New perspectives in B-1 B cell development and function

The ICF2 gene Zbtb24 specifically regulates the differentiation of B1 cells via promoting heme synthesis

BACKGROUND

Loss-of-function mutations of ZBTB24 cause immunodeficiency, centromeric instability, and facial anomalies syndrome 2 (ICF2). ICF2 is a rare autosomal recessive disorder with immunological defects in serum antibodies and circulating memory B cells, resulting in recurrent and sometimes fatal respiratory and gastrointestinal infections. The genotype-phenotype correlation in patients with ICF2 indicates an essential role of ZBTB24 in the terminal differentiation of B cells.

METHODS

We used the clustered regularly interspaced short palindromic repeats (CRISPER)/Cas9 technology to generate B cell specific Zbtb24-deficient mice and verified the deletion specificity and efficiency by quantitative polymerase chain reaction (Q-PCR) and western blotting analyses in fluorescence-activated cell sorting (FACS)-sorted cells. The development, phenotype of B cells and in vivo responses to T cell dependent or independent antigens post immunization were analyzed by flow cytometry and enzyme-linked immunosorbent assay (ELISA). Adoptive transfer experiment in combination with in vitro cultures of FACS-purified B cells and RNA-Seq analysis were utilized to specifically determine the impact of Zbtb24 on B cell biology as well as the underlying mechanisms.

RESULTS

Zbtb24 is dispensable for B cell development and maintenance in naive mice. Surprisingly, B cell specific deletion of Zbtb24 does not evidently compromise germinal center reactions and the resulting primary and secondary antibody responses induced by T cell dependent antigens (TD-Ags), but significantly inhibits T cell independent antigen-elicited antibody productions in vivo. At the cellular level, Zbtb24-deficiency specifically impedes the plasma cell differentiation of B1 cells without impairing their survival, activation and proliferation in vitro. Mechanistically, Zbtb24-ablation attenuates heme biosynthesis partially through mTORC1 in B1 cells, and addition of exogenous hemin abrogates the differentiation defects of Zbtb24-null B1 cells.

CONCLUSIONS

Zbtb24 seems to regulate antibody responses against TD-Ags B cell extrinsically, but it specifically promotes the plasma cell differentiation of B1 cells via heme synthesis in mice. Our study also suggests that defected B1 functions contribute to recurrent infections in patients with ICF2.

The bidirectional relationship of depression and disturbances in B cell homeostasis: Double trouble

Major depressive disorder (MDD) is a recurrent, persistent, and debilitating neuropsychiatric syndrome with an increasing morbidity and mortality, representing the leading cause of disability worldwide. The dysregulation of immune systems (including innate and adaptive immune systems) has been identified as one of the key contributing factors in the progression of MDD. As the main force of the humoral immunity, B cells have an essential role in the defense against infections, antitumor immunity and autoimmune diseases. Several recent studies have suggested an intriguing connection between disturbances in B cell homeostasis and the pathogenesis of MDD, however, the B-cell-dependent mechanism of MDD remains largely unexplored compared to other immune cells. In this review, we provide an overview of how B cell abnormality regulates the progression of MMD and the potential consequence of the disruption of B cell homeostasis in patients with MDD. Abnormalities of B-cell homeostasis not only promote susceptibility to MDD, but also lead to an increased risk of developing infection, malignancy and autoimmune diseases in patients with MDD. A better understanding of the contribution of B cells underlying MDD would provide opportunities for identification of more targeted treatment approaches and might provide an overall therapeutic benefit to improve the long-term outcomes of patients with MDD.

The role of B-1 cells in cancer progression and anti-tumor immunity

In recent years, in addition to the well-established role of T cells in controlling or promoting tumor growth, a new wave of research has demonstrated the active involvement of B cells in tumor immunity. B-cell subsets with distinct phenotypes and functions play various roles in tumor progression. Plasma cells and activated B cells have been linked to improved clinical outcomes in several types of cancer, whereas regulatory B cells have been associated with disease progression. However, we are only beginning to understand the role of a particular innate subset of B cells, referred to as B-1 cells, in cancer. Here, we summarize the characteristics of B-1 cells and review their ability to infiltrate tumors. We also describe the potential mechanisms through which B-1 cells suppress anti-tumor immune responses and promote tumor progression. Additionally, we highlight recent studies on the protective anti-tumor function of B-1 cells in both mouse models and humans. Understanding the functions of B-1 cells in tumor immunity could pave the way for designing more effective cancer immunotherapies.

Progression of Notch signaling regulation of B cells under radiation exposure

With the continuous development of nuclear technology, the radiation exposure caused by radiation therapy is a serious health hazard. It is of great significance to further develop effective radiation countermeasures. B cells easily succumb to irradiation exposure along with immunosuppressive response. The approach to ameliorate radiation-induced B cell damage is rarely studied, implying that the underlying mechanisms of B cell damage after exposure are eager to be revealed. Recent studies suggest that Notch signaling plays an important role in B cell-mediated immune response. Notch signaling is a critical regulator for B cells to maintain immune function. Although accumulating studies reported that Notch signaling contributes to the functionality of hematopoietic stem cells and T cells, its role in B cells is scarcely appreciated. Presently, we discussed the regulation of Notch signaling on B cells under radiation exposure to provide a scientific basis to prevent radiation-induced B cell damage.

B cell-specific knockout of AID protects against atherosclerosis

Antigen-naive IgM-producing B cells are atheroprotective, whereas mature B cells producing class-switched antibodies promote atherosclerosis. Activation-induced cytidine deaminase (AID), which mediates class switch recombination (CSR), would thus be expected to foster atherosclerosis. Yet, AID also plays a major role in the establishment of B cell tolerance. We sought to define whether AID affects atherosclerotic plaque formation. We generated Ldlr^-/- chimeras transplanted with bone marrow from Aicda^-/- or wild-type (WT) mice, fed a HFD for 14 weeks. Decreased B cell maturation in Ldlr^-/-Aicda^-/- mice was demonstrated by 50% reduction in splenic and aortic BAFFR expression, a key signaling component of B2 cell maturation. This was associated with increased plasma IgM in Ldlr^-/-Aicda^-/- compared with Ldlr^-/-WT animals. Importantly, Ldlr^-/-Aicda^-/- mice had reduced atherosclerotic lesion area (0.20 ± 0.03mm²) compared with Ldlr^-/-WT (0.30 ± 0.04mm², P < 0.05), although no differences in plaque composition were noted between groups. In addition, immunofluorescence analysis revealed increased splenic B and T cell areas independent of cell number. AID depletion directly inhibits atherosclerotic plaque formation.

Shaping immunity for life: Layered development of CD8+ T cells

Historically, the immune system was believed to develop along a linear axis of maturity from fetal life to adulthood. Now, it is clear that distinct layers of immune cells are generated from unique waves of hematopoietic progenitors during different windows of development. This model, known as the layered immune model, has provided a useful framework for understanding why distinct lineages of B cells and γδ T cells arise in succession and display unique functions in adulthood. However, the layered immune model has not been applied to CD8+ T cells, which are still often viewed as a uniform population of cells belonging to the same lineage, with functional differences between cells arising from environmental factors encountered during infection. Recent studies have challenged this idea, demonstrating that not all CD8+ T cells are created equally and that the functions of individual CD8+ T cells in adults are linked to when they were created in the host. In this review, we discuss the accumulating evidence suggesting there are distinct ontogenetic subpopulations of CD8+ T cells and propose that the layered immune model be extended to the CD8+ T cell compartment.

Reduction of peritoneal cavity B1a cells in adult Slc7a5 knockdown mice via dysregulating the mTOR pathway

Slc7a5 is an important amino acid transporter that is highly expressed in metabolically active and rapidly proliferating cells. To explore the effect of Slc7a5 on adult B cell development, we conditionally deleted Slc7a5 in murine B cells and observed a significant reduction of B1a cells. In contrast to PI3K-Akt pathway activation, activity of the mTOR pathway was decreased. This may result from intracellular amino acid starvation in Slc7a5 knockdown (Slc7a5 KD) bone marrow B cells, thereby dampening B1a development. RNA-seq analysis demonstrated increased translation and reduced proliferation in Slc7a5 KD bone marrow B cells. Overall, the results of our study highlight the importance of Slc7a5 in peritoneal B1a cell development.

B2 cells contribute to hypertension and natural killer cell activation possibly via AT1-AA in response to placental ischemia

Preeclampsia, new onset hypertension during pregnancy, is associated with activated T helper cells (Th) and B cells secreting agonistic autoantibodies against the angiotensin II type 1 receptor (AT1-AA). The reduced uterine perfusion pressure (RUPP) model of placental ischemia recapitulates these characteristics. We have shown that Th-B cell communication contributes to AT1-AA and symptoms of preeclampsia in the RUPP rat. B2 cells are classical B cells that communicate with Th cells and are then transformed into memory B cells. We hypothesize that B2 cells cause hypertension, natural killer (NK) cell activation, and complement activation during pregnancy through the production of AT1-AA. To test this hypothesis, total splenic B cells and B2 cells were isolated from normal pregnant (NP) or RUPP rats on gestational day (GD)19 and adoptively transferred into GD12 NP rats. A group of recipient rats was treated with a specific inhibitor peptide of AT1-AA. On GD19, mean arterial pressure was measured, tissues were collected, activated NK cells were measured by flow cytometry, and AT1-AA was measured by cardiomyocyte assay. NP recipients of RUPP B cells or RUPP B2 cells had increased mean arterial pressure, AT1-AA, and circulating activated NK cells compared with recipients of NP B cells. Hypertension in NP recipients of RUPP B cells or RUPP B2 was attenuated with AT1-AA blockade. This study demonstrates that B cells and B2 cells from RUPP rats cause hypertension and increased AT1-AA and NK cell activation in response to placental ischemia during pregnancy.NEW & NOTEWORTHY This study demonstrates that placental ischemia-stimulated B2 cells induce hypertension and circulating natural killer cell activation and angiotensin II type 1 receptor production in normal pregnant rats.

Isolation and Characterization of Fetal Liver Hematopoietic Stem Cells

Hematopoietic stem cells (HSCs) are responsible for the generation and maintenance of pools of multipotent precursors that ultimately give rise to all fully differentiated blood and immune cells. Proper identification and isolation of HSCs for functional analysis has greatly facilitated our understanding of both normal and abnormal adult hematopoiesis. Whereas adult hematopoiesis in mice and humans is driven by quiescent HSCs that reside almost exclusively within the bone marrow (BM), developmental hematopoiesis is characterized by a series of transient progenitors driving waves of increasingly mature hematopoietic cell production that occur across multiple anatomical sites. These waves of hematopoietic cell production are also responsible for the generation of distinct immune cell populations during development that persist into adulthood and contribute uniquely to adult immunity. Therefore, methods to properly isolate and characterize fetal progenitors with high purity across development become increasingly important not only for defining developmental hematopoietic pathways, but also for understanding the contribution of developmental hematopoiesis to the immune system. Here, we describe and discuss methods and considerations for the isolation and characterization of HSCs from the fetal liver, the primary hematopoietic organ during fetal development.

Autophagy and Apoptosis: Current Challenges of Treatment and Drug Resistance in Multiple Myeloma

Over the past two decades, the natural history of multiple myeloma (MM) has evolved dramatically, owing primarily to novel agents targeting MM in the bone marrow microenvironment (BMM) pathways. However, the mechanisms of resistance acquisition remain a mystery and are poorly understood. Autophagy and apoptosis are tightly controlled processes and play a critical role in the cell growth, development, and survival of MM. Genetic instability and abnormalities are two hallmarks of MM. During MM progression, plasma malignant cells become genetically unstable and activate various signaling pathways, resulting in the overexpression of abnormal proteins that disrupt autophagy and apoptosis biological processes. Thus, achieving a better understanding of the autophagy and apoptosis processes and the proteins that crosslinked both pathways, could provide new insights for the MM treatment and improve the development of novel therapeutic strategies to overcome resistance. This review presents a sufficient overview of the roles of autophagy and apoptosis and how they crosslink and control MM progression and drug resistance. Potential combination targeting of both pathways for improving outcomes in MM patients also has been addressed.

Prenatal inflammation perturbs murine fetal hematopoietic development and causes persistent changes to postnatal immunity

Adult hematopoietic stem and progenitor cells (HSPCs) respond directly to inflammation and infection, causing both acute and persistent changes to quiescence, mobilization, and differentiation. Here we show that murine fetal HSPCs respond to prenatal inflammation in utero and that the fetal response shapes postnatal hematopoiesis and immune cell function. Heterogeneous fetal HSPCs show divergent responses to maternal immune activation (MIA), including changes in quiescence, expansion, and lineage-biased output. Single-cell transcriptomic analysis of fetal HSPCs in response to MIA reveals specific upregulation of inflammatory gene profiles in discrete, transient hematopoietic stem cell (HSC) populations that propagate expansion of lymphoid-biased progenitors. Beyond fetal development, MIA causes the inappropriate expansion and persistence of fetal lymphoid-biased progenitors postnatally, concomitant with increased cellularity and hyperresponsiveness of fetal-derived innate-like lymphocytes. Our investigation demonstrates how inflammation in utero can direct the output and function of fetal-derived immune cells by reshaping fetal HSC establishment.

Landscape of B Cell Receptor Repertoires in COVID-19 Patients Revealed Through CDR3 Sequencing of Immunoglobulin Heavy and Light Chains

The outbreak and persistence of coronavirus disease 2019 (COVID-19) threaten human health. B cells play a vital role in fighting the infections caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Despite many studies on the immune responses in COVID-19 patients, it is still unclear how B cell receptor (BCR) constituents, including immunoglobulin heavy (IGHs) and light chains (IGLs), respond to SARS-CoV-2 in patients with varying symptoms. In this study, we conducted complementarity-determining region 3 (CDR3) sequencing of BCR IGHs and IGLs from the peripheral blood of COVID-19 patients and healthy donors. The results showed significantly reduced clonal diversity, more expanded clones, and longer CDR3 lengths of IGH and IGL in COVID-19 patients than those in healthy individuals. The IGLs had a much higher percentage of VJ skew usage (47.83% IGLV and 42.86% IGLJ were significantly regulated) than the IGHs (12.09% IGHV and 0% IGHJ) between the healthy individuals and patients, which indicated the importance of BCR light chains. Furthermore, we found a largely expanded IGLV3-25 gene cluster mostly pairing with IGLJ1 and ILGJ2 in COVID-19 patients and a newly identified upregulated IGLJ1 gene and IGLJ2+IGLV13-21 recombination, both of which are potential sources of SARS-CoV-2-targeting antibodies. Our findings on specific immune B-cell signatures associated with COVID-19 have clinical implications for vaccine and biomarker development for disease diagnosis.

The Role of B Cells in PE Pathophysiology: A Potential Target for Perinatal Cell-Based Therapy?

The pathophysiology of preeclampsia (PE) is poorly understood; however, there is a large body of evidence that suggests a role of immune cells in the development of PE. Amongst these, B cells are a dominant element in the pathogenesis of PE, and they have been shown to play an important role in various immune-mediated diseases, both as pro-inflammatory and regulatory cells. Perinatal cells are defined as cells from birth-associated tissues isolated from term placentas and fetal annexes and more specifically from the amniotic membrane, chorionic membrane, chorionic villi, umbilical cord (including Wharton's jelly), the basal plate, and the amniotic fluid. They have drawn particular attention in recent years due to their ability to modulate several aspects of immunity, making them promising candidates for the prevention and treatment of various immune-mediated diseases. In this review we describe main findings regarding the multifaceted in vitro and in vivo immunomodulatory properties of perinatal cells, with a focus on B lymphocytes. Indeed, we discuss evidence on the ability of perinatal cells to inhibit B cell proliferation, impair B cell differentiation, and promote regulatory B cell formation. Therefore, the findings discussed herein unveil the possibility to modulate B cell activation and function by exploiting perinatal immunomodulatory properties, thus possibly representing a novel therapeutic strategy in PE.

The catalytic domain of the histone methyltransferase NSD2/MMSET is required for the generation of B1 cells in mice

Humoral immunity in mammals relies on the function of two developmentally and functionally distinct B-cell subsets-B1 and B2 cells. While B2 cells are responsible for the adaptive response to environmental antigens, B1 cells regulate the production of polyreactive and low-affinity antibodies for innate humoral immunity. The molecular mechanism of B-cell specification into different subsets is understudied. In this study, we identified lysine methyltransferase NSD2 (MMSET/WHSC1) as a critical regulator of B1 cell development. In contrast to its minor impact on B2 cells, deletion of the catalytic domain of NSD2 in primary B cells impairs the generation of B1 lineage. Thus, NSD2, a histone H3 K36 dimethylase, is the first-in-class epigenetic regulator of a B-cell lineage in mice.

Live attenuated Edwardsiella ictaluri vaccines enhance the protective innate immune responses of channel catfish B cells

Edwardsiella ictaluri causes enteric septicemia of catfish. Our group developed two E. ictaluri live attenuated vaccines (LAVs). However, their effects on the innate functions of catfish B cells are still unexplored. We evaluated phagocytosis and killing of wild-type (WT) E. ictaluri opsonized with sera from vaccinated fish and the survival of B cells exposed to E. ictaluri strains. We assessed phagocytosis of the opsonized WT at 30 °C and 4 °C. B cells killed the internalized E. ictaluri opsonized with sera from vaccinated fish with LAVs more efficiently than other groups at 30 °C. However, catfish B cells were unable to destroy E. ictaluri at 4 °C. Furthermore, E. ictaluri opsonized with serum from fish exposed to WT induce apoptosis and decreased live B cells numbers. Results indicate that opsonization of E. ictaluri with sera from vaccinated fish enhanced phagocytosis and killing activity in B cells and inhibited apoptotic changes in the infected B cells.

Neonatal T Cells: A Reinterpretation

Neonatal CD4⁺ and CD8⁺ T cells have historically been characterized as immature or defective. However, recent studies prompt a reinterpretation of the functions of neonatal T cells. Rather than a population of cells always falling short of expectations set by their adult counterparts, neonatal T cells are gaining recognition as a distinct population of lymphocytes well suited for the rapidly changing environment in early life. In this review, I will highlight new evidence indicating that neonatal T cells are not inert or less potent versions of adult T cells but instead are a broadly reactive layer of T cells poised to quickly develop into regulatory or effector cells, depending on the needs of the host. In this way, neonatal T cells are well adapted to provide fast-acting immune protection against foreign pathogens, while also sustaining tolerance to self-antigens.

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.

Reproductive immunomodulatory functions of B cells in pregnancy

Pregnancy, a challenging physiological state, requires shuffling of conventional immune work-sets. Strategies to tolerate the semi-allogenic fetus in normal human pregnancy are multivariate with perfect modulation of the immune cells. Pregnancy is marked by B cell lymphocytopenia accompanied by reduced responsiveness to infectious agents. Besides this old age concept, plenty of research confirms that B cells have other crucial roles in pregnancy and undergo a wide range of modifications in terms of its proliferation, switching between its subtypes, variation in antibody productions, shifting the tides of cytokines as well as regulating other immune cells. B cells establish tolerant environment in pregnancy by producing protective antibodies to encounter the foreign paternal antigens. Regulatory B cells (Bregs) have adopted anti-inflammatory characteristics to sustain normal pregnancy. Moreover, the colossal physiological alterations during human pregnancy also include synchronized changes in the cross-talks between the pregnancy hormones and B cells. These aspects of pregnancy from the view point of B cell functions have so far appeared individually in discrete reports. This review finds its novelty in concisely presenting every facet of association of B cell with human pregnancy.

Immune Effects of M51R Vesicular Stomatitis Virus Treatment of Carcinomatosis From Colon Cancer

BACKGROUND

The purpose of this study was to analyze the oncolytic and immunomodulatory functions of an M protein mutant of vesicular stomatitis virus (M51R VSV) in a murine model of peritoneal surface dissemination from colon cancer (PSD from CRC).

METHODS

Luciferase-expressing CT26 peritoneal tumors were established in Balb/c mice to evaluate the impact of M51R VSV treatment on intraperitoneal tumor growth and overall survival. The mice were treated with either intraperitoneal phosphate buffered saline (n = 10) or 5 × 10⁶ PFU M51R VSV (n = 10) at 5 d after tumor implantation. Tumor bioluminescence was measured every 3 d during the 60-day study period. The immunomodulatory effect of M51R VSV treatment was evaluated in mice treated with either intraperitoneal phosphate buffered saline (n = 21) or M51R VSV (n = 21). Peritoneal lavages were collected at days 1, 3, and 7 after M51R VSV treatment for flow cytometry and multiplex cytokine bead analysis.

RESULTS

A single, intraperitoneal treatment with M51R VSV inhibited the growth of PSD from CRC as evidenced by decreased bioluminescence and improved survival. This treatment approach also resulted in significantly higher frequencies of peritoneal CD4+ T (10.95 ± 1.17 versus 6.19 ± 0.44, P = 0.004) and B1b cells (5.01 ± 0.97 versus 2.20 ± 0.2, P = 0.024). On the other hand, treatment with M51R VSV resulted in fewer myeloid-derived suppressor cells relative to controls (10.66 ± 1.48 versus 14.47 ± 1.06, P = 0.035). M51R-treated peritoneal cavities also contained lower concentrations of immunosuppressive monocyte chemoattractant protein-1 and interleukin 6 cytokines relative to controls.

CONCLUSIONS

Our findings suggest that M51R VSV alters the innate and adaptive immune responses in PSD from CRC. Future studies will delineate specific components of antitumor immunity that result in its therapeutic effect.

Correlation of natural autoantibodies and cardiovascular disease-related anti-bacterial antibodies in pericardial fluid of cardiac surgery patients

Our previous studies showed that anti-citrate synthase (anti-CS) immunoglobulin (Ig)M natural autoantibodies are present in healthy individuals without previous antigen stimulation, but no studies have investigated their presence in the pericardial fluid (PF). Therefore, we detected the natural anti-CS IgG/M autoantibody levels in plasma and PF of cardiac surgery patients and investigated their relationship with cardiovascular disease-associated bacterial pathogens. PF and blood samples of 22 coronary artery bypass graft (CABG) and 10 aortic valve replacement (AVR) patients were tested for total Ig levels, natural autoantibodies and infection-related antibodies using enzyme-linked immunosorbent assay (ELISA) and Luminex methods. The B cell subsets were measured by flow cytometry. The total Ig subclass levels were four to eight times lower in PF than in plasma, but the natural anti-CS IgM autoantibodies showed a relative increase in PF. The frequency of CD19⁺ B lymphocytes was significantly lower in PF than in blood (P = 0·01), with a significant relative increase of B1 cells (P = 0·005). Mycoplasma pneumoniae antibody-positive patients had significantly higher anti-CS IgM levels. In CABG patients we found a correlation between anti-CS IgG levels and M. pneumoniae, Chlamydia pneumoniae and Borrelia burgdorferi antibody titres. Our results provide the first evidence that natural autoantibodies are present in the PF, and they show a significant correlation with certain anti-bacterial antibody titres in a disease-specific manner.

IL-10-producing B cells are characterized by a specific methylation signature

Among the family of regulatory B cells, the subset able to produce interleukin-10 (IL-10) is the most studied, yet its biology is still a matter of investigation. The DNA methylation profiling of the il-10 gene locus revealed a novel epigenetic signature characterizing murine B cells ready to respond through IL-10 synthesis: a demethylated region located 4.5 kb from the transcription starting site (TSS), that we named early IL10 regulatory region (eIL10rr). This feature allows to distinguish B cells that are immediately prone and developmentally committed to IL-10 production from those that require a persistent stimulation to exert an IL-10-mediated regulatory function. These late IL-10 producers are instead characterized by a delayed IL10 regulatory region (dIL10rr), a partially demethylated DNA portion located 9 kb upstream from the TSS. A demethylated region was also found in human IL-10-producing B cells and, very interestingly, in some B-cell malignancies, such as chronic lymphocytic leukemia and mantle cell lymphoma, characterized by an immunosuppressive microenvironment. Our findings define murine and human regulatory B cells as an epigenetically controlled functional state of mature B cell subsets and open a new perspective on IL-10 regulation in B cells in homeostasis and disease.

Injury derived autoimmunity: Anti-perlecan/LG3 antibodies in transplantation

Ischemic, immunologic or pharmacological stressors can induce vascular injury and endothelial apoptosis in organ donors, in transplant candidates due to the impact of end stage organ failure on the vasculature, and in association with peri-transplantation events. Vascular injury may shape innate and adaptive immune responses, leading to dysregulation in the balance between tolerance and immunoreactivity to vascular-derived antigens. Mounting evidence shows that the early stages of apoptosis, characterized by the absence of membrane permeabilization, are prone to trigger various modes of intercellular communication allowing neoantigen production, exposure, or both. In this review, we present the evidence for the release of LG3, an immunogenic fragment of perlecan, as a consequence of caspase-3 dependent vascular apoptosis leading to the genesis of anti-LG3 autoantibodies and the consequences of these autoantibodies in native and transplanted kidneys.

New insights into immune mechanisms of antiperlecan/LG3 antibody production: Importance of T cells and innate B1 cells

Autoantibodies against perlecan/LG3 (anti-LG3) have been associated with increased risks of delayed graft function, acute rejection, and reduced long-term survival. High titers of anti-LG3 antibodies have been found in de novo renal transplants recipients in the absence of allosensitizing or autoimmune conditions. Here, we seek to understand the pathways controlling anti-LG3 production prior to transplantation. Mice immunized with recombinant LG3 produce concomitantly IgM and IgG anti-LG3 antibodies suggesting a memory response. ELISpot confirmed the presence of LG3-specific memory B cells in nonimmunized mice. Purification of B1 and B2 subtypes identified peritoneal B1 cells as the major source of memory B cells reactive to LG3. Although nonimmunized CD4-deficient mice were found to express LG3-specific memory B cells, depletion of CD4⁺ T cells in wild type mice during immunization significantly decreased anti-LG3 production. These results demonstrate that B cell memory to LG3 is T cell independent but that production of anti-LG3 antibodies requires T cell help. Further supporting an important role for T cells in controlling anti-LG3 levels, we found that human renal transplant recipients show a significant decrease in anti-LG3 titers upon the initiation of CNI-based immunosuppression. Collectively, these results identify T cell targeting interventions as a means of reducing anti-LG3 levels in renal transplant patients.

Emerging Roles for Immune Cells and MicroRNAs in Modulating the Response to Cardiac Injury

Stimulating cardiomyocyte regeneration after an acute injury remains the central goal in cardiovascular regenerative biology. While adult mammals respond to cardiac damage with deposition of rigid scar tissue, adult zebrafish and salamander unleash a regenerative program that culminates in new cardiomyocyte formation, resolution of scar tissue, and recovery of heart function. Recent studies have shown that immune cells are key to regulating pro-inflammatory and pro-regenerative signals that shift the injury microenvironment toward regeneration. Defining the genetic regulators that control the dynamic interplay between immune cells and injured cardiac tissue is crucial to decoding the endogenous mechanism of heart regeneration. In this review, we discuss our current understanding of the extent that macrophage and regulatory T cells influence cardiomyocyte proliferation and how microRNAs (miRNAs) regulate their activity in the injured heart.

Plasma Cell Alloantigen 1 and IL-10 Secretion Define Two Distinct Peritoneal B1a B Cell Subsets With Opposite Functions, PC1high Cells Being Protective and PC1low Cells Harmful for the Growing Fetus

B cells possess various immuno regulatory functions. However, research about their participation in tolerance induction toward the fetus is just emerging. Accumulating evidence supports the idea that B cells can play seemingly conflicting roles during pregnancy, either protecting or harming the fetus. Previous findings indicated the presence of two different peritoneal B cell subsets, defined by the expression of the plasma cell alloantigen 1 (PC1) and with distinct immune modulatory functions. Here, we aimed to study the participation of these two B cell subsets, on pregnancy outcome in a murine model of disturbed fetal tolerance. The frequencies and cell numbers of peritoneal and splenic CD19⁺IL-10⁺ and CD19⁺CD5⁺IL-10⁺PC1⁺ cells were assessed in virgin as well as normal pregnant (NP) and abortion-prone (AP) females during the course of gestation. Peritoneal PC1^low or PC1^high B1a B cells were sorted, analyzed for their ability to secrete IL-10 and adoptively transferred into NP or AP females. On gestation day (gd) 12, the abortion rate as well as the frequencies and cell numbers of regulatory T cells, TH1 and TH17 cells were determined in spleens and decidua. In addition, mRNA expression of IL-10, TGF-β, IFN-γ, and TNF-α was analyzed in decidual tissue. Peritoneal CD19⁺IL-10⁺ and CD19⁺CD5⁺IL-10⁺PC1⁺ frequencies fluctuated during the progression of normal pregnancies while no significant changes were observed in spleen. AP females showed significantly reduced frequencies of both B cell populations and exhibited an altered peritoneal PC1^high/PC1^low ratio at gd10. Adoptive transfers of PC1^low B1a B cells into NP females increased the abortion rate in association with a reduced splenic regulatory T/TH17 ratio. By contrast, the transfer of PC1^high B1a B cells into AP females significantly diminished the fetal rejection rate and significantly reduced the numbers of splenic TH17 cells. Our results suggest that the peritoneum harbors two distinct B1a B cell subsets that can be distinguished by their PC1 expression. Whereas PC1^high B1a B cells seem to support fetal survival, PC1^low cells B1a B cells may compromise fetal well-being.

Many layers of embryonic hematopoiesis: new insights into B-cell ontogeny and the origin of hematopoietic stem cells

In adult hematopoiesis, the hematopoietic stem cell (HSC) sits at the top of a hierarchy of hematopoietic progenitors responsible for generating the diverse repertoire of blood and immune cells. During embryonic development, however, the initial waves of hematopoiesis provide the first functioning blood cells of the developing embryo, such as primitive erythrocytes arising in the yolk sac, independently of HSCs. In the field of developmental immunology, it has been recognized that some components of the immune system, such as B-1a lymphocytes, are uniquely produced during the embryonic and neonatal period, suggesting a "layered" development of immunity. Several recent studies have shed new light on the developmental origin of the layered immune system, suggesting complex and sometimes multiple contributions to unique populations of innate-like immune cells from both fetal HSCs and earlier HSC-independent progenitors. In this review, we will attempt to synthesize these studies to provide an integrated model of developmental hematopoiesis and layered immunity that may offer new insights into the origin of HSCs.

PD-L2 Regulates B-1 Cell Antibody Production against Phosphorylcholine through an IL-5-Dependent Mechanism

B-1 cells produce natural Abs which provide an integral first line of defense against pathogens while also performing important homeostatic housekeeping functions. In this study, we demonstrate that programmed cell death 1 ligand 2 (PD-L2) regulates the production of natural Abs against phosphorylcholine (PC). Naive PD-L2-deficient (PD-L2^-/-) mice produced significantly more PC-reactive IgM and IgA. This afforded PD-L2^-/- mice with selectively enhanced protection against PC-expressing nontypeable Haemophilus influenzae, but not PC-negative nontypeable Haemophilus influenzae, relative to wild-type mice. PD-L2^-/- mice had significantly increased PC-specific CD138⁺ splenic plasmablasts bearing a B-1a phenotype, and produced PC-reactive Abs largely of the T15 Id. Importantly, PC-reactive B-1 cells expressed PD-L2 and irradiated chimeras demonstrated that B cell-intrinsic PD-L2 expression regulated PC-specific Ab production. In addition to increased PC-specific IgM, naive PD-L2^-/- mice and irradiated chimeras reconstituted with PD-L2^-/- B cells had significantly higher levels of IL-5, a potent stimulator of B-1 cell Ab production. PD-L2 mAb blockade of wild-type B-1 cells in culture significantly increased CD138 and Blimp1 expression and PC-specific IgM, but did not affect proliferation. PD-L2 mAb blockade significantly increased IL-5⁺ T cells in culture. Both IL-5 neutralization and STAT5 inhibition blunted the effects of PD-L2 mAb blockade on B-1 cells. Thus, B-1 cell-intrinsic PD-L2 expression inhibits IL-5 production by T cells and thereby limits natural Ab production by B-1 cells. These findings have broad implications for the development of therapeutic strategies aimed at altering natural Ab levels critical for protection against infectious disease, autoimmunity, allergy, cancer, and atherosclerosis.

Microbiota-Induced Antibodies Are Essential for Host Inflammatory Responsiveness to Sterile and Infectious Stimuli

The indigenous intestinal microbiota is frequently considered an additional major organ of the human body and exerts profound immunomodulating activities. Germ-free (GF) mice display a significantly different inflammatory responsiveness pattern compared with conventional (CV) mice, and this was dubbed a "hyporesponsive phenotype." Taking into account that the deposition of immune complexes is a major event in acute inflammation and that GF mice have a distinct Ig repertoire and B cell activity, we aimed to evaluate whether this altered Ig repertoire interferes with the inflammatory responsiveness of GF mice. We found that serum transfer from CV naive mice was capable of reversing the inflammatory hyporesponsiveness of GF mice in sterile inflammatory injury induced by intestinal ischemia and reperfusion, as well as in a model of lung infection by Klebsiella pneumoniae Transferring serum from Ig-deficient mice to GF animals did not alter their response to inflammatory insult; however, injecting purified Abs from CV animals restored inflammatory responsiveness in GF mice, suggesting that natural Abs present in serum were responsible for altering GF responsiveness. Mechanistically, injection of serum and Ig from CV mice into GF animals restored IgG deposition, leukocyte influx, NF-κB activation, and proinflammatory gene expression in inflamed tissues and concomitantly downregulated annexin-1 and IL-10 production. Thus, our data show that microbiota-induced natural Abs are pivotal for host inflammatory responsiveness to sterile and infectious insults.

Fetal and adult progenitors give rise to unique populations of CD8+ T cells

During the ontogeny of the mammalian immune system, distinct lineages of cells arise from fetal and adult hematopoietic stem cells (HSCs) during specific stages of development. However, in some cases, the same immune cell type is produced by both HSC populations, resulting in the generation of phenotypically similar cells with distinct origins and divergent functional properties. In this report, we demonstrate that neonatal CD8⁺ T cells preferentially become short-lived effectors and adult CD8⁺ T cells selectively form long-lived memory cells after infection because they are derived from distinct progenitor cells. Notably, we find that naïve neonatal CD8⁺ T cells originate from a progenitor cell that is distinguished by expression of Lin28b. Remarkably, ectopic expression of Lin28b enables adult progenitors to give rise to CD8⁺ T cells that are phenotypically and functionally analogous to those found in neonates. These findings suggest that neonatal and adult CD8⁺ T cells belong to separate lineages of CD8⁺ T cells, and potentially explain why it is challenging to elicit memory CD8⁺ T cells in early life.

The role of B-1 cells in inflammation

B-1 lymphocytes exhibit unique phenotypic, ontogenic, and functional characteristics that differ from the conventional B-2 cells. B-1 cells spontaneously secrete germline-like, repertoire-skewed polyreactive natural antibody, which acts as a first line of defense by neutralizing a wide range of pathogens before launching of the adaptive immune response. Immunomodulatory molecules such as interleukin-10, adenosine, granulocyte-macrophage colony-stimulating factor, interleukin-3, and interleukin-35 are also produced by B-1 cells in the presence or absence of stimulation, which regulate acute and chronic inflammatory diseases. Considerable progress has been made during the past three decades since the discovery of B-1 cells, which has improved not only our understanding of their phenotypic and ontogenic uniqueness but also their role in various inflammatory diseases including influenza, pneumonia, sepsis, atherosclerosis, inflammatory bowel disease, autoimmunity, obesity and diabetes mellitus. Recent identification of human B-1 cells widens the scope of this field, leading to novel innovations that can be implemented from bench to bedside. Among the vast number of studies on B-1 cells, we have carried out a literature review highlighting current trends in the study of B-1 cell involvement during inflammation, which may result in a paradigm shift toward sustainable therapeutics in various inflammatory diseases.

An Overview of B-1 Cells as Antigen-Presenting Cells

The role of B cells as antigen-presenting cells (APCs) has been extensively studied, mainly in relation to the activation of memory T cells. Considering the B cell subtypes, the role of B-1 cells as APCs is beginning to be explored. Initially, it was described that B-1 cells are activated preferentially by T-independent antigens. However, some reports demonstrated that these cells are also involved in a T-dependent response. The aim of this review is to summarize information about the ability of B-1 cells to play a role as APCs and to briefly discuss the role of the BCR and toll-like receptor signals in this process. Furthermore, some characteristics of B-1 cells, such as natural IgM production and phagocytic ability, could interfere in the participation of these cells in the onset of an adaptive response.

Role of B cells in host defense against primary Coxiella burnetii infection

Despite Coxiella burnetii being an obligate intracellular bacterial pathogen, our recent study demonstrated that B cells play a critical role in vaccine-induced immunity to C. burnetii infection by producing protective antibodies. However, the role of B cells in host defense against primary C. burnetii infection remains unclear. In this study, we investigated whether B cells play an important role in host defense against primary C. burnetii infection. The results showed that peritoneal B cells were able to phagocytose virulent C. burnetii bacteria and form Coxiella-containing vacuoles (CCVs) and that C. burnetii can infect and replicate in peritoneal B1a subset B cells in vitro, demonstrating a potential role for peritoneal B cells in host defense against C. burnetii infection in vivo. In addition, the results showing that B1a cells secreted a high level of interleukin-10 (IL-10) in response to C. burnetii infection in vitro suggest that B1a cells may play an important role in inhibiting the C. burnetii infection-induced inflammatory response. The observation that adoptive transfer of peritoneal B cells did not significantly affect the severity of C. burnetii infection-induced diseases in both severe combined immunity-deficient (SCID) and μMT mice indicates that peritoneal B cells alone may not be able to control C. burnetii infection. In contrast, our finding that C. burnetii infection induced more-severe splenomegaly and a higher bacterial burden in the spleens of B1a cell-deficient Bruton's tyrosine kinase x-linked immunity-deficient (BTK(xid)) mice than in their wild-type counterparts further suggests that B1a cells play an important role in host defense against primary C. burnetii infection.

Hematopoiesis in the equine fetal liver suggests immune preparedness

We investigated how the equine fetus prepares its pre-immune humoral repertoire for an imminent exposure to pathogens in the neonatal period, particularly how the primary hematopoietic organs are equipped to support B cell hematopoiesis and immunoglobulin (Ig) diversity. We demonstrated that the liver and the bone marrow at approximately 100 days of gestation (DG) are active sites of hematopoiesis based on the expression of signature messenger RNA (mRNA) (c-KIT, CD34, IL7R, CXCL12, IRF8, PU.1, PAX5, NOTCH1, GATA1, CEBPA) and protein markers (CD34, CD19, IgM, CD3, CD4, CD5, CD8, CD11b, CD172A) of hematopoietic development and leukocyte differentiation molecules, respectively. To verify Ig diversity achieved during the production of B cells, V(D)J segments were sequenced in primary lymphoid organs of the equine fetus and adult horse, revealing that similar heavy chain VDJ segments and CDR3 lengths were most frequently used independent of life stage. In contrast, different lambda light chain segments were predominant in equine fetal compared to adult stage, and surprisingly, the fetus had less restricted use of variable gene segments to construct the lambda chain. Fetal Igs also contained elements of sequence diversity, albeit to a smaller degree than that of the adult horse. Our data suggest that the B cells produced in the liver and bone marrow of the equine fetus generate a wide repertoire of pre-immune Igs for protection, and the more diverse use of different lambda variable gene segments in fetal life may provide the neonate an opportunity to respond to a wider range of antigens at birth.

B1b cells recognize protective antigens after natural infection and vaccination

There are multiple, distinct B-cell populations in human beings and other animals such as mice. In the latter species, there is a well-characterized subset of B-cells known as B1 cells, which are enriched in peripheral sites such as the peritoneal cavity but are rare in the blood. B1 cells can be further subdivided into B1a and B1b subsets. There may be additional B1 subsets, though it is unclear if these are distinct populations or stages in the developmental process to become mature B1a and B1b cells. A limitation in understanding B1 subsets is the relative paucity of specific surface markers. In contrast to mice, the existence of B1 cells in human beings is controversial and more studies are needed to investigate the nature of these enigmatic cells. Examples of B1b antigens include pneumococcal polysaccharide and the Vi antigen from Salmonella Typhi, both used routinely as vaccines in human beings and experimental antigens such as haptenated-Ficoll. In addition to inducing classical T-dependent responses some proteins are B1b antigens and can induce T-independent (TI) immunity, examples include factor H binding protein from Borrelia hermsii and porins from Salmonella. Therefore, B1b antigens can be proteinaceous or non-proteinaceous, induce TI responses, memory, and immunity, they exist in a diverse range of pathogenic bacteria, and a single species can contain multiple B1b antigens. An unexpected benefit to studying B1b cells is that they appear to have a propensity to recognize protective antigens in bacteria. This suggests that studying B1b cells may be rewarding for vaccine design as immunoprophylactic and immunotherapeutic interventions become more important due to the decreasing efficacy of small molecule antimicrobials.

Spinal cord injury impacts B cell production, homeostasis, and activation

Complex interactions govern the interplay of central nervous and immune systems, including the generation, homeostatic maintenance, and activation of B cells. Accordingly, spinal cord injury will likely impact all of these processes. Several laboratories have recently explored this possibility, and their observations in aggregate reveal both acute and chronic consequences that can vary based on the injury location. Acute effects include a transient cessation of bone marrow B lymphopoiesis, with a corresponding drop in the peripheral follicular and transitional B cell subsets, whereas the marginal zone subset is preserved. Despite recovery of B lymphopoiesis by 28 days post injury, follicular B cell numbers remain depressed; this may reflect reduced levels of the homeostatic cytokine BLyS. In general, the ability to mount T dependent antibody responses after injury are intact, as are pre-existing memory B cell pools and antibody levels. In contrast, T-independent responses are chronically compromised. Both glucocorticoid-dependent and -independent processes mediate these effects, but a detailed understanding of the mechanisms involved awaits further study. Nonetheless, these observations in toto strengthen the growing appreciation for bidirectional interactions between the CNS and immune system, highlighting the need for further basic and translational efforts.

Multiple potential roles for B cells in atherosclerosis

The development of atherosclerosis is the major etiological factor causing cardiovascular disease and constitutes a lipid-induced, chronic inflammatory and autoimmune disease of the large arteries. A long-standing view of the protective role of B cells in atherosclerosis has been challenged by recent studies using B cell depletion in animal models. Whereas complete B cell deficiency increases atherosclerosis, depletion of B2 but not B1 cells reduces atherosclerosis. This has led to a re-evaluation of the multiple potential pathways by which B cells can regulate atherosclerosis, and the apparent opposing roles of B1 and B2 cells. B cells, in addition to having the unique ability to produce antibodies, are now recognized to play a number of important roles in the immune system, including cytokine production and direct regulation of T cell responses. This review summarizes current knowledge on B cell subsets and functions, and how these could distinctly influence atherosclerosis development.

B cells and humoral immunity in atherosclerosis

Insights into the important contribution of inflammation and immune functions in the development and progression of atherosclerosis have greatly improved our understanding of this disease. Although the role of T cells has been extensively studied for decades, only recently has the role of B cells gained more attention. Recent studies have identified differential effects of different B-cell subsets and helped to clarify the still poorly understood mechanisms by which these act. B1 cells have been shown to prevent lesion formation, whereas B2 cells have been suggested to promote it. Natural IgM antibodies, mainly derived from B1 cells, have been shown to mediate atheroprotective effects, but the functional role of other immunoglobulin classes, particularly IgG, still remains elusive. In this review, we will focus on recent insights on the role of B cells and various immunoglobulin classes and how these may mediate their effects in atherosclerotic lesion formation. Moreover, we will highlight potential therapeutic approaches focusing on B-cell depletion that could be used to translate experimental evidence to human disease.

Gene expression in B-1 cells from lupus-prone mice

New Zealand Black X New Zealand White F1 [(NZB/NZW)F1] mice develop an autoimmune condition with similarities to human systemic lupus erythematosus (SLE). In this study, we demonstrate that B-1 cells, which have previously been reported to be involved in several autoimmune diseases, have altered gene expression in these mice. RNA was extracted from purified B-1 cells of disease-free C57BL/6 mice and lupus-prone (NZB/NZW)F1 mice. Gene expression was analysed using DNA microarray techniques and validated by real time reverse transcriptase polymerase chain reaction (RT-PCR). In (NZB/NZW)F1 mice, some genes had altered expression patterns compared to disease-free controls. Specifically, the upregulation of Ifitm1, Pvrl2 and Ifi202b and downregulation of Trp53bp1 mRNA were observed in (NZB/NZW)F1 mice. These genes are known to be associated with autoimmune diseases. This pattern of gene expression in B-1 cells could understanding of the pathogenesis of SLE. Thus, it is reasonable to hypothesise that the altered gene expression observed in B-1 cells in our experimental model is important for SLE prognosis and therapy, and these implications are discussed herein.

Endocrine factors modulating immune responses in pregnancy

How the semi-allogeneic fetus is tolerated by the maternal immune system remains a fascinating phenomenon. Despite extensive research activity in this field, the mechanisms underlying fetal tolerance are still not well understood. However, there are growing evidences that immune–immune interactions as well as immune–endocrine interactions build up a complex network of immune regulation that ensures fetal survival within the maternal uterus. In the present review, we aim to summarize emerging research data from our and other laboratories on immune modulating properties of pregnancy hormones with a special focus on progesterone, estradiol, and human chorionic gonadotropin. These pregnancy hormones are critically involved in the successful establishment, maintenance, and termination of pregnancy. They suppress detrimental maternal alloresponses while promoting tolerance pathways. This includes the reduction of the antigen-presenting capacity of dendritic cells (DCs), monocytes, and macrophages as well as the blockage of natural killer cells, T and B cells. Pregnancy hormones also support the proliferation of pregnancy supporting uterine killer cells, retain tolerogenic DCs, and efficiently induce regulatory T (Treg) cells. Furthermore, they are involved in the recruitment of mast cells and Treg cells into the fetal–maternal interface contributing to a local accumulation of pregnancy-protective cells. These findings highlight the importance of endocrine factors for the tolerance induction during pregnancy and encourage further research in the field.

Glucose impairs B-1 cell function in diabetes

B-1 lymphocytes produce natural immunoglobulin (Ig)M, among which a large proportion is directed against apoptotic cells and altered self-antigens, such as modified low-density lipoprotein (LDL). Thereby, natural IgM maintains homeostasis in the body and is also protective against atherosclerosis. Diabetic patients have an increased risk of developing certain infections as well as atherosclerosis compared with healthy subjects, but the underlying reason is not known. The aim of this study was to investigate whether diabetes and insulin resistance affects B-1 lymphocytes and their production of natural IgM. We found that diabetic db/db mice had lower levels of peritoneal B-1a cells in the steady state-condition compared to controls. Also, activation of B-1 cells with the Toll-like receptor (TLR)-4 agonist Kdo2-Lipid A or immunization against Streptococcus pneumoniae led to a blunted IgM response in the diabetic db/db mice. In-vitro experiments with isolated B-1 cells showed that high concentrations of glucose, but not insulin or leptin, caused a reduced secretion of total IgM and copper-oxidized (CuOx)-LDL- and malondialdehyde (MDA)-LDL-specific IgM from B-1 cells in addition to a decreased differentiation into antibody-producing cells, proliferation arrest and increased apoptosis. These results suggest that metabolic regulation of B-1 cells is of importance for the understanding of the role of this cell type in life-style-related conditions.

Exploring binding and effector functions of natural human antibodies using synthetic immunomodulators

The ability to profile the prevalence and functional activity of endogenous antibodies is of vast clinical and diagnostic importance. Serum antibodies are an important class of biomarkers and are also crucial elements of immune responses elicited by natural disease-causing agents as well as vaccines. In particular, materials for manipulating and/or enhancing immune responses toward disease-causing cells or viruses have exhibited significant promise for therapeutic applications. Antibody-recruiting molecules (ARMs), bifunctional organic molecules that redirect endogenous antibodies to pathological targets, thereby increasing their recognition and clearance by the immune system, have proven particularly interesting. Notably, although ARMs capable of hijacking antibodies against oligosaccharides and electron-poor aromatics have proven efficacious, systematic comparisons of the prevalence and effectiveness of natural anti-hapten antibody populations have not appeared in the literature. Herein we report head-to-head comparisons of three chemically simple antigens, which are known ligands for endogenous antibodies. Thus, we have chemically synthesized bifunctional molecules containing 2,4-dinitrophenyl (DNP), phosphorylcholine (PC), and rhamnose. We have then used a combination of ELISA, flow cytometry, and cell-viability assays to compare these antigens in terms of their abilities both to recruit natural antibody from human serum and also to direct serum-dependent cytotoxicity against target cells. These studies have revealed rhamnose to be the most efficacious of the synthetic antigens examined. Furthermore, analysis of 122 individual serum samples has afforded comprehensive insights into population-wide prevalence and isotype distributions of distinct anti-hapten antibody populations. In addition to providing a general platform for comparing and studying anti-hapten antibodies, these studies serve as a useful starting point for the optimization of antibody-recruiting molecules and other synthetic strategies for modulating human immunity.

Antiphospholipid IgM antibody response in acute and chronic Mycobacterium tuberculosis mouse infection model

BACKGROUND AND AIMS

The clinical management of tuberculosis (TB) could be greatly improved by an affordable biomarker test to monitor treatment response. Here, we examined changes in immunoglobulin M (IgM) antibody response to lipids as a potential biomarker for monitoring TB treatment in an experimental mouse model.

METHODS

We performed enzyme-linked immunosorbent assay to investigate changes in IgM antibody response against cardiolipin (CL), phosphatidylcholine (PTC), phosphatidylethanolamine (PE), phosphatidylinositol (PI) and sphingolipid (SL) in BALB/c mice that were treated after being infected with Mycobacterium tuberculosis for 4 weeks (acute infection) and 20 weeks (chronic infection). Cytokine levels [interleukin (IL)-5, IL-10, interferon-gamma (IFN-γ), monocyte chemoattractant protein-1 (MCP-1)] in lung and spleen homogenates as well as in blood were also compared.

RESULTS

In both acutely and chronically infected mice, lungs were sterilised of M. tuberculosis infection after 8 weeks of treatment. The IgM response to CL, PTC, PE, PI and SL were consistently elevated throughout the course of infection in chronically infected mice compared with acutely infected mice. In acutely infected mice, the IgM antibody response against CL significantly decreased after 8 weeks of treatment, but not against other lipids. In chronically infected mice, the IgM response showed no significant changes against any of the lipids after 8 weeks of treatment. Of the cytokines examined, only MCP-1 levels in lungs decreased significantly after treatment.

CONCLUSION

These findings demonstrate that antilipid IgM antibody can remain elevated in chronically infected mice, but with treatment, only anti-CL IgM antibody levels decreased together with M. tuberculosis bacterial burden in acutely infected mice. Treatment did not affect antilipid IgM levels in chronically infected mice.

The parity-associated microenvironmental niche in the omental fat band is refractory to ovarian cancer metastasis

Ovarian cancer is an insidious and aggressive disease of older women, typically undiscovered before peritoneal metastasis due to its asymptomatic nature and lack of early detection tools. Epidemiologic studies suggest that child-bearing (parity) is associated with decreased ovarian cancer risk, although the molecular mechanisms responsible for this phenomenon have not been delineated. Ovarian cancer preferentially metastasizes to the omental fat band (OFB), a secondary lymphoid organ that aids in filtration of the peritoneal serous fluid (PSF) and helps combat peritoneal infections. In the present study, we assessed how parity and age impact the immune compositional profile in the OFB of mice, both in the homeostatic state and as a consequence of peritoneal implantation of ovarian cancer. Using fluorescence-activated cell sorting analysis and quantitative real-time PCR, we found that parity was associated with a significant reduction in omental monocytic subsets and B1-B lymphocytes, correlating with reduced homeostatic expression levels of key chemoattractants and polarization factors (Ccl1, Ccl2, Arg1, and Cxcl13). Of note, parous animals exhibited significantly reduced tumor burden following intraperitoneal implantation compared with nulliparous animals. This was associated with a reduction in tumor-associated neutrophils and macrophages, as well as in the expression levels of their chemoattractants (Cxcl1 and Cxcl5) in the OFB and PSF. These findings define a preexisting "parity-associated microenvironmental niche" in the OFB that is refractory to metastatic tumor seeding and outgrowth. Future studies designed to manipulate this niche may provide a novel means to mitigate peritoneal dissemination of ovarian cancer.

Specificity, promiscuity, and precursor frequency in immunoreceptors

The immune system is comprised of various immune cell populations that utilize a spectrum of immunoreceptors characterized by different levels of specificity, diversity, and prevalence within a host and across a population. These range from the universal receptors employed by both innate cells and innate-like cells, such as NKT and MAIT cells, through to receptors expressed on T cells with sporadic incidence. Here we review recent advances in understanding the molecular mechanisms that drive the observed spectra of T cell receptors in vivo.

Intra-abdominal fat depots represent distinct immunomodulatory microenvironments: a murine model

White adipose tissue (WAT) is a multi-faceted endocrine organ involved in energy storage, metabolism, immune function and disease pathogenesis. In contrast to subcutaneous fat, visceral fat (V-WAT) has been associated with numerous diseases and metabolic disorders, indicating specific functions related to anatomical location. Although visceral depots are often used interchangeably in V-WAT-associated disease studies, there has been a recent subdivision of V-WAT into "true visceral" and non-visceral intra-abdominal compartments. These were associated with distinct physiological roles, illustrating a need for depot-specific information. Here, we use FACS analysis to comparatively characterize the leukocyte and progenitor populations in the stromal vascular fraction (SVF) of peritoneal serous fluid (PSF), parametrial (pmWAT), retroperitoneal (rpWAT), and omental (omWAT) adipose tissue from seven-month old C57BL/6 female mice. We found significant differences in SVF composition between all four microenvironments. PSF SVF was comprised almost entirely of CD45(+) leukocytes (>99%), while omWAT contained less, but still almost two-fold more leukocytes than pmWAT and rpWAT (75%, 38% and 38% respectively; p<0.01). PmWAT was composed primarily of macrophages, whereas rpWAT more closely resembled omWAT, denoted by high levels of B1 B-cell and monocyte populations. Further, omWAT harbored significantly higher proportions of T-cells than the other tissues, consistent with its role as a secondary lymphoid organ. These SVF changes were also reflected in the gene expression profiles of the respective tissues. Thus, intra-abdominal fat pads represent independent immunomodulatory microenvironments and should be evaluated as distinct entities with unique contributions to physiological and pathological processes.

Nuclear antigens and auto/alloantibody responses: friend or foe in transplant immunology

In addition to cellular immune responses, humoral immune responses, mediated by natural antibodies, autoantibodies, and alloantibodies, have increasingly been recognized as causes of organ transplant rejection. In our previous studies, we have demonstrated the induction of antinuclear antibodies against histone H1 and high-mobility group box 1 (HMGB1), in both experimental and clinical liver transplant tolerance. The active induction of antinuclear antibodies is usually an undesirable phenomenon, but it is often observed after liver transplantation. However, the release of nuclear antigens and its suppression by neutralizing antibodies are proposed to be important in the initiation and regulation of immune responses. In this review article, we summarize the current understanding of nuclear antigens and corresponding antinuclear regulatory antibodies (Abregs) on infection, injury, inflammation, transplant rejection, and tolerance induction and discuss the significance of nuclear antigens as diagnostic and therapeutic targets.