Oral tungstate (Na₂WO₄) exposure reduces adaptive immune responses in mice after challenge

Abstract

Tungstate (WO²⁻₄) has been identified as a ground water contaminant at military firing ranges and can be absorbed by ingestion. In this study, C57BL6 mice were exposed to sodium tungstate (Na2WO4·2H2O) (0, 2, 62.5, 125, and 200 mg/kg/day) in their drinking water for an initial 28-day screen and in a one-generation (one-gen) model. Twenty-four hours prior to euthanasia, mice were intraperitoneally injected with Staphylococcal enterotoxin B (SEB) (20 μg/mouse) or saline as controls. After euthanasia, splenocytes and blood were collected and stained with lymphocyte and/or myeloid immunophenotyping panels and analyzed by flow cytometry. In the 28-day and one-gen exposure, statistically significant reductions were observed in the quantities of activated cytotoxic T-cells (TCTL; CD3(+)CD8(+)CD71(+)) and helper T-cells (TH; CD3(+)CD4(+)CD71(+)) from spleens of SEB-treated mice. In the 28-day exposures, CD71(+) TCTL cells were 12.87 ± 2.05% (SE) in the 0 tungstate (control) group compared to 4.44 ± 1.42% in the 200 mg/kg/day (p < 0.001) group. TH cells were 4.85 ± 1.23% in controls and 2.76 ± 0.51% in the 200 mg/kg/day (p < 0.003) group. In the one-gen exposures, TCTL cells were 7.98 ± 0.49% and 6.33 ± 0.49% for P and F1 mice after 0 mg/kg/day tungstate vs 1.58 ± 0.23% and 2.52 ± 0.25% after 200 mg/kg/day of tungstate (p < 0.001). Similarly, TH cells were reduced to 6.21 ± 0.39% and 7.20 ± 0.76%, respectively, for the 0 mg/kg/day P and F1 mice, and 2.28 ± 0.41% and 2.85 ± 0.53%, respectively, for the 200 mg/kg/day tungstate P and F1 groups (p < 0.001). In delayed-type hypersensitivity Type IV experiments, tungstate exposure prior to primary and secondary antigen challenge significantly reduced footpad swelling at 20 and 200 mg/kg/day. These data indicate that exposure to tungstate can result in immune suppression that may, in turn, reduce host defense against pathogens.

Immunotoxic effects of sodium tungstate dihydrate on female B6C3F1/N mice when administered in drinking water

“…In the present study, the functional activity of T CTL cells decreased at 1000 mg STD/L when splenic T CTL lymphocytes from control and STD-treated mice were sensitized to P815 mastocytoma cells ex vivo , prior to functional assessment in the effector phase. Similarly, other studies have shown that tungstate-treated C57BL/6 mice developed significant splenomegaly when inoculated with the T-cell activating RSV (Fastje et al, 2012), and demonstrated suppression of activated T H and T CTL cells, when challenged with SEB (Osterburg et al, 2014). In the absence of RVS or SEB challenge, tungstate had no effect on spleen size or T-cell populations (Fastje et al, 2012; Osterburg et al, 2014).…”

“…Published reports indicated that sodium tungstate may modulate hematopoiesis, immune cell populations, and immune responses in rodent models (Osterburg et al, 2010, 2014; Fastje et al, 2012). …”

“…However, the type of response varied depending on the form of tungsten and the route of exposure. Osterburg, et al (2014) demonstrated adverse effects on T-cell activation by soluble tungsten, and hypothesized that the suppression of acquired immunity could result in reduced host defense to immune challenges. Exposure to sodium tungstate in drinking water (200 mg/kg, ≈ 1140 mg/L) led to a reduction in the percentage of activated (CD71 + , transferrin receptor-positive) T CTL cells and T-helper (T H ) cells in the spleens of C57BL/6 mice that had been challenged with T-cell activating bacterial antigen staphylococcal enterotoxin (SEB).…”

“…The doses, vehicle, and route of exposure were selected for consistency with the 13-wk NTP mouse toxicology studies, and were based on mechanistic immunotoxicology studies conducted by the Naval Health Research Center Detachment Environmental Health Effects Laboratory (NHRC Det) (Osterburg et al, 2014), and published long-term exposure studies (Barbera et al, 2001). Although these doses were higher than what is typically encountered in the natural environment, they represented the maximum concentration found in tap water (337 mg/L) (Koutsospyros et al, 2006) measured in Nevada, soil pore waters (400 mg/L) at military firing ranges (Clausen and Korte, 2009), and doses used in a clinical study (200 mg/day) (Hanzu et al, 2010).…”

“…Although evidence is limited, rodent studies suggest that tungsten exposure may affect the immune system, as indicated by localization of tungsten in bone and spleen (McDonald et al, 2007; Guandalini et al, 2011; Kelly et al, 2013); attenuation of the delayed-type hypersensitivity response; alteration of T-cell populations (Osterburg et al, 2014); transcriptomic changes associated with regulation of some immune responses and hematological/immunological disease (Fastje et al, 2008, 2009); and, induction of splenomegaly and neutrophilia following co-exposure to sodium tungstate and respiratory syncytial virus (RSV) (Fastje et al, 2012). Published reports indicated that sodium tungstate dysregulated cytokine production, the cell cycle, and apoptosis in human peripheral blood lymphocytes (Osterburg et al, 2010).…”