Human regulatory B cells in health and disease: therapeutic potential

Target the Host, Kill the Bug; Targeting Host Respiratory Immunosuppressive Responses as a Novel Strategy to Improve Bacterial Clearance During Lung Infection

The lung is under constant pressure to protect the body from invading bacteria. An effective inflammatory immune response must be tightly orchestrated to ensure complete clearance of any invading bacteria, while simultaneously ensuring that inflammation is kept under strict control to preserve lung viability. Chronic bacterial lung infections are seen as a major threat to human life with the treatment of these infections becoming more arduous as the prevalence of antibiotic resistance becomes increasingly commonplace. In order to survive within the lung bacteria target the host immune system to prevent eradication. Many bacteria directly target inflammatory cells and cytokines to impair inflammatory responses. However, bacteria also have the capacity to take advantage of and strongly promote anti-inflammatory immune responses in the host lung to inhibit local pro-inflammatory responses that are critical to bacterial elimination. Host cells such as T regulatory cells and myeloid-derived suppressor cells are often enhanced in number and activity during chronic pulmonary infection. By increasing suppressive cell populations and cytokines, bacteria promote a permissive environment suitable for their prolonged survival. This review will explore the anti-inflammatory aspects of the lung immune system that are targeted by bacteria and how bacterial-induced immunosuppression could be inhibited through the use of host-directed therapies to improve treatment options for chronic lung infections.

Vascularized composite allotransplantation versus solid organ transplantation: innate-adaptive immune interphase

PURPOSE OF REVIEW

Vascularized composite allotransplantation (VCA), a life-enhancing treatment for patients with complex tissue defects, trauma or illness, expounds upon the foundation of solid organ transplantation (SOT), the gold standard in end-stage organ failure. As innate and adaptive immunity remain the fundamental concern, this review highlights divergent immunobiology responses in VCA and SOT recipients.

RECENT FINDINGS

Host innate immune activation drives peritransplant tissue ischemia-reperfusion injury (IRI). Despite the direct relationship between ischemia-reperfusion (IR)-stress and cell-mediated acute rejection, the mechanism of how IRI may affect VCA loss needs investigation. With skin grafts being highly immunogenic, the incidence of cell-mediated rejection is higher in VCA than SOT; whereas ex-vivo perfusion may exert cytoprotection against IRI in VCA and SOT. New treatment concepts, such as topical immunosuppression or cell-based tolerogenic therapies, may avoid systemic immunosuppression in VCA. Although antibody-mediated rejection is relatively rare in VCA and its disease seems to be distinct from that in SOT, little is known as to whether and how IRI may influence humoral immune rejection cascade in VCA or SOT.

SUMMARY

Further understanding of the innate-adaptive immune crosstalk should contribute to much needed development of novel therapies to improve VCA outcomes, based on strategies established in SOT.

Immune dysfunction complexity in chronic lymphocytic leukemia ‒ an issue to consider when designing novel therapeutic strategies

A complex interplay between chronic lymphocytic leukemia (CLL) cells and different constituents of the immune system generally results in immune tolerance. As targeted therapies are gaining a critical role in the therapeutic landscape of this disease, their impact on the already perturbed immune milieu needs to be considered. This review addresses the issues of basic immune dysfunction in CLL which is further complicated by the effects of a number of novel targeted therapies used for this malignancy. These new approaches may simultaneously facilitate both anti- and pro-cancer activity, potentially compromising the depth of response to therapy. Current evidence suggests that exploiting combination therapy could potentially overcome at least part of these deleterious effects, thereby prolonging response to treatment and helping to restore immune activity.

The Resistance Mechanisms of Checkpoint Inhibitors in Solid Tumors

The emergence of cancer immunotherapy has already shown some remarkable results, having changed the treatment strategy in clinical practice for solid tumors. Despite these promising long-term responses, patients seem to lack the ability to respond to immune checkpoint inhibitors, thus demonstrating a primary resistance to immunotherapy. Moreover, a significant number of patients who initially respond to treatment eventually acquire resistance to immunotherapy. Both resistance mechanisms are a result of a complex interaction among different molecules, pathways, and cellular processes. Several resistance mechanisms, such as tumor microenvironment modification, autophagy, genetic and epigenetic alterations, tumor mutational burden, neo-antigens, and modulation of gut microbiota have already been identified, while more continue to be uncovered. In this review, we discuss the latest milestones in the field of immunotherapy, resistance mechanisms against this type of therapy as well as putative therapeutic strategies to overcome resistance in solid tumors.

Deficit of circulating CD19+ CD24hi CD38hi regulatory B cells in severe aplastic anaemia

Immune aplastic anaemia (AA) is caused by cytotoxic T lymphocytes (CTLs) that destroy haematopoietic stem and progenitor cells. Enhanced type 1 T helper (Th1) responses and reduced regulatory T cells (Tregs) are involved in the immune pathophysiology. CD24^hiCD38^hi regulatory B cells (Bregs) suppress CTLs and Th1 responses, and induce Tregs via interleukin 10 (IL‐10). We investigated circulating B‐cell subpopulations, including CD24^hiCD38^hi Bregs, as well as total B cells, CD4⁺ T cells, CD8⁺ T cells and natural killer cells in 104 untreated patients with severe and very severe AA, aged ≥18 years. All patients were treated with standard immunosuppressive therapy (IST) plus eltrombopag. CD24^hiCD38^hi Bregs were markedly reduced in patients with AA compared to healthy individuals, especially in very severe AA, but residual Bregs remained functional, capable of producing IL‐10; total B‐cell counts and the other B‐cell subpopulations were similar to those of healthy individuals. CD24^hiCD38^hi Bregs did not correlate with responses to IST, and they recovered to levels present in healthy individuals after therapy. Mature naïve B‐cell counts were unexpectedly associated with IST response. Markedly reduced CD24^hiCD38^hi Bregs, especially in very severe AA, with recovery after IST suggest Breg deficits may contribute to the pathophysiology of immune AA.

CD19+CD1dhiCD5hi B Cells Can Downregulate Malaria ITV Protection by IL-10 Secretion

Infection treatment vaccine (ITV) can lead to sterile protection against malaria infection in mice and humans. However, parasite breakthrough is frequently observed post-challenge. The mechanism of rapid decline in protection after the last immunization is unclear. Herein, C57BL/6 mice were immunized with 10³, 10⁵, or 10⁷ ITV thice at 14-day intervals. Mice were challenged with 10³ parasites at 1, 3, and 6 months after last immunization and the protection was checked using blood smear. The phenotypes of B cells were analyzed by flow cytometry. The levels of serum cytokines were quantified using cytometric bead array. The 10³ ITV vaccination group exhibited 100% protection at 1 month after last immunization, and the 10⁵ group showed sterile protection at 3 months after last immunization. However, the 10⁷ group showed only partial protection. Further, the protection declined to 16.7% at 6 months after last immunization in 10⁵ and 10⁷ groups, whereas it maintained for more than 60% in 10³ group. The number of memory B cells (MBC) decreased along with the decline in protection. However, programmed cell death protein 1 (PD-1) expressed on MBCs did not show significant variation among the three groups. Interestingly, CD19⁺CD1d^hiCD5^hi B cells, defined as B10 cells, exhibited negative regulation with respect to protection. The numbers of CD19⁺CD1d^hiCD5^hi B cells in the 10³ group at 1 months and in the 10⁵ group at 3 months post-immunization were the lowest compared to those in the other groups. Moreover, the serum levels of interleukin 10 (IL-10) in these two groups were also significantly lower than those in other groups. We conclude that higher immunization dose may not lead to better protection with the malaria vaccine as CD19⁺CD1d^hiCD5^hi B cells can downregulate ITV protection against malaria via IL-10 secretion. These results could facilitate the design of an effective long-lasting malaria vaccine with the aim of maintaining MBC function.

Apremilast increases IL-10-producing regulatory B cells and decreases proinflammatory T cells and innate cells in psoriatic arthritis and psoriasis

OBJECTIVES

Psoriatic arthritis (PsA) and psoriasis are immune-mediated inflammatory diseases sharing common immunological mechanisms. Regulatory B cells (Breg cells) producing IL-10 (B10 cells), a critical anti-inflammatory B-cell subset, were found to be decreased in both PsA and psoriasis. Apremilast, a phosphodiesterase-4(PDE4) inhibitor, increases IL-10 and therefore, we examined the effect of apremilast on Breg cells.

METHODS

Fifty patients, including 20 with PsA and 30 with psoriasis, were included in the study. The effect of apremilast on Breg cells at 3, 6 and 12 months post-treatment, was examined by flow cytometry in ODN2006 (TLR9)-stimulated peripheral blood mononuclear cells and magnetically-isolated cells. Th1 cells, Th17 cells and NKT were also measured.

RESULTS

Ex vivo stimulated cell analysis identified that post-apremilast (IL-10+CD19+) B10 cells were increased in all PsA and psoriasis patients and correlated with psoriatic skin and joint clinical improvement. Apremilast decreased IFNγ(+) T and NKT cells and IL-17(+)NKT cells. B10 cells also inversely correlated with Th1 cells, and IFNγ(+)NKT cells.

CONCLUSION

These results suggest that Breg cells are a major target of apremilast in PsA and psoriasis and that apremilast-induced increase of Breg cells is associated with a decrease of Th1 cells, IFNγ-producing NKT cells and IL-17-producing NKT cells.

Characterization of pulmonary immune responses to hyperoxia by high-dimensional mass cytometry analyses

Prolonged exposure to hyperoxia has deleterious effects on the lung, provoking both inflammation and alveolar injury. The elements of hyperoxic injury, which result in high rates of lethality in experimental models, are thought to include multicellular immune responses. To characterize these alterations in immune cell populations, we performed time-of-flight mass cytometry (CyTOF) analysis of CD45-expressing immune cells in whole lung parenchyma and the bronchoalveolar space of mice, exposed to 48 hours of hyperoxia together with normoxic controls. At the tested time point, hyperoxia exposure resulted in decreased abundance of immunoregulatory populations (regulatory B cells, myeloid regulatory cells) in lung parenchyma and markedly decreased proliferation rates of myeloid regulatory cells, monocytes and alveolar macrophages. Additionally, hyperoxia caused a shift in the phenotype of alveolar macrophages, increasing proportion of cells with elevated CD68, CD44, CD11c, PD-L1, and CD205 expression levels. These changes occurred in the absence of histologically evident alveolar damage and abundance of neutrophils in the parenchyma or alveolar space did not change at these time points. Collectively, these findings demonstrate that pulmonary response to hyperoxia involves marked changes in specific subsets of myeloid and lymphoid populations. These findings have important implications for therapeutic targeting in acute lung injury.

Tumor-educated B cells promote renal cancer metastasis via inducing the IL-1β/HIF-2α/Notch1 signals

While B cells in the tumor microenvironment (TME) might play important roles in cancer progression, their impacts on the renal cell carcinoma (RCC) metastasis remained unclear, which drew our attention to further explore. We found that RCC tissues could recruit more B cells than the surrounding normal renal tissues from human clinical RCC samples. Wound healing assay, transwell assay and 3D invasion assays demonstrated that recruited B cells, also known as tumor-educated B cells (TEB), could significantly increase the RCC cell migration and invasion. In addition, in vivo data from xenograft RCC mouse model also confirmed that TEB could enhance RCC cell invasive and metastatic capability. Mechanism dissection revealed that TEB activated IL-1β/HIF-2α signals in RCC cells that could induce the downstream Notch1 signaling pathway. The above results demonstrated the key roles of TEB within renal cancer associated tumor microenvironment were metastasis-promotor and might help us to develop the potential therapies via targeting these newly identified IL-1β/HIF-2α/Notch1 signals in RCC progression.

Regulatory B cells in infection, inflammation, and autoimmunity

Regulatory B (Breg) cells are characterized by differential expression of CD5 and CD1d in mouse and CD24 and CD38 in human immune systems. The Breg family also includes LAG-3⁺CD138^hi plasma cells, CD1d CD5 CD21 CD23 cells, Tim1, PD-L1, PD-L2, CD200- expressing B cells, and CD39^hiKi67⁺ cells originating from the transitional, marginal zone or germinal centre of the spleen. Breg cells produce IL10 and IL35 and to cause immunosuppression. These cells respond to TLR2, TLR4, and TLR9 agonists, CD40 ligands, IL12p35 and heat shock proteins. Emerging evidence suggests that TLR signalling component Myd88 impacts the modulation of Breg cell responses and the host's susceptibility to infection. Breg cells are found to reduce relapsing-remitting experimental autoimmune encephalomyelitis. However, the Breg-mediated mechanism used to control T cell-mediated immune responses is still unclear. Here, we review the existing literature to find gaps in the current knowledge and to build a pathway to further research.

Anti-inflammatory and immune-regulatory cytokines in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by a failure of spontaneous resolution of inflammation. Although the pro-inflammatory cytokines and mediators that trigger RA have been the focus of intense investigations, the regulatory and anti-inflammatory cytokines responsible for the suppression and resolution of disease in a context-dependent manner have been less well characterized. However, knowledge of the pathways that control the suppression and resolution of inflammation in RA is clinically relevant and conceptually important for understanding the pathophysiology of the disease and for the development of treatments that enable long-term remission. Cytokine-mediated processes such as the activation of T helper 2 cells by IL-4 and IL-13, the resolution of inflammation by IL-9, IL-5-induced eosinophil expansion, IL-33-mediated macrophage polarization, the production of IL-10 by regulatory B cells and IL-27-mediated suppression of lymphoid follicle formation are all involved in governing the regulation and resolution of inflammation in RA. By better understanding these immune-regulatory signalling pathways, new therapeutic strategies for RA can be envisioned that aim to balance and resolve, rather than suppress, inflammation.

Type 1 diabetes pathogenesis and the role of inhibitory receptors in islet tolerance

Type 1 diabetes (T1D) affects over a million Americans, and disease incidence is on the rise. Despite decades of research, there is still no cure for this disease. Exciting beta cell replacement strategies are being developed, but in order for such approaches to work, targeted immunotherapies must be designed. To selectively halt the autoimmune response, researchers must first understand how this response is regulated and which tolerance checkpoints fail during T1D development. Herein, we discuss the current understanding of T1D pathogenesis in humans, genetic and environmental risk factors, presumed roles of CD4+ and CD8+ T cells as well as B cells, and implicated autoantigens. We also highlight studies in non-obese diabetic mice that have demonstrated the requirement for CD4+ and CD8+ T cells and B cells in driving T1D pathology. We present an overview of central and peripheral tolerance mechanisms and comment on existing controversies in the field regarding central tolerance. Finally, we discuss T cell- and B cell-intrinsic tolerance mechanisms, with an emphasis on the roles of inhibitory receptors in maintaining islet tolerance in humans and in diabetes-prone mice, and strategies employed to date to harness inhibitory receptor signaling to prevent or reverse T1D.

Bacterial Immunogenicity Is Critical for the Induction of Regulatory B Cells in Suppressing Inflammatory Immune Responses

B cells fulfill multifaceted functions that influence immune responses during health and disease. In autoimmune diseases, such as inflammatory bowel disease, multiple sclerosis and rheumatoid arthritis, depletion of functional B cells results in an aggravation of disease in humans and respective mouse models. This could be due to a lack of a pivotal B cell subpopulation: regulatory B cells (Bregs). Although Bregs represent only a small proportion of all immune cells, they exhibit critical properties in regulating immune responses, thus contributing to the maintenance of immune homeostasis in healthy individuals. In this study, we report that the induction of Bregs is differentially triggered by the immunogenicity of the host microbiota. In comparative experiments with low immunogenic Bacteroides vulgatus and strong immunogenic Escherichia coli, we found that the induction and longevity of Bregs depend on strong Toll-like receptor activation mediated by antigens of strong immunogenic commensals. The potent B cell stimulation via E. coli led to a pronounced expression of suppressive molecules on the B cell surface and an increased production of anti-inflammatory cytokines like interleukin-10. These bacteria-primed Bregs were capable of efficiently inhibiting the maturation and function of dendritic cells (DCs), preventing the proliferation and polarization of T helper (Th)1 and Th17 cells while simultaneously promoting Th2 cell differentiation in vitro. In addition, Bregs facilitated the development of regulatory T cells (Tregs) resulting in a possible feedback cooperation to establish immune homeostasis. Moreover, the colonization of germfree wild type mice with E. coli but not B. vulgatus significantly reduced intestinal inflammatory processes in dextran sulfate sodium (DSS)-induced colitis associated with an increase induction of immune suppressive Bregs. The quantity of Bregs directly correlated with the severity of inflammation. These findings may provide new insights and therapeutic approaches for B cell-controlled treatments of microbiota-driven autoimmune disease.

Skin-Associated B Cells in Health and Inflammation

Traditionally, the skin was believed to be devoid of B cells, and studies of the skin immune system have largely focused on other types of leukocytes. Exciting recent data show that B cells localize to the healthy skin of humans and other mammalian species with likely homeostatic functions in host defense, regulation of microbial communities, and wound healing. Distinct skin-associated B cell subsets drive or suppress cutaneous inflammatory responses with important clinical implications. Localized functions of skin-associated B cell subsets during inflammation comprise Ab production, interactions with skin T cells, tertiary lymphoid tissue formation, and production of proinflammatory cytokines but also include immunosuppression by providing IL-10. In this review, we delve into the intriguing new roles of skin-associated B cells in homeostasis and inflammation.

Decrease in the proportion of CD24hi CD38hi B cells and impairment of their regulatory capacity in type 1 diabetes patients

B10 cells restore immune balance by producing interleukin (IL)-10. Impaired B10 cell responses are related to numerous autoimmune diseases. However, the function of B10 cells in type 1 diabetes (T1D) patients is controversial. We hypothesized that there are numerical and functional defects of B10 cells in T1D. Sixty-two patients with T1D and 74 healthy volunteers were included in our study. We showed that B10 cells in human peripheral blood belong to a CD24^hi CD38^hi B cell subpopulation. CD24^hi CD38^hi B cells from healthy individuals possessed regulatory capacity, suppressed interferon (IFN)-γ, tumor necrosis factor (TNF)-α and IL-17A production and promoted IL-4 production and forkhead box protein 3 (FoxP3) expression in CD4⁺ T cells through an IL-10-dependent mechanism. Compared to healthy controls, B10 cell percentages in T1D were significantly lower (5·6 ± 3·5 versus 6·9 ± 3·3%; P < 0·05), produced less IL-10 (15·4 ± 4·3 versus 29·0 ± 4·5%; P < 0·001) and lacked regulatory capacity. In addition, Pearson's correlation analysis showed that the frequency of circulating B10 cells was negatively correlated with the frequency of CD4⁺ IFN-γ⁺ and CD4⁺ TNF-α⁺ T cells (r = -0·248 and r = -0·283, P = 0·008 and P = 0·017, respectively), positively correlating with the frequency of CD4⁺ CD25⁺ FoxP3⁺ T cells (r = 0·247, P = 0·001). These data offer direct proof that there is a deficiency of circulating CD24^hi CD38^hi B cells in peripheral blood of patients with T1D, which participate in the T1D immune imbalance involved in the development of T1D.

The Role of Microbial Translocation and Immune Activation in AIDS-Associated Non-Hodgkin Lymphoma Pathogenesis: What Have We Learned?

Human immunodeficiency virus (HIV) infection is associated with greatly increased risk for development of non-Hodgkin lymphoma (NHL). Nearly all acquired immunodeficiency syndrome (AIDS)-associated NHL (AIDS-NHL) is of B-cell origin. Two major mechanisms are believed to contribute to the genesis of AIDS-NHL: (1) loss of immunoregulation of Epstein-Barr virus (EBV)+ B cells, resulting from impaired T-cell function late in the course of HIV disease and (2) chronic B-cell activation, leading to DNA-modifying events that contribute to oncogene mutations/ translocations. HIV infection has long been known to be associated with chronic inflammation and polyclonal B-cell activation, and more recently, microbial translocation. Microbial translocation is bacterial product leakage from gut lumen into the peripheral circulation, resulting in high levels of lipopolysaccharide (LPS) in the peripheral circulation, leading to chronic immune activation and inflammation. We review recent literature linking microbial translocation to lymphom-agenesis. This includes epidemiological studies of biomarkers of microbial translocation with risk of AIDS-NHL and emerging data on the mechanisms by which microbial translocation may lead to AIDS-NHL development.

Regulatory B Cells

B cells are typically characterized by their ability to produce antibodies, function as secondary antigen-present cells, and produce various immunoregulatory cytokines. The regulatory B (Breg)-cell population is now widely accepted as an important modulatory component of the immune system that suppresses inflammation. Recent studies indicate that Breg-cell populations are small under physiological conditions but expand substantially in both human patients and murine models of chronic inflammatory diseases, autoimmune diseases, infection, transplantation, and cancer. Almost all B-cell subsets can be induced to form Breg cells. In addition, there are unique Breg-cell subsets such as B10 and Tim-1⁺ B cells. Immunoregulatory function may be mediated by production of cytokines such as IL-10 and TGF-β and ensuing suppression of T cells, by direct cell-cell interactions, and (or) by altering the immune microenvironment. In this chapter, we describe in detail the discovery of Breg cells, their phenotypes, differentiation, function, contributions to disease, and therapeutic potential.

B Cell-Mediated Autoimmune Diseases

Extensive studies have suggested a central role of B cells in the autoimmune pathogenesis, as loss of B cell tolerance results in increased serum levels of autoantibodies, enhanced effector T cell response and tissue damages. Here, we provide an overview of dysregulated B cell responses in the development of autoimmunity. In addition to their presence in the target organs, autoreactive B cells can promote the formation of ectopic lymphoid structures and differentiate into plasma cells that produce large amounts of autoantibodies and cytokines. In animal models that recapitulate the key features of human autoimmune disease, mechanistic studies have indicated two categories of autoantibodies: (1) serological markers for disease diagnosis and prognosis; (2) effector molecules that induce organ hypofunction or damage directly in an epitope-specific manner, or indirectly by activating other immune cell subsets. Moreover, B cell-derived cytokines usually promote the autoreactive T cell response during autoimmune development, but there is compelling evidence that a subpopulation of B cells negatively regulates immune responses, also known as regulatory B cells via secreting anti-inflammatory cytokines (IL-10, IL-35, etc.) or a contact-dependent fashion. Although B cell depletion could eliminate most circulating B cells in the periphery, the clinical outcomes of B cell depletion therapy for autoimmune diseases vary among individuals due to differential activation or survival signals for B cells provided by tissue microenvironment. Thus, therapeutic combinations that target immune checkpoints and B cell activation may represent a promising strategy for the effective treatment of human autoimmune diseases.

Intratumoral injection of the seasonal flu shot converts immunologically cold tumors to hot and serves as an immunotherapy for cancer

Immunotherapy has revolutionized cancer treatment, yielding unprecedented long-term responses and survival. However, a significant proportion of patients remain refractory, which correlates with the absence of immune-infiltrated (“hot”) tumors. Here, we observed that FDA-approved unadjuvanted seasonal influenza vaccines administered via intratumoral injection not only provide protection against active influenza virus lung infection, but also reduce tumor growth by increasing antitumor CD8⁺ T cells and decreasing regulatory B cells within the tumor. Ultimately, intratumoral unadjuvanted seasonal influenza vaccine converts immunologically inactive “cold” tumors to “hot,” generates systemic responses, and sensitizes resistant tumors to checkpoint blockade. Repurposing the “flu shot” may increase response rates to immunotherapy, and based on its current FDA approval and safety profile, may be quickly translated for clinical care.

Reprogramming the tumor microenvironment to increase immune-mediated responses is currently of intense interest. Patients with immune-infiltrated “hot” tumors demonstrate higher treatment response rates and improved survival. However, only the minority of tumors are hot, and a limited proportion of patients benefit from immunotherapies. Innovative approaches that make tumors hot can have immediate impact particularly if they repurpose drugs with additional cancer-unrelated benefits. The seasonal influenza vaccine is recommended for all persons over 6 mo without prohibitive contraindications, including most cancer patients. Here, we report that unadjuvanted seasonal influenza vaccination via intratumoral, but not intramuscular, injection converts “cold” tumors to hot, generates systemic CD8⁺ T cell-mediated antitumor immunity, and sensitizes resistant tumors to checkpoint blockade. Importantly, intratumoral vaccination also provides protection against subsequent active influenza virus lung infection. Surprisingly, a squalene-based adjuvanted vaccine maintains intratumoral regulatory B cells and fails to improve antitumor responses, even while protecting against active influenza virus lung infection. Adjuvant removal, B cell depletion, or IL-10 blockade recovers its antitumor effectiveness. Our findings propose that antipathogen vaccines may be utilized for both infection prevention and repurposing as a cancer immunotherapy.

Vitamin D and microbiota: Two sides of the same coin in the immunomodulatory aspects

The gut microbiota is crucial for host immune response, vitamin synthesis, short chain fatty acids (SCFAs) production, intestinal permeability, nutrient digestion energy metabolism and protection from pathogens. Therefore, gut microbiota guarantees the host's predisposition to gastrointestinal diseases. Intestinal microbiota may be damaged by environmental components with negative health conditions. Dysbiosis consisting in alteration in the gut microbiota has been involved in several disorders including inflammation, allergic reactions, autoimmune diseases, heart diseases, obesity, and metabolic syndrome and even in the state of malignant carcinogenesis existing in humans. Several epidemiological studies have shown that inadequate solar exposure results in vitamin D insufficiency/deficiency which has a strong impact on different immune responses and the occurrence of a wide range of pathological conditions. Additionally, new evidence indicates that the vitamin D pathway plays a key role in gut homeostasis. Due to the strong connection between vitamin D and microbiota, herein we focus on the new findings about intestinal bacteria-immune crosstalk and the impact of vitamin D in gut microbiota regulation, in order to offer new clarifications on their interaction. Understanding the mechanism by which vitamin D can affect the gut microbiota composition and its dynamic activities, as well as the innate and adaptive state of the immune system, is not only a fundamental research but also an opportunity to improve health status.

Tumour-associated B cells in urothelial urinary bladder cancer

Tumour infiltrating B cells and CD38⁺ plasma cells have been correlated with survival in different malignancies but their role in urinary bladder cancer is unclear. IL-10 is a multifunctional cytokine with both anti-inflammatory and immunostimulatory properties, that can be released by regulatory B cells (Bregs). We have stained paraffin-embedded tumour sections from 31 patients with invasive urothelial urinary bladder cancer with respect to CD20⁺ B cells, CD38⁺ cells, IL-10-expressing cells, IgG, C1q and C3a and analysed the impact of these markers on survival. Interestingly, we observe tumour-associated CD20⁺ B cells forming follicle-like structures in tumours of some patients. We demonstrate that follicle-like structures, tumour-associated CD38⁺ cells, IL-10 produced by non-B cells, tumour infiltrating IgG and activation of the complement system, may associate to longer survival of urinary bladder cancer patients. IL-10 expression by tumour-associated Bregs may instead negatively affect prognosis. More research is needed to fully understand the role of B cells and IL-10 in urinary bladder cancer.

Multiple Functions of B Cells in the Pathogenesis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by excessive autoantibody production and multi-organ involvement. Although the etiology of SLE still remains unclear, recent studies have characterized several pathogenic B cell subsets and regulatory B cell subsets involved in the pathogenesis of SLE. Among pathogenic B cell subsets, age-associated B cells (ABCs) are a newly identified subset of autoreactive B cells with T-bet-dependent transcriptional programs and unique functional features in SLE. Accumulation of T-bet+ CD11c+ ABCs has been observed in SLE patients and lupus mouse models. In addition, innate-like B cells with the autoreactive B cell receptor (BCR) expression and long-lived plasma cells with persistent autoantibody production contribute to the development of SLE. Moreover, several regulatory B cell subsets with immune suppressive functions have been identified, while the impaired inhibitory effects of regulatory B cells have been indicated in SLE. Thus, further elucidation on the functional features of B cell subsets will provide new insights in understanding lupus pathogenesis and lead to novel therapeutic interventions in the treatment of SLE.

Immunotherapeutic maintenance treatment with toll-like receptor 9 agonist lefitolimod in patients with extensive-stage small-cell lung cancer: results from the exploratory, controlled, randomized, international phase II IMPULSE study

Background

The immune surveillance reactivator lefitolimod (MGN1703), a DNA-based TLR9 agonist, might foster innate and adaptive immune response and thus improve immune-mediated control of residual cancer disease. The IMPULSE phase II study evaluated the efficacy and safety of lefitolimod as maintenance treatment in extensive-stage small-cell lung cancer (ES-SCLC) after objective response to first-line chemotherapy, an indication with a high unmet medical need and stagnant treatment improvement in the last decades.

Patients and methods

103 patients with ES-SCLC and objective tumor response (as per RECIST 1.1) following four cycles of platinum-based first-line induction therapy were randomized to receive either lefitolimod maintenance therapy or local standard of care at a ratio of 3 : 2 until progression or unacceptable toxicity.

Results

From 103 patients enrolled, 62 were randomized to lefitolimod, 41 to the control arm. Patient demographics and response patterns to first-line therapy were balanced. Lefitolimod exhibited a favorable safety profile and pharmacodynamic assessment confirmed the mode-of-action showing a clear activation of monocytes and production of interferon-gamma-induced protein 10 (IP-10). While in the intent-to-treat (ITT) population no relevant effect of lefitolimod on progression-free and overall survival (OS) could be observed, two predefined patient subgroups indicated promising results, favoring lefitolimod with respect to OS: in patients with a low frequency of activated CD86⁺ B cells (hazard ratio, HR 0.53, 95% CI: 0.26–1.08; n = 38 of 88 analyzed) and in patients with reported chronic obstructive pulmonary disease (COPD) (HR 0.48, 95% CI: 0.20–1.17, n = 25 of 103).

Conclusions

The IMPULSE study showed no relevant effect of lefitolimod on the main efficacy end point OS in the ITT, but (1) the expected pharmacodynamic response to lefitolimod, (2) positive OS efficacy signals in two predefined subgroups and (3) a favorable safety profile. These data support further exploration of lefitolimod in SCLC.

B cell targeted therapies in autoimmune disease

PURPOSE OF REVIEW

FDA-approved B cell-targeted therapy has expanded to a multitude of autoimmune diseases ranging from organ specific diseases, like pemphigus and multiple sclerosis, to systemic diseases such as ANCA-associated vasculitis, rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). In this review, we discuss the variability in response to B cell-targeted therapies with a focus on the diversity of human B cells and plasma cells, and will discuss several of the promising new B cell-targeted therapies.

RECENT FINDING

The pathogenic roles for B cells include autoantibody-dependent and autoantibody-independent functions whose importance may vary across diseases or even in subsets of patients with the same disease. Recent data have further demonstrated the diversity of human B cell subsets that contribute to disease as well as novel pathways of B cell activation in autoimmune disease. The importance of eliminating autoreactive B cells and plasma cells will be discussed, as well as new approaches to do so.

SUMMARY

The past several years has witnessed significant advances in our knowledge of human B cell subsets and function. This has created a nuanced picture of the diverse ways B cells contribute to autoimmunity and an ever-expanding armamentarium of B cell-targeted therapies.

Memory B Cells and Long-lived Plasma Cells

The importance of B cell and antibody-mediated immune response in the acute and long-term persistence of transplanted solid organs has become increasingly evident in recent years. A variety of therapeutic innovations target antibodies directed toward HLA or blood groups (ABO) to allow better allocation and posttransplant longevity of organs. Antibodies originate from plasma cells (PCs), which are terminally differentiated B cells. Long-term production and persistence of these antibodies is partly due to fast reactivation of previously generated memory B cells; however, there is increasing evidence that some differentiated PCs can persist independently in the bone marrow for years or even decades, producing specific antibodies or even experiencing regeneration without proliferation without need to be replaced by newly differentiating B cells. This review outlines the currently presumed pathways of differentiation, antibody, and memory generation on both B-cell and PC levels. On this background, current therapeutic concepts for antibody reduction before and after solid organ transplantation are considered, to better understand their mechanisms, possible synergisms, and specific risks. Specific differences in regards to ABO versus HLA antibodies as well as practical relevance for generation of desensitization and posttransplant antibody-directed therapy protocols are discussed.

Il-10 producing T and B cells in allergy

The molecular and cellular mechanisms of allergen tolerance in humans have been intensively studied in the past few decades. The demonstration of epitope-specific T cell tolerance, particularly mediated by the immune suppressor functions of IL-10 led to a major conceptual change in this area more than 20 years ago. Currently, the known essential components of allergen tolerance include the induction of allergen-specific regulatory of T and B cells, the immune suppressive function of secreted factors, such as IL-10, IL-35, IL-1 receptor antagonist and TGF-β, immune suppressive functions of surface molecules such as CTLA-4 and PD-1, the production IgG4 isotype allergen-specific blocking antibodies, and decreased allergic inflammatory responses by mast cells, basophils, and eosinophils in inflamed tissues. In this review, we explain the importance of the role of IL-10 in allergen tolerance.

Intratumoral immunoglobulin isotypes predict survival in lung adenocarcinoma subtypes

BACKGROUND

The role of tumor-infiltrating B-cells (TIBs) and intratumorally-produced antibodies in cancer-immunity interactions essentially remains terra incognita. In particular, it remains unexplored how driver mutations could be associated with distinct TIBs signatures and their role in tumor microenvironment.

METHODS

Here we analyzed associations of immunoglobulin isotypes and clonality with survival in TCGA RNA-Seq data for lung adenocarcinoma (LUAD), stratifying patients into 12 driver mutation and phenotypic tumor subgroups.

RESULTS

We revealed several unexpected associations between TIBs behavior and prognosis. Abundance and high proportion of IgG1 isotype, and low proportion of IgA among all intratumorally produced immunoglobulins were specifically associated with improved overall survival for KRAS^mut but not KRAS^wt LUAD, revealing the first link between a driver mutation and B-cell response. We found specific IgG1 signature associated with long survival, which suggests that particular specificities of IgG1+ TIBs could be beneficial in KRAS^mut LUAD. In contrast to our previous observations for melanoma, highly clonal IgG1 production by plasma cells had no meaningful effect on prognosis, suggesting that IgG1+ TIBs may exert a beneficial effect in KRAS^mut cases in an alternative way, such as efficient presentation of cognate antigens or direct B cell attack on tumor cells. Notably, a high proportion of the IgG1 isotype is positively correlated with the non-silent mutation burden both in the general LUAD cohort and in most patient subgroups, supporting a role for IgG1⁺ TIBs in antigen presentation. Complementing the recent finding that the presence of stromal IgG4-producing cells is associated with a favorable prognosis for patients with stage I squamous cell carcinoma, we show that the abundance of IgG4-producing TIBs likewise has a strong positive effect on overall survival in STK11^mut and proximal proliferative subgroups of LUAD patients. We hypothesize that the positive role of IgG4 antibodies in some of the lung cancer subtypes could be associated with reported inability of IgG4 isotype to form immune complexes, thus preventing immunosuppression via activation of the myeloid-derived suppressor cell (MDSC) phenotype.

CONCLUSIONS

We discover prominent and distinct associations between TIBs antibody isotypes and survival in lung adenocarcinoma carrying specific driver mutations. These findings indicate that particular types of tumor-immunity relations could be beneficial in particular driver mutation context, which should be taken into account in developing strategies of cancer immunotherapy and combination therapies. Specificity of protective B cell populations in specific cancer subgroups could become a clue to efficient targeted immunotherapies for appropriate cohorts of patients.

Challenges and Opportunities for Consistent Classification of Human B Cell and Plasma Cell Populations

The increasingly recognized role of different types of B cells and plasma cells in protective and pathogenic immune responses combined with technological advances have generated a plethora of information regarding the heterogeneity of this human immune compartment. Unfortunately, the lack of a consistent classification of human B cells also creates significant imprecision on the adjudication of different phenotypes to well-defined populations. Additional confusion in the field stems from: the use of non-discriminatory, overlapping markers to define some populations, the extrapolation of mouse concepts to humans, and the assignation of functional significance to populations often defined by insufficient surface markers. In this review, we shall discuss the current understanding of human B cell heterogeneity and define major parental populations and associated subsets while discussing their functional significance. We shall also identify current challenges and opportunities. It stands to reason that a unified approach will not only permit comparison of separate studies but also improve our ability to define deviations from normative values and to create a clean framework for the identification, functional significance, and disease association with new populations.

NR4A Expression by Human Marginal Zone B-Cells

We have previously characterized a human blood CD19⁺CD1c⁺IgM⁺CD27⁺CD21^loCD10⁺ innate-like B-cell population, which presents features shared by both transitional immature and marginal zone (MZ) B-cells, named herein “precursor-like” MZ B-cells. B-cells with similar attributes have been associated with regulatory potential (Breg). In order to clarify this issue and better characterize this population, we have proceeded to RNA-Seq transcriptome profiling of mature MZ and precursor-like MZ B-cells taken from the blood of healthy donors. We report that ex vivo mature MZ and precursor-like MZ B-cells express transcripts for the immunoregulatory marker CD83 and nuclear receptors NR4A1, 2, and 3, known to be associated with T-cell regulatory (Treg) maintenance and function. Breg associated markers such as CD39 and CD73 were also expressed by both populations. We also show that human blood and tonsillar precursor-like MZ B-cells were the main B-cell population to express elevated levels of CD83 and NR4A1-3 proteins ex vivo and without stimulation. Sorted tonsillar precursor-like MZ B-cells exerted regulatory activity on autologous activated CD4⁺ T-cells, and this was affected by a CD83 blocking reagent. We believe these observations shed light on the Breg potential of MZ populations, and identify NR4A1-3 as potential Breg markers, which as for Tregs, may be involved in stabilization of a regulatory status. Since expression and activity of these molecules can be modulated therapeutically, our findings may be useful in strategies aiming at modulation of Breg responses.

Rebalancing Immune Homeostasis to Treat Autoimmune Diseases

During homeostasis, interactions between tolerogenic dendritic cells (DCs), self-reactive T cells, and T regulatory cells (Tregs) contribute to maintaining mammalian immune tolerance. In response to infection, immunogenic DCs promote the generation of proinflammatory effector T cell subsets. When complex homeostatic mechanisms maintaining the balance between regulatory and effector functions become impaired, autoimmune diseases can develop. We discuss some of the newest advances on the mechanisms of physiopathologic homeostasis that can be employed to develop strategies to restore a dysregulated immune equilibrium. Some of these designs are based on selectively activating regulators of immunity and inflammation instead of broadly suppressing these processes. Promising approaches include the use of nanoparticles (NPs) to restore Treg control over self-reactive cells, aiming to achieve long-term disease remission, and potentially to prevent autoimmunity in susceptible individuals.

Regulatory B cells and transplantation: almost prime time?

PURPOSE OF REVIEW

Regulatory B cells (Bregs) are potent inhibitors of the immune system with the capacity to suppress autoimmune and alloimmune responses. Murine transplant models showing that Bregs can promote allograft tolerance are now supported by clinical data showing that patients who develop operational tolerance have higher frequency of Bregs. Breg function has been widely studied resulting in improved understanding of their biology and effector mechanisms. However, our overall understanding of Bregs remains poor due the lack of specific marker, limited knowledge of how and where they act in vivo, and whether different Breg subpopulations exhibit different functions.

RECENT FINDINGS

In this review we detail murine and human phenotypic markers used to identify Bregs, their induction, maintenance, and mechanisms of immune suppression. We highlight recent advances in the field including their use as biomarkers to predict allograft rejection, in-vitro expansion of Bregs, and the effects of commonly used immunosuppressive drugs on their induction and frequency.

SUMMARY

Clinical data continue to emerge in support of Bregs playing an important role in preventing transplant rejection. Hence, it is necessary for the transplant field to better comprehend the mechanisms of Breg induction and approaches to preserve or even enhance their activity to improve long-term transplant outcomes.

Myeloid-Derived Suppressive Cells Promote B cell-Mediated Immunosuppression via Transfer of PD-L1 in Glioblastoma

The potent immunosuppression induced by glioblastoma (GBM) is one of the primary obstacles to finding effective immunotherapies. One hallmark of the GBM-associated immunosuppressive landscape is the massive infiltration of myeloid-derived suppressor cells (MDSC) and, to a lesser extent, regulatory T cells (Treg) within the tumor microenvironment. Here, we showed that regulatory B cells (Breg) are a prominent feature of the GBM microenvironment in both preclinical models and clinical samples. Forty percent of GBM patients (n = 60) scored positive for B-cell tumor infiltration. Human and mouse GBM-associated Bregs were characterized by immunosuppressive activity toward activated CD8⁺ T cells, the overexpression of inhibitory molecules PD-L1 and CD155, and production of immunosuppressive cytokines TGFβ and IL10. Local delivery of B cell-depleting anti-CD20 immunotherapy improved overall survival of animals (IgG vs. anti-CD20 mean survival: 18.5 vs. 33 days, P = 0.0001), suggesting a potential role of Bregs in GBM progression. We unveiled that GBM-associated MDSCs promoted regulatory B-cell function by delivering microvesicles transporting membrane-bound PD-L1, able to be up-taken by tumoral B cells. The transfer of functional PD-L1 via microvesicles conferred Bregs the potential to suppress CD8⁺ T-cell activation and acquisition of an effector phenotype. This work uncovered the role of B cells in GBM physiopathology and provides a mechanism by which the GBM microenvironment controls B cell-mediated immunosuppression.See related Spotlight on p. 1902.

B cells sustain inflammation and predict response to immune checkpoint blockade in human melanoma

Tumor associated inflammation predicts response to immune checkpoint blockade in human melanoma. Current theories on regulation of inflammation center on anti-tumor T cell responses. Here we show that tumor associated B cells are vital to melanoma associated inflammation. Human B cells express pro- and anti-inflammatory factors and differentiate into plasmablast-like cells when exposed to autologous melanoma secretomes in vitro. This plasmablast-like phenotype can be reconciled in human melanomas where plasmablast-like cells also express T cell-recruiting chemokines CCL3, CCL4, CCL5. Depletion of B cells in melanoma patients by anti-CD20 immunotherapy decreases tumor associated inflammation and CD8+ T cell numbers. Plasmablast-like cells also increase PD-1+ T cell activation through anti-PD-1 blockade in vitro and their frequency in pretherapy melanomas predicts response and survival to immune checkpoint blockade. Tumor associated B cells therefore orchestrate and sustain melanoma inflammation and may represent a predictor for survival and response to immune checkpoint blockade therapy.

CD24hiCD38hi and CD24hiCD27+ Human Regulatory B Cells Display Common and Distinct Functional Characteristics

Although IL-10-producing regulatory B cells (Bregs) play important roles in immune regulation, their surface phenotypes and functional characteristics have not been fully investigated. In this study, we report that the frequency of IL-10-producing Bregs in human peripheral blood, spleens, and tonsils is similar, but they display heterogenous surface phenotypes. Nonetheless, CD24^hiCD38^hi transitional B cells (TBs) and CD24^hiCD27⁺ B cells (human equivalent of murine B10 cells) are the major IL-10-producing B cells. They both suppress CD4⁺ T cell proliferation as well as IFN-γ/IL-17 expression. However, CD24^hiCD27⁺ B cells were more efficient than TBs at suppressing CD4⁺ T cell proliferation and IFN-γ/IL-17 expression, whereas they both coexpress IL-10 and TNF-α. TGF-β1 and granzyme B expression were also enriched within CD24^hiCD27⁺ B cells, when compared with TBs. Additionally, CD24^hiCD27⁺ B cells expressed increased levels of surface integrins (CD11a, CD11b, α1, α4, and β1) and CD39 (an ecto-ATPase), suggesting that the in vivo mechanisms of action of the two Breg subsets are not the same. Lastly, we also report that liver allograft recipients with plasma cell hepatitis had significant decreases of both Breg subsets.

Nasal instillation of probiotic extracts inhibits experimental allergic rhinitis

Aim: Allergic rhinitis (AR) is a common disease. The therapeutic efficacy of AR needs to be improved. This study aims to evaluate the effects of local administration of probiotic extracts on inhibiting experimental AR. Methods: Epithelial cells (ECs) were primed by exposing to Clostridium butyricum extracts (CBe) in the culture to upregulate the expression of IL-10. A mouse AR model was developed to assess the therapeutic potential of CBe in AR. Results: CBe markedly induced the expression of IL-10 in ECs. Co-culture of naive B cells with CBe-primed ECs significantly increased IL-10 expression in the B cells (iB10 cells). The iB10 cells showed immune suppressive function in suppressing effector CD4⁺ T-cell proliferation. Treatment with nasal drops containing CBe efficiently inhibited experimental AR in mice. Conclusion: Local administration of CBe can efficiently inhibit experimental AR.

Phenotypic identification of CD19+CD5+CD1d+ regulatory B cells that produce interleukin 10 and transforming growth factor β1 in human peripheral blood

INTRODUCTION

Regulatory B cells (Bregs), a novel subpopulation of B cells, are a significant area of research due to their immune regulatory function in the immunological response. Bregs have been reported to regulate acute inflammation and immunity through the production of anti-inflammatory cytokines.

MATERIAL AND METHODS

A B cell subpopulation was identified using flow cytometric analysis in two different processes: 1) after preparation and storage of peripheral blood mononuclear cells (PBMCs) using Ficoll density gradient centrifugation from a human blood sample, 2) followed by isolation and storage of B cells through magnetic separation using a B cell isolation kit and MS column. ELISA assays were performed to observe the cytokine production of interkleukin 10 (IL-10) and transforming growth factor β₁ (TGF-β₁) by this novel B cell subpopulation.

RESULTS

Double positive staining of CD5+CD1d+ Bregs represents (19.27 ±1.52) from PBMCs, (33.32 ±2.95) from B cells accordingly (n = 40). Through ELISA assays, it has been found that B cell subpopulation produces IL-10 (0.56 ±0.08) and TGF-β₁ (0.90 ±0.12) (n = 40).

CONCLUSIONS

These methods should be able to facilitate progress in research on Bregs through the following steps: 1) the regulatory role may be observed in comparison with particular autoimmune diseases, inflammation, cancer, and immunologic responses to find out whether Breg alteration and/or cytokine production is altered as well in these disorders or conditions. 2) If the alteration of Bregs and cytokine production is significant along with the clinical correlation, a further in vitro study can be initiated with exposure of certain drugs to overcome the alteration of the cytokine production; then, an in vivo study can be initiated.

Potential role of regulatory B cells in immunological diseases

Regulatory B cells (Bregs) are immune-modulating cells that affect the immune system by producing cytokines or cellular interactions. These cells have immunomodulatory effects on the immune system by cytokine production. The abnormalities in Bregs could be involved in various disorders such as autoimmunity, chronic infectious disease, malignancies, allergies, and primary immunodeficiencies are immune-related scenarios. Ongoing investigation could disclose the biology and the exact phenotype of these cells and also the assigned mechanisms of action of each subset, as a result, potential therapeutic strategies for treating immune-related anomalies. In this review, we collect the findings of human and mouse Bregs and the therapeutic efforts to change the pathogenicity of these cells in diverse disease.

Paradoxical role of Breg-inducing cytokines in autoimmune diseases

Regulatory B cells (Breg) are crucial immunoregulators that maintain peripheral tolerance and suppress inflammatory autoimmune responses. In recent years, our understanding on the nature and mechanism of action of Bregs has revealed the important role of cytokines in promoting the regulatory properties of this unique B cell subset, both in animal and human models. In this review, we compiled the cytokines that have been reported by multiple studies to induce the expansion of Breg. The Breg-inducing cytokines which are currently known include IL-21, IL-6, IL1β, IFNα, IL-33, IL-35, BAFF and APRIL. As cytokines are also known to play a pivotal role in the pathogenesis of autoimmune diseases, in parallel we reviewed the pattern of expression of the Breg-inducing cytokines in Systemic Lupus Erythematosus (SLE), Rheumatoid Arthritis (RA), Inflammatory Bowel Diseases (IBD) and Multiple Sclerosis (MS). We show here that Breg-inducing cytokines are commonly implicated in these inflammatory diseases where they typically have a higher expression than in healthy individuals, suggesting their paradoxical nature. Interestingly, despite the general overexpression of Breg-inducing cytokines, it is known that Breg cells are often numerically or functionally impaired in various autoimmune conditions. Considering these alterations, we explored the possible parameters that may influence the function of Breg-inducing cytokines in exhibiting either their regulatory or pro-inflammatory properties in the context of autoimmune conditions.

Pregnancy and lactation interfere with the response of autoimmunity to modulation of gut microbiota

BACKGROUND

Dysbiosis of gut microbiota exists in the pathogenesis of many autoimmune diseases, including systemic lupus erythematosus (lupus). Lupus patients who experienced pregnancy usually had more severe disease flares post-delivery. However, the possible role of gut microbiota in the link between pregnancy and exacerbation of lupus remains to be explored.

RESULTS

In the classical lupus mouse model MRL/lpr, we compared the structures of gut microbiota in pregnant and lactating individuals vs. age-matched naïve mice. Consistent with studies on non-lupus mice, both pregnancy and lactation significantly changed the composition and diversity of gut microbiota. Strikingly, modulation of gut microbiota using the same strategy resulted in different disease outcomes in postpartum (abbreviated as "PP," meaning that the mice had undergone pregnancy and lactation) vs. control (naïve; i.e., without pregnancy or lactation) MRL/lpr females; while vancomycin treatment attenuated lupus in naïve mice, it did not do so, or even exacerbated lupus, in PP mice. Lactobacillus animalis flourished in the gut upon vancomycin treatment, and direct administration of L. animalis via oral gavage recapitulated the differential effects of vancomycin in PP vs. control mice. An enzyme called indoleamine 2,3-dioxygenase was significantly inhibited by L. animalis; however, this inhibition was only apparent in PP mice, which explained, at least partially, the lack of beneficial response to vancomycin in these mice. The differential production of immunosuppressive IL-10 and proinflammatory IFNγ in PP vs. control mice further explained why the disease phenotypes varied between the two types of mice bearing the same gut microbiota remodeling strategy.

CONCLUSIONS

These results suggest that pregnancy and lactation interfere with the response of autoimmunity to modulation of gut microbiota. Further studies are necessary to better understand the complex relationship between pregnancy and lupus.

Dual immune functions of IL-33 in inflammatory bowel disease

Interleukin-33 (IL-33) has emerged as a critical regulator in a variety of diseases, including inflammatory bowel disease (IBD). IL-33 can be produced by various tissues and cells, and typically induces Th2-type immune responses via binding to the receptor ST2. In addition, accumulated data have shown that IL-33 also plays a modulatory role in the function of regulatory T cells (Tregs), B cells, and innate immune cells such as macrophages and innate lymphoid cells (ILCs). IBD, including Crohn's disease and ulcerative colitis, are characterized by aberrant immunological responses leading to intestinal tissue injury and destruction. Although IL-33 expression is increased in IBD patients and correlates with the patients' disease activity index, mechanistic studies to date have demonstrated both pathogenic and protective roles in animal models of experimental colitis. In this review, we will summarize the roles and mechanisms of IL-33 in IBD, which is essential to understand the pathogenesis of IBD and determine potential therapies.

Phenotypic and functional alterations of regulatory B cell subsets in adult allergic asthma patients

BACKGROUND

IL-10-producing regulatory B cells (Bregs) are widely ascribed immune regulatory functions. However, Breg subsets in human asthma have not been fully investigated.

OBJECTIVE

We studied Breg subsets in adult allergic asthma patients by assessing two major parameters, frequency and IL-10 expression. We then investigated factors that affect these two parameters in patients.

METHODS

Peripheral blood mononuclear cells (PBMCs) of adult allergic asthma patients (N = 26) and non-asthmatic controls (N = 28) were used to assess the frequency of five subsets of transitional B cells (TBs), three subsets of CD24^high CD27⁺ B cells and B1 cells. In addition to clinical data, IL-10 expression by individual Breg subsets was assessed by flow cytometry.

RESULTS

Asthma patients had decreases of CD5⁺ and CD1d⁺ CD5⁺ , but an increase of CD27⁺ TBs which was significant in patients with moderate asthma (60 < FEV1 < 80). Regardless of asthma severity, there was no significant alteration in the frequencies of 6 other Breg subsets tested. However, we found that oral corticosteroid (OCS) significantly affected the frequency of Bregs in Breg subset-specific manners. OCS decreased CD5⁺ and CD1d⁺ CD5⁺ TBs, but increased CD27⁺ TBs and CD10⁺ CD24^high CD27⁺ cells. Furthermore, OCS decreased IL-10 expression by CD27⁺ TBs, all 3 CD24^high CD27⁺ B cell subsets (CD5⁺ , CD10⁺ and CD1d⁺ ) and B1 cells. OCS-mediated inhibition of IL-10 expression was not observed in the other Breg subsets tested.

CONCLUSION & CLINICAL RELEVANCE

Alterations in the frequency of Bregs and their ability to express IL-10 are Breg subset-specific. OCS treatment significantly affects the frequency as well as their ability to express IL-10 in Breg subset-specific manners.

Low Serum Interleukin-10 Is an Independent Predictive Factor for the Risk of Second Event in Clinically Isolated Syndromes

Objective: To evaluated the prognostic ability of several serum cytokines in clinically isolated syndrome (CIS) patients regarding second events and conversion to multiple sclerosis (MS) or neuromyelitis optica spectrum disorder (NMOSD). Methods: We enrolled 69 CIS patients whose serum samples were collected during the acute phase of the first onset before immunotherapy. Fifteen other non-inflammatory neurological disorder (OND) patients were also included. The serum levels of interleukin (IL)-2, IL-4, IL-6, IL-10, IL-13, IL-17A, IL-21, IL-23, interferon-γ (IFN-γ), and transforming growth factor beta 1 (TGF-β1) were measured using the human cytokine multiplex assay or ELISA. Patients were seen every 3-6 months. Unscheduled visits occur in case of exacerbations. Clinical measures of disease progression were recorded. Results: Twenty CIS cases had second events during follow-up at a mean time of 15.3 ± 9.9 months. Serum IL-10 levels were significantly lower in CIS patients who relapsed compared to patients who did not. Low serum IL-10 levels were associated with higher risk and shorter times to second events. In clinical correlations, a significantly higher CSF white blood cells count, number of T2 lesions, and gadolinium-enhancing (Gd+) lesions in baseline MRI were found in the low serum IL-10 level group. Of the 20 relapsed cases, seven converted to MS, and eight converted to NMOSD. No significant differences were found in any cytokine levels between these patients at first onset. Conclusions: These findings support using serum IL-10 as a biomarker associated with the risk of relapse and the time to second events in patients with CIS. However, serum cytokine levels can not differentiate between the conversion from CIS to MS or NMOSD.

Non-canonical B cell functions in transplantation

B cells are differentiated to recognize antigen and respond by producing antibodies. These activities, governed by recognition of ancillary signals, defend the individual against microorganisms and the products of microorganisms and constitute the canonical function of B cells. Despite the unique differentiation (e.g. recombination and mutation of immunoglobulin gene segments) toward this canonical function, B cells can provide other, "non-canonical" functions, such as facilitating of lymphoid organogenesis and remodeling and fashioning T cell repertoires and modifying T cell responses. Some non-canonical functions are exerted by antibodies, but most are mediated by other products and/or direct actions of B cells. The diverse set of non-canonical functions makes the B cell as much as any cell a central organizer of innate and adaptive immunity. However, the diverse products and actions also confound efforts to weigh the importance of individual non-canonical B cell functions. Here we shall describe the non-canonical functions of B cells and offer our perspective on how those functions converge in the development and governance of immunity, particularly immunity to transplants, and hurdles to advancing understanding of B cell functions in transplantation.