Inhibition of murine B1 lymphocytes by interleukin-12

B1 cells are a subset of B lymphocytes found in many spectes and are implicated in the development of autoimmunity. B1 cells have previously been shown to be suppressed by the T helper (Th)1 cytokine interferon (IFN)-γ, and to be stimulated by the Th2 cytokines interleukin (IL)-2, IL-4, IL-5 and IL-10. To examine further the interactions of B1 cells and Th1 cells, we have now tested the effects of the Th1 cell-inducing cytokine IL-12 on murine B1 cells. BALB/c mice were immunized with phosphorylcholine conjugated to keyhole limpet hemocyanin (PC-KLH) and simultaneously treated with 1 μg recombinant murine IL-12 for 3 consecutive days. In addition to altering the isotype and idiotype distribution of anti-PC antibodies, IL-12 treatment was found to cause a loss of peritoneal, but not splenic B lymphocytes in immunized mice. B cell depletion required exposure to IL-12 plus antigenic stimulation. Levels of peritoneal B lymphocytes were fully restored by day 45, but the majority of these cells belonged to the B2 subset. Additionally, proliferation of B1 cells in vitro induced by IL-5 was substantially inhibited by IL-12. IL-12 itself had no effect on viable cell recovery of peritoneal cells (PeC) cultured in vitro, but viable cell recovery was significantly decreased in PeC cultured with IL-5 plus IL-12. These results show that IL-12 causes the loss of murine peritoneal B1 cells and suggest that treatment with this cytokine may be useful for disease conditions that involve B1 cell dysfunction.     

CD5+/Mac-1- peritoneal B cells: a novel B cell subset that exhibits characteristics of B-1 cells

The peritoneal cavity of mice is enriched for B-1 B cells, a lymphocyte subset that differs from conventional B-2 cells phenotypically, functionally, and developmentally. According to current paradigms, all peritoneal B-1 cells express Mac-1 whereas B-2 cells do not and thus these populations are often purified by FACS sorting or magnetic bead isolation based on B cell expression of Mac-1 or lack thereof. However, in the course of studying B220+/Mac-1- peritoneal B-2 cells, we discovered that this population is actually heterogeneous, with approximately 30-40% of these B220+/Mac-1- cells expressing the B-1 cell marker CD5. It was unclear whether this B220+/CD5+/Mac-1- peritoneal B cell population represented aberrantly CD5 expressing B-2 cells or Mac-1- B-1 cells. To address this issue we tested CD5+/Mac-1- peritoneal B cells for several traits that distinguish B-1 and B-2 cells. We found that CD5+/Mac-1- peritoneal B cells resembled CD5+ B-1 cells and not B-2 cells in terms of expression of several additional surface markers (IgM, IgD, CD23, CD43, and CD80). Further, CD5+/Mac-1- peritoneal B cells expressed high levels of V(H)11 and V(H)12, two Ig variable genes that are expressed mainly by B-1 but not B-2 cells. In addition, CD5+/Mac-1- peritoneal B cells responded to PMA, a mitogen that stimulates B-1 cells but not B-2 cells, and not to anti-Ig, that stimulates B-2 cells but not B-1 cells. ELISPOT analyses of freshly isolated CD5+/Mac-1- peritoneal B cells revealed that they secreted IgM constitutively, like B-1 cells and unlike B-2 cells. These results indicate that CD5+/Mac-1- peritoneal B cells are a new subset of B-1 cells, here termed B-1c, and stress the importance of using multiple surface markers to identify and purify specific B cell populations.     

IgG1 production by sIgD+ splenic B cells and peritoneal B-1 cells in response to IL-5 and CD38 ligation.

CD38 ligation on mouse B cells by CS/2, an anti-mouse CD38 mAb, induces proliferation, IL-5 receptor alpha chain expression and tyrosine phosphorylation of Bruton's tyrosine kinase. Furthermore, stimulation of splenic B cells with IL-5 together with CS/2 induces Blimp-1 expression and differentiation into Ig-producing cells. Here we examined the role of IL-5 in IgG1 and IgA production by B cells isolated from the spleen and peritoneal cavity. CD38 recognized by CS/2 was expressed in the follicular mantle B cells surrounding the germinal center, sIgD+ splenic B cells and peritoneal B cells. IL-5 induced IgG1 production in splenic sIgD+ B cells stimulated with CS/2, while it was ineffective to induce IgA production. Among the various cytokines tested, only IL-5 had a synergistic effect on IgG1 production with CS/2. IL-5 could induce the generation of S micro-Sgamma1 reciprocal recombination DNA products in CS/2-stimulated B cells. IL-4 was ineffective to induce either micro-gamma1 switch recombination or IgG1 secretion with CS/2, demonstrating that IL-5 promotes both micro-gamma1 switch recombination and IgG1 secretion in an IL-4-independent manner. The peritoneal B-2 cells exhibited both IgG1 and IgA production in response to IL-5 plus CS/2, while B-1 cells produced IgG1. These results imply that the pattern of differentiation to Ig-producing cells seen with peritoneal B cells is not identical to the pattern seen with splenic B cells and that peritoneal B-2 cells contain precursors of IgA-producing cells responding to IL-5 plus CS/2.     

Cytokines and Ly-1 (B1) B Cells

In an attempt to elucidate the possible role of cytokines in autocrine growth of Ly-1 + B cells, and the role of this subset of B cells in immune regulation, both in normal and diseased hosts, we have performed a systematic analysis of cytokine production by a series of mouse Ly-1⁺ B lymphomas, as well as normal peritoneal Ly-1⁺ and conventional B cells. The lymphomas all express TGF-β, and some express IL-3 and IL-4. We observed that both the lymphomas and the peritoneal cells produce TNF-α, TNF-β and IL-6. Another cytokine, IL-10, is produced predominantly by peritoneal Ly-1⁺ B cells from healthy mice and by Ly-1⁺ B lymphomas, but not by conventional B cells. As IL-10 regulates the production of monokines and a subset of T-cell derived cytokines, our results suggest a broad immunoregulatory role for Ly-1 B cells. To complement these studies we have also examined the responses of Ly-1 B cells to mitogens and cytokines previously shown to stimulate conventional B cells. In summary, Ly-1 B cells, in contrast to conventional B cells do not respond to anti-Ig antibodies, even in the presence of IL-4. They do respond to LPS, and this response is preferentially enhanced by IL-5, and marginally enhanced by IL-3. Surprisingly LPS-induced proliferation of peritoneal B cells is inhibited by IL-6 and to a greater extent by IL-10. Whether this inhibition is a result of differentiation into Ig secreting cells is currently being evaluated. We discuss our findings in terms of the potential of Ly-1 B cells to regulate their own development and the immunocompetence of other cells.     

Interleukin-12 and -10 and gamma interferon regulate polyclonal and ligand-specific expansion of murine B-1 cells.

B-1 cells (CD5+ B220+) are a self-replenishing lineage of B cells which are autoreactive and capable of producing large amounts of interleukin-10 (IL-10). In mice experimentally infected with the human helminth parasite Schistosoma mansoni, expansion of B-1 cells is seen in the peritoneal cavity just prior to egg laying. In naive mice, B-1 cell expansion can be elicited by intraperitoneal injection of saline soluble egg antigens (SEA) or the polylactosamine sugar lacto-N-fucopentaose III (LNFPIII), which contains the Lewis-X trisaccharide. In this study, we demonstrate that LNFPIII is the major stimulus in SEA responsible for expansion of B-1 cells, since SEA-induced B-1 outgrowth is blocked by multiple injections of non-cross-linked free LNFPIII. IL-10 is an autocrine growth factor for B-1 cells, and we show that B-1 outgrowth after SEA and LNFPIII administration is inhibited by injection of anti-IL-10 antibodies. Furthermore, SEA- and LNFPIII-induced expansion of B-1 cells is inhibited by in vivo administration of recombinant murine IL-12 or recombinant gamma interferon. These data suggest that activation and expansion of IL-10-producing B-1 cells are governed via cross-regulatory cytokines.     

Interleukin-8 differentially modulates interleukin-4- and interleukin-2-induced human B cell growth

The effect of interleukin-8 (IL)-8 on human B cell growth, as determined by thymidine uptake and viable cell numbers was studied. IL-8 inhibited IL-4-induced growth of B cells costimulated with anti-μ antibodies (Ab) or Staphylococcus aureus Cowan strain I (SAC) in a dose-dependent fashion. In contrast, IL-8 did not inhibit IL-2-induced growth of B cells. The IL-8-mediated inhibition was specific, since it was blocked by anti-IL-8 mAb but not by control IgG1. Moreover, anti-tumor necrosis factor-α (anti-TNF-α) Ab blocked IL-8-mediated inhibition. On the other hand, TNF-α, but not other cytokines including IL-1β, IL-3, IL-5, IL-6, interferon-α (IFN-α) or IFN-γ, inhibited IL-4-mediated growth, and inhibition by TNF-α was blocked by anti-TNF-α Ab but not by control IgG. IL-4 had no effect on TNF-α binding by B cells while it decreased TNF-α production by B cells. IL-8 had no effect in binding of IL-4, IL-2 or TNF-α by B cells, however, it enhanced TNF-α production by B cells. These results indicate that IL-8 inhibited IL-4-induced human B cell growth by enhancement of endogenous TNF-α production.     

Cytokines and Ly-1 (B1) B cells.

In an attempt to elucidate the possible role of cytokines in autocrine growth of Ly-1+B cells, and the role of this subset of B cells in immune regulation, both in normal and diseased hosts, we have performed a systematic analysis of cytokine production by a series of mouse Ly-1+B lymphomas, as well as normal peritoneal Ly-1+ and conventional B cells. The lymphomas all express TGF-beta, and some express IL-3 and IL-4. We observed that both the lymphomas and the peritoneal cells produce TNF-alpha, TNF-beta and IL-6. Another cytokine, IL-10, is produced predominantly by peritoneal Ly-1+B cells from healthy mice and by Ly-1+ B lymphomas, but not by conventional B cells. As IL-10 regulates the production of monokines and a subset of T-cell derived cytokines, our results suggest a broad immunoregulatory role for Ly-1 B cells. To complement these studies we have also examined the responses of Ly-1 B cells to mitogens and cytokines previously shown to stimulate conventional B cells. In summary, Ly-1 B cells, in contrast to conventional B cells do not respond to anti-Ig antibodies, even in the presence of IL-4. They do respond to LPS, and this response is preferentially enhanced by IL-5, and marginally enhanced by IL-3. Surprisingly LPS-induced proliferation of peritoneal B cells is inhibited by IL-6 and to a greater extent by IL-10. Whether this inhibition is a result of differentiation into Ig secreting cells is currently being evaluated. We discuss our findings in terms of the potential of Ly-1 B cells to regulate their own development and the immunocompetence of other cells.     

Association of interleukin-1B and interleukin-1RN polymorphisms with gastric cancer in a high-risk population of Costa Rica

Abstract Several risk factors have been associated with gastric cancer, among them Helicobacter pylori infection. This bacterium yields inflammation, the degree of which depends on the bacterial strain and the severity of the host response. The inflammatory response involves a complex cytokine network. Recently, polymorphisms of the genes coding for interleukin-1β (IL-1B), interleukin-1Ra (ILRN) and interleukin-10 have been associated with an increased risk of gastric cancer. In order to determine the association of the IL-1B, IL-1RN and IL-10 polymorphisms with gastric cancer in a high-risk Costa Rican population, we analysed purified DNA of 58 gastric cancer patients, 99 controls and 41 patients classified as group I or II, according to the Japanese classification. Genotyping was carried out by PCR, PCR-RFLP and pyrosequencing analysis. We did not find any association of the IL-1B-31, IL-1B-511 and IL-10 polymorphisms with the risk for developing gastric cancer in the studied population. Carriers of the IL-1B+3954T/– had an increased risk for developing gastric cancer (OR 3.7; 95%CI: 1.34–10.2). Also we found an increased risk for developing gastric cancer for allele 2 heterozygotes of the IL-1RN (OR 2.94; 95%CI: 1.09–7.93). This is the first time that IL-1B+3954 has been associated with gastric cancer. This is one of the first studies trying to describe the role played by IL-1B, IL-1RN and IL-10 genetic polymorphisms in gastric cancer in one of the highest risk American countries. Further investigation on American countries is needed.     

IgA production by peritoneal cavity B cells is IL-6 independent: Implications for intestinal IgA response

We have shown previously both in vitro and in vivo that IL-6 is an important factor for the development of IgA-producing B cells. However, despite the lack of this cytokine in mice with targeted disruption of the interleukin (IL)-6 gene (gene knockout mice), a substantial number of IgA-producing plasma cells occur in their intestinal mucosa. The experiments reported here indicate that there is a population of IgA-producing B cell precursors originating from the peritoneal cavity, distinguished from conventional Peyer's patch-derived precursors by their expression of CD5, and that IgA secretion by these cells is IL-6-independent. Further, there is an increase in CD5 expression among brightly staining IgA-producing cells obtained from the intestinal lamina propria of IL-6 gene-disrupted mice compared to normal controls. These data suggest an explanation for the persistence of IgA-producing plasma cells in the intestinal mucosa of IL-6-depleted mice and indicate the importance of IL-6 for development of conventional precursors of IgA-producing B cells, but not those derived from the peritoneal cavity pool.     

Involvement of IL-10 in induction of autoimmune hemolytic anemia in anti-erythrocyte Ig transgenic mice

Activation of peritoneal B-1 cells triggers autoimmune anemia in anti- erythrocyte Ig transgenic mice (HL mice). Numbers of peritoneal B-1 cells and Ig-producing cells were negligible in the T cell-deficient HL mice generated by the cross with RAG-2-/- mice (RAG-2-/- x HL mice). Proliferation and activation of B-1 cells in RAG-2-/- x HL mice were recovered by fetal thymus transfer, indicating involvement of T cells in B-1 cell-mediated autoimmune hemolytic anemia. Involvement of T cells in proliferation and activation of B-1 cells could be by-passed by administration of lipopolysaccharide (LPS), IL-5 or IL-10 to RAG-2-/- x HL mice. Administration of LPS elevated the serum IL-10 level in HL, RAG-2-/- x HL and normal mice. Proliferation and activation of B-1 cells were blocked by an anti-IL-10 antibody in conventionally bred as well as LPS-treated HL mice. Taken together, IL-10 plays a pivotal role in activation of peritoneal B-1 cells.      

Kinetics of peritoneal B-1a cells (CD5 B cells) in young adult mice

In the mouse, conventional B cells are continuously generated from precursor cells located in the bone marrow (BM), whereas the small subset of B-1 cells (formerly called Ly-1 B cells) constitute a self-replenishing population of cells. Here we studied the kinetics of murine peritoneal B-1a cells (i.e. B-1 cells expressing CD5). The actual number of B-1a cells in the peritoneal cavity that are proliferating, as detected by metaphase arrest and S-phase index, was below detection level, indicating that these cells do not divide significantly at this anatomical location. To establish the life-span of B-1a cells we used long-term administration of 5-bromo-2′-deoxyuridine in combination with three-color immunocytology on cytospin preparations. The renewal rate of peritoneal B-1a cells was 1.3% per day representing a 50% renewal time of 38 days. Splenic B cells and popliteal lymph node B cells (predominantly conventional B cells) showed an almost identical renewal rate of 1.1% per day. The data show that peripheral B cells from various lymphoid tissues and locations do not differ significantly in their renewal capacity, even though there are differences in their developmental origin.     

Effects of interleukin (IL)-13 on immediate-early response gene expression,phenotype and differentiation of human mast cells. Comparison with IL-4

The recently cloned interleukin 13 (IL-13) shares most investigated biological activities on B lymphocytes and monocytes with IL-4. In this study we investigated the potential role of IL-13 in regulating human mast cell activities. The effects of IL-13 on the expression of an immediate-early response gene (c-fos), proliferation, expression of mast cell-associated cell surface antigen (CD54 and Kit), and in vitro differentiation of human mast cells, were investigated. We compared the effect of IL-13 with that of IL-4. Both IL-13 and IL-4 induced expression of c-fos in cells from the human mast cell line HMC-1. This indicates that mast cells express functional receptors for IL-13. IL-13 and IL-4 decreased the proliferation rate of HMC-1 cells. However, IL-13 was less potent than IL-4. Human mast cells constitutively express the adhesion molecule ICAM-1 (CD54) and the receptor for stem cell factor (Kit) (CD117). The expression of CD54 was increased after treatment with IL-13 or IL-4, whereas the expression of Kit was decreased. Also in this action IL-4 was more potent than IL-13. By culturing mononuclear cells from cord blood in the presence of stem cell factor there is a differentiation of tryptase-positive mast cells in the cultures. This process was inhibited when IL-4 was present. In contrast, IL-13 did not affect the expression of tryptase during differentiation of stem cell factor dependent cord blood-derived mast cells. Taken together, these findings indicate that IL-13 has regulatory effects on human mast cells. The effect overlaps with but is also different from that of IL-4.     

Effect of c-fos overexpression on development and proliferation of peritoneal B cells

We examined effects of c-fos overexpression on the development and property of peritoneal B-1 cells using transgenic (H2-c-fos) mice carrying the c-fos gene under the control of the constitutive H-2Kb promoter. The number of B-1b cells in the peritoneal cavity of H2-c-fos mice was 4-fold larger than that in control littermates. Although the numbers of total peritoneal B cells and B-1a cells were similar between them, the peritoneal B-2 cell number in H2-c-fos mice was reduced to 50% of control littermates, suggesting the effect of c-fos overexpression on a balance of B-1b and B-2 cells in a peritoneal cavity. Adoptive transfer experiments with hematopoietic stem cells of H2-c-fos and control mice into irradiated H2-c-fos mice demonstrated that the augmentation of B-1b cells is due to the c-fos effect in B cells and the effect on environment of the peritoneal cavity of H2-c-fos mice. When peritoneal B cells were cultured with LPS in the presence or absence of IL-4, cell proliferation of B-1b cells was the highest among these peritoneal B cell subsets, and the proliferation of H2-c-fos B-1b cells was 3-fold higher than that of control B-1b cells. This augmentation is due to the c-fos effect in B cells. IgG1 production of B-1b cells in these cultures was slightly higher than those of B-1a and peritoneal B-2 cells. Thus, the c-fos overexpression augments development of B-1b cells in a peritoneal cavity and proliferation of peritoneal B-1b cells to LPS.     

不同体外刺激对小鼠腹腔产生IL-10的B细胞的影响

目的:探索不同体外刺激对小鼠腹膜腔B细胞产生IL-10的影响.方法:在不同刺激剂作用下,体外培养小鼠腹腔细胞5或48小时,流式细胞仪分析CD19+IL-10+ B细胞比例.结果:PIM刺激5小时后,小鼠腹腔CD19+IL-10+ B细胞比例明显升高至14.69%(P<0.01),在PIM刺激的基础上加入anti-IgM F(ab′)2或anti-CD40均不能进一步提高腹腔B细胞IL-10的表达(P>0.05),而加入IPS后,CD19+IL-10+ B细胞比例升高至平均26.53%(P< 0.01).LPS、anti-CD40刺激48小时可明显升高CD19+IL-10+ B细胞比例,但能够产生更强BCR信号的coated anti-IgM刺激抑制小鼠腹腔B细胞IL-10的表达.结论:体外刺激5小时,LPS+PIM是腹腔产生IL-10的B细胞活化的最佳刺激,刺激48小时,LPS和anti-CD40可进一步促进腹腔B细胞IL-10的表达,这一作用可能是通过诱导腹腔B10前体细胞成熟实现的.而anti-IgM刺激对腹腔B细胞产生IL-10的影响依赖于刺激时间和信号强度.     

LPS-induced migration of peritoneal B-1 cells is associated with upregulation of CXCR4 and increased migratory sensitivity to CXCL12

B-1 cells, which constitute a predominant lymphocyte subset in serosal cavities and produce most of natural antibodies, are subdivided into the CD5(+) B-1a and CD5(-) B-1b cell subpopulations, but the differential roles of B-1a and B-1b cells are not well understood. We report that B-1a cells preferentially migrate out of the peritoneal cavity and upregulate the expression of CXCR4 with heightened sensitivity to CXCL12 and CXCL13 upon LPS treatment compared to B-1b and B-2 cells. Whereas B-1a cells were slightly more abundant than B-1b and B-2 cells in the homeostatic condition, the number of B-1a cells preferentially decreased 48 hr after LPS treatment. The decrease in the peritoneal B-1a cell number was accompanied with increased migration of B-1a cells toward CXCL-12 and CXCL-13 in in vitro transmigration assay using peritoneal B cells from LPS treated mice. The expression level of CXCR4, but not of CXCR5, was also more prominently increased in B-1a cells upon LPS stimulation. LPS-stimulated B-1a cells did not accumulate in omental milky spots in contrast to B-2 cells. These results suggest that B-1a cells actively migrate out of the peritoneal cavity through the regulation of the migratory responsiveness to chemokines and actively participate in systemic immune responses.     

Regulation of T helper cell cytokine expression: functional dichotomy of antigen-presenting cells

A bias to either cell-mediated or antibody-mediated effector mechanisms is induced in an immune response against a pathogen, if activated T helper cells (T_h) predominantly express T_h1 [interleukin (IL)-2, interferon (IFN)-γ, and tumor necrosis factor (TNF)-β] or T_h2 (IL-4, IL-5, IL-6 and IL-10) cytokines. Here we provide evidence that, due to the capability to secrete IL-1, macrophages, but not B cells, as antigen-presenting cells (APC) induce production of IFN-γ in resting T_h cells. Normal murine splenic Th cells were activated in vitro with the superantigen Staphylococcus aureus enterotoxin B (SEB) presented by macrophages as compared to other APC from murine spleen. As determined by immunofluorescence, T_h cells producing IL-2 but almost none producing IL-4 and IL-5 are generated, irrespective of the type of APC. Generation of IFN-γ-producing T_h cells is largely dependent on presentation of SEB by macrophages. The requirement for macrophages, however, is overcome if IL-1 is provided. Expression of IFN-y by T_h cells is not induced, if production of IL-1 by macrophages is inhibited by IL-10. Our results suggest a functional dichotomy of APC: normal resting T_h cells differentiate into IL-2 and IFN-γ secreting cells (T_h1 cells) if antigen is presented by macrophages, whereas presentation by B cells generates T_h cells secreting IL-2, which might differentiate into T_h2 cells upon re-stimulation.     

Role of B-1a cells in autoimmunity

B-1a cells are distinguished from conventional B cells (B2) by their developmental origin, their surface marker expression and their functions. They were originally identified as a B cell subset of fetal origin that expresses the pan-T cell surface glycoprotein, CD5. B-1a cells also differ from B2 by the expression levels of several surface markers, including IgM, IgD, CD43 and B220 [R. Berland, H.H. Wortis, Origins and functions of B-1 cells with notes on the role of CD5. Ann Rev Immunol, 20 (2002) 253-300.]. The majority of B-1a cells are located in peritoneal and pleural cavities. Compared to B2 cells, B-1a are long-lived, non-circulating, with reduced BCR diversity and affinity [A.B. Kantor, C.E. Merrill, L.A. Herzenberg, J.L. Hillson, An unbiased analysis of V-H-D-J(H) sequences from B-1a, B-1b, and conventional B cells. J Immunol, 158 (1997) 1175-1186.]. B-1a cells are largely responsible for the production of circulating IgM referred to as natural antibodies. These low affinity antibodies are polyreactive and constitute as such a first line of defense against bacterial pathogens [M.C. Carroll, A.P. Prodeus, Linkages of innate and adaptive immunity. Curr Opin Immunol, 10 (1998) 36-40.]. This polyreactivity also results into the recognition of autoantigens, which serves in the clearance of apoptosis products. The weak autoreactivity of the B-1a cells has been postulated to play a role in autoimmune pathogenesis. In addition, other characteristics, such as the production of high level of IL-10 [A. O'Garra, R. Chang, N. Go, R. Hastings, G. Haughton, M. Howard, et al. Ly-1 B (B-1) cells are the main source of B cell-derived interleukin 10. Eur J Immunol, 22 (1992) 711-717.] and enhanced antigen presentation capacities [C. Mohan, L. Morel, P. Yang, E.K. Wakeland, Accumulation of splenic B1a cells with potent antigen-presenting capability in NZM2410 lupus-prone mice. Arthritis and Rheumatism, 41 (1998) 1652-1662.], have implicated B-1a cells in autoimmunity. This review will discuss the current understandings of their role in autoimmune diseases with focus on lupus.     

Requirement of IL-5 for induction of autoimmune hemolytic anemia in anti-red blood cell autoantibody transgenic mice

IL-5, IL-10 and lipopolysaccharide (LPS) are known to activateB-1 cells in vivo in normal mice and anti-red blood cell autoantibodytransgenic mice (HL mice). To assess the exact role of IL-5in proliferation and activation of peritoneal B-1 cells, weanalyzed IL-5 receptor chain-deficient HL (IL-5R^–/–x HL) mice generated by the cross between IL-5R^–/–and HL mice. In IL-5R^–/– x HL mice, Ig-producingB-1 cells in the peritoneal cavity were negligible, althoughthe total number of B-1 cells in the peritoneal cavity wereas many as 30% of that in HL mice. Moreover, LPS- or IL-10-induceddifferentiation of B-1 cells into antibody-producing cells wasseverely impaired in IL-5R^–/– x HL mice. We alsoused in vivo 5-bromo-2'-deoxyuridine labeling to estimate theproliferation of B-1 cells in IL-5R^–/– mice. Theabsence of IL-5R did not affect spontaneous proliferation ofperitoneal B-1 cells. However, induced proliferation of peritorealB-1 cells by oral administration of LPS was markedly impairedin IL-5R^–/– mice. These results suggest that IL-5is required for activation-associated proliferation of B-1 cellsbut not for their spontaneous proliferation and support theidea that IL-5 plays an important role on the induction of autoantibodyproduction from B-1 cells.     

Fas Ligand-Expressing B-1a Lymphocytes Mediate CD4+-T-Cell Apoptosis during Schistosomal Infection: Induction by Interleukin 4 (IL-4) and IL-10

A previous study of the murine model of Schistosoma mansoni infection has implicated splenic CD19(+) B lymphocytes as Fas ligand (FasL)-bearing mediators of CD4(+) T-lymphocyte apoptosis. The present study shows that B-cell deficiency leads to decreased CD4(+) T-cell apoptosis during infection and compares FasL expression and killer function of B-1a- and CD5(-) B-lymphocyte subsets. B-1a cells from uninfected mice displayed constitutive expression of FasL compared with that of CD5(-) B cells. FasL expression was enhanced following worm egg deposition and antigenic stimulation on both subsets of B cells. Purified B-1a cells from uninfected mice were potent effectors of CD4(+) T-cell apoptosis, and the killing effect was enhanced during schistosome infection. FasL expression by splenic B cells required CD4(+)-T-cell help that was replaced by addition of culture supernatants from antigen-stimulated splenocytes of infected mice. The culture-supernatant-stimulated FasL expression was inhibited by anti-interleukin 10 (IL-10) and anti-IL-4 antibodies. Culture of purified B cells with recombinant IL-4 (rIL-4), rIL-10, and soluble egg antigens (SEA) led to increased expression of FasL on B-1a cells. These results suggest that FasL-expressing, splenic B-1a cells are important mediators of SEA-stimulated CD4(+)-T-cell apoptosis and that maximal FasL expression on B-1a cells is dependent on antigenic stimulation and the presence of IL-4 and IL-10.     

Human interleukin-5 induces staphylococcal A Cowan 1 strain-activated human B cells to secrete IgM

Studies on the role of human interleukin (IL)-5 in B cell growth and differentiation have yielded conflicting results. To clarify this issue, we studied the role of purified recombinant IL-5 on activated human B cells which were depleted of Tcells and adherent cells. Human IL-5 augments IgM secretion, but not IgG or IgA secretion of purified human B cells activated with staphylococcal A Cowan 1 strain (SAC). However, the period of B cell activation with SAC is critical for the B cell to respond to IL-5. After 24 h of SAC activation, human B cells are responsive to the IL-5 signal, but with longer periods of activation, IL-5 responsiveness diminishes. This may explain some of the previous conflicting results. The IgM enhancement was not seen when B cells were activated with pokeweed mitogen. In addition, human recombinant IL-4 synergized with IL-5 in augmenting IgM secretion by SAC-activated B cells, while IL-5 synergized with IL-2 to augment IgM, IgG and IgA secretion by SAC-activated B cells. As the purified IL-5 was derived from a COS-1 cell supernatant, and COS-1 cells secrete IL-6, we examined whether a polyclonal IL-6 antibody blocked the IgM-enhancing activity of IL-5. IL-6 antibody did not block the IL-5 enhancement of IgM secretion, but a monoclonal antibody to IL-5 inhibited the human IL-5 activity on human B cells. These results demonstrate that human IL-5 augments IgM secretion of SAC-activated human B-cells. In addition, this lymphokine synergizes with IL-4 and IL-2 in supporting Ig secretion.