Major Source Of IL-10 Research Articles

A critical role for IL-10 in limiting inflammation during toxoplasmic encephalitis

IL-10 plays a vital role in controlling the inflammatory response during acute Toxoplasma gondii infection, however the production of IL-10 during the chronic phase of toxoplasmosis has been associated with parasite persistence. To address this paradox, the production and effect of IL-10 in the brain during toxoplasmic encephalitis (TE) was investigated. Analysis of brain mononuclear cells (BMNC) from chronically infected mice revealed that infiltrating macrophages and CD4 + T cells were the major sources of IL-10. Endogenous levels of IL-10 inhibited the production of IL-12, IFN-γ, TNF-α, and IL-6 from both hematopoetic and non-hematopoetic cells in the brain, as well as anti-microbial activity of astrocytes. Furthermore, IL-10-/- mice that progressed to the chronic phase of infection had equivalent parasite burden to WT mice but developed a lethal inflammatory response within the brain characterized by increased numbers of CD4 + T cells and macrophages, and elevated production of inflammatory cytokines. Finally, partial depletion of CD4 + T cells decreased the severity of the inflammation in the brain and allowed IL-10-/- mice to survive infection. Together these results point to a vital role for IL-10 in the control of CD4 + T cell mediated inflammation in the brain during TE.

Regulation of IL-10 Gene Expression in Th2 Cells by Jun Proteins

IL-10 is a key regulatory cytokine produced by T lymphocytes. Although Th2 cells are a major source of IL-10, little is known about IL-10 gene regulation in Th2 cells. High levels of IL-10 mRNA transcription are induced in the Th2 clone D10 after PMA plus ionomycin (P/I) stimulation; however we found that the IL-10 promoter was not inducible by P/I in D10 cells. We therefore sought regulatory regions in the IL-10 gene that could promote P/I-activated transcription in Th2 cells. Two strong DNase I-hypersensitive sites (DHSSs) were identified in the IL-10 gene in mouse T cells, and conserved noncoding sequences (CNSs) between the mouse and human IL-10 genes were also identified. One IL-10 DHSS maps within or next to a highly conserved CNS region, CNS-3. The CNS-3 region contains an AP-1 site that binds JunB and c-Jun proteins specifically in Th2 cells and not in Th1 cells. The CNS-3 element activates transcription from the IL-10 promoter after P/I stimulation and is responsive to c-Jun and JunB. Retroviral mediated-expression of either c-Jun or JunB in primary T cells led to a large increase in IL-10 expression, and inhibition of AP-1 activity by a dominant negative form of c-Jun in primary T cells strongly repressed IL-10 expression. IFN-gamma was relatively unaffected by modulations in AP-1 activity. These data indicate that we have identified a novel regulatory element that can specifically activate transcription of the IL-10 gene in Th2 cells via the AP-1/Jun pathway.

TLR-9 Activation of Marginal Zone B Cells in Lupus Mice Regulates Immunity Through Increased IL-10 Production

Bacterial DNA triggers B-cell proliferation and induces immunoglobulin secretion. Chromatin-IgG complexes activate autoreactive B cells by co-engaging B-cell receptor (BCR) and TLR-9, thus suggesting a role for innate signaling in systemic autoimmunity. Spleen cells from lupus prone Palmerston North (PN) mice produce several fold less IL-12p40 than controls in response to CpG-oligodeoxynucleotides (ODNs). Here we show that B cells are primarily responsible for this abnormality. The removal of B cells from PN cultures markedly increased IL-12p40. Moreover, the addition of purified B cells back to PN splenocyte cultures resulted in a B-cell number dependent/ IL-10-mediated suppression of IL-12p40. The B cells were the major source of IL-10. In response to CpG, B cells from several lupus strains produced twice as a much IL-10 as controls, but failed to produce IL-10 when stimulated through BCR or CD40. PN and control mice expressed IL-10R similarly, and the difference in IL-10 secretion remained when anti-IL-10R blocking antibodies were used. IFN-gamma and IL-4 regulated CpG-induced IL-10 secretion in opposite directions. The abnormal IL-10 response in lupus mice was derived from B cells with the marginal zone phenotype, and could be downregulated with inhibitory ODNs. We hypothesize that TLR-9 activated lupus B cells can modulate T-cell mediated inflammatory responses through IL-10 production. Therefore, B cells may contribute to the lupus pathogenesis in many different ways: as antigen-presenting cells for self antigens, as effector cells for autoantibody production, and as IL-10 secreting regulatory cells.

5. IgE, mast cells, basophils, and eosinophils

IgE, mast cells, basophils, and eosinophils constitute essential elements in allergic inflammation. Allergen-specific IgE, synthesized in response to allergens in the environment, becomes fixed to FcepsilonRI on the membranes of mast cells and basophils. Aggregation of receptor-bound IgE molecules on re-exposure to specific allergen results in the production of mediators that produce the allergic response. Principal among the cells drawn to sites of mediator release is the eosinophil.

Fantastic new insight into mechanisms of lung T H2 responses

The understanding of the complex steps that occur during the development of TH2 responses remains incomplete, largely because of the apparent overlapping function of rare cells. For example, while it is appreciated that CD4 T cells are a major source of IL-4, the contribution of NKT cells, eosinophils, basophils, and mast cells is unclear. To examine the orchestration of TH2 immunity in the lung, the investigators used experimental infection of mice with the nematode Nippostrongylus brasiliensis (Np). The investigators took advantage of mice containing a bicistronic knock-in IL-4 gene linked via an internal ribosomal entry site (IRES) with enhanced green fluorescent protein; these mice, designated 4get, allow easy identification of IL-4–producing cells. Using these animals, the investigators demonstrate that eosinophils are the predominant source of IL-4, followed by TH2 cells and basophils (mast cells and NKT cells failed to make substantial levels of IL-4 in their system). To further characterize eosinophils and basophils—cell types that have not been understudied at a molecular level—the investigators purified both populations of cells from the Np-challenged lungs. Microarray analysis of RNA transcripts expressed in both cell types revealed more than 1000 genes that were differentially expressed between the 2 cell types. Indeed, some very interesting genes were identified, including (a) CCR3, CD11c, CD24, GATA1, and IL27 (all expressed only by eosinophils) and (b) GATA2, 2B4, H4 receptor, IL-18 receptor, and a variety of cytokines (all expressed only by basophils). The investigators subsequently examined the signals required for recruitment of both cell types into the Np-infected lung. Eosinophil and basophil expansion in the blood and their capacity to express IL-4 were independent of Stat6 and T cells. In contrast, eosinophil (and TH2 cell) recruitment to the lung was dependent on Stat6 expression by a bone marrow–derived tissue-resident cell. However, basophil recruitment was Stat6-independent (and IL-4/IL-13–independent) but T cell–dependent. Taken together, these results show that innate production of IL-4 by basophils and eosinophils makes a substantial contribution to TH2 lung responses and that diverse mechanisms orchestrate recruitment of these cells to the lung. The understanding of the complex steps that occur during the development of TH2 responses remains incomplete, largely because of the apparent overlapping function of rare cells. For example, while it is appreciated that CD4 T cells are a major source of IL-4, the contribution of NKT cells, eosinophils, basophils, and mast cells is unclear. To examine the orchestration of TH2 immunity in the lung, the investigators used experimental infection of mice with the nematode Nippostrongylus brasiliensis (Np). The investigators took advantage of mice containing a bicistronic knock-in IL-4 gene linked via an internal ribosomal entry site (IRES) with enhanced green fluorescent protein; these mice, designated 4get, allow easy identification of IL-4–producing cells. Using these animals, the investigators demonstrate that eosinophils are the predominant source of IL-4, followed by TH2 cells and basophils (mast cells and NKT cells failed to make substantial levels of IL-4 in their system). To further characterize eosinophils and basophils—cell types that have not been understudied at a molecular level—the investigators purified both populations of cells from the Np-challenged lungs. Microarray analysis of RNA transcripts expressed in both cell types revealed more than 1000 genes that were differentially expressed between the 2 cell types. Indeed, some very interesting genes were identified, including (a) CCR3, CD11c, CD24, GATA1, and IL27 (all expressed only by eosinophils) and (b) GATA2, 2B4, H4 receptor, IL-18 receptor, and a variety of cytokines (all expressed only by basophils). The investigators subsequently examined the signals required for recruitment of both cell types into the Np-infected lung. Eosinophil and basophil expansion in the blood and their capacity to express IL-4 were independent of Stat6 and T cells. In contrast, eosinophil (and TH2 cell) recruitment to the lung was dependent on Stat6 expression by a bone marrow–derived tissue-resident cell. However, basophil recruitment was Stat6-independent (and IL-4/IL-13–independent) but T cell–dependent. Taken together, these results show that innate production of IL-4 by basophils and eosinophils makes a substantial contribution to TH2 lung responses and that diverse mechanisms orchestrate recruitment of these cells to the lung.

Nonredundant roles for CD1d-restricted natural killer T cells and conventional CD4+ T cells in the induction of immunoglobulin E antibodies in response to interleukin 18 treatment of mice.

Interleukin (IL)-18 synergizes with IL-12 to promote T helper cell (Th)1 responses. Somewhat paradoxically, IL-18 administration alone strongly induces immunoglobulin (Ig)E production and allergic inflammation, indicating a role for IL-18 in the generation of Th2 responses. The ability of IL-18 to induce IgE is dependent on CD4+ T cells, IL-4, and signal transducer and activator of transcription (stat)6. Here, we show that IL-18 fails to induce IgE both in CD1d−/− mice that lack natural killer T (NKT) cells and in class II−/− mice that lack conventional CD4+ T cells. However, class II−/− mice reconstituted with conventional CD4+ T cells show the capacity to produce IgE in response to IL-18. NKT cells express high levels of IL-18 receptor (R)α chain and produce significant amounts of IL-4, IL-9, and IL-13, and induce CD40 ligand expression in response to IL-2 and IL-18 stimulation in vitro. In contrast, conventional CD4+ T cells express low levels of IL-18Rα and poorly respond to IL-2 and IL-18. Nevertheless, conventional CD4+ T cells are essential for B cell IgE responses after the administration of IL-18. These findings indicate that NKT cells might be the major source of IL-4 in response to IL-18 administration and that conventional CD4+ T cells demonstrate their helper function in the presence of NKT cells.

Mast cells and T cells in Kimura's disease express increased levels of interleukin-4, interleukin-5, eotaxin and RANTES.

Kimura's disease (KD) is a chronic inflammatory disorder characterized by tumours in the head and neck region, enlarged lymph nodes, increased eosinophil counts andhigh serum IgE. Mast cells are known to play a central role in IgE-mediated allergic diseases through the release of inflammatory mediators like IL-4, IL-5 and chemokines. We hypothesized that mast cells may play a role in the pathogenesis of KD by regulating eosinophilic infiltration and IgE synthesis. In order to investigate the role of mast cells in the pathogenesis of KD, we examined the expression of cytokines/chemokines in the lesions of KD. We examined the number of tryptase+ cells, EG2+ cells, CD3+ cells, IL-4+ cells, IL-5+ cells, eotaxin+ cells, RANTES+ cells and CCR3+ cells in five specimens of KD versus normal tissues by immunohistochemistry. The sources of IL-4, IL-5, eotaxin and RANTES and the expression of CCR3 were examined by immunostaining of serial sections with antibodies to IL-4, IL-5, eotaxin, RANTES and CCR3, and antibodies to tryptase, ECP (EG2) and CD3. Mast cells, activated eosinophils, T cells, IL-4+ cells, IL-5+ cells, eotaxin+ cells, RANTES+ cells and CCR3+ cells were all increased in the lesions of KD as compared with those in normal tissue. Mast cells and T cells were the major source of IL-4, whereas mast cells, T cells and activated eosinophils were the main source of IL-5. Mast cells, T cells and activated eosinophils were the main source of eotaxin and RANTES. The number of IL-4, IL-5, eotaxin and RANTES-expressing mast cells and T cells were increased in the lesions of KD. As mast cells are lesional resident cells, these cells may play an important role in the pathogenesis of KD by regulating IgE synthesis and orchestrating eosinophilic infiltration.

Regulatory Role of Endogenous Interleukin-10 in Cutaneous Inflammatory Response of Murine Wound Healing

This study investigated the role of endogenous interleukin (IL)-10 in cutaneous wound healing. Both IL-10 mRNA and protein were detectable in murine incised wounds for 10 days after injury. The IL-10 protein level peaked 3 h after incision, returned to the normal level by 24 h, but increased again to another peak at 72 h. In situ hybridization studies and immunostaining revealed that epidermal cells and infiltrating mononuclear cells were the major source of IL-10. Neutralizing antibody studies demonstrated that IL-10 inhibited the infiltration of neutrophils and macrophages toward the site of injury. IL-10 also inhibited overexpression of C-C chemokines (monocyte chemoattractant protein-1, macrophage inflammatory protein-1α) and proinflammatory cytokines (IL-1β, IL-6, tumor necrosis factor-α) in vivo. These results suggest that IL-10 may play an important regulatory role in the phase-specific infiltration of neutrophils and macrophages as well as the cytokine production in the inflammatory response of cutaneous wound healing.

Eotaxin Potentiates Antigen-Dependent Basophil IL-4 Production

AbstractBasophils are a major source of IL-4, which is a critical factor in the generation of allergic inflammation. Eotaxin induces chemotaxis mediated through the CC chemokine receptor 3 (CCR3) present on basophils as well as eosinophils and Th2 cells, thereby promoting cell recruitment. To determine whether eotaxin has other proinflammatory activity, we examined the effect of eotaxin on basophil IL-4 expression by flow cytometry. Eotaxin alone had no effect on basophil IL-4 production, but further increased allergen-stimulated IL-4 expression. Eotaxin also enhanced IL-4 release from purified basophils 2- to 4-fold, as determined by ELISA (p < 0.01). Addition of eotaxin to cultures resulted in a 40-fold left shift in the dose response to Ag. This effect was obtained with physiologic concentrations of eotaxin (10 ng/ml), was abrogated by an Ab to the CCR3 receptor, and was noted with other chemokine ligands of CCR3. Additionally, eotaxin augmented IL-3 priming of basophil IL-4 production in a synergistic manner (p < 0.01). In contrast, no priming was observed with either IL-5 or GM-CSF. These results establish a novel function for eotaxin and other chemokine ligands of CCR3: the potentiation of Ag-mediated IL-4 production in basophils, and suggest a potential nonchemotactic role for CC chemokines in the pathogenesis and amplification of inflammation.

Age-related alteration of cytokine production profile by T cell subsets in mice: a flow cytometric study.

Spleen cells from young and old C57BL/6 mice were stimulated with a combination of anti-CD3 and anti-CD28 antibodies, and the profile of cytokine production was examined by two different methods; the concentrations of cytokines as measured by ELISA, and identification of cytokine-positive cells by flow cytometry. The ELISA method revealed that IL-2 production by spleen cells after stimulation was significantly lower in the old mice compared to the young mice. while IFN-gamma production was the reverse. The flow cytometric analysis showed that the percentage of IL-2 positive cells in spleen cells after the stimulation was significantly lower in the older mice than in the young mice, and vice versa for the percentage of IFN-gamma-positive cells. Regarding the T cell subsets, CD4+ T cells were a major source of IL-2 in both the young and old mice. IL-2-positive cells in both CD4+ and CD8+ T cells showed a significant decrease with age. On the contrary, CDX T cells were the major source of IFN-gamma. An age-related increase of IFN-gamma positive cells was observed in both CD4+ and CD8+ T cells. CD4 T cells were the major source of IL-4, and the percentage of IL-4-positive CD4+ T cells also increased with age, although the level of IL-4 production was modest in C57BL/6 mice compared with IL-2 and IFN-gamma. Such age-related changes of cytokine production are presumed to play an important role in the alteration of immunological capacity with age.

Hepatic release of interleukin-10 during cardiopulmonary bypass in steroid-pretreated patients

With its antiinflammatory properties, interleukin (IL)–10 may play an important role in limiting complications associated with cardiopulmonary bypass (CPB). We previously demonstrated that pretreatment with steroids can significantly increase IL-10 production during CPB, but neither the heart nor the lung was found to be its main source. To define whether the liver is the source of IL-10, hepatic venous cannulation was performed in 12 patients undergoing CPB. Each patient received 30 mg/kg of methylprednisolone before operation. Plasma levels of IL-10 were simultaneously measured in peripheral arterial blood and hepatic venous blood before heparin administration, before aortic cross-clamping, and 5, 30, 60, 90, and 120 minutes after aortic declamping. The duration of CPB and aortic cross-clamping was 113 ± 7 minutes and 75 ± 6 minutes (mean ± SEM), respectively. IL-10 levels 30 minutes after declamping were significantly higher in hepatic venous blood than in arterial blood (1187 ± 573 pg/ml vs 911 ± 405 pg/ml, p < 0.01 by Wilcoxon's signed-rank test). To determine whether steroids can also induce the release of another antiinflammatory cytokine, IL-4, plasma IL-4 levels were measured simultaneously. IL-4 was detected in the arterial blood of only 4 of the 12 patients, transiently after aortic declamping. IL-4 was not detected in hepatic venous blood. In conclusion, the liver is a major source of IL-10 during CPB. However, steroid-treated patients do not show an increase in IL-4, and the liver is not the source of IL-4 during and after CPB. (Am Heart J 1997;133:335-9.)

Transcription Mediated by NFAT Is Highly Inducible in Effector CD4+ T Helper 2 (Th2) Cells but Not in Th1 Cells

Transcriptional factors of the NFAT family play an important role in regulating the expression of several cytokine genes during the immune response, such as the genes for interleukin 2 (IL-2) and IL-4, among others. Upon antigen stimulation, precursor CD4+ T helper (pTh) cells proliferate and differentiate into two populations of effector cells (eTh1 and eTh2), each one expressing a specific pattern of cytokines that distinguishes them from their precursors. eTh2 cells are the major source of IL-4, while gamma interferon is produced by eTh1 cells. Here we have used reporter transgenic mice to show that DNA binding and transcriptional activities of NFAT are transiently induced during the differentiation of pTh cells into either eTh1 or eTh2 cells to mediate the expression of IL-2 as a common growth factor in both pathways. However, although NFAT DNA binding is similarly induced in both eTh1 and eTh2 cells upon antigen stimulation, only the NFAT complexes present in eTh2 cells are able to mediate high-level transcription, and relatively little NFAT transcriptional activity was induced in eTh1 cells. In contrast to activated pTh cells, neither eTh1 nor eTh2 cells produced significant IL-2 upon stimulation, but the high levels of NFAT transcriptional activities directly correlate with the IL-4 production induced in response to antigen stimulation in eTh2 cells. These data suggest that activated NFAT is involved in the effector function of eTh2 cells and that the failure of eTh1 cells to produce IL-4 in response to an antigen is due, at least partially, to a failure to induce high-level transcription of the IL-4 gene by NFAT. Regulation of NFAT could be therefore a critical element in the polarization to eTh1 or eTh2.

Cytokine Responses to Cardiopulmonary Bypass: Lessons Learned From Cardiac Transplantation

Background. A growing body of evidence relates the release during cardiopulmonary bypass (CPB) of proinflammatory cytokines, such as tumor necrosis factor-α, interleukin (IL)-6, and IL-8, to the postoperative systemic inflammatory response syndrome. Antiinflammatory cytokines, such as IL-10, however, may also play an important role in limiting these complications. Methods. The English-language literature was reviewed. Emphasis was placed on cytokine responses during clinical CPB for cardiac operations and, in particular, for heart and heart-lung transplantation. Results. The recent data indicate that (1) although cytokine release can be triggered by many factors during CPB, ischemia-reperfusion may play the most important role; (2) the levels of tumor necrosis factor-α, IL-6, and IL-8 are correlated with the duration of cardiac ischemia and the myocardium is a major source of these three cytokines during CPB; (3) IL-10 levels are correlated with the duration of CPB and the liver is a major source of IL-10 during CPB; and (4) steroid pretreatment is an effective intervention to inhibit the release of proinflammatory cytokines and enhance IL-10 production. Conclusions. The improved knowledge of cytokine responses to CPB may help to develop interventions aimed at reducing postoperative morbidity and mortality. (Ann Thorac Surg 1997;63:269–76)

Contribution of interleukin-3 to antigen-induced Th2 cytokine production.

Short-term stimulation of mouse spleen cells in vitro with interleukin (IL)-3 induces the secretion of the Th2 cytokines IL-4 and IL-6. Non-B/non-T cells were the target of this IL-3 effect. However, during long-term antigen-dependent culture, T cells are the major source of IL-4 and IL-6. The addition of IL-3 to such cultures also led to a significant increase in IL-4 and IL-6 production. This Th2 cytokine secretion was amplified by the addition of irradiated non-B/non-T cells at the initiation of culture, and was inhibited by anti-IL-4 antibodies. These findings suggest that IL-3 induces the rapid release of IL-4 and IL-6 by non-B/non-T cells, thereby creating an immune milieu conducive to the development of antigen-specific IL-4 and IL-6-secreting Th2 cells.

Analysis of cytokine gene expression in Graves' disease and multinodular goiter.

Cytokines have a central role in the generation of an autoimmune response and can directly affect the target organ. In Graves' disease, both the infiltrating mononuclear cells and the thyroid follicular cells produce certain cytokines, but the relative contribution of each is unclear, and there are conflicting data on the exact profile of cytokines expressed within the thyroid. To clarify these issues, we used the method of reverse transcription-polymerase chain reaction amplification to analyze cytokine gene expression by intrathyroidal lymphocytes (ITL) and purified thyroid follicular cells (TFC) from six patients with Graves' disease. All ITL samples were positive for interleukin-1 alpha (IL-1 alpha), IL-1 beta, IL-6, IL-8, IL-10, and tumor necrosis factor-alpha (TNF alpha) messenger ribonucleic acids (mRNAs). Four samples were positive for IL-2 mRNA, and of these, three were also positive for interferon-gamma (IFN gamma). All TFC samples contained IL-6 and IL-8 mRNAs, even after depletion of CD3-positive T-cells. One TFC sample was additionally positive for IL-10 and TNF alpha mRNAs, and in the case of IL-10, this signal was not eliminated by CD3-positive T-cell depletion. IL-4 was not detected in any sample of ITL, TFC, or whole tissue. Semiquantitative analysis showed that the ITL fraction represented the major source of IL-6, IL-8, and TNF alpha mRNAs. By contrast, only three of five multinodular goiter samples were positive for IL-1 alpha mRNA; of these, two were also positive for IL-6, and 1 was positive for IL-8 mRNA. One multinodular goiter sample was positive for IL-8 mRNA alone, but IL-2, IL-4, IL-10, and TNF alpha mRNAS were not detected. These results suggest that although the TFC themselves may express certain cytokines, the ITL population represents the most important source of cytokine production in Graves' thyroid glands. The presence of IL-2, IFN-gamma, and TNF alpha and the absence of IL-4 mRNA in samples of ITL indicate a pattern of cytokine production that most closely resembles that of the TH1 helper T-cell subset. Given the etiological role of thyroid-stimulating antibodies in Graves' disease, the production of which is likely to depend upon TH2 helper T-cell function, it is perhaps surprising that the TH1 subset appears to predominate. It is possible that IL-10 is important in stimulating intrathyroidal autoantibody production, and this cytokine may also play a role in inhibiting cell-mediated thyroid injury in Graves' disease.

Anti-IL-4 treatment of Schistosoma mansoni-infected mice inhibits development of T cells and non-B, non-T cells expressing Th2 cytokines while decreasing egg-induced hepatic fibrosis.

Increasing evidence suggests that schistosome egg granulomas are primarily Th2 cellular reactions. Mice infected with Schistosoma mansoni were treated with a neutralizing mAb against IL-4 to evaluate the role of this cytokine in the generation of parasite egg-induced cell-mediated responses and hepatic pathology. Animals treated with anti-IL-4 before egg deposition showed decreased IL-4, IL-5, and IL-10 production in response to in vitro antigenic stimulations and decreased IL-5 and IL-13 mRNA levels in the liver. As observed previously, non-B, non-T cells were a major source of IL-4 in infected mice treated with control mAb, and the diminished IL-4 response in anti-IL-4-treated animals was shown to be caused at least in part by a reduction in the number of these cells, as well as by decreased secretion of IL-4 per cell. In contrast, production of the Th1 cytokines IL-2 and IFN-gamma was elevated in anti-IL-4-treated infected mice in vitro, and the corresponding mRNAs in the liver were increased. Anti-IL-4 treatment did not consistently reduce the size of hepatic granulomas around S. mansoni eggs, but markedly inhibited granuloma formation in the lungs of the same animals after i.v. egg injection. Nevertheless, anti-IL-4-treated infected mice showed consistent and marked reductions in hepatic collagen deposition. These findings indicate that IL-4 plays a major role in the development of the Th2 response in S. mansoni-infected mice and contributes to the pathogenesis of hepatic fibrosis.

Tissue-specific regulation of IL-6 production by IL-4. Differential effects of IL-4 on nuclear factor-kappa B activity in monocytes and fibroblasts.

IL-4 inhibits production of certain proinflammatory cytokines, including IL-1 beta, TNF-alpha, and IL-6, by activated monocytes. Although monocytes are a major source of IL-6, other cell types such as fibroblasts and endothelial cells can also express this cytokine. To determine whether IL-4 inhibits IL-6 expression in non-hemopoietic cells, we investigated the effects of IL-4 on IL-6 production in both primary human fibroblasts and fibroblast lines. Rheumatoid synovial fibroblasts were evaluated in these studies because, like monocytes, they produce high levels of IL-6 when stimulated with IL-1. Although peripheral blood monocytes did not constitutively express IL-6 mRNA or protein, stimulation with IL-1 or LPS induced de novo IL-6 expression in these cells. In contrast, synovial fibroblasts displayed a significant basal level of IL-6 production, which was markedly increased after stimulation with IL-1. IL-4 suppressed IL-6 expression in monocytes, but did not inhibit IL-6 production in synovial fibroblasts. The inability of IL-4 to suppress IL-6 synthesis in rheumatoid synovial fibroblasts was not caused by a lack of IL-4R and was not unique to these cells because IL-4 also failed to inhibit IL-6 production in normal fibroblast lines derived from other tissues. Inhibition of IL-6 production by IL-4 in monocytes was associated with decreased nuclear NF-kappa B levels. However, IL-4 does not globally suppress the activity of all DNA-binding proteins because IL-4 treatment did not reduce the levels of NF-IL-6 or NF-IL-1 beta B in the same cells. Because NF-kappa B activation is required for transcription of many cytokine genes, including IL-6, the ability of IL-4 to suppress NF-kappa B activity in monocytes suggests a potential mechanism by which this molecule may inhibit the expression of multiple cytokines.

Interleukin-3-treated non-B, non-T cells switch activated B cells to IgG1/IgE synthesis.

The switch of activated B cells to IgE synthesis is an interleukin (IL)-3-dependent process. It is currently thought that specific T cells activated by antigen presented in the context of class II major histocompatibility complex are the major source of IL-4. Recently it has been demonstrated that a splenic non-T non-B cell population (termed NBNT) has the capacity to produce IL-4 following IgE and IgG receptor cross-linkage. In this study we demonstrate that IL-4 producing NBNT cells can induce the switch of lipopolysaccharide-activated B cells to the synthesis of IgG1 and IgE antibodies. Furthermore, it was found that not only IgE receptor cross-linkage but IL-3 was able to stimulate NBNT cells to produce IL-4 and induce the switch of B cells to IgE synthesis. NBNT cells derived from the spleen and bone marrow of SCID mice were able to produce IL-4 on exposure to IL-3. This suggested that the ability of IL-3 to stimulate IL-4 production was not dependent on prior exposure of the NBNT cells to antibody complexes in vivo. Taken together these findings represent the first observation that enough IL-4 is produced by NBNT cells to actually influence a B cell IgG/Ig response. The findings also clearly demonstrate that B cells do not need high concentrations of IL-4 to be directed to switch to IgG1 and IgE synthesis.