Immunotoxicity Induced by Acute Subtoxic Doses of Paraquat Herbicide: Implication of Shifting Cytokine Gene Expression toward T-Helper (TH)-17 Phenotype

Toxic effects of pesticides on cellular and humoral immunity: an overview

People are exposed to pesticides through food, drinking water, and the environment. These compounds are associated with several disorders, such as inflammatory diseases, rheumatoid arthritis, cancer, and a condition related to metabolic syndrome. The immunotoxicants or immunotoxic compounds can cause a wide variety of effects on immune function, altering humoral immunity and cell-mediated immunity, resulting in adverse effects to the body. Here, immune system disorders are highlighted because they are closely linked to multiple organs, including the nervous, endocrine, reproductive, cardiovascular, and respiratory systems, leading to transient or permanent changes. Therefore, this study reviewed the mechanisms involved in the immunotoxicity of fungicides, herbicides, and insecticides in cells, animals, and humans in the past 11 years. According to the studies analyzed, the pesticides interfere with innate and adaptive immune functions, but the effects observed mainly on cellular and humoral immunity were highlighted. These compounds affected specific immune cells, causing apoptosis, changes in factor nuclear kappa B (NF-κB) expression, pro-inflammatory factors interleukin 6 (IL-6), interleukin 8 (IL-8), interferon-gamma (IFN-γ), chemokines (CXCL-c1c), and anti-inflammatory factor, such as interleukin 10 (IL-10). To verify the threats of these compounds, new evaluations with immunotoxicological biomarkers are necessary. HighlightsPesticides interfere with the innate and adaptive immune response.Cells, animals and human studies demonstrate the immunotoxicity of pesticides in the cellular and humoral immune response.Fungicides, herbicides, and insecticides alter the immune system by various mechanisms, such as pro-inflammatory and anti-inflammatory factors.

Potential protective effects of chrysin against immunotoxicity induced by diazinon

Acute intoxication with diazinon (DZN) as a pesticide causes mortality and morbidity annually. This study shows the impact of sub-acute toxicity of DZN 20 mg/kg and the protective activities of chrysin (CH) as a flavone under the flavonoids family (12.5, 25 and 50 mg/kg) were assessed on BALB/c mouse immune system. The changes in morphological and functional properties of the immune system on thymus, spleen and liver histopathology, sub-populations of T lymphocytes, cytokines levels, transcription factors, complement function, phagocytosis, specific and total antibody productions were considered. The histopathological effects of DZN on the spleen and thymus were not significant, but the liver was damaged remarkably. In the presence of CH, the toxic effect of DZN is suppressed. DZN significantly decreased the number of whole blood TCD4⁺, TCD8⁺ and NK cells and suppressed the phagocytosis, delayed-type hypersensitivity (DTH) responses to sheep red blood cell (SRBC). Furthermore, it suppressed specific anti-SRBC-Ab, total IgG and IgM production, T-bet expression, and IFN-γ production. In contrast, DZN did not significantly affect complement function and the number of NK cells, TCD4⁺ and TCD8⁺ splenocytes. However, it potentiated the expression of GATA-3, ROR-γt and FOXP3 gene expression and consequently produced IL-4, IL-10, IL-17 and TGF-β in whole blood. CH not only significantly increased the variables mentioned above at 12.5, 25 and 50 mg/kg but also could overcome the toxic effects of DZN on whole blood lymphocyte sub-populations and specific and total Ab production in 25 and 50 mg/kg concentrations, phagocytosis and DTH responses in 50 mg/kg, and modulation of the transcription factors and cytokine production, mainly in 25 and 50 mg/kg. In conclusion, DZN in sub-acute doses could remarkably deteriorate immune responses. However, CH can overcome the toxic effects of DZN on the immune components and functions of the immune system.

Depletion of NK cells attenuates paraquat-induced acute lung injury by manipulating macrophage polarization

Acute lung injury is the main causative factor in paraquat dichloride (PQ)-induced mortality. The innate immune system-triggered detrimental inflammatory cascade plays a vital role in PQ-induced acute lung injury. However, the role of natural killer (NK) cells, which are essential for innate response, in PQ-induced acute lung injury remains largely unknown. Here, we found that in an acute PQ poisoning model, depletion of NK cells attenuated PQ-induced lung injury by inhibiting macrophage polarization towards the M1 type. Specifically, the percentages of NK cells were reduced in the lung, spleen, and peripheral blood in a murine model of acute PQ poisoning. NK cells were aberrantly activated, evidenced by upregulation of the activating markers CD69, CD107a, and NKG2D and downregulation of the inhibitive marker KLRG1. Further, NK-specific depletion in mice greatly prolonged the survival time and ameliorated reactive oxygen species-induced damage following PQ treatment compared with the control group. Importantly, NK cell depletion alleviated macrophage and neutrophil infiltration in the lung and reversed PQ induced-macrophage polarization towards the pro-inflammatory M1 type. Our study demonstrates a crucial role of NK cells and NK cell-to-macrophage interaction in PQ-induced acute lung injury.

Paraquat Preferentially Induces Apoptosis of Late Stage Effector Lymphocyte and Impairs Memory Immune Response in Mice

Paraquat (PQ) is a toxic non-selective herbicide. To date, the effect of PQ on memory immune response is still unknown. We investigated the impact of PQ on memory immune response. Adult C57BL/6 mice were subcutaneously injected with 2 mg/kg PQ, 20 mg/kg PQ or vehicle control every three days for two weeks. A single injection of keyhole limpet hemocyanin (KLH) at day four after the initial PQ treatment was used to induce a primary immune response; a second KLH challenge was performed at three months post the first KLH immunization to induce a secondary immune response. In steady state, treatment with 20 mg/kg PQ reduced the level of serum total IgG, but not that of IgM; treatment with 20 mg/kg PQ decreased the number of effector and memory lymphocytes, but not naïve or inactivated lymphocytes. During the primary immune response to KLH, treatment with 20 mg/kg PQ did not influence the proliferation of lymphocytes or expression of co-stimulatory molecules. Instead, treatment with 20 mg/kg PQ increased the apoptosis of lymphocytes at late stage, but not early stage of the primary immune response. During the secondary immune response to KLH, treatment with 20 mg/kg PQ reduced the serum anti-KLH IgG and KLH-responsive CD4 T cells and B cells. Moreover, effector or activated lymphocytes were more sensitive to PQ-induced apoptosis in vitro. Treatment with 2 mg/kg PQ did not impact memory immune response to KLH. Thus, treatment with 20 mg/kg PQ increased apoptosis of late stage effector cells to yield less memory cells and thereafter impair memory immune response, providing a novel understanding of the immunotoxicity of PQ.

Apigenin reverses lung injury and immunotoxicity in paraquat-treated mice

Paraquat (PQ) induces acute lung injury (ALI) and immunotoxicity. Apigenin exerts anti-oxidant and anti-inflammatory properties. The purpose of this study was to investigate the possible protective effects of apigenin on PQ-induced ALI and immunotoxicity in mice. Female C57BL/6 mice received a single injection of PQ (50 mg/kg). Apigenin was given for 7 consecutive days starting 5 days before PQ exposure. The toxicity markers were evaluated in terms of weight loss, lung histopathology, oxidative stress, inflammation, and T cell functions after PQ exposure. Poisoned mice exhibited severe lung tissue lesions, inflammatory cell infiltration and the release of pro-inflammatory cytokines IL-6 and TNF-α. PQ administration increased the lung wet/dry ratios and lipid peroxidation by the increase of MDA levels and decreased anti-oxidase activity including SOD, GSH-PX, and CAT. While such effect on lung was reversed by apigenin. Importantly, PQ-induced immunotoxicity was also observed in a decrease of spleen weight, inhibition of T cell proliferation and T-cell secreting IL-2 from splenocytes. Further mechanism analysis found that PQ administration could decrease total splenocytes, CD4⁺ and CD8⁺ T cells, SOD, GSH-PX, and CAT activity, and increased the levels of MDA and the concentrations of pro-inflammatory cytokines IL-6 and TNF-α compared to control mice. However, apigenin treatment reversed PQ-induced immunotoxicity. In summary, all results suggest that apigenin has beneficial effects on PQ-induced ALI and immunotoxicity possibly, and it could be related, at least in part, to its ability in modulating inflammation and oxidative stress, although in-depth studies might be needed to fully understand the mechanism of action.

Paraquat reduces natural killer cell activity via metallothionein induction

Paraquat (PQ), one of the most widely used herbicides, has been used for several decades in agriculture. Some studies suggest that PQ has effects on the immune system. Moreover, previous studies have shown that PQ imparted some immunosuppressive effects. In the present study, cytotoxicity assays using splenic NK cells from mice treated for 28 days with PQ (at 0.2, 1, and 5 mg/kg) were performed to determine whether PQ altered the function of NK cells. Given that PQ was expected to induce an immunosuppressive effect, it was hypothesized that a gene involved in cellular metal ion homeostasis, metallothionein-1 (MT-1), could play an important role in this outcome. This belief was based on the fact that MT1 encodes a protein responsible for zinc ion homeostasis, and that a reduction in free zinc ion levels impairs NK cell function. The results showed that PQ treatments led to increased MT expression in several organs (liver, kidneys, testes) and in splenocytes, caused a reduction of both free zinc ions in sera and in free intracellular zinc, and reduced the expression of GATA-3, a zinc-finger transcription factor important for maturation and activity of T-cells and NK cells. These results provide a basis for a new molecular mechanism to describe potential immunosuppressive effects of PQ in vivo.