Defect in regulatory B-cell function and development of systemic autoimmunity in T-cell Ig mucin 1 (Tim-1) mucin domain-mutant mice

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.

CD27+TIM-1+ memory B cells promoted the development of Foxp3+ Tregs and were associated with better survival in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a rapid onset life-threatening condition involving uncontrolled propagation of inflammatory responses. Here, we observed that ARDS patients that survived presented significantly higher frequencies of TIM-1⁺ B cells, especially the CD27⁺TIM-1⁺ B cells, than the ARDS patients who succumbed to the condition. We then found that using BCR/CD40 antigen-dependent stimulation or Staphylococcus aureus Cowan (SAC) antigen-independent stimulation, TIM-1⁺ B cells presented significantly higher IL-10 secretion and/or TGF-β1 secretion, with SAC stimulation being more effective. CD4⁺ T cells that incubated with TIM-1⁺ B cells presented significantly elevated IL-10 secretion, TGF-β1 secretion, and Foxp3 expression, than CD4⁺ T cells that incubated with TIM-1^- B cells, suggesting TIM-1⁺ B cells promoted the in vitro development of Foxp3⁺ Treg cells. Interestingly, this TIM-1⁺ B cell-mediated promotion of Foxp3 expression was mostly dependent on TGF-β1 but not IL-10, since neutralization of TGF-β1, but not IL-10, resulted in the suppression of Foxp3 expression. We further showed that in TIM-1⁺ B cells, the CD27⁺ classical memory B cell subset demonstrated more regulatory potency than the CD27^- subset. Together, our results suggested that the TIM-1⁺ B cells, especially those that expressed CD27, could promote Foxp3 expression. Their clinical efficacy in treating ARDS should be examined in in vivo experiments.

Association of interleukin-27 gene polymorphisms with susceptibility to HIV infection and disease progression

Interleukin‐27 (IL‐27) gene polymorphisms are linked to infectious disease susceptibility and IL‐27 plasma level is associated with HIV infection. Therefore, we aimed to investigate the association between IL‐27 polymorphisms and susceptibility to HIV infection and disease progression. A total of 300 patients with HIV infection (48 long‐term nonprogressors and 252 typical progressors) and 300 healthy controls were genotyped for three IL‐27 polymorphisms, rs17855750, rs181206, rs40837 which were performed by using multiple single nucleotide primer extension technique. Significant association was found between IL‐27 rs40837 polymorphisms with susceptibility to HIV infection (AG vs AA: adjusted OR = 1.60, 95% CI, 1.11‐2.30, P = 0.012; AG+GG vs AA: adjusted OR = 1.44, 95% CI, 1.02‐2.03, P = 0.038) and disease progression (LTNP: AG vs AA: adjusted OR = 2.33, 95% CI, 1.13‐4.80, P = 0.021; TP: AG vs AA: adjusted OR = 1.50, 95% CI, 1.04‐2.24, P = 0.030). Serum IL‐27 levels were significantly lower in cases compared to controls (P < 0.001). There were lower serum IL‐27 levels in TPs than in LTNPs (P < 0.001). We further found that LTNPs with rs40837 AG or GG genotype had lower serum IL‐27 levels than with AA genotype (P < 0.05). The CD4⁺T counts in cases were significantly lower than controls (P < 0.001). In contrast, individuals with rs40837 AG genotype had lower CD4⁺T counts than with AA genotype in cases (P < 0.05). In addition, CD4⁺T counts in TPs were significantly lower than LTNPs (P < 0.001). IL‐27 rs40837 polymorphism might influence the susceptibility to HIV infection and disease progression probably by regulating the level of serum IL‐27 or the quantity of CD4⁺T.

Merkel cell polyomavirus-specific immune responses in patients with Merkel cell carcinoma receiving anti-PD-1 therapy

BACKGROUND

Merkel cell carcinoma (MCC) is an aggressive skin cancer that frequently responds to anti-PD-1 therapy. MCC is associated with sun exposure and, in 80% of cases, Merkel cell polyomavirus (MCPyV). MCPyV-specific T and B cell responses provide a unique opportunity to study cancer-specific immunity throughout PD-1 blockade therapy.

METHODS

Immune responses were assessed in patients (n = 26) with advanced MCC receiving pembrolizumab. Peripheral blood mononuclear cells (PBMC) were collected at baseline and throughout treatment. MCPyV-oncoprotein antibodies were quantified and T cells were assessed for MCPyV-specificity via tetramer staining and/or cytokine secretion. Pre-treatment tumor biopsies were analyzed for T cell receptor clonality.

RESULTS

MCPyV oncoprotein antibodies were detectable in 15 of 17 (88%) of virus-positive MCC (VP-MCC) patients. Antibodies decreased in 10 of 11 (91%) patients with responding tumors. Virus-specific T cells decreased over time in patients who had a complete response, and increased in patients who had persistent disease. Tumors that were MCPyV(+) had a strikingly more clonal (less diverse) intratumoral TCR repertoire than virus-negative tumors (p = 0.0001).

CONCLUSIONS

Cancer-specific T and B cell responses generally track with disease burden during PD-1 blockade, in proportion to presence of antigen. Intratumoral TCR clonality was significantly greater in VP-MCC than VN-MCC tumors, suggesting expansion of a limited number of dominant clones in response to fewer immunogenic MCPyV antigens. In contrast, VN-MCC tumors had lower clonality, suggesting a diverse T cell response to numerous neoantigens. These findings reveal differences in tumor-specific immunity for VP-MCC and VN-MCC, both of which often respond to anti-PD-1 therapy.

Association Between C1q, TRAIL, and Tim-1 Gene Polymorphisms and Systemic Lupus Erythematosus

AIM

The present study was designed to examine the relationship between gene polymorphisms of C1q, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), T cell immunoglobulin mucin (Tim-1), and systemic lupus erythematosus (SLE).

MATERIALS AND METHODS

A total of 245 SLE patients were selected from February 2012 to August 2016, along with 245 healthy donors as the control group. Genomic DNA was extracted from peripheral blood samples from all subjects followed by mutational analyses. Gene polymorphisms of the C1q gene (rs292001, rs631090, rs294223 loci); the TRAIL gene (1525A/G, 1588A/G, 1595T/C locus); and the Tim-1 gene were detected by sequencing after polymerase chain reaction amplification. The concentration of anti-C1q antibody and the protein levels of sTRAIL/Tim-1 in serum of all subjects were measured by enzyme-linked immunosorbent assay.

RESULTS

As for the C1q gene, the frequency of the T allele at the rs631090 locus in the study group was lower than that in the controls, and the frequency of the C allele was higher in the study group than in the healthy donors. The frequency of the G allele at the 1525A/G locus of TRAIL gene in the study group was significantly higher than those in the control group. The frequency of the G allele at -1454G/A of Tim-1 was dramatically higher in the study group than in the control group. Anti-C1q antibody concentrations of subjects carrying CC and CT genotype at the rs631090 locus were statistically higher than TT genotype carriers. The sTRAIL protein level of the TRAIL 1525A/G GG genotype carriers was significantly higher than that of GA and AA genotype carriers, as well as CC genotype carriers at 1595T/C site compared with CT/TT genotype carriers. GG genotype carriers at -1454G/A had higher Tim-1 expression levels than GA/AA genotype carriers.

CONCLUSION

The C allele at the rs631090 locus of C1q, the G allele at 1525A/G site of TRAIL, and the G allele of Tim-1 at -1454G/A site are susceptibility variants associated with SLE.

Kidney injury molecule-1 identifies antemortem injury in postmortem adult and fetal kidney

There is currently no technique to unambiguously diagnose antemortem kidney injury on postmortem examination since postmortem tissue damage and autolysis are common. We assessed the ability to detect kidney injury molecule-1 (KIM-1) expression in adult and fetal kidneys examined at autopsy. In adult kidneys ( n = 52 subjects), we found that the intensity of KIM-1 staining significantly correlated with the antemortem level of serum creatinine, and this was independent of the extent of tissue autolysis. In addition, kidneys from a total of 52 fetal/neonatal subjects, 30 stillborns and 22 liveborns, were assessed for KIM-1 staining. Given that serum creatinine is unreliable and often unavailable in fetuses and newborns, we assessed preterminal hypoxia in fetuses by the presence of squames in pulmonary alveoli and by required intubation. KIM-1 expression correlated with these clinical indexes of hypoxia. The expression of KIM-1 was seen in a majority of the fetal and neonatal autopsy kidneys (77%, 40/52) as early as 16 wk of gestation, even in the presence of autolysis. Thus KIM-1 is a specific and stable marker of antemortem tubular injury in kidneys of adults and fetuses despite postmortem autolysis.

Meis1 is specifically upregulated in kidney myofibroblasts during aging and injury but is not required for kidney homeostasis or fibrotic response

The homeobox transcription factor Meis1 is required for mammalian development, and its overexpression plays a role in tumorigenesis, especially leukemia. Meis1 is known to be expressed in kidney stroma, but its function in kidney is undefined. We hypothesized that Meis1 may regulate stromal cell proliferation in kidney development and disease and tested the hypothesis using cell lineage tracing and cell-specific Meis1 deletion in development, aging, and fibrotic disease. We observed strong expression of Meis1 in platelet-derived growth factor receptor-β-positive pericytes and perivascular fibroblasts, both in adult mouse kidney and to a lesser degree in human kidney. Either bilateral ischemia-reperfusion injury or aging itself led to strong upregulation of Meis1 protein and mRNA in kidney myofibroblasts, and genetic lineage analysis confirmed that Meis1-positive cells proliferate as they differentiate into myofibroblasts after injury. Conditional deletion of Meis1 in all kidney stroma with two separate tamoxifen-inducible Cre recombinase drivers had no phenotype with the exception of consistent induction of the tubular injury marker kidney injury molecule-1 (Kim-1) only in Meis1 mutants. Further examination of Kim-1 expression revealed linkage disequilibrium of Kim-1 and Meis1, such that Meis1 mutants carried the longer BALB/c Kim-1 allele. Unexpectedly, we report that this Kim-1 allele is expressed at baseline in wild-type BALB/c mice, without any associated abnormalities, including long-term fibrosis, as predicted from the literature. We conclude that Meis1 is specifically expressed in stroma and myofibroblasts of mouse and human kidney, that it is not required for kidney development, disease, or aging, and that BALB/c mice unexpectedly express Kim-1 protein at baseline without other kidney abnormality.

Under-Evaluated or Unassessed Pathogenic Pathways in Autoimmune Hepatitis and Implications for Future Management

Autoimmune hepatitis is a consequence of perturbations in homeostatic mechanisms that maintain self-tolerance but are incompletely understood. The goals of this review are to describe key pathogenic pathways that have been under-evaluated or unassessed in autoimmune hepatitis, describe insights that may shape future therapies, and encourage investigational efforts. The T cell immunoglobulin mucin proteins constitute a family that modulates immune tolerance by limiting the survival of immune effector cells, clearing apoptotic bodies, and expanding the population of granulocytic myeloid-derived suppressor cells. Galectins influence immune cell migration, activation, proliferation, and survival, and T cell exhaustion can be induced and exploited as a possible management strategy. The programmed cell death-1 protein and its ligands comprise an antigen-independent inhibitory axis that can limit the performance of activated T cells by altering their metabolism, and epigenetic changes can silence pro-inflammatory genes or de-repress anti-inflammatory genes that affect disease severity. Changes in the intestinal microbiota and permeability of the intestinal mucosal barrier can be causative or consequential events that affect the occurrence and phenotype of immune-mediated disease, and they may help explain the female propensity for autoimmune hepatitis. Perturbations within these homeostatic mechanisms have been implicated in experimental models and limited clinical experiences, and they have been favorably manipulated by monoclonal antibodies, recombinant molecules, pharmacological agents or dietary supplements. In conclusion, pathogenic mechanisms that have been implicated in other systemic immune-mediated and liver diseases but under-evaluated or unassessed in autoimmune hepatitis warrant consideration and rigorous evaluation.

A splenic IgM memory subset with antibacterial specificities is sustained from persistent mucosal responses

Le Gallou et al. use an AID fate-mapping model to identify an IgM memory population in the spleen of unimmunized mice, originating from persistent gut immune responses and endowed with cross-reactivity against bacteria.

To what extent immune responses against the gut flora are compartmentalized within mucosal tissues in homeostatic conditions remains a much-debated issue. We describe here, based on an inducible AID fate-mapping mouse model, that systemic memory B cell subsets, including mainly IgM⁺ B cells in spleen, together with IgA⁺ plasma cells in spleen and bone marrow, are generated in mice in the absence of deliberate immunization. While the IgA component appears dependent on the gut flora, IgM memory B cells are still generated in germ-free mice, albeit to a reduced extent. Clonal relationships and renewal kinetics after anti-CD20 treatment reveal that this long-lasting splenic population is mainly sustained by output of B cell clones persisting in mucosal germinal centers. IgM-secreting hybridomas established from splenic IgM memory B cells showed reactivity against various bacterial isolates and endogenous retroviruses. Ongoing activation of B cells in gut-associated lymphoid tissues thus generates a diversified systemic compartment showing long-lasting clonal persistence and protective capacity against systemic bacterial infections.

Decreased Breg/Th17 Ratio Improved the Prognosis of Patients with Ulcerative Colitis

OBJECTIVE

To investigate the effects of regulatory B (Breg) cells and T helper 17 (Th17) cells on pathogenesis of ulcerative colitis, explore the clinical significance of Breg/Th17 ratio on the prognosis of ulcerative colitis, and provide the theoretical basis for the targeted therapy, diagnosis, and prognosis of the disease.

METHODS

Peripheral blood and colonic mucosa were collected from patients with ulcerative colitis. Hematoxylin-eosin staining was used to observe the pathological changes of colonic mucosa. Flow cytometry was utilized to analyze the percentages of Breg cells and Th17 cells. Real-time fluorescent quantitative polymerase chain reaction and immunohistochemistry were applied to determine the expression of Breg cells-related cytokines IL-10 and Th17 cell transcription factor RORγT. Enzyme-linked immunosorbent assay was employed to detect serum IL-10 and IL-17 levels.

RESULTS

The colonic mucosa of ulcerative colitis patients presented massive inflammatory cell infiltration and hemorrhagic necrosis. The number of Breg cells and Th17 cells, the gene expressions of IL-10 and RORγT, and serum levels of IL-10 and IL-17 all increased in peripheral blood. Compared with nonremission group, the remission group showed that the percentage of Breg cells reduced, the percentage of Th17 cells increased, and thus the B10/Th17 ratio was significantly decreased in peripheral blood. In addition, serum IL-10 levels diminished, IL-17 levels increased, and thus IL-10/IL-17 ratio was remarkably reduced in remission group. B10/Th17 ratio and IL-10/IL-17 ratio were positively correlated with the severity of disease.

CONCLUSIONS

Breg and Th17 cells participate in the occurrence and development of ulcerative colitis. B10/Th17 ratio and IL-10/IL-17 ratio can be used as prognostic markers for ulcerative colitis. This provides a theoretical basis for design of targeted treatment and prognosis assessment of the disease.

Galectin-1 is required for the regulatory function of B cells

Galectin-1 (Gal-1) is required for the development of B cells in the bone marrow (BM), however very little is known about the contribution of Gal-1 to the development of B cell regulatory function. Here, we report an important role for Gal-1 in the induction of B cells regulatory function. Mice deficient of Gal-1 (Gal-1^−/−) showed significant loss of Transitional-2 (T2) B cells, previously reported to include IL-10⁺ regulatory B cells. Gal-1^−/− B cells stimulated in vitro via CD40 molecules have impaired IL-10 and Tim-1 expression, the latter reported to be required for IL-10 production in regulatory B cells, and increased TNF-α expression compared to wild type (WT) B cells. Unlike their WT counterparts, T2 and T1 Gal-1^−/− B cells did not suppress TNF-α expression by CD4⁺ T cells activated in vitro with allogenic DCs (allo-DCs), nor were they suppressive in vivo, being unable to delay MHC-class I mismatched skin allograft rejection following adoptive transfer. Moreover, T cells stimulated with allo-DCs show an increase in their survival when co-cultured with Gal-1^−/− T2 and MZ B cells compared to WT T2 and MZ B cells. Collectively, these data suggest that Gal-1 contributes to the induction of B cells regulatory function.

Immune Tolerance to Apoptotic Self Is Mediated Primarily by Regulatory B1a Cells

The chronic autoimmune inflammatory diseases, systemic lupus erythematosus and Sjogren's syndrome, develop when tolerance to apoptotic cells (ACs) is lost. We have previously reported that this tolerance is maintained by innate-like, IL-10 secreting regulatory B cells. Two questions remained. First, do these regulatory B cells belong predominantly to a single subset of steady-state B cells and second, what is their specificity? We report here that innate-like B cells with markers characteristic for B1a cells (CD43+veCD19hiCD5+veIgMhiIgDlo) constitute 80% of splenic and 96% of peritoneal B cells that respond to ACs by secreting IL-10. AC responsive B1a cells secrete self-reactive natural antibodies (NAbs) and IL-10, which is augmented by toll-like receptor (TLR) 7 or TLR9 stimulation. In so doing, they both accelerate the clearance of dying cells by macrophages and inhibit their potential to mount proinflammatory immune responses. While B1a cells make prolonged contact with ACs, they do not require TIM1 or complement to mediate their regulatory function. In an animal model of neural inflammation (experimental autoimmune encephalomyelitis), just 105 activated B1a B cells was sufficient to restrain inflammation. Activated B1a B cells also induced antigen-specific T cells to secrete IL-10. Hence, regulatory B1a cells specifically recognize and augment tolerance to apoptotic self via IL-10 and NAbs; but once activated, can also prevent autoimmune mediated inflammation.

CD19+ Tim-1+ B cells are decreased and negatively correlated with disease severity in Myasthenia Gravis patients

T cell immunoglobulin mucin domain-1(Tim-1) was recently identified to be critical and essential for optimal regulatory B cells function in maintaining immune tolerance. We aimed to measure the expression levels of Tim-1 on B cells from patients with Myasthenia Gravis (MG) and to investigate whether the expression of Tim-1 is associated with pathogenesis of MG. A total of 34 patients with MG (18 generalized MG (GMG) and 16 ocular MG (OMG) and 24 healthy donors were recruited in this study. The quantitative myasthenia gravis score (QMGS) was used to evaluate the clinical severity. Real-time PCR and flow cytometry were used to measure the levels of Tim-1 expressed on peripheral B cells. Peripheral CD138+ plasma cells were assayed by flow cytometry. Serum Th17-related cytokines (IL-6, IL-1β and IL-17) and anti-AChR antibody (Ab) titers were tested by enzyme-linked immunosorbent assay (ELISA). Our data demonstrated that the mRNA and protein expression levels of B cell Tim-1 in both the GMG and OMG groups were significantly lower than those in healthy controls, with lower expression in GMG than in OMG. Tim-1 expression on B cells from OMG/GMG was negatively correlated with clinical severity, plasma cells frequency, serum Th17-related cytokines and anti-AChR Ab levels. Our results indicated that aberrant expression of Tim-1 exists on B cells and may contribute to the Th17 polarization and antibody-secreting plasma cells differentiation in MG patients.

miR-21 silencing ameliorates experimental autoimmune encephalomyelitis by promoting the differentiation of IL-10-producing B cells

IL-10-producing regulatory B (IL-10⁺ Breg) cells promote tolerance in autoimmune diseases and transplantation. However, it remains unclear whether microRNAs are involved in the development of IL-10⁺ Breg cells. Here, we found that microRNA-21 (miR-21) acts as an upstream regulator of IL-10 by targeting the 3' untranslated region of IL-10 mRNA. We also demonstrated that IL-10⁺ Breg cells exhibit lower miR-21 expression than non-Breg cells and that miR-21 acts as a potent negative regulator of the differentiation of IL-10⁺ Breg cells. Accordingly, specific inhibition of miR-21 using antisense oligonucleotides markedly promoted B cell IL-10 expression. Thus, IL-10 is a direct target of miR-21. Moreover, silencing of miR-21 significantly alleviated the severity of experimental autoimmune encephalomyelitis (EAE), and this change was associated with an increase in the number of IL-10⁺ Breg cells. Finally, we demonstrated that miR-21-silenced B cells exert their suppressive activity through effector T cells in an IL-10-dependent manner.

Thus, we characterized a B cell-intrinsic microRNA pathway that inhibits the differentiation of IL-10⁺ Breg cells and promotes autoimmunity. miR-21 silencing therefore represents a new therapeutic strategy for the treatment of autoimmune diseases.

IL-21/anti-Tim1/CD40 ligand promotes B10 activity in vitro and alleviates bone loss in experimental periodontitis in vivo

IL-10-expressing regulatory B cells (B10) play an essential role in immune system balance by suppressing excessive inflammatory responses. In this study, we investigated induction of B 10 cell's IL-10 competency in vitro and its effect on ligature-induced experimental periodontitis in vivo. Spleen B cells were isolated from C57BL/6J mice and cultured for 48h under the following conditions: control, CD40L, IL-21, anti-Tim1, CD40L+IL-21, CD40L+anti-Tim1, CD40L+IL-21+anti-Tim1. Silk ligatures were tied around both maxillary second molars of C57BL/6J mice for two weeks. Optimized combination of CD40L, IL-21 and anti-Tim1 and vehicle were injected into contralateral side of palatal gingiva on days 3, 6 and 9. The palatal gingival tissues and maxillary bone were collected on day 14 to determine expressions of IL-10 and periodontal bone resorption respectively. Our results demonstrated that IL-10 expressions of cultured spleen B cells were significantly increased in the presence of CD40L, IL-21 and anti-Tim1 combination when compared with control groups. Gingival IL-10 mRNA and protein expressions were significantly increased after injection of CD40L, IL-21 and anti-Tim1 combination, when compared to the control side. The gingival RANKL expression and periodontal bone loss were significantly decreased on the combination treatment side, as compared to the control side. These results suggest that combination of IL-21, anti-Tim1 and CD40L treatment induced B10 cell's IL-10 competency in vitro and inhibited periodontal bone loss in ligature-induced experimental periodontitis.

Immune checkpoint proteins: exploring their therapeutic potential to regulate atherosclerosis

The immune system provides a large variety of immune checkpoint proteins, which involve both costimulatory and inhibitory proteins. Costimulatory proteins can promote cell survival, cell cycle progression and differentiation to effector and memory cells, whereas inhibitory proteins terminate these processes to halt ongoing inflammation. Immune checkpoint proteins play a pivotal role in atherosclerosis by regulating the activation and proliferation of various immune and non-immune cells, such as T-cells, macrophages and platelets. Upon activation within the atherosclerotic lesions or in secondary lymphoid organs, these cells produce large amounts of pro-atherogenic cytokines that contribute to the growth and destabilization of lesions, which can result in rupture of the lesion causing acute coronary syndromes, such as a myocardial infarction. Given the presence and regulatory capacity of immune checkpoint proteins in the circulation and atherosclerotic lesions of cardiovascular patients, modulation of these proteins by, for example, the use of monoclonal antibodies, offers unique opportunities to regulate pro-inflammatory immune responses in atherosclerosis. In this review, we highlight the latest advances on the role of immune checkpoint proteins, such as OX40-OX40L, CTLA-4 and TIM proteins, in atherosclerosis and discuss their therapeutic potential as promising immunotherapies to treat or prevent cardiovascular disease.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.

What do we know about the role of regulatory B cells (Breg) during the course of infection of two major parasitic diseases, malaria and leishmaniasis?

Parasitic diseases, such as malaria and leishmaniasis, are relevant public health problems worldwide. For both diseases, the alarming number of clinical cases and deaths reported annually has justified the incentives directed to better understanding of host's factors associated with susceptibility to infection or protection. In this context, over recent years, some studies have given special attention to B lymphocytes with a regulator phenotype, known as Breg cells. Essentially important in the maintenance of immunological tolerance, especially in autoimmune disease models such as rheumatoid arthritis and experimentally induced autoimmune encephalomyelitis, the function of these lymphocytes has so far been poorly explored during the course of diseases caused by parasites. As the activation of Breg cells has been proposed as a possible therapeutic or vaccine strategy against several diseases, here we reviewed studies focused on understanding the relation of parasite and Breg cells in malaria and leishmaniasis, and the possible implications of these strategies in the course of both infections.

Schistosome-induced pulmonary B cells inhibit allergic airway inflammation and display a reduced Th2-driving function

Chronic schistosome infections protect against allergic airway inflammation (AAI) via the induction of IL-10-producing splenic regulatory B (Breg) cells. Previous experiments have demonstrated that schistosome-induced pulmonary B cells can also reduce AAI, but act independently of IL-10. We have now further characterized the phenotype and inhibitory activity of these protective pulmonary B cells. We excluded a role for regulatory T (Treg) cell induction as putative AAI-protective mechanisms. Schistosome-induced B cells showed increased CD86 expression and reduced cytokine expression in response to Toll-like receptor (TLR) ligands compared with control B cells. To investigate the consequences for T cell activation we cultured ovalbumin (OVA)-pulsed, schistosome-induced B cells with OVA-specific transgenic T cells and observed less Th2 cytokine expression and T cell proliferation compared with control conditions. This suppressive effect was preserved even under optimal T cell stimulation by anti-CD3/28. Blocking of the inhibitory cytokines IL-10 or TGF-β only marginally restored Th2 cytokine induction. These data suggest that schistosome-induced pulmonary B cells are impaired in their capacity to produce cytokines to TLR ligands and to induce Th2 cytokine responses independent of their antigen-presenting function. These findings underline the presence of distinct B cell subsets with different stimulatory or inhibitory properties even if induced by the same type of helminth.

Regulatory B cells: Phenotype, function and role in transplantation

While B cells are traditionally known for their roles in antibody production, antigen presentation and cytokine production, recent studies have highlighted the existence of B cells with regulatory properties, which have been termed Bregs, analogous to regulatory T cells (Tregs). Bregs have been found to play a role in autoimmune disease, malignancies, infections, and may also be involved in solid organ transplantation. Their main mechanism of action is by promoting the development of Tregs while suppressing effector CD4⁺ and CD8⁺ T cells, primarily by IL-10 secretion. In the field of transplantation evidence for an active role of Bregs is scarce. While the presence of Bregs has been associated with improved graft survival and operational tolerance in kidney transplant recipients, these findings are not without controversy. Since the majority of fundamental research on Bregs has been performed in the fields in autoimmunity and infectious diseases, we will first focus on what these fields taught us on basic Breg biology, after which the relevance for the transplant setting is discussed.

TIM-1 defines a human regulatory B cell population that is altered in frequency and function in systemic sclerosis patients

BACKGROUND

Systemic sclerosis (SSc) is a systemic autoimmune disease characterized by excessive production of extracellular matrix by fibroblasts on skin and internal organs. Although Th2 cells have been involved in fibroblast stimulation, hyperactivated B cells may also play an important role. Regulatory B cells (Bregs) are cells capable of inhibiting inflammatory responses and controlling autoimmune diseases. Although many Breg populations have in common the ability to produce high amounts of IL-10, a unique surface marker defining most human Bregs is lacking. It has been described in mice that T cell Ig and mucin domain protein 1 (TIM-1) is an inclusive marker for Bregs, and that TIM-1+ B cells are able to prevent the development of autoimmunity. The aim of this work was to evaluate TIM-1 as a marker for human IL-10⁺ Bregs, and to determine whether TIM-1+ B cells are defective in SSc patients.

METHODS

SSc patients (n = 39) and 53 healthy subjects were recruited. TIM-1 and IL-10 expression was assessed in resting or activated peripheral blood CD19⁺ B cells by flow cytometry. The regulatory function of TIM-1⁺ or activated B cells from SSc patients and healthy subjects was assessed in autologous and allogenic co-cultures with CD4⁺ T cells, where T cell proliferation and IFN-γ, IL-17, TNF-α and IL-4 production by T cells was measured by flow cytometry.

RESULTS

TIM-1 and IL-10 were preferentially expressed in transitional B cells, but were upregulated in naïve and memory B cells upon stimulation. The frequency of transitional TIM-1⁺ IL-10⁺ B cells was significantly decreased in SSc patients compared to healthy controls. In addition, activated B cells from SSc patients induced stronger allogenic Th1 and Th2 responses than activated B cells from healthy controls. Finally, TIM-1⁺ B cells, including transitional and non-transitional cells, exhibited a higher CD4⁺ T cell suppressive ability than TIM-1^- B cells in healthy controls, but not in SSc patients.

CONCLUSIONS

TIM-1 is a unique marker for the identification of a human IL-10⁺ Breg subpopulation which is partially superimposed with transitional B cells. Alterations in TIM-1⁺ B cells could contribute to the development of autoimmune diseases such as SSc.

Potential importance of B cells in aging and aging-associated neurodegenerative diseases

Our understanding of B cells as merely antibody producers is slowly changing. Alone or in concert with antibody, they control outcomes of seemingly different diseases such as cancer, rheumatoid arthritis, diabetes, and multiple sclerosis. While their role in activation of effector immune cells is beneficial in cancer but bad in autoimmune diseases, their immunosuppressive and regulatory subsets (Bregs) inhibit autoimmune and anticancer responses. These pathogenic and suppressive functions are not static and appear to be regulated by the nature and strength of inflammation. Although aging increases inflammation and changes the composition and function of B cells, surprisingly, little is known whether the change affects aging-associated neurodegenerative disease, such as Alzheimer's disease (AD). Here, by analyzing B cells in cancer and autoimmune and neuroinflammatory diseases, we elucidate their potential importance in AD and other aging-associated neuroinflammatory diseases.

Expression of Tim-1 in primary CNS lymphoma

Primary central nervous system lymphoma (PCNSL) is a distinct subtype of extranodal lymphoma with aggressive clinical course and poor outcome. As increased IL‐10/IL‐6 ratio is recognized in the cerebrospinal fluid (CSF) of PCNSL patients, we hypothesized that PCNSL might originate from a population of B cells with high IL‐10‐producing capacity, an equivalent of “regulatory B cells” in mice. We intended in this study to clarify whether Tim‐1, a molecule known as a marker for regulatory B cells in mice, is expressed in PCNSL. By immunohistochemical analysis, Tim‐1 was shown to be positive in as high as 54.2% of PCNSL (26 of 58 samples), while it was positive in 19.1% of systemic diffuse large B‐cell lymphoma (DLBCL) samples (17 of 89 samples; P < 0.001). Tim‐1 expression positively correlated with IL‐10 expression in PCNSL (Cramer's V = 0.55, P < 0.001), and forced expression of Tim‐1 in a PCNSL cell line resulted in increased IL‐10 secretion, suggesting that Tim‐1 is functionally linked with IL‐10 production in PCNSL. Moreover, soluble Tim‐1 was detectable in the CSF of PCNSL patients, and was suggested to parallel disease activity. In summary, PCNSL is characterized by frequent Tim‐1 expression, and its soluble form in CSF may become a useful biomarker for PCNSL.

New insights into B cell biology in systemic lupus erythematosus and Sjögren's syndrome

PURPOSE OF REVIEW

Our understanding of the physiological and pathogenic functions of B cells in systemic lupus erythematosus (SLE) and Primary Sjögren's syndrome (pSS) continues to expand. In this review, we discuss novel insights published in the last 18 months into the roles of B cells in systemic autoimmunity.

RECENT FINDINGS

Data have continued to expand regarding the diverse mechanisms by which innate immune signals including Toll-like receptors (TLRs) regulate the B cell compartment. Localized B cells and long-lived plasma cells have been identified as playing an important role in target tissue including the development of ectopic lymphoid structures in kidney and salivary gland. In addition to pathogenic roles for B cells, there is mounting evidence for regulatory B cell subsets that play a protective role and new insights into the signals that regulate their development.

SUMMARY

The past few years have provided insights into the multiple paths by which innate immune signals can lead to B cell activation in SLE and pSS and the increasingly diverse ways in which B cells contribute to disease expression. Further understanding the imbalance between protective and pathogenic functions for B cells in disease including in understudied target tissue should yield new treatment approaches.

Immune Regulation and Antitumor Effect of TIM-1

T cells play an important role in antitumor immunity, and the T cell immunoglobulin domain and the mucin domain protein-1 (TIM-1) on its surface, as a costimulatory molecule, has a strong regulatory effect on T cells. TIM-1 can regulate and enhance type 1 immune response of tumor association. Therefore, TIM-1 costimulatory pathways may be a promising therapeutic target in future tumor immunotherapy. This review describes the immune regulation and antitumor effect of TIM-1.

Renal Transplant Recipients Treated with Calcineurin-Inhibitors Lack Circulating Immature Transitional CD19+CD24hiCD38hi Regulatory B-Lymphocytes

Background

CD19⁺CD24^hiCD38^hi transitional immature B-lymphocytes have been demonstrated to play an important role in regulating the alloimmune response in transplant recipients. Here, we analyzed the effect of calcineurin inhibition on these peripherally circulating regulatory B-cells (Breg) in renal transplant recipients receiving cyclosporine A (CsA) or tacrolimus.

Methods

PBMCs from healthy subjects (HS) (n = 16) and renal transplant recipients (n = 46) were isolated. Flow cytometry was performed for CD19, CD24, CD38 and IL-10 either after isolation or after 72 hours of co-culture in presence of PMA/Ionomycin and TLR9-ligand in presence or absence of increasing concentrations of tacrolimus or CsA.

Results

The amount of CD19⁺ B-cells among lymphocytes was ∼9.1% in HS, ∼3.6% in CsA (n = 11, p<0.05) and ∼6.4% in TAC (n = 35, p<0.05) treated patients. Among B-cells, a distinct subset of Breg was found to be 4.7% in HS, 1.4% in tacrolimus treated patients and almost blunted in patients receiving CsA. Similarily, ∼4% of B-cells in HS and even fewer in CsA or tacrolimus treated patients produced IL-10 (0.5% and 1.5%, p<0.05) and this was confirmed both in non-transplanted CsA-treated healthy subjects and in in vitro co-culture experiments. Among 29 patients with <1% of Breg, 9 cases (31%) displayed an allograft rejection in contrast to only one case of rejection (6%) among 17 patients with >1%.

Conclusion

Calcineurin inhibitors reduce number and IL-10 production of Bregs in the peripheral circulation of both renal transplant recipients and non-transplanted healthy subjects. CNI induced Breg reduction is not restricted to a solid organ transplant setting and is not mediated by co-medication with steroids or MPA. A low proportion of Breg cells is associated with an elevated frequency of allograft rejection events.

The clearance of dying cells: table for two

Phagocytic cells of the immune system must constantly survey for, recognize, and efficiently clear the billions of cellular corpses that arise as a result of development, stress, infection, or normal homeostasis. This process, termed efferocytosis, is critical for the prevention of autoimmune and inflammatory disorders, and persistence of dead cells in tissue is characteristic of many human autoimmune diseases, notably systemic lupus erythematosus. The most notable characteristic of the efferocytosis of apoptotic cells is its ‘immunologically silent' response. Although the mechanisms by which phagocytes facilitate engulfment of dead cells has been a well-studied area, the pathways that coordinate to process the ingested corpse and direct the subsequent immune response is an area of growing interest. The recently described pathway of LC3 (microtubule-associated protein 1A/1B-light chain 3)-associated phagocytosis (LAP) has shed some light on this issue. LAP is triggered when an extracellular particle, such as a dead cell, engages an extracellular receptor during phagocytosis, induces the translocation of autophagy machinery, and ultimately LC3 to the cargo-containing phagosome, termed the LAPosome. In this review, we will examine efferocytosis and the impact of LAP on efferocytosis, allowing us to reimagine the impact of the autophagy machinery on innate host defense mechanisms.

Mast cell activation is enhanced by Tim1:Tim4 interaction but not by Tim-1 antibodies

Polymorphisms in the T cell (or transmembrane) immunoglobulin and mucin domain 1 ( TIM-1) gene, particularly in the mucin domain, have been associated with atopy and allergic diseases in mice and human. Genetic- and antibody-mediated studies revealed that Tim-1 functions as a positive regulator of Th2 responses, while certain antibodies to Tim-1 can exacerbate or reduce allergic lung inflammation. Tim-1 can also positively regulate the function of B cells, NKT cells, dendritic cells and mast cells. However, the precise molecular mechanisms by which Tim-1 modulates immune cell function are currently unknown. In this study, we have focused on defining Tim-1-mediated signaling pathways that enhance mast cell activation through the high affinity IgE receptor (FceRI). Using a Tim-1 mouse model lacking the mucin domain (Tim-1 ^Dmucin), we show for the first time that the polymorphic Tim-1 mucin region is dispensable for normal mast cell activation. We further show that Tim-4 cross-linking of Tim-1 enhances select signaling pathways downstream of FceRI in mast cells, including mTOR-dependent signaling, leading to increased cytokine production but without affecting degranulation.

Apoptosis inhibitor of macrophage protein enhances intraluminal debris clearance and ameliorates acute kidney injury in mice

Acute kidney injury (AKI) is associated with prolonged hospitalization and high mortality, and it predisposes individuals to chronic kidney disease. To date, no effective AKI treatments have been established. Here we show that the apoptosis inhibitor of macrophage (AIM) protein on intraluminal debris interacts with kidney injury molecule (KIM)-1 and promotes recovery from AKI. During AKI, the concentration of AIM increases in the urine, and AIM accumulates on necrotic cell debris within the kidney proximal tubules. The AIM present in this cellular debris binds to KIM-1, which is expressed on injured tubular epithelial cells, and enhances the phagocytic removal of the debris by the epithelial cells, thus contributing to kidney tissue repair. When subjected to ischemia-reperfusion (IR)-induced AKI, AIM-deficient mice exhibited abrogated debris clearance and persistent renal inflammation, resulting in higher mortality than wild-type (WT) mice due to progressive renal dysfunction. Treatment of mice with IR-induced AKI using recombinant AIM resulted in the removal of the debris, thereby ameliorating renal pathology. We observed this effect in both AIM-deficient and WT mice, but not in KIM-1-deficient mice. Our findings provide a basis for the development of potentially novel therapies for AKI.

Negative immune checkpoints on T lymphocytes and their relevance to cancer immunotherapy

The term 'inhibitory checkpoint' refers to the broad spectrum of co-receptors expressed by T cells that negatively regulate T cell activation thus playing a crucial role in maintaining peripheral self-tolerance. Co-inhibitory receptor ligands are highly expressed by a variety of malignancies allowing evasion of anti-tumour immunity. Recent studies demonstrate that manipulation of these co-inhibitory pathways can remove the immunological brakes that impede endogenous immune responses against tumours. Antibodies that block the interactions between co-inhibitory receptors and their ligands have delivered very promising clinical responses, as has been shown by recent successful trials targeting the CTLA-4 and PD-1 pathways. In this review, we discuss the mechanisms of action and expression pattern of co-inhibitory receptors on different T cells subsets, emphasising differences between CD4(+) and CD8(+) T cells. We also summarise recent clinical findings utilising immune checkpoint blockade.

The expanding family of regulatory B cells

Over the last decade it has become evident that in addition to producing antibody, B cells activate the immune system by producing cytokines and via antigen presentation. In addition, B cells also exhibit immunosuppressive functions via diverse regulatory mechanisms. This subset of B cells, known as regulatory B cells (Bregs), contributes to the maintenance of tolerance, primarily via the production of IL-10. Studies in experimental animal models, as well as in patients with autoimmune diseases, have identified multiple Breg subsets exhibiting diverse mechanisms of immune suppression. In this review, we describe the different Breg subsets identified in mice and humans, and their diverse mechanisms of suppression in different disease settings.

Regulatory B cell: New member of immunosuppressive cell club

Historically, the pivotal role of B cells or B lymphocytes in immunity has been attributed to the production of antibodies. They were also demonstrated to present antigens to T cells and to secrete cytokines, thereby acting as positive regulators in immune responses. A series of studies on autoimmune diseases, however, led researchers to find a unique subset of B cells, later described as "regulatory B cells" (Bregs), that has the ability to suppress immune responses. Bregs occur not only in autoimmune diseases, but also in inflammation and transplantation. Furthermore, recently published literatures suggested that Bregs contributed to the growth and metastasis of certain cancers. In this review, we will discuss these unique subsets of B cells in different kinds of disorders, with particular emphasis on the mechanisms of their immunoregulatory role that were collected from mice and humans.

KIM-1-/TIM-1-mediated phagocytosis links ATG5-/ULK1-dependent clearance of apoptotic cells to antigen presentation

Phagocytosis of apoptotic cells by both professional and semi-professional phagocytes is required for resolution of organ damage and maintenance of immune tolerance. KIM-1/TIM-1 is a phosphatidylserine receptor that is expressed on epithelial cells and can transform the cells into phagocytes. Here, we demonstrate that KIM-1 phosphorylation and association with p85 results in encapsulation of phagosomes by lipidated LC3 in multi-membrane organelles. KIM-1-mediated phagocytosis is not associated with increased ROS production, and NOX inhibition does not block LC3 lipidation. Autophagy gene expression is required for efficient clearance of apoptotic cells and phagosome maturation. KIM-1-mediated phagocytosis leads to pro-tolerogenic antigen presentation, which suppresses CD4 T-cell proliferation and increases the percentage of regulatory T cells in an autophagy gene-dependent manner. Taken together, these data reveal a novel mechanism of epithelial biology linking phagocytosis, autophagy and antigen presentation to regulation of the inflammatory response.

Role of B cells in tolerance induction

PURPOSE OF REVIEW

B cells are known to play a central role in humoral immunity and to boost cellular immunity, however, in a variety of experimental models, B-cell subsets ameliorate inflammation and autoimmune disease, indicating that they can also play a regulatory role. Here, we highlight the advances in regulatory B-cell (Breg) biology of the past year with an emphasis on findings pertinent to transplantation. Several recent observations highlight the relevance to clinical transplantation. Data from at least three independent groups demonstrated that spontaneously tolerant renal transplant recipients exhibit a peripheral blood B-cell signature although the significance of these data remains unclear. Moreover, new data suggest that regulatory B cells may serve as a biomarker for long-term allograft outcomes. Finally, recent evidence suggesting that plasma cells may be an essential component of Bregs raises new concerns about targeting antibody producing cells.

RECENT FINDINGS

We describe new information on Breg mechanisms of action to suppress the alloresponse, signals to expand Bregs in vitro, and more functional evidence of Breg involvement in operationally tolerant kidney patients and in maintaining stable allograft function.

SUMMARY

Although lymphocyte depletion remains central to tolerance induction therapy, the sparing or expansion of regulatory B cells may be an additional strategy to preempt graft rejection.

Regulatory B Cell Function Is Suppressed by Smoking and Obesity in H. pylori-Infected Subjects and Is Correlated with Elevated Risk of Gastric Cancer

Helicobacter pylori infection occurs in more than half of the world’s population and is the main cause for gastric cancer. A series of lifestyle and nutritional factors, such as tobacco smoking and obesity, have been found to elevate the risk for cancer development. In this study, we sought to determine the immunological aspects during H. pylori infection and gastric cancer development. We found that B cells from H. pylori-infected patients presented altered composition and function compared to uninfected patients. IL-10-expressing CD24⁺CD38⁺ B cells were upregulated in H. pylori-infected patients, contained potent regulatory activity in inhibiting T cell pro-inflammatory cytokine secretion, and responded directly to H. pylori antigen stimulation. Interestingly, in H. pylori-infected smoking subjects and obese subjects, the number of IL-10⁺ B cells and CD24⁺CD38⁺ B cells were reduced compared to H. pylori-infected asymptomatic subjects. Regulatory functions mediated by CD24⁺CD38⁺ B cells were also impaired. In addition, gastric cancer positive patients had reduced IL-10-producing B cell frequencies after H. pylori-stimulation. Altogether, these data suggest that in H. pylori-infection, CD24⁺CD38⁺ B cell is upregulated and plays a role in suppressing pro-inflammatory responses, possibly through IL-10 production, a feature that was not observed in smoking and obese patients.

Regulatory B cells: origin, phenotype, and function

Regulatory B (Breg) cells are immunosuppressive cells that support immunological tolerance. Through the production of interleukin-10 (IL-10), IL-35, and transforming growth factor β (TGF-β), Breg cells suppress immunopathology by prohibiting the expansion of pathogenic T cells and other pro-inflammatory lymphocytes. Recent work has shown that different inflammatory environments induce distinct Breg cell populations. Although these findings highlight the relevance of inflammatory signals in the differentiation of Breg cells, they also raise other questions about Breg cell biology and phenotype. For example, what are the functional properties and phenotype of Breg cells? Can a Breg cell arise at every stage in B cell development? Is inflammation the primary requisite for Breg cell differentiation? Here, we use these questions to discuss the advances in understanding Breg cell biology, with a particular emphasis on their ontogeny; we propose that multiple Breg cell subsets can be induced in response to inflammation at different stages in development.

Signals controlling the development and activity of regulatory B-lineage cells

The fundamental concepts surrounding B cells with inhibitory function (regulatory B cells) are now being established. In the context of autoimmune and inflammatory animal models, B cells play an immunomodulatory role via IL-10 production and contribute to limitation of the pathogenesis. Recent studies have notably identified the human counterparts of these cells, which have been suggested to be relevant to the pathophysiology of disease. Clear criteria to identify these cell subsets and the key molecular mechanisms underlying their physiological features are required for understanding the big picture of regulatory B cells. Plasmablasts have recently been identified as a major IL-10-producing regulatory B-cell subset and Ca(2+) signaling has furthermore been found to contribute to B-cell IL-10 expression. In this review, the signaling components controlling IL-10-dependent B-cell regulatory function and the development of IL-10-competent/-producing B cells and plasmablasts are discussed.

Immunosuppressive plasma cells impede T-cell-dependent immunogenic chemotherapy

Cancer-associated genetic alterations induce expression of tumour antigens that can activate CD8(+) cytotoxic T cells (CTLs), but the microenvironment of established tumours promotes immune tolerance through poorly understood mechanisms. Recently developed therapeutics that overcome tolerogenic mechanisms activate tumour-directed CTLs and are effective in some human cancers. Immune mechanisms also affect treatment outcome, and certain chemotherapeutic drugs stimulate cancer-specific immune responses by inducing immunogenic cell death and other effector mechanisms. Our previous studies revealed that B cells recruited by the chemokine CXCL13 into prostate cancer tumours promote the progression of castrate-resistant prostate cancer by producing lymphotoxin, which activates an IκB kinase α (IKKα)-BMI1 module in prostate cancer stem cells. Because castrate-resistant prostate cancer is refractory to most therapies, we examined B cell involvement in the acquisition of chemotherapy resistance. Here we focus on oxaliplatin, an immunogenic chemotherapeutic agent that is effective in aggressive prostate cancer. We show that mouse B cells modulate the response to low-dose oxaliplatin, which promotes tumour-directed CTL activation by inducing immunogenic cell death. Three different mouse prostate cancer models were refractory to oxaliplatin unless genetically or pharmacologically depleted of B cells. The crucial immunosuppressive B cells are plasmocytes that express IgA, interleukin (IL)-10 and programmed death ligand 1 (PD-L1), the appearance of which depends on TGFβ receptor signalling. Elimination of these cells, which also infiltrate human-therapy-resistant prostate cancer, allows CTL-dependent eradication of oxaliplatin-treated tumours.

TIM-1 signaling is required for maintenance and induction of regulatory B cells

Apart from their role in humoral immunity, B cells can exhibit IL-10-dependent regulatory activity (Bregs). These regulatory subpopulations have been shown to inhibit inflammation and allograft rejection. However, our understanding of Bregs has been hampered by their rarity, lack of a specific marker, and poor insight into their induction and maintenance. We previously demonstrated that T cell immunoglobulin mucin domain-1 (TIM-1) identifies over 70% of IL-10-producing B cells, irrespective of other markers. We now show that TIM-1 is the primary receptor responsible for Breg induction by apoptotic cells (ACs). However, B cells that express a mutant form of TIM-1 lacking the mucin domain (TIM-1(Δmucin) ) exhibit decreased phosphatidylserine binding and are unable to produce IL-10 in response to ACs or by specific ligation with anti-TIM-1. TIM-1(Δmucin) mice also exhibit accelerated allograft rejection, which appears to be due in part to their defect in both baseline and induced IL-10(+) Bregs, since a single transfer of WT TIM-1(+) B cells can restore long-term graft survival. These data suggest that TIM-1 signaling plays a direct role in Breg maintenance and induction both under physiological conditions (in response to ACs) and in response to therapy through TIM-1 ligation. Moreover, they directly demonstrate that the mucin domain regulates TIM-1 signaling.

KIM-1-mediated phagocytosis reduces acute injury to the kidney

Kidney injury molecule 1 (KIM-1, also known as TIM-1) is markedly upregulated in the proximal tubule after injury and is maladaptive when chronically expressed. Here, we determined that early in the injury process, however, KIM-1 expression is antiinflammatory due to its mediation of phagocytic processes in tubule cells. Using various models of acute kidney injury (AKI) and mice expressing mutant forms of KIM-1, we demonstrated a mucin domain-dependent protective effect of epithelial KIM-1 expression that involves downregulation of innate immunity. Deletion of the mucin domain markedly impaired KIM-1-mediated phagocytic function, resulting in increased proinflammatory cytokine production, decreased antiinflammatory growth factor secretion by proximal epithelial cells, and a subsequent increase in tissue macrophages. Mice expressing KIM-1Δmucin had greater functional impairment, inflammatory responses, and mortality in response to ischemia- and cisplatin-induced AKI. Compared with primary renal proximal tubule cells isolated from KIM-1Δmucin mice, those from WT mice had reduced proinflammatory cytokine secretion and impaired macrophage activation. The antiinflammatory effect of KIM-1 expression was due to the interaction of KIM-1 with p85 and subsequent PI3K-dependent downmodulation of NF-κB. Hence, KIM-1-mediated epithelial cell phagocytosis of apoptotic cells protects the kidney after acute injury by downregulating innate immunity and inflammation.

Tim-1 is essential for induction and maintenance of IL-10 in regulatory B cells and their regulation of tissue inflammation

T cell Ig and mucin domain (Tim)-1 identifies IL-10-producing regulatory B cells (Bregs). Mice on the C57BL/6 background harboring a loss-of-function Tim-1 mutant showed progressive loss of IL-10 production in B cells and with age developed severe multiorgan tissue inflammation. We demonstrate that Tim-1 expression and signaling in Bregs are required for optimal production of IL-10. B cells with Tim-1 defects have impaired IL-10 production but increased proinflammatory cytokine production, including IL-1 and IL-6. Tim-1-deficient B cells promote Th1 and Th17 responses but inhibit the generation of regulatory T cells (Foxp3(+) and IL-10-producing type 1 regulatory T cells) and enhance the severity of experimental autoimmune encephalomyelitis. Mechanistically, Tim-1 on Bregs is required for apoptotic cell (AC) binding to Bregs and for AC-induced IL-10 production in Bregs. Treatment with ACs reduces the severity of experimental autoimmune encephalomyelitis in hosts with wild-type but not Tim-1-deficient Bregs. Collectively, these findings suggest that in addition to serving as a marker for identifying IL-10-producing Bregs, Tim-1 is also critical for maintaining self-tolerance by regulating IL-10 production in Bregs.

Contribution of Defective PS Recognition and Efferocytosis to Chronic Inflammation and Autoimmunity

The rapid and efficient clearance of apoptotic cells results in the elimination of auto-antigens and provides a strong anti-inflammatory and immunosuppressive signal to prevent autoimmunity. While professional and non-professional phagocytes utilize a wide array of surface receptors to recognize apoptotic cells, the recognition of phosphatidylserine (PS) on apoptotic cells by PS receptors on phagocytes is the emblematic signal for efferocytosis in metazoans. PS-dependent efferocytosis is associated with the production of anti-inflammatory factors such as IL-10 and TGF-β that function, in part, to maintain tolerance to auto-antigens. In contrast, when apoptotic cells fail to be recognized and processed for degradation, auto-antigens persist, such as self-nucleic acids, which can trigger immune activation leading to autoantibody production and autoimmunity. Despite the fact that genetic mouse models clearly demonstrate that loss of PS receptors can lead to age-dependent auto-immune diseases reminiscent of systemic lupus erythematosus (SLE), the link between PS and defective clearance in chronic inflammation and human autoimmunity is not well delineated. In this perspective, we review emerging questions developing in the field that may be of relevance to SLE and human autoimmunity.

Regulatory functions of B cells in allergic diseases

B cells are essentially described for their capacity to produce antibodies ensuring anti-infectious immunity or deleterious responses in the case of autoimmunity or allergy. However, abundant data described their ability to restrain inflammation by diverse mechanisms. In allergy, some regulatory B-cell subsets producing IL-10 have been recently described as potent suppressive cells able to restrain inflammatory responses both in vitro and in vivo by regulatory T-cell differentiation or directly inhibiting T-cell-mediated inflammation. A specific deficit in regulatory B cells participates to more severe allergic inflammation. Induction of allergen tolerance through specific immunotherapy induces a specific expansion of these cells supporting their role in establishment of allergen tolerance. However, the regulatory functions carried out by B cells are not exclusively IL-10 dependent. Indeed, other regulatory mechanisms mediated by B cells are (i) the production of TGF-β, (ii) the promotion of T-cell apoptosis by Fas-Fas ligand or granzyme-B pathways, and (iii) their capacity to produce inhibitory IgG4 and sialylated IgG able to mediate anti-inflammatory mechanisms. This points to Bregs as interesting targets for the development of new therapies to induce allergen tolerance. In this review, we highlight advances in the study of regulatory mechanisms mediated by B cells and outline what is known about their phenotype as well as their suppressive role in allergy from studies in both mice and humans.

Phosphatidylserine receptors: enhancers of enveloped virus entry and infection

A variety of both RNA and DNA viruses envelop their capsids in a lipid bilayer. One of the more recently appreciated benefits this envelope is incorporation of phosphatidylserine (PtdSer). Surface exposure of PtdSer disguises viruses as apoptotic bodies; tricking cells into engulfing virions. This mechanism is termed apoptotic mimicry. Several PtdSer receptors have been identified to enhance virus entry and we have termed this group of proteins PtdSer-mediated virus entry enhancing receptors or PVEERs. These receptors enhance entry of a range of enveloped viruses. Internalization of virions by PVEERs provides a broad mechanism of entry with little investment by the virus itself. PVEERs may allow some viruses to attach to cells, thereby making viral glycoprotein/cellular receptor interactions more probable. Alternatively, other viruses may rely entirely on PVEERs for internalization into endosomes. This review provides an overview of PtdSer receptors that serve as PVEERs and the biology behind virion/PVEER interaction.

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Phosphatidylserine (PtdSer) receptors can mediate entry of enveloped viruses.

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PtdSer is present on the outer leaflet of the virion envelope.

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PtdSer receptors are expressed on a variety of primary cells and cell lines.

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Characteristics of PtdSer receptors that mediate virus entry are defined.