Role of distinct immune components in the radiation-induced abrogation of systemic lupus erythematosus development in mice

Age-related accumulation of B-1 cell progenitors in mice reflects changes in miR15a/16-1 expression and radioresistance capacity

Hyperproliferative diseases such as Chronic Lymphocytic Leukemia (CLL) and Systemic Lupus Erythematosus (SLE) are potentially related to some disturbance in the apoptosis pathway, specifically in B-1a cells (CD5⁺). Accumulation of B-1a cells in lymphoid organs, bone marrow or periphery is observed in some leukemia experimental murine models along aging. It is known that aging also increases the healthy B-1 cell population. However, it is not yet clear if it happens due to self-renewal of mature cells or proliferation of progenitor cells. Herein we demonstrated that the B-1 cell precursor population (B-1p) from bone marrow of middle-aged mice is higher than from young mice. Also, these aged cells are more resistant to irradiation and have downregulation of microRNA15a/16. Alterations in these microRNAs expression and in Bcl-2 regulation were already described in human hematological malignancies and new therapeutically approaches focus on that axis. This finding could explain the early events related to cell transformation during aging and correlate with beginning of symptoms in hyperproliferative diseases. Moreover, studies have already reported these pro-B-1 as a contributor to the origin of other leukemia (Acute Myeloid Leukemia - AML). Our results point to a possible relation between B-1 cell precursors and hyperproliferation during aging. We hypothesized that this population could be maintained until the mature status of the cell or reveal changes that result in re-activation of precursor in adult bone marrow, culminating in accumulation of B-1 cells later. Based on this, B-1 cell progenitor could represent an origin for B cell malignancies and a new candidate target to diagnose and treatments in the future.

Impact of sleep restriction in B-1 cells activation and differentiation

B-1 lymphocytes are a subtype of B cells with functional and phenotypic features that differ from conventional B lymphocytes. These cells are mainly located in mice's pleural and peritoneal cavities and express unconventional B cell surface markers. B-1 cells participate in immunity by producing antibodies, cytokines, and chemokines and physically interacting with other immune cells. In addition, B-1 cells can differentiate into mononuclear phagocyte-like cells and phagocytize several pathogens. However, the activation and differentiation of B-1 cells are not entirely understood. It is known that several factors can influence B-1 cells, such as pathogens components and the immune response. This work aimed to evaluate the influence of chronic stress on B-1 cell activation and differentiation into phagocytes. The experimental sleep restriction was used as a stress model since the sleep alteration alters several immune cells' functions. Thus, mice were submitted to sleep restriction for 21 consecutive days, and the activation and differentiation of B-1 cells were analyzed. Our results demonstrated that B-1 cells initiated the differentiation process into mononuclear phagocytes after the period of sleep restriction. In addition, we detected a significant decrease in lymphoid lineage commitment factors (EBF, E2A, Blnk) (*P < 0.05) and an increase in the G-CSFR gene (related to the myeloid lineage commitment factor) (****P < 0.0001), as compared to control mice no submitted to sleep restriction. An increase in the co-stimulatory molecules CD80 and CD86 (**P < 0.01 and *P < 0.05, respectively) and a higher production of nitric oxide (NO) (*P < 0.05) and reactive oxygen species (ROS) (*P < 0.05) were also observed in B-1 cells from mice submitted to sleep restriction. Nevertheless, B-1 cells from sleep-restricted mice showed a significant reduction in the Toll-like receptors (TLR)-2, -6, and -9, and interleukine-10 (IL-10) cytokine expression (***P < 0.001) as compared to control. Sleep-restricted mice intraperitoneally infected withL. amazonensispromastigotes showed a reduction in the average internalized parasites (*P < 0.05) by B-1 cells. These findings suggest that sleep restriction interferes with B-1 lymphocyte activation and differentiation. In addition, b-1 cells assumed a more myeloid profile but with a lower phagocytic capacity in this stress condition.

Quercetin shortened survival of radio-resistant B-1 cells in vitro and in vivo by restoring miR15a/16 expression

Chronic lymphocytic leukemia (CLL) is a malignancy disease characterized by the expansion of CD5⁺ B-1 cells. The NZB mouse model of CLL shows similarities to human CLL, has age-associated increase in malignant B-1 clones and decreased expression of miR-15a/16. It was demonstrated that systemic lentiviral delivery of miR-15a/16 ameliorates disease manifestations in this mouse model. Nowadays, new therapeutic approaches have been focus on miRNA in cancer cells. Natural compounds like quercetin can modulate these miRNAs, consequently, suppress oncogenes or stimulate tumor suppressor genes by altering miRNA expressions. Here we investigate the effects of quercetin on miRNA15a/16 expression by radio-resistant B-1 cells. It has been described that a small percentage of B-1 cell survives to irradiation in vitro, and these cells show similarities to B-CLL cells. In these cells, the level of miR15a/16 is diminished and Bcl-2 is overexpressed. Quercetin treatment restore both, miR15a/16 and Bcl-2, to normal levels. Furthermore, transference of radioresistant B-1 cells to NOD/SCID mice causes an expansion of this population and also a migration to the liver. However, after quercetin treatment, even radioresistant B-1 cells are not able to expand or disseminate in vivo, and the levels of miR15a/16 and Bcl-2 are also normalized. Our data support the hypothesis that quercetin is an important adjuvant molecule that acts on miRNA15a/16 level and leads cells more permissive to apoptosis. This work could help to design new approaches to therapy in CLL patients.

Effects of extracellular vesicles released by peritoneal B-1 cells on experimental Leishmania (Leishmania) amazonensis infection

B-1 cells are a B-lymphocyte subtype whose roles in immunity are not completely defined. These cells can produce cytokines (mainly IL-10) and natural and specific antibodies. Currently, extracellular vesicles (EVs) released by immune cells have emerged as new important entities in cell-cell communication. Immune cells release EVs that can activate and/or modulate other immune cells. Here, we characterized the EVs released by peritoneal B-1 cells infected or not with Leishmania (Leishmania) amazonensis. This Leishmania species causes cutaneous leishmaniasis and can infect macrophages and B-1 cells. Our results showed that peritoneal B-1 cells spontaneously release EVs, but the parasite stimulated an increase in EVs production by peritoneal B-1 cells. The treatment of BALB/c and C57BL/6 bone marrow-derived macrophages (BMDM) with EVs from infected peritoneal B-1 cells led to differential expression of iNOS, IL-6, IL-10, and TNF-α. Additionally, BALB/c mice previous treated with EVs released by peritoneal B-1 cells showed a significant lower lesion size and parasite burden. Thus, this study demonstrated that peritoneal B-1 cells could release EVs that can alter the functions of macrophages in vitro and in vivo these EVs altered the course of L. amazonensis infection. These findings represent the first evidence that EVs from peritoneal B-1 cells can act as a new mechanism of cellular communication between macrophages and B-1 cells, contributing to immunity against experimental leishmaniasis.

Extracellular Vesicles Released by Leishmania (Leishmania) amazonensis Promote Disease Progression and Induce the Production of Different Cytokines in Macrophages and B-1 Cells

The extracellular vesicles (EVs) released by Leishmania can contribute to the establishment of infection and host immunomodulation. In this study, we characterized the shedding of EVs from Leishmania (Leishmania) amazonensis promastigotes. This species is the causative agent of cutaneous leishmaniasis, and its role during interactions with bone marrow-derived macrophages (BMDMs) and peritoneal B-1 cells was evaluated. Leishmania amazonensis promastigotes cultivated in vitro at different times and temperatures spontaneously released EVs. EVs were purified using size-exclusion chromatography (SEC) and quantitated by nanoparticle tracking analysis (NTA). NTA revealed that the average size of the EVs was approximately 180 nm, with concentrations ranging from 1.8 × 10⁸ to 2.4 × 10⁹ vesicles/mL. In addition, the presence of LPG and GP63 were detected in EVs obtained at different temperatures. Naïve BMDMs stimulated with EVs exhibited increased IL-10 and IL-6 expression. However, incubating B-1 cells with parasite EVs did not stimulate IL-10 expression but led to an increase in the expression of IL-6 and TNFα. After 7 weeks post-infection, animals infected with L. amazonensis promastigotes in the presence of parasite EVs had significant higher parasite load and a polarization to Th2 response, as compared to the group infected with the parasite alone. This work demonstrated that EVs isolated from L. amazonensis promastigotes were able to stimulate macrophages and B-1 cells to express different types of cytokines. Moreover, the immunomodulatory properties of EVs probably contributed to an increase in parasite burden in mice. These findings suggest that the functionality of L. amazonensis EVs on immune system favor of parasite survival and disease progression.

In vivo and in vitro phagocytosis of Leishmania (Leishmania) amazonensis promastigotes by B-1 cells

Leishmaniasis is caused by Leishmania parasites that infect several cell types. The promastigote stage of Leishmania is internalized by phagocytic cells and transformed into the obligate intracellular amastigote form. B-1 cells are a subpopulation of B cells that are able to differentiate in vitro and in vivo into mononuclear phagocyte-like cells with phagocytic properties. B-1 cells use several receptors for phagocytosis, such as the mannose receptor and third complement receptor. Leishmania binds to the same receptors on macrophages. In this study, we demonstrated that phagocytes derived from B-1 cells (B-1 CDP) were able to internalize promastigotes of L. (L.) amazonensis in vitro. The internalized promastigotes differentiated into amastigotes. Our results showed that the phagocytic index was higher in B-1 CDP compared to peritoneal macrophages and bone marrow-derived macrophages. The in vivo phagocytic ability of B-1 cells was also demonstrated. Parasites were detected inside purified B-1 cells after intraperitoneal infection with L. (L.) amazonensis promastigotes. Intraperitoneal stimulation with the parasites led to an increase in both IL-10 and TNF-α. These results highlight the importance of studying B-1 CDP cells as phagocytic cells that can participate and contribute to immunity to parasites.

Propionibacterium acnes induces an adjuvant effect in B-1 cells and affects their phagocyte differentiation via a TLR2-mediated mechanism

B-1 lymphocytes are present in large numbers in the mouse peritoneal cavity, as are macrophages, and are responsible for natural IgM production. These lymphocytes migrate to inflammatory foci and are also involved in innate immunity. It was also demonstrated that B-1 cells are able to differentiated into phagocytes (B-1CDP), which is characterized by expression of F4/80 and increased phagocytic activity. B-1 cell responses to antigens and adjuvants are poorly characterized. It has been shown that Propionibacterium acnes suspensions induce immunomodulatory effects in both macrophages and B-2 lymphocytes. We recently demonstrated that this bacterium has the ability to increase B-1 cell populations both in vitro and in vivo. P. acnes induces B-1CDP differentiation, increases the expression of TLR2, TLR4 and TLR9 and augments the expression of CD80, CD86 and CD40 in B-1 and B-1CDP cells. Because P. acnes has been shown to modulate TLR expression, in this study, we investigated the role of TLR2 and TLR4 in B-1 cell population, including B-1CDP differentiation and phagocytic activity in vitro and in vivo. Interestingly, we have demonstrated that TLR2 signaling could be involved in the increase in the B-1 cell population induced by P. acnes. Furthermore, the early differentiation of B-1CDP is also dependent of TLR2. It was also observed that TLR signals also interfere in the phagocytic ability of B-1 cells and their phagocytes. According to these data, it is clear that P. acnes promotes an important adjuvant effect in B-1 cells by inducing them to differentiate into B-1CDP cells and modulates their phagocytic functions both in vivo and in vitro. Moreover, most of these effects are mediated primarily via TLR2. These data reinforce the findings that such bacterial suspensions have powerful adjuvant properties. The responses of B-1 cells to exogenous stimulation indicate that these cells are important to the innate immune response.

Radiation-resistant B-1 cells: A possible initiating cells of neoplastic transformation

The role of B-1 cells in the hyperproliferative hematologic disease has been described. Several reports bring evidences that B-1 cells are the main cell population in the chronic lymphatic leukemia. It is also described that these cells have an important involvement in the lupus erythematous systemic. The murine model used to investigate both disease models is NZB/NZW. Data from literature point that mutation in micro-RNA 15a and 16 are the responsible for the B-1 hyperplasia in these mice. Interestingly, it was demonstrated that NZB/NZW B-1 cells are radioresistant, contrariwise to observe in other mouse lineage derived B-1 cells and B-2 cells. However, some reports bring evidences that a small percentage of B-1 cells in healthy mice are also able to survive to irradiation. Herein, we aim to investigate the malignant potential of ionizing-radiation resistant B-1 cells in vitro. Our main goal is to establish a model that mimics the neoplastic transformation originate to a damage exposure of DNA, and not only related to intrinsic mutations. Data shown here demonstrated that radiation-resistant B-1 cells were able to survive long periods in culture. Further, these cells show proliferation index increase in relation to non-irradiated B-1 cells. In addition, radiation resistant B-1 cells showed hyperploid, morphologic alterations, increased induction of apoptosis after anti-IgM stimulation. Based on these results, we could suggest that radiation resistant B-1 cells showed some modifications in that could be related to induction of malignant potential.

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.

Adjuvant effect of killed Propionibacterium acnes on mouse peritoneal B-1 lymphocytes and their early phagocyte differentiation

B-1 lymphocytes are the predominant cells in mouse peritoneal cavity. They express macrophage and lymphocyte markers and are divided into B-1a, B-1b and B-1c subtypes. The role of B-1 cells is not completely clear, but they are responsible for natural IgM production and seem to play a regulatory role. An enriched B-1b cell population can be obtained from non-adherent peritoneal cell cultures, and we have previously demonstrated that these cells undergo differentiation to acquire a mononuclear phagocyte phenotype upon attachment to the substrate in vitro. Nevertheless, the B-1 cell response to antigens or adjuvants has been poorly investigated. Because killed Propionibacterium acnes exhibits immunomodulatory effects on both macrophages and B-2 lymphocytes, we analyzed whether a killed bacterial suspension or its soluble polysaccharide (PS) could modulate the absolute number of peritoneal B-1 cells in BALB/c mice, the activation status of these cells and their ability to differentiate into phagocytes in vitro. In vivo, P. acnes treatment elevated the absolute number of all B-1 subsets, whereas PS only increased B-1c. Moreover, the bacterium increased the number of B-1b cells that were positive for MHC II, TLR2, TLR4, TLR9, IL-4, IL-5 and IL-12, in addition to up-regulating TLR9, CD80 and CD86 expression. PS increased B-1b cell expression of TLR4, TLR9, CD40 and CD86, as well as IL-10 and IL-12 synthesis. Both of the treatments decreased the absolute number of B-1b cells in vitro, suggesting their early differentiation into B-1 cell-derived phagocytes (B-1CDP). We also observed a higher phagocytic activity from the phagocytes that were derived from B-1b cells after P. acnes and PS treatment. The adjuvant effect that P. acnes has on B-1 cells, mainly the B-1b subtype, reinforces the importance of B-1 cells in the innate and adaptive immune responses.

In Vitro and In Vivo Phagocytic Ability of Mouse B-1 Cells

B-1 cells are a peculiar subpopulation of B cells found in the peritoneal and pleural cavities in mice. These cells are typically IgM+ and CD11b+. B-1 cells are able to migrate from the peritoneal cavity to non-specific inflammatory sites in mice. In addition, they can differentiate into mononuclear phagocyte-like cells in vitro; however, it is still unknown whether B-1 cells are capable of performing phagocytosis in vivo. Here we further characterized B-1 cells as phagocytes in vitro, and we investigated their ability to phagocytose apoptotic cells and bacteria in vivo. Our results demonstrate that B-1 phagocytes are able to uptake apoptotic thymocytes and Escherichia coli bacteria, both in vitro and in vivo. These findings indicate that along with macrophages, B-1 phagocytic cells might play a role in fundamental processes such as tissue remodeling, resolution of inflammation and pathogen clearance.

Resident peritoneal inflammatory cells are pivotal in the development of experimental atherosclerosis

AIM

Based on evidence that ionizing radiation can ameliorate chronic and autoimmune diseases in patients and experimental animals, we investigated the effects of radiation on the induction and development of experimental atherogenesis.

METHODS

Male New Zealand rabbits were divided into 5 groups and given an atherogenic diet for 90 days. Peritoneal and thoracic areas (9 Gy) were irradiated on the 1st and 45th days for groups 1 and 2, the 45th day for groups 3 and 4, and not at all for group 5. Prior to irradiation, the peritoneal cavity of animals from groups 1 and 3 was washed with buffered saline. Cells collected by peritoneal washing were reinfused into the peritoneal cavity of the same animal after irradiation. Animals from groups 2 and 4 were intraperitoneally injected with saline as a control.

RESULTS

Despite similar lipid profiles among the experimental groups, the percentage of aortas covered by plaques was remarkably reduced (p<0.001) among animals submitted to irradiation (groups 2 and 4). These differences were completely abolished in irradiated animals reconstituted with their own peritoneal cells.

CONCLUSIONS

These findings point to an important role of resident inflammatory peritoneal cells in experimental atherogenesis.

B-1 cell: the precursor of a novel mononuclear phagocyte with immuno-regulatory properties

Characterization of the origin, properties, functions and fate of cells is a fundamental task for the understanding of physiological and pathological phenomena. Despite the bulk of knowledge concerning the diverse characteristics of mammalian cells, some of them, such as B-1 cells, are still poorly understood. Here we report the results obtained in our laboratory on these cells in the last 10 years. After showing that B-1 cells could be cultured and amplified in vitro, a series of experiments were performed with these cells. They showed that B1 cells reside mostly in the peritoneal and pleural cavities, migrate to distant inflammatory foci, coalesce to form giant cells and participate in granuloma formation, both in vitro and in vivo. They are also able to present antigens to immunologically responsive cells and are endowed with regulatory properties. Further, we have also shown that these cells facilitate different types of infection as well as tumor growth and spreading. These data are presently reviewed pointing to a pivotal role that these cells may play in innate and acquired immunity.

Long-term follow-up after non-myeloablative transplant of bone and marrow in BXSB mice

We present long-term outcomes of BXSB mice after non-myeloablative bone marrow transplants using major histocompatability complex (MHC)-matched cells. Groups differed in sources of donor lymphocytes or mesenchymal stromal cells (MSC). Unfractionated marrow cells from green fluorescent protein (GFP) transgenic (Tg) mice (BMT group) or from RAG1−/− B6 mice (RAG group) were injected intravenously (i.v.) into irradiated (550 cGy) hosts. As a source of mesenchymal cells, bone chips from GFP-Tg were injected intraperitoneally alone (MSC group) or along with i.v. bone marrow cells (BMT + MSC group). Controls were untreated mice (UnTx) or mice exposed to radiation only (Rad Cont). At 62 weeks post-transplant, surviving mice were harvested for histopathology, flow cytometry and real time polymerase chain reaction (RT-PCR). The mice from BMT + MSC group had the best outcomes for survival rates (71.4% vs. 43.8%), renal scores (2.9% vs. 28.8% glomerular sclerosis) and percent splenic monocytes (4.2 vs. 11.3%) compared with mice from Rad Cont. Improvement in RAG and BMT groups was less prominent but were comparable with one another. Although MSC alone were not sufficient to control the renal pathology, it limited the expansion of CD4−CD8− T cell populations without a change in Foxp3 expression. The results suggest the importance of the innate immune system in disease pathogenesis and a role for MSC in immunomodulation.

A subset of host B lymphocytes controls melanoma metastasis through a melanoma cell adhesion molecule/MUC18-dependent interaction: evidence from mice and humans

Host immunity affects tumor metastasis but the corresponding cellular and molecular mechanisms are not entirely clear. Here, we show that a subset of B lymphocytes (termed B-1 population), but not other lymphocytes, has prometastatic effects on melanoma cells in vivo through a direct heterotypic cell-cell interaction. In the classic B16 mouse melanoma model, one mechanism underlying this phenomenon is a specific up-regulation and subsequent homophilic interaction mediated by the cell surface glycoprotein MUC18 (also known as melanoma cell adhesion molecule). Presence of B-1 lymphocytes in a panel of tumor samples from melanoma patients directly correlates with MUC18 expression in melanoma cells, indicating that the same protein interaction exists in humans. These results suggest a new but as yet unrecognized functional role for host B-1 lymphocytes in tumor metastasis and establish a biochemical basis for such observations. Our findings support the counterintuitive central hypothesis in which a primitive layer of the immune system actually contributes to tumor progression and metastasis in a mouse model and in melanoma patients. Given that monoclonal antibodies against MUC18 are in preclinical development but the reason for their antitumor activity is not well understood, these translational results are relevant in the setting of human melanoma and perhaps of other cancers.

Long-term administration of IgG2a anti-NK1.1 monoclonal antibody ameliorates lupus-like disease in NZB/W mice in spite of an early worsening induced by an IgG2a-dependent BAFF/BLyS production

The role of natural killer (NK) T cells in the development of lupus-like disease in mice is still controversial. We treated NZB/W mice with anti-NK1.1 monoclonal antibodies (mAbs) and our results revealed that administration of either an irrelevant immunoglobulin G2a (IgG2a) mAb or an IgG2a anti-NK1.1 mAb increased the production of anti-dsDNA antibodies in young NZB/W mice. However, the continuous administration of an anti-NK1.1 mAb protected aged NZB/W mice from glomerular injury, leading to prolonged survival and stabilization of the proteinuria. Conversely, the administration of the control IgG2a mAb led to an aggravation of the lupus-like disease. Augmented titres of anti-dsDNA in NZB/W mice, upon IgG2a administration, correlated with the production of BAFF/BLyS by dendritic, B and T cells. Treatment with an anti-NK1.1 mAb reduced the levels of interleukin-16, produced by T cells, in spleen cell culture supernatants from aged NZB/W. Adoptive transfer of NK T cells from aged to young NZB/W accelerated the production of anti-dsDNA in recipient NZB/W mice, suggesting that NK T cells from aged NZB/W are endowed with a B-cell helper activity. In vitro studies, using purified NK T cells from aged NZB/W, showed that these cells provided helper B-cell activity for the production of anti-dsDNA. We concluded that NK T cells are involved in the progression of lupus-like disease in mature NZB/W mice and that immunoglobulin of the IgG2a isotype has an enhancing effect on antibody synthesis due to the induction of BAFF/BLyS, and therefore have a deleterious effect in the NZB/W mouse physiology.