Differential sensitivities of bone marrow, spleen and thymus to genotoxicity induced by environmentally relevant concentrations of arsenite.

It is known in humans and mouse models, that drinking water exposures to arsenite (As+3) leads to immunotoxicity. Previously, our group showed that certain types of immune cells are extremely sensitive to arsenic induced genotoxicity. In order to see if cells from different immune organs have differential sensitivities to As+3, and if the sensitivities correlate with the intracellular concentrations of arsenic species, male C57BL/6J mice were dosed with 0, 100 and 500ppb As+3via drinking water for 30d. Oxidation State Specific Hydride Generation- Cryotrapping- Inductively Coupled Plasma- Mass Spectrometry (HG- CT- ICP- MS) was applied to analyze the intracellular arsenic species and concentrations in bone marrow, spleen and thymus cells isolated from the exposed mice. A dose-dependent increase in intracellular monomethylarsonous acid (MMA+3) was observed in both bone marrow and thymus cells, but not spleen cells. The total arsenic and MMA+3 levels were correlated with an increase in DNA damage in bone marrow and thymus cells. An in vitro treatment of 5, 50 and 500nM As+3 and MMA+3 revealed that bone marrow cells are most sensitive to As+3 treatment, and MMA+3 is more genotoxic than As+3. These results suggest that the differential sensitivities of the three immune organs to As+3 exposure are due to the different intracellular arsenic species and concentrations, and that MMA+3 may play a critical role in immunotoxicity.

Changes in HPBMC markers of immmune function following controlled short-term inhalation exposures of humans to hardwood smoke.

Previous studies have shown that complex mixtures containing particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) produce systemic immunotoxicity in animal models following inhalation exposures. While we and others have shown that emissions associated with hardwood smoke (HWS), cigarette smoke and diesel exhaust can suppress the immune systems of animals in vitro and in vivo, there have been few immune function studies on human peripheral blood mononuclear cells (HPBMC) following exposure of humans to HWS. Our work shows that T cells are an important targets of PM and PAH immunotoxicity. These studies were conducted on HPBMC from 14 human volunteers receiving four 2 h nightly exposures to clean air or HWS at a concentration of 500 ug/m(3). We measured anti-CD3/anti-CD28 stimulated T-cell proliferation and HPBMC cytokine production in cell supernatants, including interleukin 1ß (IL-1ß), tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), interleukin 8 (IL-8), TH1 cytokines γIFN and IL-2, TH2 cytokine IL-4, Th17 cytokine interleukin 17A (IL-17A) and interleukin 10 (IL-10). We analyzed results using analysis of variance (ANOVA), t-tests and Pearson correlation. Results showed that there was significant variation in the amount of T-cell proliferation observed following polyclonal activation with anti-CD3/anti-CD28 antibodies in both the air and HWS-exposed groups. There was not a significant effect of HWS on T-cell proliferation. However, we did find a strong relationship between the presence of proinflammatory cytokines (IL-1ß, TNF-α, IL-6, but not IL-8) and the amount of T-cell proliferation seen in individual donors, demonstrating that brief exposures of humans to HWS can produce changes in systemic immunity that is associated with proinflammatory cytokines.

Arsenite selectively inhibits mouse bone marrow lymphoid progenitor cell development in vivo and in vitro and suppresses humoral immunity in vivo.

It is known that exposure to As(+3) via drinking water causes a disruption of the immune system and significantly compromises the immune response to infection. The purpose of these studies was to assess the effects of As(+3) on bone marrow progenitor cell colony formation and the humoral immune response to a T-dependent antigen response (TDAR) in vivo. In a 30 day drinking water study, mice were exposed to 19, 75, or 300 ppb As(+3). There was a decrease in bone marrow cell recovery, but not spleen cell recovery at 300 ppb As(+3). In the bone marrow, As(+3) altered neither the expression of CD34+ and CD38+ cells, markers of early hematopoietic stem cells, nor CD45-/CD105+, markers of mesenchymal stem cells. Spleen cell surface marker CD45 expression on B cells (CD19+), T cells (CD3+), T helper cells (CD4+) and cytotoxic T cells (CD8+), natural killer (NK+), and macrophages (Mac 1+) were not altered by the 30 day in vivo As(+3) exposure. Functional assays of CFU-B colony formation showed significant selective suppression (p<0.05) by 300 ppb As(+3) exposure, whereas CFU-GM formation was not altered. The TDAR of the spleen cells was significantly suppressed at 75 and 300 ppb As(+3). In vitro studies of the bone marrow revealed a selective suppression of CFU-B by 50 nM As(+3) in the absence of apparent cytotoxicity. Monomethylarsonous acid (MMA(+3)) demonstrated a dose-dependent and selective suppression of CFU-B beginning at 5 nM (p<0.05). MMA(+3) suppressed CFU-GM formation at 500 nM, a concentration that proved to be nonspecifically cytotoxic. As(+5) did not suppress CFU-B and/or CFU-GM in vitro at concentrations up to 500 nM. Collectively, these results demonstrate that As(+3) and likely its metabolite (MMA(+3)) target lymphoid progenitor cells in mouse bone marrow and mature B and T cell activity in the spleen.