Ly1- (CD5-) B cells produce interleukin (IL)-10

The regulatory role of B cells in autoimmunity, infections and cancer: Perspectives beyond IL10 production

The term regulatory B cells (B regs) is ascribed to a heterogeneous population of B cells with the function of suppressing inflammatory responses. They have been described mainly during the last decade in the context of different immune-mediated diseases. Most of the work on B regs has been focused on IL-10-producing B cells. However, B cells can exert regulatory functions independently of IL-10 production. Here we discuss the phenotypes, development and effector mechanisms of B regs and advances in their role in autoimmunity, infections and cancer.

Allergen-specific responses of CD19(+)CD5(+)Foxp3(+) regulatory B cells (Bregs) and CD4(+)Foxp3(+) regulatory T cell (Tregs) in immune tolerance of cow milk allergy of late eczematous reactions

Foxp3-expressing cells among CD19(+)CD5(+) B cells were identified as regulatory B cells. Food allergy manifesting as late eczematous reactions is regarded as a non-IgE-mediated food allergy. The diagnosis for milk allergy manifesting as late eczematous reactions was made on the basis of the findings obtained from a double-blind placebo-controlled food challenge in patients with atopic dermatitis. Twelve patients with milk allergy and 12 patients who could tolerate milk were selected. On casein stimulation, the CD19(+)CD5(+)Foxp3(+) B cell (Breg) fraction in CD5(+) B cells decreased from 4.4±1.1% to 3.1±0.7% (P=0.047, n=12) in the milk allergy group and increased from 4.4±1.3% to 5.2±1.4% (P=0.001, n=10) in the milk-tolerant group. On the other hand, on allergen stimulation, the number of CD4(+)Foxp3(+) regulatory T cells (Tregs) in the milk allergy group and milk-tolerant group increased from 2.6±0.7% to 3.4±0.6% (P=0.014, n=9) and from 2.7±1.0% to 3.5±1.0% (P=0.038, n=10), respectively. In conclusion, allergen-specific responses of Bregs, rather than those of Tregs, seem to influence the immune responses (i.e., allergy or tolerance) to a food allergen.

IL-10 is predominantly produced by CD19(low)CD5(+) regulatory B cell subpopulation: characterisation of CD19 (high) and CD19(low) subpopulations of CD5(+) B cells

IL-10 production by CD19(+)CD5(+) B cells was investigated, by determining the expression levels of CD19, a classical B cell marker. Peripheral mononuclear cells were stained with fluorescence-conjugated anti-CD5, anti-CD19, anti-IL-10, and Annexin V. Interestingly, IL-10-producing B cells were found to be localised within the CD19(low)CD5(+) B cell subset. Apoptotic changes were also observed mainly in CD19(low) cells among B cells. Thus, CD5(+) B cells should be classified as CD19(high) and CD19(low) cells, and the immunological significance of CD19 for the IL-10 production by CD5(+) B cells requires further studies.

Retroviral vectors induce epigenetic chromatin modifications and IL-10 production in transduced B cells via activation of toll-like receptor 2

The immune response toward viral vectors used for gene therapy and genetic vaccination appears to be critically important in determining the therapeutic outcome. However, the mechanisms that control the immune response following gene transfer are poorly understood. Unexpectedly, we found that integrating retroviral vector particles induce stable interleukin-10 (IL-10) production in murine (BALB/c H-2(d)) transduced B cells. This requires a novel mechanism whereby the interaction of retroviral vector particle with its cognate cellular receptor activates intracellular signaling pathways resulting in stable epigenetic modifications. Murine B cells exposed to retroviral vector particles triggered the colocalization of the retroviral cellular receptor [mouse cationic amino acid transporter 1 (mCAT1)] and Toll-like receptor 2 (TLR2) into lipid microrafts, which in turn activated TLR2 signaling pathways. TLR2 activation induced STAT3 phosphorylation and increased phosphorylated histone 3 (H3) at the STAT3-binding site of the IL-10 promoter. In addition, TLR2 activation during transduction activates nuclear factor of κ light polypeptide gene enhancer in B-cells inhibitor, α (NFKBIA), thereby preventing the translocation of the nuclear factor-κB (NF-κB) complex to the nucleus and the transcription of proinflammatory cytokines. These findings open new perspectives for controlling immune responses following gene therapy and genetic vaccination.

Presence of Foxp3-expressing CD19(+)CD5(+) B Cells in Human Peripheral Blood Mononuclear Cells: Human CD19(+)CD5(+)Foxp3(+) Regulatory B Cell (Breg)

Foxp3 is a transcript factor for regulatory T cell development. Interestingly, Foxp3-expressing cells were identified in B cells, especially in CD19(+)CD5(+) B cells, while those were not examined in CD19(+)CD5(-) B cells. Foxp3-expressing CD5(+) B cells in this study were identified in human PBMCs and were found to consist of 8.5±3.5% of CD19(+)CD5(+) B cells. CD19(+)CD5(+)Foxp3(+) B cells showed spontaneous apoptosis. Rare CD19(+)CD5(+) Foxp3(+) regulatory B cell (Breg) population was unveiled in human peripheral blood mononuclear cells and suggested as possible regulatory B cells (Breg) as regulatory T cells (Treg). The immunologic and the clinical relevant of Breg needs to be further investigated.

Cell type-specific regulation of IL-10 expression in inflammation and disease

IL-10 plays an essential part in controlling inflammation and instructing adaptive immune responses. Consequently, dysregulation of IL-10 is linked with susceptibility to numerous infectious and autoimmune diseases in mouse models and in humans. It has become increasingly clear that appropriate temporal/spatial expression of IL-10 may be the key to how IL-10 contributes to the delicate balance between inflammation and immunoregulation. The mechanisms that govern the cell type- and receptor-specific induction of IL-10, however, remain unclear. This is due largely to the wide distribution of cellular sources that express IL-10 under diverse stimulation conditions and in a variety of tissue compartments. Further complicating the issue is the fact that human IL-10 expression patterns appear to be under genetic influence resulting in differential expression and disease susceptibility. In this review, we discuss the cellular sources of IL-10, their link to disease phenotypes and the molecular mechanisms implicated in IL-10 regulation.

Characterisation of allergen-specific responses of IL-10-producing regulatory B cells (Br1) in Cow Milk Allergy

CD19+CD5+ regulatory B cells regulate immune responses by producing IL-10. IL-10-producing regulatory B cell (Br1) responses by allergen stimulation were investigated in human food allergy. Six milk allergy patients and eight milk-tolerant subjects were selected according to DBPCFC. PBMCs were stimulated by casein in vitro and stained for intracellular IL-10 and apoptosis. In response to allergen stimulation, Br1 decreased from 26.2+/-18.3 to 15.5+/-8.9% (p=0.031, n=6) in the milk allergy group and increased from 15.4+/-9.0 to 23.7+/-11.2% (p=0.023, n=8) in the milk-tolerant group. Apoptotic non-IL-10-producing regulatory B cells increased from 21.8+/-9.3 to 38.0+/-16.1% (p=0.031, n=6) in the milk allergy group and unchanged from 28.8+/-13.8 to 28.0+/-15.0% (p=0.844, n=8) in the milk-tolerant group. Br1 may be involved in the immune tolerance of food allergies by producing IL-10 and simultaneously undergoing apoptosis in humans. The exact roles for Br1 in immune tolerance needs to be further investigated.

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.

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.

The modulatory effects of lipopolysaccharide-stimulated B cells on differential T-cell polarization

Lipopolysaccharide (LPS) is a major component of environmental microbial products. Studies have defined the LPS dose as a critical determining factor in driving differential T-cell polarization but the direct effects of LPS on individual antigen-presenting cells is unknown. Here, we investigated the effects of LPS doses on naive B cells and the subsequent modulatory effects of these LPS-activated B cells on T-cell polarization. The LPS was able to induce a proliferative response starting at a dose of 100 ng/ml and was capable of enhancing antigen internalization at a dose of 1 microg/ml in naive B cells. Following LPS stimulation, up-regulation of the surface markers CD40, CD86, I-Ad, immunoglobulin M, CD54 and interleukin-10 production, accompanied by down-regulation of CD5 and CD184 (CXCR4) were observed in a LPS dose-dependent manner. Low doses (<10 ng/ml) of LPS-activated B cells drove T helper type 2 polarization whereas high doses (>0.1 microg/ml) of LPS-activated B cells resulted in T regulatory type 1 cell polarization. In conclusion, LPS-activated B cells acquire differential modulatory effects on T-cell polarization. Such modulatory effects of B cells are dependent on the stimulation with LPS in a dose-dependent manner. These observations may provide one of the mechanistic explanations for the influence of environmental microbes on the development of allergic diseases.

Dietary fish oil increases the number of splenic macrophages secreting TNF-alpha and IL-10 but decreases the secretion of these cytokines by splenic T cells from mice

Dietary fish oil has immunomodulatory effects that are partly mediated by its effects on cytokine secretion. In this paper, we examine whether dietary fish oil has different effects on cytokine secretion by T cells and macrophages. Female BalbC mice were fed diets supplemented with 18% fish oil + 2% corn oil or 20% corn oil. Concanavalin A (ConA)- and LPS-induced TNF-alpha and IL-10 secretion by splenocytes was examined using ELISA. Dietary fish oil decreased ConA induced-, but increased LPS-induced, TNF-alpha and IL-10 secretion by total murine splenocytes. Dietary fish oil increased the number of splenocytes secreting TNF-alpha and IL-10, following stimulation with LPS, by 123 and 38%, respectively, but did not affect cytokine secretion by each cell, as determined using enzyme-linked immunospot. Spleens from mice fed the fish oil diet had over 2-fold higher proportion of macrophages with high expression of CD11b than spleens from mice fed the corn oil diet. In addition, fish oil increased the proportion of total and CD11b(+) splenocytes that expressed the LPS receptor complex molecules, CD14 and toll-like receptor (TLR)4/myeloid differentiation factor-2 (MD-2), by 85 and 28%, respectively. The increased proportion of macrophages expressing the LPS receptor complex molecules, CD14 and TLR4/MD-2, in spleens from mice fed the fish oil diet may explain the increased number of cells that secreted the cytokines after LPS stimulation.

A B lymphocyte mitogen is a Brucella abortus virulence factor required for persistent infection

Microbial pathogens with the ability to establish chronic infections have evolved strategies to actively modulate the host immune response. Brucellosis is a disease caused by a Gram-negative intracellular pathogen that if not treated during the initial phase of the infection becomes chronic as the bacteria persist for the lifespan of the host. How this pathogen and others achieve this action is a largely unanswered question. We report here the identification of a Brucella abortus gene (prpA) directly involved in the immune modulation of the host. PrpA belongs to the proline-racemase family and elicits a B lymphocyte polyclonal activation that depends on the integrity of its proline-racemase catalytic site. Stimulation of splenocytes with PrpA also results in IL-10 secretion. Construction of a B. abortus-prpA mutant allowed us to assess the contribution of PrpA to the infection process. Mice infected with B. abortus induced an early and transient nonresponsive status of splenocytes to both Escherichia coli LPS and ConA. This phenomenon was not observed when mice were infected with a B. abortus-prpA mutant. Moreover, the B. abortus-prpA mutant had a reduced capacity to establish a chronic infection in mice. We propose that an early and transient nonresponsive immune condition of the host mediated by this B cell polyclonal activator is required for establishing a successful chronic infection by Brucella.

Recombinant Dirofilaria immitis polyprotein that stimulates murine B cells to produce nonspecific polyclonal immunoglobulin E antibody

Nonspecific immunoglobulin E (IgE) production is an event characteristically observed in parasitic helminth infections, but its mechanisms are still unclear. To define these mechanisms, we prepared a recombinant Dirofilaria immitis protein (rDiAg) and assessed its effect on nonspecific IgE production. rDiAg preferentially induced nonspecific IgE production, without eliciting specific IgE production, as well as a Th2-type cytokine profile (high interleukin-4 [IL-4] and IL-10 production but low gamma interferon production) in BALB/c mice. rDiAg significantly elicited the proliferative response of naive B cells. This response was not abolished by polymyxin B, an inhibitor of lipopolysaccharide (LPS), and rDiAg normally expanded splenic B cells from LPS nonresponder C3H/HeJ mice. Thus, the mitogenic effect of rDiAg was not due to LPS contamination. rDiAg also enhanced levels of CD23 expression on splenic B cells. Splenic B cells produced marked levels of IgE when cultured with the combination of rDiAg and IL-4 (rDiAg-IL-4), whereas peritoneal B cells produced negligible levels of IgE. rDiAg-IL-4-induced IgE production by splenic B cells was synergistically increased by coculture with peritoneal B cells. rDiAg-driven IL-10 secretion was higher in peritoneal B cells than in splenic B cells. IgE production by splenic B cells cocultured with peritoneal B cells was decreased to a level comparable to that by splenic B cells in the presence of a neutralizing anti-IL-10 monoclonal antibody. Collectively, these results suggest that rDiAg-induced polyclonal expansion and IgE class switching of splenic B cells contribute to nonspecific IgE production and that these responses are enhanced by peritoneal B-cell-derived IL-10.

IL-10 gene knockout attenuates allergen-induced airway hyperresponsiveness in C57BL/6 mice

Intratracheal administration of interleukin-10 (IL-10) has been reported to inhibit allergic inflammation but augment airway hyperresponsiveness (AHR). In the present study, airway and smooth muscle responsiveness to methacholine (MCh) were compared in wild-type (WT) and IL-10-deficient (IL-10-KO) mice to investigate the role of endogenous IL-10 in AHR development. Naive WT and IL-10-KO mice exhibited similar dose-dependent increases in airway resistance (Raw) to intravenous MCh. Sensitization and challenge with ragweed (RW) induced a twofold increase in responsiveness to intravenous MCh in WT mice, but hyperresponsiveness was not observed in similarly treated IL-10-KO mice. Likewise, tracheal rings from RW-sensitized and -challenged WT mice exhibited a fourfold greater responsiveness to MCh than IL-10-KO tracheal preparations. Measurements of airway constriction by whole body plethysmography further supported the Raw and tracheal ring data (i.e., AHR was not observed in the absence of IL-10). Interestingly, factors previously implicated in the development of AHR, including IL-4, IL-5, IL-13, IgA, IgG1, IgE, eosinophilia, and lymphocyte recruitment to the airways, were upregulated in the IL-10-KO mice. Treatment with recombinant murine IL-10 at the time of allergen challenge reduced the magnitude of inflammation but reinstated AHR development in IL-10-KO mice. Adoptive transfer of mononuclear splenocytes to IL-10-sufficient severe combined immunodeficient mice indicated that lymphocytes were an important source of the IL-10 impacting AHR development. These results provide evidence that IL-10 expression promotes the development of allergen-induced smooth muscle hyperresponsiveness.

Lymphokine dependence of STAT3 activation produced by surface immunoglobulin cross-linking and by phorbol ester plus calcium ionophore treatment in B cells

Stimulation of B cells by surface immunoglobulin (sIg) triggering, or through the mitogenic combination of phorbol ester and calcium ionophore, is accompanied by activation of STAT transcription factors. The mechanism responsible for the delayed nuclear accumulation of phosphorylated STAT3 was examined in detail, focusing on the role of B cell-derived lymphokines. sIg-induced activation of STAT3 was partially inhibited in B cells obtained from IL-6- or IL-10-deficient mice, and was partially blocked by neutralizing antibodies directed against either of these lymphokines. sIg-induced STAT3 activation was completely inhibited by combining IL-6- and IL-10-specific neutralizing antibodies, or by adding individual neutralizing antibodies to B cells obtained from lymphokine-deficient animals. In contrast, IL-10 alone appeared to account for STAT3 activation resulting from B cell stimulation with phorbol ester and calcium ionophore. In keeping with these results, soluble IL-6 and IL-10 were found in supernatant fluid obtained from stimulated B cells. This work indicates that a lymphokine pathway is responsible for STAT3 activation that occurs late after B cell stimulation, and points out differences in B cell activation that result from stimulation through the antigen receptor and through pharmacological mimicry of signaling mediators.

CD5 expression in human B-cell populations

The origin of CD5+ B cells remains controversial. The differential response to ligation of CD5 resulting in apoptosis or proliferation provides insight into its roles in distinct human B cells. Here, Pierre Youinou, Christophe Jamin and Peter Lydyard review current knowledge of B-1 and B-2 cells, and propose that CD5 has different functions when expressed by different B-cell subpopulations.

Efficient presentation of house dust mite allergen Der p 2 by monocyte-derived dendritic cells and the role of beta 2 integrins

Monocyte-derived dendritic cells (MDDC) are potent antigen-presenting cells (APC). The APC functions of MDDC in allergy were examined. MDDC presentation of the major house dust mite allergen Der p 2 resulted in 4-12-fold higher T-cell proliferation and markedly higher IFN-gamma and IL-5 production than PBMC cultures. Comparable T-cell proliferation was obtained with 10-fold fewer MDDC than purified monocytes. MDDC cultured from adherent cells, or CD14+, CD11b+ or Percoll-purified monocytes were comparable in presenting soluble Ag, and in stimulating allogeneic MLR. Importantly, MDDC presentation of Der p 2 resulted in both Th1 and Th2 stimulation, although MDDC are known to produce high levels of IL-12 and stimulate biased Th1 responses. The basis for the potent APC function of MDDC was further examined. MDDC were found to be highly phagocytic. Immunoprecipitation studies showed markedly elevated ICAM-1 expression but > 10-fold reduction in LFA-1 expression on MDDC compared with monocytes. Monoclonal antibody (MoAb)-blocking experiments showed that ICAM-LFA-1 interaction was essential for MDDC stimulation of Der p 2-specific T-cell proliferative responses. These results show that the use of MDDC as APC provides a simple, sensitive and versatile method for detecting T-cell responses to allergens and that the strong phagocytic capability and the increased ICAM-1 expression of MDDC contribute significantly to their Ag presentation potency.

Splenic B cells are required for tolerogenic antigen presentation in the induction of anterior chamber-associated immune deviation (ACAID)

Ocular immune privilege is the result of a number of protective mechanisms, including a specialized immune response to antigen encountered in the anterior chamber of the eye. Anterior chamber-associated immune deviation, or ACAID, is characterized by the antigen-specific, selective down-regulation of systemic cell-mediated and humoral immune responses. One current hypothesis of the initiation of ACAID predicts that ocular APC process antigen and then migrate out of the eye and to the spleen where various regulatory T-cell populations are generated. A novel in vitro model of the ACAID spleen was developed to study the cells involved in the generation of suppressed T-cell immunity. ACAID APC co-cultured with whole splenocytes or splenic B and T cells induced efferent suppressors of delayed-type hypersensitivity (DTH). However, ACAID APC co-cultured with splenic T cells did not generate efferent suppressors of DTH. The requirement for B cells was confirmed with B-cell knockout mice. ACAID APC co-cultured with splenocytes from B-cell knockout mice did not induce efferent suppressors of DTH. Moreover, ACAID could not be induced in B-cell knockout mice in vivo. The reconstitution of B-cell knockout mice with wild-type B cells restored ACAID. In summary, these data confirm the role for B cells in the splenic phase of ACAID. A putative mechanism predicts that ACAID APC release antigenic peptides to B cells in the spleen. B cells then present antigen in a tolerogenic manner leading to the generation of regulatory T cells.

The role of IL-10 in iNOS and cytokine mRNA expression during in vitro differentiation of bovine mononuclear phagocytes

In the study reported here, we used RT-PCR with primers specific for interleukin-1 (IL-1), IL-6, IL-10, tumor necrosis factor-alpha (TNF-alpha), and nitric oxide synthase (iNOS) to assess the cytokine mRNA expression associated with bovine blood monocytes during their differentiation to macrophages cultured on plastic (1 week). In addition, we used RT-PCR to assess the contribution of gammadelta T cells as a source of interferon-gamma (IFN-gamma), the induction signal for iNOS. Further, we evaluated cytocentrifuge preparations from the cultures for the production of IL-10 using specific antibody. We previously demonstrated that iNOS can be induced in cultured bovine monocytes in response to IFN-gamma and TNF-alpha but lose this capability in a short period of time. However, we demonstrate here that iNOS induction from monocytes cultured with IFN-gamma secreting gammadelta T cells is prolonged, suggesting that this source of IFN-gamma primes the monocytes before exogenous stimulation. Based on mRNA expression, placement of monocytes in culture resulted in activation, followed by quiescence. By 6 days in culture, the iNOS message was reduced below the basal level. In addition, the TNF-alpha message was substantially reduced, and IL-1 and IL-6 messages were reduced below detectable levels. This correlated with an increase in IL-10 message. Downregulation of these same cytokine messages as well as IFN-gamma message occurred within a 20-h period when IL-10 was added exogenously to cultures of total leukocytes. At the same time, there was an increase in the number of IL-10-positive cells and an increase in the intensity of anti-IL-10 staining within adherent cells. These results provide evidence for IL-10 regulation of some bovine mononuclear phagocyte effector functions.