Interleukin 1ß and interleukin 6 production in human immune cells is stimulated by the antibacterial compound Triclosan.

Triclosan (TCS) is an antimicrobial compound widely used in personal hygiene products such as mouthwash and toothpaste; and has been found in human blood, breast milk, and urine. Interleukin (IL)-6 and IL-1 beta (IL-1ß) are pro-inflammatory cytokines regulating cell growth, tissue repair, and immune function; increased levels of each have been associated with many diseases, including cancer. Previous studies showed that TCS at concentrations between 0.05 and 5 µM consistently increased the secretion of IL-1ß and IL-6 from human immune cells within 24 h of exposure. The current study demonstrates that this increase in secretion was not due simply to release of existing stores but was due to an increase in cellular production/levels (both secreted and intracellular levels) of each of these cytokines. Production of IL-1ß and IL-6 was increased by exposure to one or more concentration of TCS at each length of exposure (10 min, 30 min, 6 h, and 24 h). TCS-induced stimulation of cytokine production was shown to be dependent on the mitogen-activated protein kinase (MAPK) p44/42 (ERK 1/2). It was also shown that these TCS-induced increases in IL-1ß and IL6 production were accompanied by increased mRNA for IL-1ß and IL-6. The ability of TCS to increase production indicates that rather than activating a self-limiting process of depleting cells of already existing stores of IL-1ß or IL-6, TCS can stimulate a process that has the capacity to provide sustained production of these cytokines and thus may lead to chronic inflammation and its pathological consequences.

Organotin and organochlorine toxicants activate key translational regulatory proteins in human immune cells.

Environmental contaminant exposures occur due to the widespread use of synthetic chemicals. Tributyltin (TBT), dibutyltin (DBT), and pentachlorophenol (PCP) are each used in a variety of applications, including antifouling paints and stabilizers in certain plastics. Each of these compounds has been found in human blood, as well as other tissues, and they have been shown to stimulate pro-inflammatory cytokine production in human immune cells, Inflammatory cytokines mediate response to injury or infection. However, if their levels are increased in the absence of an appropriate stimulus, chronic inflammation can occur. Chronic inflammation is associated with a number of pathologies including cancer. Stimulation of pro-inflammatory cytokine production by these toxicants is dependent on activation of ERK 1/2 and/or p38 MAPK pathways. MAPK pathways have the capacity to regulate translation by increasing phosphorylation of key translation regulatory proteins. There have been no previous studies examining the effects of TBT, DBT, or PCP on translation. The current study shows that ribosomal protein S6 (S6), eukaryotic initiation factor 4B (eIF4B), and eIF4E are phosphorylated (activated) and/or their total levels are elevated in response to each of these compounds at concentrations found in human blood. Activation/increased levels of translational proteins occurred at concentrations of the compounds that have been shown to elevate pro-inflammatory cytokine production, but where there is no increase in mRNA for those proteins was seen. Compound-stimulated increases in translation appear to be part of the mechanism by which they elevate protein production in immune cells.

Dibutyltin alters immune cell production of the pro-inflammatory cytokines interleukin (IL) 1ß and IL-6: role of mitogen-activated protein kinases and changes in mRNA.

Dibutyltin (DBT) is used to stabilize plastics and as a deworming agent in some poultry. It is found in human blood (levels as high as 0.3 µM). Interleukin (IL) 1ß (IL-1ß) and IL-6 are pro-inflammatory cytokines produced by lymphocytes, monocytes, and other cells. Elevated levels of IL-1ß and IL-6 have been associated with pathologies including rheumatoid arthritis and cancers. DBT was shown to decrease IL-1ß and IL-6 secretion from immune cells at higher concentrations while causing increases at lower concentrations. However, it was not clear if these changes were due to DBT's alteration of the secretory process or due its ability to change cellular synthesis/production of these proteins. This study addresses this question, as well as mechanisms for any observed changes in synthesis/production. Monocyte-depleted peripheral blood mononuclear cells (MD-PBMCs) were exposed to DBT at concentrations of 5, 2.5, 1, 0.5, 0.25, 0.1, and 0.05 µM for 1, 6, and 24 h and the production (combination of secreted and intracellular levels from the same cells) of both IL-1ß and IL-6 were measured. Effects of selected DBT exposures on cytokine production were also examined in PBMCs and DBT's effects were similar when monocytes were present. The 24-h exposures to DBT decreased production of both IL-1ß and IL-6 at the two highest concentrations but increased production at lower concentrations. Both decreases and increases in cytokine production appear to be explained by DBT-induced changes in mRNA levels. DBT-induced increases in cellular production of the cytokines appear to require p38 and ERK1/2 MAPK pathways.

Exposures to the environmental contaminants pentachlorophenol and dichlorodiphenyltrichloroethane increase production of the proinflammatory cytokine, interleukin-1ß, in human immune cells.

Pentachlorophenol (PCP) and dichlorodiphenyltrichloroethane (DDT) are organochlorine environmental contaminants found in human blood at very significant levels (as high as 5 µm for PCP and 260 nm for DDT). Cancers of the blood (lymphoma and myeloma) and kidney as well as others have been associated with exposure to these contaminants. Interleukin (IL)-1ß is a proinflammatory cytokine and is involved in stimulating cell proliferation. High levels of IL-1ß are associated with inflammatory diseases and tumor progression. Previous studies showed that PCP and DDT at certain concentrations were able to stimulate secretion of IL-1ß. This study shows that the increased secretion of IL-1ß seen with both contaminants is due to compound-induced increases in the production of this cytokine. Increased production began within 6 hours of exposure to PCP and continued to increase up to 24 hours. DDT-induced stimulation of IL-1ß appeared to be maximal after 6 hours of exposure and then diminished by 24 hours. The increases seen in IL-1ß production stimulated by PCP appear to be at least partially due to compound-induced increases in IL-1ß mRNA. Although DDT caused increased production of IL-1ß, it did not appear to cause consistent increases in its mRNA. PCP- and DDT-induced increases in IL-1ß production were dependent primarily on the p38 mitogen-activated protein kinase pathway. These results indicate that both PCP and DDT are able to increase IL-1ß production in a p38 mitogen-activated protein kinase-dependent manner, which may have the potential to influence chronic inflammation.

Flame retardants, hexabromocyclododecane (HCBD) and tetrabromobisphenol a (TBBPA), alter secretion of tumor necrosis factor alpha (TNFα) from human immune cells.

Hexabromocyclododecane (HBCD) and tetrabromobisphenol A (TBBPA) are flame retardants, used in a variety of applications, which contaminate the environment and are found in human blood. HBCD and TBBPA have been shown to alter the tumor killing function of natural killer (NK) lymphocytes and the secretion of the inflammatory cytokines interferon gamma (IFNγ) and interleukin 1 beta (IL-1ß). The current study examined the effects of HBCD and TBBPA on secretion of the critical pro-inflammatory cytokine tumor necrosis factor alpha (TNFα) from human immune cells. Preparations of human immune cells that ranged in complexity were studied to determine if the effects of the compounds were consistent as the composition of the cell preparation became more heterogeneous. Cell preparations studied were: NK cells, monocyte-depleted (MD) peripheral blood mononuclear cells (PBMCs), and PBMCs. Exposure of NK cells to higher concentrations of HBCD (5 and 2.5 µM) caused decreased secretion of TNFα. However, when the cell preparation contained T lymphocytes (MD-PBMCs and PBMCs) these same concentrations of HBCD increased TNFα secretion as did nearly all other concentrations. This suggests that HBCD's ability to increase TNFα secretion from immune cells was dependent on the presence of T lymphocytes. In contrast, exposures to TBBPA decreased the secretion of TNFα from all immune cell preparations regardless of the composition of the cell preparation. Further, HBCD-induced increases in TNFα secretion utilized the p38 MARK pathway. Thus, both HBCD and TBBPA may have the capacity to disrupt the inflammatory response with HBCD having the potential to cause chronic inflammation.

Synthesis of interleukin 1 beta and interleukin 6 in human lymphocytes is stimulated by tributyltin.

Tributyltin (TBT) is a widespread environmental contaminant that is present in human blood and other tissues. It has been shown to disrupt the immune function of human natural killer (NK) cells and to alter the secretion of a number of pro-inflammatory cytokines from immune cells. Secretion of both interleukin 1ß (IL-1ß) and interleukin 6 (IL-6) from human lymphocytes can be increased dependent upon the level of TBT exposure. This study shows that the TBT-induced increases in secretion of both cytokines are due to TBT-induced increases in the synthesis of these proteins and not simply because of the release of pre-existing cytokine. Furthermore, the data indicate that these TBT-induced increases in IL-1ß and IL-6 synthesis require MAP kinase signaling pathways. Additionally, elevated synthesis of IL-1ß and IL-6 seen at the highest exposures to TBT (200, 200, 50 nM) were accompanied by increases in the mRNA for these cytokines. TBT-induced increases in IL-1ß and IL-6 mRNAs were also shown to be dependent on MAP kinase signaling. The study suggests that TBT has the capacity to increase immune cell production of these 2 important pro-inflammatory cytokines and that this increase is in part explained by increased mRNA for the cytokines.

Butyltin compounds alter secretion of interleukin 6 from human immune cells.

Butyltins (BTs), tributyltin (TBT) and dibutyltin (DBT) are organotin compounds that have been used in a variety of industrial applications; as a result, these compounds have been found in human blood. Interleukin (IL)-6 is a proinflammatory mediator that is produced by T lymphocytes and monocytes. It is responsible for immune response regulation as well as tissue repair and cellular growth. Both BTs decrease the ability of human natural killer cells to destroy tumor cells and alter the secretion of proinflammatory cytokines tumor necrosis factor alpha, interferon gamma and IL-1 beta (ß) from human lymphocytes ex vivo. Here, we show that BTs alter the secretion of IL-6 from increasingly reconstituted preparations of human immune cells. IL-6 secretion was examined after 24 hour, 48 hour or 6 day exposures to TBT and DBT in highly enriched human natural killer cells, monocyte-depleted peripheral blood mononuclear cells (PBMCs), PBMCs, granulocytes and a preparation combining both PBMCs and granulocytes (PBMCs + granulocytes). The results indicated that both BTs altered IL-6 secretion from all cell preparations. Significant decreases of IL-6 secretion were seen at the highest concentration of TBT (200 nm) and DBT (5-2.5 µm) while the lower concentrations of DBT (0.05 and 0.1 µm) caused elevation of IL-6 secretion. The data indicate that BT-induced alterations of IL-6 secretion from immune cells may be a significant consequence of BT exposures that may potentially affect immune competence.

Tributyltin stimulates synthesis of interferon gamma and tumor necrosis factor alpha in human lymphocytes.

Tributyltin (TBT) is found in human blood and other tissues and thus is of considerable concern as to its effects on human health. Previous studies have demonstrated that TBT has detrimental effects on immune function. Recently, we found that exposures to TBT caused increased secretion of two important proinflammatory cytokines, tumor necrosis factor alpha (TNFα) and interferon gamma (IFNγ). Elevation of either of these cytokines has the potential to cause chronic inflammation, which is an important factor in a number of diseases including cancer. The current study examined the mechanism of TBT-induced elevations of TNFα and IFNγ secretion and found that the p38 mitogen-activated protein kinase pathway was essential to the ability of TBT to stimulate secretion. Additionally, this study demonstrated that increased secretion of these cytokines was due to TBT-induced increases in their overall synthesis, rather than simply being due to an increase in the release of already formed proteins. The TBT-induced increases in synthesis were evident within 6 hours of exposure. The p38 mitogen-activated protein kinase pathway is also necessary for the TBT-induced increases in both TNFα and IFNγ synthesis. The role of increased transcription of TNFα and IFNγ mRNA in response to TBT exposures as a possible explanation for the increased synthesis of these cytokines was also examined. It was found that increased mRNA levels did not appear to explain fully the increases in either TNFα or IFNγ synthesis. Thus, TBT is able to increase secretion of two important proinflammatory cytokines by increasing their synthesis.

Exposures to the environmental toxicants pentachlorophenol (PCP) and dichlorodiphenyltrichloroethane (DDT) modify secretion of interleukin 1-beta (IL-1ß) from human immune cells.

Pentachlorophenol (PCP) and Dichlorodiphenyltrichloroethane (DDT) are environmental contaminants found in human blood. Previous studies have shown that PCP and DDT inhibit the lytic function of highly purified human natural killer (NK) lymphocytes and decrease the expression of several surface proteins on NK cells. Interleukin-1 ßeta (IL-1ß) is a cytokine produced by lymphocytes and monocytes, and anything that elevates its levels inappropriately can lead to chronic inflammation, which among other consequences can increase tumor development and invasiveness. Here, PCP and DDT were examined for their ability to alter secretion of IL-1ß from immune cell preparations of various complexity: NK cells; monocyte-depleted (MD) peripheral blood mononuclear cells (PBMCS); and PBMCs. Cells were exposed to concentrations of PCP ranging from 5 to 0.05 µM and DDT concentrations of 2.5-0.025 µM for 24, 48 h, and 6 days. Results showed that both PCP and DDT increased IL-1ß secretion from all of the immune cell preparations. The specific concentrations of PCP and DDT that increased IL-1ß secretion varied by donor. Immune cells from all donors showed compound-induced increases in IL-1ß secretion at one or more concentration at one or more length of exposure. The mechanism of PCP stimulation of IL1-ß secretion was also addressed, and it appears that the MAPKs, ERK1/2 and p38, may be utilized by PCP to stimulate secretion of IL-1ß.

Dibutyltin-induced alterations of interleukin 1beta secretion from human immune cells.

Dibutyltin (DBT) is used to stabilize polyvinyl chloride plastics (including pipes that distribute drinking water) and as a de-worming agent in poultry. DBT is found in human blood, and DBT exposures alter the secretion of tumor necrosis factor alpha and interferon gamma from lymphocytes. Interleukin (IL)-1ß is a proinflammatory cytokine that regulates cellular growth, tissue restoration and immune response regulation. IL-1ß plays a role in increasing invasiveness of certain tumors. This study reveals that exposures to DBT (24 h, 48 h and 6 days) modify the secretion of IL-1ß from increasingly reconstituted preparations of human immune cells (highly enriched human natural killer cells, monocyte-depleted [MD] peripheral blood mononuclear cells [PBMCs], PBMCs, granulocytes and a preparation combining both PBMCs and granulocytes). DBT altered IL-1ß secretion from all cell preparations. Higher concentrations of DBT (5 and 2.5 µm) decreased the secretion of IL-1ß, while lower concentrations of DBT (0.1 and 0.05 µm) increased the secretion of IL-1ß. Selected signaling pathways were examined in MD-PBMCs to determine if they play a role in DBT-induced elevations of IL-1ß secretion. Pathways examined were IL-1ß converting enzyme (caspase 1), mitogen-activated protein kinases and nuclear factor kappa B. Caspase 1 and mitogen-activated protein kinase pathways appear to be utilized by DBT in increasing IL-1ß secretion. These results indicate that DBT alters IL-1ß secretion from human immune cells in an ex. vivo system utilizing several IL-1ß regulating signaling pathways. Thus, DBT may have the potential to alter IL-1ß secretion in an in vivo system. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of pentachlorophenol and dichlorodiphenyltrichloroethane on secretion of interferon gamma (IFNγ) and tumor necrosis factor alpha (TNFα) from human immune cells.

Pentachlorophenol (PCP) and dichlorodiphenyltrichloroethane (DDT) are pesticides that have been widely used and significantly contaminate the environment. Both are found in human blood and have been shown to alter the lytic and binding function of human natural killer (NK) cells. Interferon gamma (IFNγ) and tumor necrosis factor alpha (TNFα) are pro-inflammatory cytokines, which regulate immune responsiveness to pathogens and tumors. Their levels require very tight control to prevent loss of immune competence or excessive inflammation. Here, we examined the capacity of PCP and DDT to alter the secretion of these critical pro-inflammatory cytokines from increasingly reconstituted (more complex) preparations of human immune cells which included NK cells, monocyte-depleted (MD) peripheral blood mononuclear cells (PBMCs) (a preparation that is predominantly lymphocytes) and PBMCs (a preparation containing lymphocytes and monocytes). Results indicated that exposure to PCP decreased IFNγ secretion at the highest exposures (2.5 and 5 µM) and increased IFNγ secretion at lower concentrations. These effects were seen irrespective of the complexity of the cell preparation. PCP at 2.5 and 5 µM generally decreased TNFα secretion from NK cells, but had inconsistent effects in MD-PBMCs and PBMCs. Exposure of each of the immune cell preparations to DDT caused increase in IFNγ secretion. DDT (2.5 µM) increased TNFα secretion from MD-PBMCs after either 24 h or 48 h of exposure. The mechanism of PCP-induced increase in IFNγ secretion appears to involve the p38 mitogen activated protein kinase (MAPK) pathway, based on loss of PCP stimulated increase when this pathway was inhibited.

Hexabromocyclododecane and tetrabromobisphenol A alter secretion of interferon gamma (IFN-γ) from human immune cells.

Hexabromocyclododecane (HBCD) and tetrabromobisphenol A (TBBPA) are brominated flame-retardant compounds used in a variety of applications including insulation, upholstery, and epoxy resin circuit boards. Interferon gamma (IFN-γ) is an inflammatory cytokine produced by activated T and NK cells that regulates immune responsiveness. HBCD and TBBPA are found in human blood, and previous studies have shown that they alter the ability of human natural killer (NK) lymphocytes to destroy tumor cells. This study examines whether HBCD and TBBPA affect the secretion of IFN-γ from increasingly complex preparations of human immune cells-purified NK cells, monocyte-depleted (MD) peripheral blood mononuclear cells (PBMCs), and PBMCs. Both HBCD and TBBPA were tested at concentrations ranging from 0.05 to 5 µM. HBCD generally caused increases in IFN-γ secretion after 24-h, 48-h, and 6-day exposures in each of the different cell preparations. The specific concentration of HBCD that caused increases as well as the magnitude of the increase varied from donor to donor. In contrast, TBBPA tended to decrease secretion of IFN-γ from NK cells, MD-PBMCs, and PBMCs. Thus, exposure to these compounds may potentially disrupt the immune regulation mediated by IFN-γ. Signaling pathways that have the capacity to regulate IFN-γ production (nuclear factor kappa B (NF-κB), p44/42, p38, JNK) were examined for their role in the HBCD-induced increases in IFN-γ. Results showed that the p44/42 (ERK1/2) MAPK pathway appears to be important in HBCD-induced increases in IFN-γ secretion from human immune cells.

Tributyltin alters secretion of interleukin 1 beta from human immune cells.

Tributyltin (TBT) has been used as a biocide in industrial applications such as wood preservation, antifouling paint and antifungal agents. Owing to its many uses, it contaminates the environment and has been found in human blood samples. Interleukin-1 beta (IL-1ß) is a pro-inflammatory cytokine that promotes cell growth, tissue repair and immune response regulation. Produced predominately by both monocytes and macrophages, IL-1ß appears to increase the invasiveness of certain tumors. This study shows that TBT modifies the secretion of IL-1ß from increasingly reconstituted preparations of human immune cells. IL-1ß secretion was examined after 24-, 48-h or 6-day exposures to TBT in highly enriched human natural killer (NK) cells, monocyte-depleted peripheral blood mononuclear cells (MD-PBMCs), PBMCs, granulocytes and a preparation combining both PBMCs and granulocytes (PBMCs+granulocytes). TBT altered IL-1ß secretion from all of the cell preparations. The 200 nM concentration of TBT normally blocked the secretion of IL-1ß, whereas lower concentrations (usually 5-50 nM) elevated secretion of IL-1ß. Examination of the signaling pathway(s) responsible for the elevated secretion of IL-1ß was carried out in MD-PBMCs. Pathways examined were IL-1ß processing (Caspase-1), mitogen-activated protein kinases (MAPKs) and nuclear factor kappa B (NFκB). Results indicated that MAPK pathways (p44/42 and p38) appear to be the targets of TBT that lead to increased IL-1ß secretion from immune cells. These results from human immune cells show IL-1ß dysregulation by TBT is occurring ex vivo. Thus, the potential for in vivo effects on pro-inflammatory cytokine levels may possibly be a consequence of TBT exposures.

Secretion of interferon gamma from human immune cells is altered by exposure to tributyltin and dibutyltin.

Tributyltin (TBT) and dibutyltin (DBT) are widespread environmental contaminants found in food, beverages, and human blood samples. Both of these butyltins (BTs) interfere with the ability of human natural killer (NK) cells to lyse target cells and alter secretion of the pro-inflammatory cytokine tumor necrosis factor alpha (TNFα) from human immune cells in vitro. The capacity of BTs to interfere with secretion of other pro-inflammatory cytokines has not been examined. Interferon gamma (IFNγ) is a modulator of adaptive and innate immune responses, playing an important role in overall immune competence. This study shows that both TBT and DBT alter secretion of IFNγ from human immune cells. Peripheral blood cell preparations that were increasingly reconstituted were used to determine if exposures to either TBT or DBT affected IFNγ secretion and how the makeup of the cell preparation influenced that effect. IFNγ secretion was examined after 24 h, 48 h, and 6 day exposures to TBT (200 - 2.5 nM) and DBT (5 - 0.05 µM) in highly enriched human NK cells, a monocyte-depleted preparation of PBMCs, and monocyte-containing PBMCs. Both BTs altered IFNγ secretion from immune cells at most of the conditions tested (either increasing or decreasing secretion). However, there was significant variability among donors as to the concentrations and time points that showed changes as well as the baseline secretion of IFNγ. The majority of donors showed an increase in IFNγ secretion in response to at least one concentration of TBT or DBT at a minimum of one length of exposure.

Activation of protein kinase C and protein kinase D in human natural killer cells: effects of tributyltin, dibutyltin, and tetrabromobisphenol A.

Up to now, the ability of target cells to activate protein kinase C (PKC) and protein kinase D (PKD) (which is often a downstream target of PKC) has not been examined in natural killer (NK) lymphocytes. Here we examined whether exposure of human NK cells to lysis sensitive tumor cells activated PKC and PKD. The results of these studies show for the first time that activation of PKC and PKD occurs in response to target cell binding to NK cells. Exposure of NK cells to K562 tumor cells for 10 and 30 min increased phosphorylation/activation of both PKC and PKD by roughly 2-fold. Butyltins (tributyltin (TBT), dibutyltin (DBT)) and brominated compounds (tetrabromobisphenol A (TBBPA)) are environmental contaminants that are found in human blood. Exposures of NK cells to TBT, DBT, or TBBPA decrease NK cell lytic function in part by activating the mitogen-activated protein kinases (MAPKs) that are part of the NK lytic pathway. We established that PKC and PKD are part of the lytic pathway upstream of MAPKs and thus we investigated whether DBT, TBT, and TBBPA exposures activated PKC and PKD. TBT-activated PKC by 2-3-folds at 10 min at concentrations ranging from 50 to 300 nM while DBT caused a 1.3-fold activation at 2.5 µM at 10 min. Both TBT and DBT caused an approximately 2-fold increase in phosphorylation/activation of PKC. Exposures to TBBPA caused no statistically significant changes in either PKC or PKD activation.

Brominated flame retardants, tetrabromobisphenol A and hexabromocyclododecane, activate mitogen-activated protein kinases (MAPKs) in human natural killer cells.

Natural killer (NK) cells provide a vital surveillance against virally infected cells, tumor cells, and antibody-coated cells through the release of cytolytic mediators and gamma interferon (IFN-γ). Hexabromocyclododecane (HBCD) is a brominated flame retardant used primarily in expanded (EPS) and extruded (XPS) polystyrene foams for thermal insulation in the building and construction industry. Tetrabromobisphenol A (TBBPA) is used both as a reactive and an additive flame retardant in a variety of materials. HBCD and TBBPA contaminate the environment and are found in human blood samples. In previous studies, we have shown that other environmental contaminants, such as the dibutyltin (DBT) and tributyltin (TBT), decrease NK lytic function by activating mitogen-activated protein kinases (MAPKs) in the NK cells. HBCD and TBBPA also interfere with NK cell(s) lytic function. The current study evaluates whether HBCD and/or TBBPA have the capacity to activate MAPKs and MAPK kinases (MAP2Ks). The effects of concentrations of HBCD and TBBPA that inhibited lytic function on the phosphorylation state and total levels of the MAPKs (p44/42, p38, and JNK) and the phosphorylation and total levels of the MAP2Ks (MEK1/2 and MKK3/6) were examined. Results indicate that exposure of human NK cells to 10-0.5 µM HBCD or TBBPA activate MAPKs and MAP2Ks. This HBCD and TBBPA-induced activation of MAPKs may leave them unavailable for activation by virally infected or tumor target cells and thus contributes to the observed decreases in lytic function seen in NK cells exposed to HBCD and TBBPA.

Effects of butyltins on mitogen-activated-protein kinase kinase kinase and Ras activity in human natural killer cells.

Butyltins (BTs) contaminate the environment and are found in human blood. BTs, tributyltin (TBT) and dibutyltin (DBT) diminish the cytotoxic function and levels of key proteins of human natural killer (NK) cells. NK cells are an initial immune defense against tumors, virally infected cells and antibody-coated cells and thus critical to human health. The signaling pathways that regulate NK cell functions include mitogen-activated protein kinases (MAPKs). Studies have shown that exposure to BTs leads to activation of specific MAPKs and MAPK kinases (MAP2Ks) in human NK cells. MAP2K kinases (MAP3Ks) are upstream activators of MAP2Ks, which then activate MAPKs. The current study examined if BT-induced activation of MAP3Ks was responsible for MAP2K and thus, MAPK activation. This study examines the effects of TBT and DBT on the total levels of two MAP3Ks, c-Raf and ASK1, as well as activating and inhibitory phosphorylation sites on these MAP3Ks. In addition, the immediate upstream activator of c-Raf, Ras, was examined for BT-induced alterations. Our results show significant activation of the MAP3K, c-Raf, in human NK cells within 10 min of TBT exposure and the MAP3K, ASK1, after 1 h exposures to TBT. In addition, our results suggest that both TBT and DBT affect the regulation of c-Raf.

Tributyltin and dibutyltin alter secretion of tumor necrosis factor alpha from human natural killer cells and a mixture of T cells and natural killer cells.

Butyltins (BTs) have been in widespread use. Tributyltin (TBT) has been used as a biocide in a variety of applications and is found in human blood samples. Dibutyltin (DBT) has been used as a stabilizer in polyvinyl chloride plastics and as a de-worming agent in poultry. DBT, like TBT, is found in human blood. Human natural killer (NK) cells are the earliest defense against tumors and viral infections and secrete the cytokine tumor necrosis factor-alpha (TNF-α). TNF-α is an important regulator of adaptive and innate immune responses. TNF-α promotes inflammation and an association between malignant transformation and inflammation has been established. Previously, we have shown that TBT and DBT were able to interfere with the ability of NK cells to lyse tumor target cells. Here we show that BTs alter cytokine secretion by NK cells as well as a mixture of T and NK lymphocytes (T/NK cells). We examined 24-, 48-h and 6-day exposures to TBT (200-2.5 nM) and DBT (5-0.05 µM) on TNF-α secretion by highly enriched human NK cells and T/NK cells. The results indicate that TBT (200-2.5 nM) decreased TNF-α secretion from NK cells. In the T/NK cells, 200 nM TBT decreased secretion whereas 100-5 nM TBT increased secretion of TNF-α. NK cells or T/NK cells exposed to higher concentrations of DBT showed decreased TNF-α secretion whereas lower concentrations showed increased secretion. The effects of BTs on TNF-α secretion are seen at concentrations present in human blood.

Effects of DDT and triclosan on tumor-cell binding capacity and cell-surface protein expression of human natural killer cells.

1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) and triclosan (TCS) are organochlorine (OC) compounds that contaminate the environment, are found in human blood and have been shown to decrease the tumor-cell killing (lytic) function of human natural killer (NK) cells. NK cells defend against tumor cells and virally infected cells. They bind to these targets, utilizing a variety of cell surface proteins. The present study examined concentrations of DDT and TCS that decrease lytic function for alteration of NK binding to tumor targets. Levels of either compound that caused loss of binding function were then examined for effects on expression of cell-surface proteins needed for binding. NK cells exposed to 2.5 µM DDT for 24 h (which caused a greater than 55% loss of lytic function) showed a decrease in NK binding function of about 22%, and a decrease in CD16 cell-surface protein of 20%. NK cells exposed to 5 µM TCS for 24 h showed a decrease in ability to bind tumor cells of 37% and a decrease in expression of CD56 of about 34%. This same treatment caused a decrease in lytic function of greater than 87%. These results indicated that only a portion of the loss of NK lytic function seen with exposures to these compounds could be accounted for by loss of binding function. They also showed that loss of binding function is accompanied by a loss of cell-surface proteins important in binding function.

Pentachlorophenol decreases tumor-cell-binding capacity and cell-surface protein expression of human natural killer cells.

Pentachlorophenol (PCP) is an organochlorine pesticide that decreases the tumor-cell killing (lytic) function of human natural killer (NK) cells. NK cells defend against tumor cells and virally infected cells. They bind to these targets, utilizing a variety of cell-surface proteins. This study examined concentrations of PCP that decrease lytic function for alteration of NK binding to tumor targets. Levels of PCP that caused loss of binding function were then examined for effects on expression of cell-surface proteins needed for binding. Exposure to 10 µM PCP for 24 h (which caused a greater than 70% loss of lytic function) decreased NK binding function (34.6%), and CD11a (21.7%) and CD56 (26.2%) cell-surface proteins. Both binding function and cell-surface proteins were decreased after longer exposures to lower concentrations of PCP. These data indicate that continuous exposures to PCP decreased binding function as well as cell-surface marker expression in NK cells and that these changes may in part explain the losses of lytic function seen with these exposures. PCP exposures have been shown to increase the incidence of blood and kidney cancers in humans. These data indicate that a possible explanation for this increased risk may be loss of NK lytic function, which is at least in part owing to the loss of the ability of the NK cell to bind to tumor cells. These data also indicate that lost binding function may be due to loss of important cell-surface proteins.