A thiol antioxidant regulates IgE isotype switching by inhibiting activation of nuclear factor-kappaB

Certain carotenoids enhance the intracellular glutathione level in a murine cultured macrophage cell line by inducing glutamate-cysteine-ligase

SCOPE

Glutathione (GSH) increases in RAW264 murine macrophage cells exposed to β-carotene or β-cryptoxanthin, however, the underlying mechanism has not been clarified. In the present study, we investigated the expression of glutamate-cysteine-ligase (GCL), the rate-limiting enzyme in GSH synthesis, in these cells.

METHODS AND RESULTS

Both the protein and mRNA expression of GCL increased in a β-carotene concentration-dependent manner. Buthionine sulfoximine, a GCL inhibitor, abolished the β-carotene-induced GSH increase without affecting the β-carotene-induced GCL protein expression. Both cycloheximide, a translation inhibitor, and actinomycin D, a transcription inhibitor, completely suppressed the β-carotene-induced GCL protein expression and the concomitant GSH increase. Actinomycin D inhibited the β-carotene-induced Gcl mRNA expression as well. Similarly to β-carotene, β-cryptoxanthin upregulated the GCL protein expression, but lutein did not. The c-Jun N-terminal kinase (JNK) inhibitor, SP600125, suppressed the β-carotene-induced GSH increase, whereas a p38 mitogen-activated protein kinase inhibitor or an extracellular signal-regulated kinase 1/2 inhibitor did not. The JNK inhibitor also suppressed the β-carotene-induced GCL protein expression, and consistently β-carotene induced JNK phosphorylation.

CONCLUSION

These findings revealed that certain carotenoids induce the Gcl mRNA expression in RAW264 cells and subsequently the GCL protein expression, which concomitantly enhances the intracellular GSH level, in a JNK pathway-related manner.

Vitamin C acts indirectly to modulate isotype switching in mouse B cells

Vitamin C, one of essential micronutrients, has been reported to modulate the humoral immune responses in some mammals. We investigated whether vitamin C might modulate this response in mice by directly affecting B cells. Splenic B cells were isolated and activated by CD40- and B cell receptor-ligation in vitro. The cells were cultured with a pretreatment of vitamin C from 0 to 1 mM of concentrations. Vitamin C slightly increased apoptosis of B cells dose-dependently and behaved as an antioxidant. We found that in vivo administration of vitamin C by intraperitoneal injection affected isotype switching as previously reported: the titer of antigen-specific IgG1 antibody was decreased, while that of IgG2a was unaffected. Somewhat different from those observed in vivo, in vitro exposure to vitamin C slightly decreased isotype switching to IgG1 and increased isotype switching to IgG2a. Pretreatment with vitamin C in the safe range did not affect either proliferation of cultured B cells or the expression of CD80 and CD86 in those cells. Taken together, in vivo results suggest that vitamin C acts to modulate isotype switching in the mouse. However, because of our in vitro results, we suggest that the modulation exerted by vitamin C in vivo is by indirectly affecting B cells, perhaps by directly influencing other immune cells such as dendritic cells.

Peripheral blood mononuclear cell NF-kappaB p105 mRNA decreases during asthmatic attacks

BACKGROUND

NF-kappaB is a transcription factor involved in expression of many inflammatory cytokines, chemical transmitters, and adhesion molecules. It has been reported to play a major role in the pathogenesis of asthma. NF-kappaB p50, which is the actual subunit that results from the cleavage of p105, is required for the induction of eosinophilia via IL-5 and chemokines.

METHODS

The subjects were 10 patients with a mean age of 59.3 years (14-82 years). NF-kappaB p105 mRNA in peripheral blood mononuclear cells during the presence or absence of asthmatic attacks was investigated. Total RNA was extracted from peripheral blood mononuclear cells. After cDNA was synthesized using random primers, NF-kappaB p105 mRNA level was measured by real-time polymerase chain reaction.

RESULTS

The NF-kappaB p105 mRNA level in peripheral blood mononuclear cells was lower during asthmatic attacks than in the absence of attacks, showing a significant difference (Wilcoxon's signed rank test: p<0.01).

CONCLUSIONS

A drop in NF-kappaB p105 during an asthma attack could result in increased NF-kappaB activity. There is a possibility that a change in the NF-kappaB p105 mRNA level might indicate some pathogenetic state in bronchial asthma attacks.

Diabetes-induced activation of nuclear transcriptional factor in the retina, and its inhibition by antioxidants

Oxidative stress is increased in the retina in diabetes, and long-term administration of antioxidants inhibits the development of retinopathy in diabetic rats. The purpose of this study is to determine how diabetes affects the activation of a redox-sensitive nuclear transcriptional factor in the retina, NF-kappaB, and its inhibition by antioxidants. Alloxan diabetic rats were assigned to receive standard diet or the diet supplemented with multiple antioxidants, including ascorbic acid, Trolox, dl alpha-tocopherol acetate, N-acetyl cysteine, beta-carotene, and selenium for up to 14 months. NF-kappaB activation, oxidative stress and nitric oxides were measured in the retina at 2, 8 and 14 months of diabetes. Retinal NF-kappaB was activated by about 60% at two months after induction of diabetes, remained activated for up to 14 months of diabetes, and the duration of diabetes had no effect on the intensity of NF-kappaB activation. Similarly, oxidative stress and nitric oxides were elevated by over 50% in the retina of rats diabetic for 14 months, and nitrotyrosine levels were elevated by over two folds. Administration of the antioxidants to the rats for the entire duration of diabetes inhibited activation of NF-kappaB and elevations in oxidative stress, nitric oxides and nitrotyrosine formation without ameliorating the severity of hyperglycemia. These in vivo results were confirmed by in vitro studies showing that high glucose activates NF-kappaB and elevates NO and lipid peroxides in both retinal endothelial cells and pericytes that can be inhibited by antioxidants. Thus, the results suggest that the activation of retinal NF-KB in diabetes is an early event in the development of retinopathy, and it remains active when the retinal capillary cell death is accelerating, and histopathology is developing. Beneficial effects of antioxidants on the development of diabetic retinopathy might involve inhibition of NF-kappaB activation and its downstream pathways in the retina.

Wheat gliadin promotes the interleukin-4-induced IgE production by normal human peripheral mononuclear cells through a redox-dependent mechanism

Increased levels of serum IgE have been described in gliadin-intolerant patients; however, biological mechanisms implicated in this immunoglobulin production remained unknown. In this study, we demonstrated that in vitro crude gliadins and gliadin lysates (Glilys) promoted the IL-4-induced IgE production by human peripheral blood mononuclear cells (PBMC), indicating that the biological process related to gliadin intolerance and/or allergy may lead to IgE production in vivo. It was found that crude gliadin and Glilys potentiated, after 13 days of culture in a dose-dependent manner, IL-4-induced IgE production and, to a lesser extent, the IgG production, while they did not affect IgA or IgM productions. This promoting effect of gliadin and Glilys on the IL-4-induced activation of normal human PBMC was also observed on the early release (2 days) of the soluble fraction of CD23, suggesting its possible involvement in IgE potentiation. The promoting effect of crude gliadin and Glilys appeared to be indirect because they did not modify purified B-lymphocytes IgE production after IL-4 and anti-CD40 monoclonal antibody stimulation. In addition, as revealed by luminol-dependent chemiluminescence, we demonstrated that crude gliadin and Glilys promoted a substantial production of free radicals by normal human PBMC, treated or not with IL-4. This redox imbalance associated with an increased IgE production led us to evaluate the effect of pharmacological antioxidants (N-acetyl-cysteine (NAC) and Cu/Zn-superoxide dismutase (SOD1)) on IgE production by human PBMC. The NAC and the intracellularly delivered SOD1 were found to suppress the IL-4+/-crude gliadin or Glilys-induced IgE production by normal human PBMC. Taken together, these data indicated that gliadin specifically enhanced IL-4-induced IgE production by normal human PBMC, probably by the regulation of redox pathways, and that this 'pro-allergenic' effect could be counteracted by natural antioxidants: thiols and/or vectorized SOD1.

CD40-mediated tumor necrosis factor receptor-associated factor 3 signaling upregulates IL-4-induced germline Cepsilon transcription in a human B cell line

Induction of germline C epsilon transcription in B cells by IL-4, which is a critical initiating step for IgE class switching, is enhanced by CD40 engagement. Although signaling by CD40 is initiated by the binding of tumor necrosis factor receptor-associated factor (TRAF) family members to its cytoplasmic domain, whether those TRAF family proteins mediate enhancement of germline Cepsilon transcription is not evident. We report here that CD40-induced TRAF3-dependent activation of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase 1 (MEK1) is involved in the upregulation of IL-4-driven germline C epsilon transcription in a human Burkitt's lymphoma B cell line, DG75. Among the six known TRAF proteins, TRAF2, 3, 5, and 6 associated with CD40 in an unstimulated state, and the levels of these four proteins were unaffected by anti-CD40 stimulation. Antisense oligodeoxynucleotide (ODN) for TRAF3 inhibited CD40-induced activation of MEK1-ERK pathway by decreasing expression of TRAF3 protein, but antisense ODNs for TRAF2, 5, and 6 were ineffective. Furthermore, CD40-mediated enhancement of IL-4-driven germline C epsilon transcription was inhibited by antisense ODN for TRAF3 and by a MEK1 inhibitor, PD98059. These results suggest that in DG75 cells, TRAF3-induced MEK1 activation may be involved in CD40-mediated upregulation of IL-4-driven germline C epsilon transcription.

N-acetylcysteine inhibits the induction of an antigen-specific antibody response down-regulating CD40 and CD27 co-stimulatory molecules

We investigated the effect of N-acetylcysteine (NAC) on normal human B cell functions. We found that NAC significantly inhibited both the induction of the specific antibody response to the T-dependent antigen Candida albicans and T-dependent pokeweed mitogen (PWM)-induced polyclonal Ig production. NAC did not induce either cell death due to a non-specific toxicity or apoptosis. The NAC-induced inhibitory effect might be a functional consequence of: (i) a down-regulation of the expression on the B cell surface of CD40 and CD27 co-stimulatory molecules and (ii) a down-regulation of interleukin (IL-4) production. In contrast, NAC up-regulated interferon-gamma (IFN-gamma) production. NAC did not induce any effect on the T cell-independent B cell polyclonal activation system. These results indicate that NAC down-regulates T dependent B cell activation and leads to T helper cell type 1 (Th1) polarization.

Inhibitory effect of peroxisome proliferator-activated receptor-gamma ligands on the expression of IgE heavy chain germline transcripts in the human B cell line DND39

The expression of epsilon germline transcripts (epsilon GT) induced by interleukin (IL)-4 stimulation is essential for the progression of IgE-directed class switching. In this study, we examined the effects of various ligands for their ability to bind to the peroxisome proliferator-activated receptors (PPARs) and to modify the IL-4-induced epsilon GT expression in the human B cell line DND39. We show here that the PPAR gamma ligand, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), can suppress epsilon GT expression at 1 microM without inhibiting cell proliferation. A synthetic and PPAR gamma-specific ligand, ciglitazone, also suppressed epsilon GT expression in a dose-dependent manner at concentrations between 10 and 50 microM. Agonists for other PPAR isoforms did not affect epsilon GT expression at concentrations between 0.01 and 10 microM. We also demonstrated that 1 microM 15d-PGJ(2) was able to suppress the IL-4-induced phosphorylation of the Signal Transducer and Activator of Transcription 6 (STAT6), which is a transcription factor essential for epsilon GT expression. Therefore, the suppression of STAT6 phosphorylation by 15d-PGJ(2) is thought to participate in the inhibition of epsilon GT expression. These results suggest that PPAR gamma ligands inhibit IL-4-induced IgE class switching in B lymphocytes.

Thiols decrease cytokine levels and down-regulate the expression of CD30 on human allergen-specific T helper (Th) 0 and Th2 cells

The thiol antioxidant N-acetyl- L-cysteine (NAC), known as a precursor of glutathione (GSH), is used in AIDS treatment trials, as a chemoprotectant in cancer chemotherapy and in treatment of chronic bronchitis. In vitro, GSH and NAC are known to enhance T cell proliferation, production of IL-2 and up-regulation of the IL-2 receptor. The 120-kD CD30 surface antigen belongs to the tumour necrosis factor (TNF) receptor superfamily. It is expressed by activated T helper (Th) cells and its expression is sustained in Th2 cells. We have analysed the effect of GSH and NAC on the cytokine profile and CD30 expression on human allergen-specific T cell clones (TCC). TCC were stimulated with anti-CD3 antibodies in the presence of different concentrations of GSH and NAC. Both thiols caused a dose dependent down-regulation of IL-4, IL-5 and IFN-gamma levels in Th0 and Th2 clones, with the most pronounced decrease of IL-4. Furthermore, they down-regulated the surface expression of CD30, and the levels of soluble CD30 (sCD30) in the culture supernatants were decreased. In contrast, the surface expression of CD28 or CD40 ligand (CD40L) was not significantly changed after treatment with 20 m M NAC. These results indicate that GSH and NAC favour a Th1 response by a preferential down-regulation of IL-4. In addition, the expression of CD30 was down regulated by GSH and NAC, suggesting that CD30 expression is dependent on IL-4, or modified by NAC. In the likely event that CD30 and its soluble counterpart prove to contribute to the pathogenesis in Th2 related diseases such as allergy, NAC may be considered as a future therapeutic agent in the treatment of these diseases.

Role of nitric oxide in the promoting effect of HIV type 1 infection and of gp120 envelope glycoprotein on interleukin 4-induced IgE production by normal human mononuclear cells

Increased levels of serum IgE have been described in HIV-1 infection; however, mechanisms implicated in this immunoglobulin production remain unknown. In this study, we demonstrate that in vitro infection of human peripheral blood mononuclear cells (PBMCs) by HIV-1 monocytotropic (Ba-L) or lymphocytotropic (LAI) strains promotes IL-4-induced IgE production, indicating that the HIV-1 infectious process may participate in the IgE production observed in vivo. The effect of membrane glycoproteins (gp160, gp120, and gp41) was also evaluated. It was found that gp120 specifically potentiates in a dose-dependent manner IL-4-induced IgE production and does not affect IL-4-induced IgG, IgA, or IgM production. In these experiments, gp160 was also found to upregulate IL-4-induced IgE production, whereas gp41 was ineffective. This effect of gp120, gp160, and HIV-1 infection on IgE synthesis was not observed in the absence of IL-4. In the presence of IL-4, the inducing effect of gp120 appeared to be indirect because gp120 did not modify purified B lymphocyte IgE production after IL-4 and anti-CD40 monoclonal antibody stimulation. As HIV-1 infection is associated with alterations of PBMC redox metabolism, the role of nitric oxide (NO) in this IgE production by human PBMCs was evaluated. In the presence of a specific inhibitor of NO synthase pathways (L-NAME), IgE production induced by IL-4 and gp120 was abolished. Taken together, these data indicate that HIV-1 envelope glycoprotein gp120 (and gp160) specifically enhances IL-4-induced IgE production by normal human PBMCs, probably through the regulation of the nitric oxide pathway.

New Insights into the Role of Nuclear Factor-κB, a Ubiquitous Transcription Factor in the Initiation of Diseases

Nuclear factor-κB (NF-κB) is a ubiquitous transcription factor that governs the expression of genes encoding cytokines, chemokines, growth factors, cell adhesion molecules, and some acute phase proteins in health and in various disease states. NF-κB is activated by several agents, including cytokines, oxidant free radicals, inhaled particles, ultraviolet irradiation, and bacterial or viral products. Inappropriate activation of NF-κB has been linked to inflammatory events associated with autoimmune arthritis, asthma, septic shock, lung fibrosis, glomerulonephritis, atherosclerosis, and AIDS. In contrast, complete and persistent inhibition of NF-κB has been linked directly to apoptosis, inappropriate immune cell development, and delayed cell growth. Therefore, development of modulatory strategies targeting this transcription factor may provide a novel therapeutic tool for the treatment or prevention of various diseases.