A 39-kDa protein on activated helper T cells binds CD40 and transduces the signal for cognate activation of B cells

CD40 is a B-cell surface molecule that has been shown to induce B-cell growth upon ligation with monoclonal antibodies. This report shows that triggering via CD40 is essential for the activation of resting B cells by helper T cells (Th). A soluble fusion protein of CD40 and human immunoglobulin, CD40-Ig, inhibited the induction of B-cell cycle entry, proliferation, and differentiation by activated Th1 and Th2. The ligand for CD40 was identified as a 39-kDa membrane protein that was selectively expressed on activated Th. A monoclonal antibody specific for the 39-kDa protein inhibited CD40-Ig binding and also inhibited the activation of B cells by Th. These data indicate that the 39-kDa membrane protein expressed on activated Th is a binding protein for CD40 and functions to transduce the signal for Th-dependent B-cell activation.

In vivo CD40-gp39 interactions are essential for thymus-dependent humoral immunity. II. Prolonged suppression of the humoral immune response by an antibody to the ligand for CD40, gp39

The ligand for CD40 has been recently identified as a 39-kd protein, gp39, expressed on the surface of activated CD4+ T helper cells (Th). In vitro, soluble CD40 and anti-gp39 have been shown to block the ability of Th to activate B cells, suggesting that gp39-CD40 interactions are important to T cell-dependent B cell activation. Here it is shown that in vivo administration of anti-gp39 dramatically reduced both primary and secondary humoral immune responses to erythrocytes and soluble protein antigens without altering responses to the T-independent type II antigen, trinitrophenyl-Ficoll. Treatment of mice for 4 d with anti-gp39 inhibited the anti-sheep red blood cell (SRBC) response for at least 3 wk and inhibited the expression of all immunoglobulin isotypes in secondary responses to the protein antigen, keyhole limpet hemocyanin. To examine the direct effect of anti-gp39 on Th function, SRBC-immune Th cells from anti-gp39-treated mice were adoptively transferred and shown to be fully capable of providing help. These results suggest that anti-gp39 treatment does not cause Th deletion or anergy. Anti-gp39 may mediate its profound immunosuppressive effects on humoral immunity by blocking gp39-CD40 interactions. Moreover, these studies establish gp39-CD40 as an important receptor-ligand pair for the targeting of therapeutic antibodies to control thymus-dependent humoral responses.

In vivo CD40-gp39 interactions are essential for thymus-dependent humoral immunity. I. In vivo expression of CD40 ligand, cytokines, and antibody production delineates sites of cognate T-B cell interactions

T-B cell interactions have a central role in the development of antibody responses. Upon activation, T helper (Th) cells express the ligand for CD40, gp39, which is essential for Th cell-dependent B cell activation. The cytokines produced by activated Th cells have a regulatory role in B cell differentiation. In this study, we investigated, using immunohistochemical techniques, the in vivo time course and localization of gp39 expression and cytokine production in relation to the specific antibody production. Both the immunization with keyhole limpet hemocyanin (KLH), a thymus-dependent (TD) antigen, and trinitrophenyl (TNP)-Ficoll, a thymus-independent type 2 (TI-2) antigen, induced Th cells to express gp39. The expression of gp39 was restricted to Th cells in the outer periarteriolar lymphocyte sheaths (outer-PALS) and around the terminal arterioles (TA). Incidentally, gp39+ Th cells were found in the corona of follicles, whereas gp39+ cells were never found in the germinal centers or marginal zones of the spleen. Maximum frequencies of gp39+ cells were observed 3 and 4 d after primary and secondary immunization with KLH. After injection of TNP-Ficoll, a marked increase in gp39+ cells was observed, confirming previous observations that activated T cells are involved in TI-2 antibody responses. Analysis of the in vivo cytokine production revealed that interleukin 2 (IL-2)-, IL-4- and interferon gamma (IFN-gamma)-producing cells (IFN-gamma-PC) developed according to similar kinetics as observed for gp39+ cells. IL-2-PC and IL-4-PC were present in higher frequencies as were IFN-gamma-PC in the immune response against TNP-KLH. Double staining experiments revealed gp39+ Th cells producing IL-2, IL-4, or IFN-gamma, suggesting that these cells were involved in both the initial activation as well as the differentiation process of B cells into antibody-forming cells. Dual immunohistochemical analysis revealed gp39+ T cells and cytokine-PC in close proximity to antigen-specific, antibody-forming B cells. In conclusion, this study shows that in vivo gp39 is expressed on activated Th cells after immunization with TD and TI-2 antigens. Furthermore, the time course and compartmentalization of gp39+ expression, cytokine production and antibody formation after immunization suggest that cognate T-B cell interactions and T cell-regulated B cell differentiation occur in the outer-PALS and around the TA of the spleen.

Aryl hydrocarbon receptor activation by TCDD reduces inflammation associated with Crohn's disease

Crohn's disease results from a combination of genetic and environmental factors that trigger an inappropriate immune response to commensal gut bacteria. The aryl hydrocarbon receptor (AhR) is well known for its involvement in the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an environmental contaminant that affects people primarily through the diet. Recently, TCDD was shown to suppress immune responses by generating regulatory T cells (Tregs). We hypothesized that AhR activation dampens inflammation associated with Crohn's disease. To test this hypothesis, we utilized the 2,4,6-trinitrobenzenesulfonic acid (TNBS) murine model of colitis. Mice were gavaged with TCDD prior to colitis induction with TNBS. Several parameters were examined including colonic inflammation via histological and flow cytometric analyses. TCDD-treated mice recovered body weight faster and experienced significantly less colonic damage. Reduced levels of interleukin (IL) 6, IL-12, interferon-gamma, and tumor necrosis factor-α demonstrated suppression of inflammation in the gut following TCDD exposure. Forkhead box P3 (Foxp3)(egfp) mice revealed that TCDD increased the Foxp3+ Treg population in gut immune tissue following TNBS exposure. Collectively, these results suggest that activation of the AhR by TCDD decreases colonic inflammation in a murine model of colitis in part by generating regulatory immune cells. Ultimately, this work may lead to the development of more effective therapeutics for the treatment of Crohn's disease.

Panax notoginseng attenuates LPS-induced pro-inflammatory mediators in RAW264.7 cells

Herbals or dietary supplements are not regulated as drugs by the United States Food and Drug Administration (USFDA) although many may have associated therapeutic effects and toxicities. Therefore, the immunomodulatory effects of the herbal extract Panax notoginseng on cultured macrophages (RAW264.7 cells) were investigated to address potential therapeutic or toxic effects. Cells were stimulated with LPS (1 microg/ml) and treated with notoginseng at 5, 25 and 50 microg/ml. Notoginseng inhibited the LPS-induced production of TNF-alpha and IL-6 by the cultured macrophages in a concentration-dependent manner. The expression of COX-2 and IL-1 beta mRNA was also attenuated by notoginseng. TNF-alpha production was inhibited in samples treated with notoginseng 24h before, or at the same time as LPS stimulation, but not in samples treated 8h after LPS stimulation. Notoginseng reduced expression of the accessory molecules CD40 and CD86 on the RAW264.7 cells while CD14 and TLR4 expression remained unaffected. Furthermore, Rb1 and Rg1 ginsenosides also inhibited macrophage production of TNF-alpha, but to a lesser extent than did the whole notoginseng extract. Collectively, these results indicate that notoginseng inhibits LPS-induced activation of RAW264.7 macrophages and demonstrates that notoginseng possesses anti-inflammatory and immunosuppressive properties in vitro.

Involvement of the histone deacetylase SIRT1 in chicken ovalbumin upstream promoter transcription factor (COUP-TF)-interacting protein 2-mediated transcriptional repression

Chicken ovalbumin upstream promoter transcription factor (COUP-TF)-interacting proteins 1 and 2 (CTIP1 and CTIP2) enhance transcriptional repression mediated by COUP-TF II and have been implicated in hematopoietic cell development and malignancies. CTIP1 and CTIP2 are also sequence-specific DNA-binding proteins that repress transcription through direct, COUP-TF-in-dependent binding to a GC-rich response element. CTIP1- and CTIP2-mediated transcriptional repression is insensitive to trichostatin A, an inhibitor of known class I and II histone deacetylases. However, chromatin immunoprecipitation assays revealed that expression of CTIP2 in mammalian cells resulted in deacetylation of histones H3 and/or H4 that were associated with the promoter region of a reporter gene. CTIP2-mediated transcriptional repression, as well as deacetylation of promoter-associated histones H3/H4 in CTIP2-transfected cells, was reversed by nicotinamide, an inhibitor of class III histone deacetylases such as the mammalian homologs of yeast Silent Information Regulator 2 (Sir2). The human homolog of yeast Sir2, SIRT1, was found to interact directly with CTIP2 and was recruited to the promoter template in a CTIP2-dependent manner. Moreover, SIRT1 enhanced the deacetylation of template-associated histones H3/H4 in CTIP2-transfected cells, and stimulated CTIP2-dependent transcriptional repression. Finally, endogenous SIRT1 and CTIP2 co-purified from Jurkat cell nuclear extracts in the context of a large (1-2 mDa) complex. These findings implicate SIRT1 as a histone H3/H4 deacetylase in mammalian cells and in transcriptional repression mediated by CTIP2.

T lymphocytes are direct, aryl hydrocarbon receptor (AhR)-dependent targets of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD): AhR expression in both CD4+ and CD8+ T cells is necessary for full suppression of a cytotoxic T lymphocyte response by TCDD

The cellular basis for the potent suppression of T cell-mediated immune responses in mice following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is not fully understood. Although activation of the aryl hydrocarbon receptor (AhR) is required, the specific AhR+ cells that transduce the suppression have been difficult to identify in vivo. The recent availability of AhR-/- mutant mice has provided a resource for novel approaches to investigate the direct targets of TCDD. In our studies, we used an in vivo acute graft versus host (GVH) model of T cell immunity to address the direct AhR-dependent effects of TCDD on T cells. In this model, T cells from C57B1/6 mice are injected into C57B1/6 x DBA/2 F1 host mice. The injected T cells recognize the MHC disparity of the host cells, resulting in the generation of an antihost cytotoxic T lymphocyte (CTL) response. By comparing the ability of TCDD to suppress the CTL response of T cells obtained from AhR+/+ and AhR-/- C57B1/6 mice, the need for AhR expression in T cells themselves could be assessed. The results of these studies showed that the CTL response of T cells from AhR+/+ mice was highly suppressed when the F1 host mice were treated with 15 microg/kg TCDD. TCDD treatment also protected the F1 host mice from the loss of body weight that accompanies the induction of the GVH response. In contrast, when grafted T cells were derived from AhR-/- mice, there was no suppression of the CTL response by TCDD, and the host animals lost significant body weight. Furthermore, when T cells from AhR+/+ and AhR-/- mice were separated into CD4+ and CD8+ subsets and recombined using one subset from each donor prior to injection into the F1 host, suppression of the CTL response by TCDD was still apparent, but the degree of suppression was significantly reduced when either subset was AhR-/-. These results indicate that direct AhR-dependent effects of TCDD occur in both CD4+ and CD8+ T cell subsets and both T cell subsets contribute to the full suppression of the CTL response by TCDD.

Dietary ligands of the aryl hydrocarbon receptor induce anti-inflammatory and immunoregulatory effects on murine dendritic cells

Activation of the aryl hydrocarbon receptor (AhR) in immune cells, such as dendritic cells (DCs), can lead to suppressed immune responses. Although AhR activation is most recognized for mediating the effects of its prototypical ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), many compounds existing in dietary sources can also bind the AhR. Because the immunomodulatory effects of indole-3-carbinol (I3C) and indirubin-3'-oxime (IO) have yet to be investigated in DCs, we evaluated the potential immunomodulatory effects of these compounds on murine DCs. We hypothesized that I3C and IO suppress immune and inflammatory responses in DCs. We found that both I3C and IO decreased the expression of CD11c, CD40, and CD54 while they increased expression of MHC2 and CD80. Following lipopolysaccharide (LPS)-activation, I3C and IO suppressed the production of pro-inflammatory mediators including tumor necrosis factor-α, interleukin (IL)-1β, IL-6, IL-12, and nitric oxide but increased IL-10 levels. These effects of I3C and IO were partially mediated by the AhR. Additionally, immunoregulatory genes, such as ALDH1A, IDO and TGFB, were upregulated following treatment with I3C or IO. Both I3C and IO decreased basal levels of nuclear factor-kappa B p65, but only I3C suppressed the LPS-induced activity of RelB. Finally, when cultured with naïve T cells, bone marrow-derived dendritic cells treated with the dietary AhR ligands increased the frequency of Foxp3+ Tregs in an antigen-specific manner. Taken together, these results indicate that I3C and IO exhibit immunosuppressive and anti-inflammatory effects on DCs. Because I3C and IO are significantly less toxic than TCDD, these natural products may ultimately become useful therapeutics for the treatment of autoimmune and inflammatory diseases.

Role of the aryl hydrocarbon receptor (AhR) in lung inflammation

Millions of individuals worldwide are afflicted with acute and chronic respiratory diseases, causing temporary and permanent disabilities and even death. Oftentimes, these diseases occur as a result of altered immune responses. The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, acts as a regulator of mucosal barrier function and may influence immune responsiveness in the lungs through changes in gene expression, cell-cell adhesion, mucin production, and cytokine expression. This review updates the basic immunobiology of the AhR signaling pathway with regards to inflammatory lung diseases such as asthma, chronic obstructive pulmonary disease, and silicosis following data in rodent models and humans. Finally, we address the therapeutic potential of targeting the AhR in regulating inflammation during acute and chronic respiratory diseases.

Use of algae or algal oil rich in n-3 fatty acids as a feed supplement for dairy cattle

Fish oil is used as a ration additive to provide n-3 fatty acids to dairy cows. Fish do not synthesize n-3 fatty acids; they must consume microscopic algae or other algae-consuming fish. New technology allows for the production of algal biomass for use as a ration supplement for dairy cattle. Lipid encapsulation of the algal biomass protects n-3 fatty acids from biohydrogenation in the rumen and allows them to be available for absorption and utilization in the small intestine. Our objective was to examine the use of algal products as a source for n-3 fatty acids in milk. Four mid-lactation Holsteins were assigned to a 4×4 Latin square design. Their rations were supplemented with 1× or 0.5× rumen-protected (RP) algal biomass supplement, 1× RP algal oil supplement, or no supplement for 7 d. Supplements were lipid encapsulated (Balchem Corp., New Hampton, NY). The 1× supplements provided 29 g/d of docosahexaenoic acid (DHA), and 0.5× provided half of this amount. Treatments were analyzed by orthogonal contrasts. Supplementing dairy rations with rumen-protected algal products did not affect feed intake, milk yield, or milk component yield. Short- and medium-chain fatty acid yields in milk were not influenced by supplements. Both 0.5× and 1× RP algae supplements increased daily milk fat yield of DHA (0.5 and 0.6±0.10 g/d, respectively) compared with 1× RP oil (0.3±0.10 g/d), but all supplements resulted in milk fat yields greater than that of the control (0.1±0.10g/d). Yield of trans-18:1 fatty acids in milk fat was also increased by supplementation. Trans-11 18:1 yield (13, 20, 27, and 15±3.0 g/d for control, 0.5× RP algae, 1× RP algae, and 1× RP oil, respectively) was greater for supplements than for control. Concentration of DHA in the plasma lipid fraction on d 7 showed that the DHA concentration was greatest in plasma phospholipid. Rumen-protected algal biomass provided better DHA yield than algal oil. Feeding lipid-encapsulated algae supplements may increase n-3 content in milk fat without adversely affecting milk fat yield; however, preferential esterification of DHA into plasma phospholipid may limit its incorporation into milk fat.

The aftermath of parental suicide for children

Thirty-six children between the ages of 2 and 17 bereaved by the suicide of a parent were followed up after 5 to 17 years. The children's home life before bereavement had been abnormal because of mental illness, and family disruption and pre-suicide stresses were significantly related to present functioning. An incidence of psychological morbidity greater than that of a comparison group was observed. Some children appear to cope with the experience of parental suicide without serious consequences; for a few there was relief from an insupportable situation.

Toll-like receptor ligand-induced activation of murine DC2.4 cells is attenuated by Panax notoginseng

The medicinal herb, Panax notoginseng, has been used for thousands of years in traditional Chinese medicine and possesses anti-inflammatory properties. Dendritic cells (DCs) play a central role in the regulation of both inflammation and adaptive immunity. The aim of this study was to investigate the potential for notoginseng extracts to modulate Toll-like receptor (TLR) ligand-induced activation of cultured DC2.4 cells. Following stimulation with LPS, CpG or poly(I:C) and treatment with 0-50micorg/ml notoginseng extract for 24 h, DCs were evaluated for various phenotypic and functional readouts. Notoginseng reduced the LPS-, CpG- and poly(I:C)-induced production of TNF-alpha by DC2.4 cells. Also, IL-6 production by notoginseng-treated cells stimulated with LPS and CpG but not poly(I:C) was reduced when compared to controls. TLR ligand-induced CD40 expression was attenuated by notoginseng. In contrast, notoginseng decreased CD86 levels on DCs activated with LPS and poly(I:C) but not CpG. Inhibition of TNF-alpha production was time-dependent in LPS-stimulated cells, occurring only with pretreatment or concurrent treatment of notoginseng but not after delayed addition of the herbal extract. Additionally, ginsenoside Rg1 more effectively inhibited LPS-stimulated cytokine production by DC2.4 cells than ginsenoside Rb1. Taken together, these results demonstrate that notoginseng inhibits the production of specific inflammatory molecules and innate immune responsiveness by DCs following TLR activation.

Consequences of AhR activation in steady-state dendritic cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the prototypical aryl hydrocarbon receptor (AhR) ligand and a potent immunotoxicant. However, the mechanisms underlying TCDD-induced immunomodulation remain to be defined. Dendritic cells are professional antigen-presenting cells that constitutively express the AhR and are sensitive to TCDD-induced AhR activation. We hypothesized that AhR activation alters the differentiation and function of steady-state bone marrow-derived dendritic cells (BMDCs). To test this hypothesis, steady-state BMDCs from C57BL/6 mice were grown in the presence of TCDD or vehicle. TCDD-treated steady-state BMDCs (TCDD-BMDCs) displayed decreased expression of CD11c and CD11a, whereas increasing the frequency of major histocompatibility complex class II, CD86, CD80, and CD54. Similar phenotypic alterations were observed with the AhR ligands 6-formylindolo[3,2-b]carbazole and 2-(1H-indole-3'-carbonyl)-thiazole-4-carboxylic acid (ITE). TCDD-BMDCs from AhR(-/-) mice were refractory to TCDD-induced surface marker alterations, whereas TCDD-BMDCs from AhR(dbd/dbd) mice displayed similar phenotypic alterations as AhR(+/+) TCDD-BMDCs. Following lipopolysaccharide (LPS), cytosine-phosphate-guanine (CpG), or Imiquimod stimulation, TCDD-BMDCs secreted less interleukin (IL)-6, tumor necrosis factor-α (TNF-α), IL-10, and IL-12. TCDD also altered NF-κB family member-binding activity in unstimulated and LPS- or CpG-stimulated steady-state BMDCs. The internalization of the soluble antigens, ovalbumin, and acetylated low-density lipoprotein was decreased, whereas internalization of latex beads was increased in TCDD-BMDCs when compared with vehicle-BMDCs. TCDD-BMDCs displayed increased messenger RNA expression of the regulatory gene IDO2 and following LPS stimulation upregulated IDO1, IDO2, TGFβ1, and TGFβ3 gene expression. Additionally, TCDD-BMDCs increased the generation of CD4(+) CD25(+) FoxP3(+) Tregs in vitro in an IDO-dependent fashion. However, TCDD-treated BMDCs did not alter antigen-specific T-cell activation in vivo. Overall, TCDD-induced AhR activation alters the differentiation, activation, innate, and immunoregulatory function but not the T cell-activating capacity of steady-state BMDCs.

Work and suicide: an empirical investigation

The work histories of 75 completed suicides and 150 controls were compared to test Durkheim's theory of the protective nature of work. The suicides showed more unemployment, more absence through illness, had more frequent job changes and held their jobs for shorter periods. They were less likely to retire gradually. There was no difference in social class mobility. Suicides were more likely to come from high risk occupations. The comparatively poor work record of the suicides is attributed to their high level of psychiatric morbidity.

Aryl hydrocarbon receptor signaling modifies Toll-like receptor-regulated responses in human dendritic cells

Currently, it is not well understood how ligands of the aryl hydrocarbon receptor (AhR) modify inflammatory responses triggered by Toll-like receptor (TLR) agonists in human dendritic cells (DCs). Here, we show that AhR ligands 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the tryptophan derivatives 6-formylindolo[3,2-b] carbazole (FICZ), kynurenine (kyn), and the natural dietary compound indole-3-carbinol (I3C) differentially modify cytokine expression in human monocyte-derived DCs (MoDCs). The results show that TLR-activated MoDCs express higher levels of AhR and are more sensitive toward the effects of AhR ligands. Depending on the cytokine, treatment with AhR ligands led to a synergistic or antagonistic effect of the TLR-triggered response in MoDCs. Thus, activation of AhR increased the expression of interleukin (IL)-1β, but decreased the expression of IL-12A in TLR-activated MoDCs. Furthermore, TCDD and FICZ may have opposite effects on the expression of cytochrome P4501A1 (CYP1A1) in TLR8-activated MoDCs indicating that the effect of the specific AhR ligand may depend on the presence of the specific TLR agonist. Gene silencing showed that synergistic effects of AhR ligands on TLR-induced expression of IL-1β require a functional AhR and the expression of NF-κB RelB. On the other hand, repression of IL-12A by TCDD and FICZ involved the induction of the caudal type homeobox 2 (CDX2) transcription factor. Additionally, the levels of DC surface markers were decreased in MoDCs by TCDD, FICZ and I3C, but not by kyn. Overall, these data demonstrate that AhR modulates TLR-induced expression of cytokines and DC-specific surface markers in MoDCs involving NFκB RelB and the immune regulatory factor CDX2.

The effects of TCDD on the activation of ovalbumin (OVA)-specific DO11.10 transgenic CD4(+) T cells in adoptively transferred mice

Exposure to the environmental contaminant 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) suppresses the generation of T cell-dependent immunity, both humoral and cell-mediated. However, the mechanism of TCDD-induced immune suppression remains to be defined. We hypothesized that exposure to TCDD suppresses the activation of naive CD4(+) T cells and prevents their expansion and differentiation into effector T-helper cells capable of driving T cell-dependent immune responses. To test this hypothesis, we adoptively-transferred DO11.10 OVA-specific T-cell receptor (TCR) transgenic T cells into syngeneic recipients and used a TCR-specific monoclonal antibody to track the in vivo activation of naive CD4(+) T lymphocytes following exposure to OVA. The production of OVA-specific antibodies was suppressed in a dose-dependent manner in adoptively transferred mice that had been exposed to TCDD. Although TCDD exposure had little effect on the expansion or activation of the adoptively transferred, OVA-specific CD4(+) T cells, these cells disappeared from the spleen more rapidly in TCDD-treated mice and produced significantly decreased levels of the T cell-derived cytokines IL-2 and IL-10. There was also a trend towards reduced IFN-gamma and IL-4 production following in vitro re-stimulation. These data suggest that TCDD may interfere with the survival and/or differentiation of OVA-specific T-helper cells. These results demonstrate for the first time the potential of the DO11.10 adoptive transfer system to directly assess immunotoxic effects of xenobiotics on antigen-specific CD4(+) T cells in vivo.

Environmental Immunology: Lessons Learned from Exposure to a Select Panel of Immunotoxicants

Exposure to environmental contaminants can produce profound effects on the immune system. Many classes of xenobiotics can significantly suppress or enhance immune responsiveness depending on the levels (i.e., dose) and context (i.e., timing, route) of exposure. Although defining the effects that toxicants can have on the immune system is a valuable component to improving public health, environmental immunology has greatly enhanced our understanding of how the immune system functions and has provided innovative avenues to explore new immunotherapies. This Brief Review focuses on three examples of how immunotoxicology has benefitted the field of immunology, presenting information on the aryl hydrocarbon receptor signaling pathway, the immunomodulatory effects of nanomaterials, and the impact of xenobiotic exposure on the developing immune system. Collectively, contributions from immunotoxicology have significantly enhanced public health and spurred seminal advances in both basic and applied immunology.

Immunotoxicology of cadmium and mercury on B-lymphocytes--I. Effects on lymphocyte function

Heavy metals have been shown to exert immunotoxic effects on humoral immunity. To ascertain the mechanisms by which these immunotoxic effects are exerted, the effects of CdCl2 and HgCl2 on the biology of murine B-lymphocytes were studied. It was shown that CdCl2 and HgCl2 inhibited B-cell RNA and DNA synthesis. The IC50 (the concentration required to inhibit a specific B-cell function by 50%) for CdCl2 was 30 microM for RNA synthesis and DNA synthesis. The IC50 for HgCl2 was 50 and 120 nM for RNA and DNA synthesis, respectively. Cell cycle analysis revealed that B-cells were arrested throughout the cell cycle with CdCl2 and HgCl2. The inhibitory effects exerted by CdCl2 and HgCl2 were rapid, inhibiting RNA synthesis within 2 h of activation. Differentiation to Ig secretion was inhibited by CdCl2 and HgCl2 in culture and there appeared to be selective effects on specific Ig isotypes. IgG3 production was most sensitive to inhibition by CdCl2 and HgCl2 followed by IgG1 and IgG2b and then IgM and IgG2a. Changes in the expression of B-cell surface antigens induced by LPS were also influenced by CdCl2. LPS-induced increases in class II MHC expression was inhibited by CdCl2, as was the constitutive expression of class I MHC antigen. A summary of the IC50 for CdCl2 and HgCl2 are presented. In summary, both CdCl2 and HgCl2 exert early, inhibitory effects on B-cell activation. This is manifested by the inhibition of RNA, DNA and antibody synthesis. However, selective effects on the production of specific Ig isotypes by these metals may influence the ability of B-cells to mount effective immune responses to pathogens.

Aryl hydrocarbon receptor (AhR) regulates silica-induced inflammation but not fibrosis

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is responsible for mediating a variety of pharmacological and toxicological effects caused by halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, recent evidence has revealed that the AhR also has numerous physiological roles aside from xenobiotic metabolism, including regulation of immune and inflammatory signaling as well as normal development and homeostasis of several organs. To investigate the role of the AhR in crystalline silica (SiO(2))-induced inflammation and fibrosis, C57Bl/6 and AhR(-/)(-) mice were exposed to SiO(2) or vehicle. Similarly, C57Bl/6 mice were exposed to SiO(2) and TCDD either simultaneously or sequentially to assess whether AhR activation alters inflammation and fibrosis. SiO(2)-induced acute lung inflammation was more severe in AhR(-)(/-) mice; however, the fibrotic response of AhR(-)(/-) mice was attenuated compared with C57Bl/6 mice. In a model of chronic SiO(2) exposure, AhR activation by TCDD in C57Bl/6 mice resulted in reduced inflammation; however, the fibrotic response was not affected. Bone marrow-derived macrophages (BMM) from AhR(-)(/-) mice also produced higher levels of cytokines and chemokines in response to SiO(2). Analysis of gene expression revealed that BMM derived from AhR(-)(/-) mice exhibit increased levels of pro-interleukin (IL)-1β, IL-6, and Bcl-2, yet decreased levels of signal transducers and activators of transcription (STAT)2, STAT5a, and serpin B2 (Pai-2) in response to SiO(2).

Early consequences of 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure on the activation and survival of antigen-specific T cells

TCDD is a potent immunotoxicant that suppresses adaptive immunity by mechanisms that are not well defined. To gain insight at the level of the T cell, we used the DO11.10 transgenic T-cell receptor (TCR) mouse model in an adoptive transfer approach to characterize the influence of TCDD on the responsiveness of antigen-specific CD4+ T cells in vivo. Flow cytometry was used to track the response of the OVA-specific transgenic CD4+ T cells in syngeneic recipients using an antibody specific for the transgenic TCR (KJ1-26 [KJ]). Consistent with a previous report, exposure of the recipient mice to TCDD (15 microg/kg po) did not alter the initial expansion of the CD4+KJ+ T cells in the spleen following immunization with OVA but resulted in a significant decline in the number of cells present on and after day 4. The degree of decline was dependent on the dose of TCDD. On day 3 after OVA injection, a higher percentage of the CD4+KJ+ T cells in the spleens of TCDD-treated mice had down-regulated the expression of CD62L, a phenotype associated with T-cell activation. Also on day 3, an increased number of CD4+KJ+ T cells were found in the blood of TCDD-treated mice. However, as in the spleen, the number of CD4+KJ+ T cells in the blood rapidly declined on day 4. CD4+KJ+ T cells in both the spleen and blood of TCDD-treated mice failed to up-regulate CD11a, an adhesion molecule important for sustained interaction between T cells and DC whereas the up-regulation of the adhesion molecule CD49d was not altered. Based on analysis of cell division history, CD4+KJ+ T cells in vehicle-treated mice continued to divide through day 4 whereas CD4+KJ+ T cells in TCDD-treated mice showed no further division after day 3. Increased annexin V staining on CD4+KJ+ T cells in TCDD-treated mice was also observed but not until days 5 and 6. Fas-deficient CD4+KJ+ T cells were depleted from the spleen of TCDD-treated mice in a manner similar to wild-type CD4+KJ+ T cells, suggesting that Fas signaling does not play a critical role in this model. On the other hand, gene array analysis of purified CD4+KJ+ T cells on day 3 showed that the expression of several genes associated with cell survival/death were altered by TCDD. Taken together, the results are consistent with our hypothesis that TCDD provides an early but inappropriate activation signal to the antigen-specific T cells that allows, and possibly enhances, the initial activation and proliferation of the T cells, yet at the same time, interferes with the vital expression of certain adhesion/costimulatory molecules that serve to enhance the survival of the T cells. These changes result in truncated proliferation, increased T-cell death, and suppression of the adaptive immune response.

Effects of TCDD on the fate of naive dendritic cells

The environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), causes immune suppression via activation of the aryl hydrocarbon receptor. Dendritic cells (DCs), the professional antigen-presenting cells in the immune system, are adversely affected by TCDD. We hypothesized that TCDD alters DC homeostasis, resulting in a loss of DCs in naive mice. To test this hypothesis, C57Bl/6 mice were gavaged with either vehicle or an immunosuppressive dose of TCDD (15 microg/kg). TCDD exposure decreased the frequency and number of splenic CD11c(high) DCs on day 7 when compared with vehicle-treated controls. TCDD increased the expression of CD86 and CD54, while decreasing the frequency of splenic CD11c(high) DCs expressing CD11a and major histocompatibility complex (MHC) class II. Moreover, TCDD selectively decreased the CD11c(high)CD8alpha(-)33D1(+) splenic DCs specialized at activating CD4(+) T cells but did not affect the regulatory CD11c(high)CD8alpha(+)DEC205(+) splenic DCs. TCDD did not alter the number or frequency of CD11c(low) splenic DCs but decreased their MHC class II and CD11a expression. Loss of splenic CD11c(high) DCs was independent of Fas-mediated apoptosis and was not due to alterations in the numbers of common DC precursors in the bone marrow or their ability to generate steady-state DCs in vitro. Instead, increased CCR7 expression on CD11c(high) DCs suggested involvement of a migratory event. Popliteal and brachial lymph node CD11c(+) cells showed elevated levels of MHC class II and CD40 following TCDD exposure. Collectively, this study shows the presence of a TCDD-sensitive splenic DC subpopulation in naive mice, suggesting that TCDD may induce suppression of T-cell-mediated immunity by disrupting DC homeostasis.

Gastric mucosal histamine and histamine methytltransferase in patients with duodenal ulcer

Histamine and histamine methyltransferase (HMT) have been measured in gastric mucosa from 110 patients with duodenal ulcer and 62 control subjects. Both antral and fundic mucosa had similar levels of HMT activity despite antral mucosa containing significantly less histamine. Patients with duodenal ulcer had significantly lower levels of fundic mucosal HMT activity and lower concentrations of fundic mucosal histamine than control subjects. An additional finding was that men who were cigarette smokers had significantly lower concentrations of fundic mucosal histamine (but not HMT) than non-smokers and, as there was an excess of cigarette smokers among patients with duodenal ulcer, this may be the explanation for the reduced concentrations of fundic mucosal histamine in these patients.

Echinacea purpurea extracts modulate murine dendritic cell fate and function

Echinacea is a top-selling herbal remedy that purportedly acts as an immunostimulant. However, the specific immunomodulatory effects of Echinacea remain to be elucidated. We focused on defining the effects of Echinacea purpurea extracts in dendritic cells (DCs), which generate innate and adaptive immune responses. We hypothesized that E. purpurea extracts would enhance murine bone marrow-derived DC (BMDC) activation leading to increased immune responses. The fate and function of DCs from C57Bl/6 mice was evaluated following 48h exposure to E. purpurea root and leaf extracts. Flow cytometry revealed that the polysaccharide-rich root extract increased the expression of MHC class II, CD86, and CD54 surface biomarkers whereas the alkylamide-rich leaf extract inhibited expression of these molecules. Production of IL-6 and TNF-alpha increased in a concentration-dependent manner with exposure to the root, but not leaf, extract. In contrast, the leaf but not root extract inhibited the enzymatic activity of cyclooxygenase-2. While both extracts decreased the uptake of ovalbumin by BMDCs, the leaf but not root extract inhibited the antigen-specific activation of naïve CD4(+) T cells from OT II/Thy1.1 mice. Collectively, these results suggest that E. purpurea can be immunostimulatory, immunosuppressive, and/or anti-inflammatory depending on the portion of the plant and extraction method.

In vitro exposure to the herbicide atrazine inhibits T cell activation, proliferation, and cytokine production and significantly increases the frequency of Foxp3+ regulatory T cells

The herbicide atrazine (2-chloro-4-[ethylamino]-6-[isopropylamino]-s-triazine) is the most common water contaminant in the United States. Atrazine is a phosphodiesterase inhibitor and is classified as an estrogen disrupting compound because it elevates estrogen levels via induction of the enzyme aromatase. Previous studies have shown that atrazine exposure alters the function of innate immune cells such as NK cells, DC, mast cells, and macrophages. In this study we have examined the impact of in vitro atrazine exposure on the activation, proliferation, and effector cytokine production by primary murine CD4(+) T lymphocytes. We found that atrazine exposure significantly inhibited CD4(+) T cell proliferation and accumulation as well as the expression of the activation markers CD25 and CD69 in a dose-dependent manner. Interestingly, the effects were more pronounced in cells from male animals. These effects were partially mimicked by pharmacological reagents that elevate intracellular cAMP levels and addition of exogenous rmIL-2 further inhibited proliferation and CD25 expression. Consistent with these findings, atrazine exposure during T cell activation resulted in a 2- to 5-fold increase in the frequency of Foxp3(+) CD4(+) T cells.