-secreting cells. Short-term IgG secretion occurs independently of TACI as DNA double-strand breaks associated with isotype class switching induce Blimp-1 transiently, independently of TACI. Our results showing that TACI induces and maintains Blimp-1 provide, for the first time, a unified molecular and cellular mechanism explaining the primary features of common variable immune deficiency, exquisite vulnerability to infection with encapsulated organisms, lymphoproliferation, and hypogammaglobulinemia.