Effects of HgCl2 on the expression of autoimmune responses and disease in diabetes-prone (DP) BB rats

In vitro and in vivo effects of mercuric chloride on thymic endocrine activity, NK and NKT cell cytotoxicity, cytokine profiles (IL-2, IFN-gamma, IL-6): role of the nitric oxide-L-arginine pathway

Mercury (Hg2+) affects cell-mediated immunity, including thymulin production. Thymulin, a zinc-dependent thymic hormone synthesized by thymic epithelial cells (TECs), is involved in NK cell cytotoxicity and Th1 cytokine production (IL-2 and IFN-gamma), which in turn affect both NKT and classic NK spleen cell cytotoxicity. High doses of Hg2+ induce an inflammatory status, increased production of IL-6 and consequent Th1/Th2 imbalance as well as cell-mediated immune depression. The mechanisms by which Hg+ affects the cell-mediated immune response are still unclear. The nitric oxide (NO) pathway may be implicated. The aim of this work was to further explore its noxious role in innate and adaptive immunity and to study the possible role played by the NO pathway. Young Balb/c mice treated in vivo for 1 month with 1.0 mg HgCl2/kg b.w. showed low thymulin activity, depressed NO production (as measured by nitrite and nitrate plasma levels), impaired classic NK spleen cell cytotoxicity, decreased Th1 (IL-2 and IFN-gamma) cytokine profiles, and increased IL-6 production. In vitro, 10(-6) M of HgCl2 inhibited active thymulin kinetics, TEC proliferation, NKT cell cytotoxicity and Th1 cytokine production, whereas IL-6 increased. L-arginine restored thymulin activity, TEC proliferation, NKT cytotoxicity, cytokine profiles and nitrite and nitrate plasma levels both in vivo and in vitro. Since L-arginine is the substrate for NO production, it may compensate for the cell-mediated immune defect induced by HgCl2, via the arginine-NO-pathway. L-arginine is also able to reduce glomerular kidney IgG antibodies deposits induced by higher dose of HgCl2 administration.

Lack of graft-versus-host-like pathology in mercury-induced autoimmunity of Brown Norway rats

The repeated administration of mercury to Brown Norway (BN) rats induces the production of autoantibodies to laminin 1 and other autoantigens, accompanied by renal deposition of immunoglobulins and a membranous glomerulonephropathy. A graft-versus-host-like (GVHL) syndrome, characterized by widespread necrotizing leukocytoclastic vasculitis of the bowel, skin, and other tissues, has also been observed after mercury treatment of BN rats. These findings have suggested that the autoimmunity caused by the administration of mercury to BN rats may result as a xenobiotic-induced GVHL effect under the control of OX22+ T lymphocytes. However, previous studies of mercury-induced autoimmunity have never reported any evidence of GVHL lesions. Therefore, we have carefully examined various tissues from a large group of BN rats injected with HgCl₂ to identify possible areas of inflammatory reactions that may have been unnoticed in previous investigations. In addition, we have determined by flow cytometry whether exposure to mercury results in percentage and numerical alterations of OX22+ or other lymphocyte subpopulations in lymphoid organs of HgCl₂-treated BN rats. The present article confirms that mercury induces autoimmune responses to laminin 1 but does not corroborate the hypothesis of a GVHL syndrome regulated by OX22+ lymphocytes. First, changes in OX22+ cells during treatment with HgCl₂ were infrequent and had no significant correlation with the kinetics of autoimmune responses to laminin 1. Second, we detected no GVHL lesions in skin and intestine of mercury-treated BN rats.

Influence of dental amalgam and heavy metal cations on in vitro interleukin-1beta production by human peripheral blood mononuclear cells

The influence of dental amalgam and heavy metal cations on interleukin-1beta (IL-1beta) expression by peripheral blood mononuclear cells from healthy donors was studied. A marked decrease in the production of IL-1beta was caused by freshly prepared amalgam or amalgam-conditioned culture medium, but not by amalgam aged for 6 weeks. When metal cations were added as salts, Cu(2+), Hg(2+), and Ag(+) at high concentrations (33.3 and 333.3 microM) were highly inhibitory. Among other heavy metal cations, Au(3+), Pt(4+), Ni(2+), Pd(2+), but not Ga(3+) or Sn(2+), inhibited IL-1beta production in a concentration-dependent manner. Flow cytometry studies indicated that Hg(2+) and Ag(+) strongly reduced the percentage of CD14(+) cells containing IL-1beta intracellularly. As shown by Northern blot analysis, Hg(2+) inhibited the level of IL-1beta-specific mRNA by 28% at 3.3 microM and completely at 33.3 microM. Only slight inhibitory effects were induced by Cu(2+) at 33.3 microM. Interestingly, Ag(+) at a concentration of 3.3 microM increased twofold the amount of IL-1beta-specific mRNA. Our data show that IL-1beta production is altered at protein and mRNA levels by components released from fresh amalgam and by other heavy metal cations, suggesting a role of these cations in changes in the cell phenotype and IL-1-mediated cell functions.

Mercury-induced autoimmunity in Brown Norway rats: kinetics of changes in RT6+ T lymphocytes correlated with IgG isotypes of circulating autoantibodies to laminin 1

Repeated exposure to mercury causes various autoimmune effects in rats of the Brown Norway (BN) strain. Previous studies from our laboratory have shown that on day 15 of HgCl2 treatment BN rats exhibit a relative decrease in RT6.2+ T cells. At the same time, they produce high levels of autoantibodies to renal antigens and experience a membranous glomerulonephropathy. In contrast, Lewis (LEW) rats are resistant to autoimmunity caused by mercury and do not demonstrate a decrease in RT6+ cells after administration of HgCl2. In the present paper we provide novel information on the correlation between changes in RT6.2+ lymph node T cells and the production of autoantibodies to laminin 1, obtained by detailed kinetic studies of HgCl2-treated BN rats. We have confirmed a decrease in the percentage of RT6.2+ lymphocytes on day 15 of mercury treatment, despite a significant increase in the number of peripheral lymphocytes. No such changes were observed in LEW rats. We have determined that on day 15 the percentage decrease in RT6+ cells is evident in both RT6.2+CD4+ and RT6.2+CD8+ T cell subsets. Kinetic studies demonstrated that significant changes in the percentage of RT6.2+ cells are first observed by day 8 and continue through days 11 and 15. We have also observed a significant percent decrease in CD4+ T lymphocytes as well as an increase in CD4-CD8- cells. The dramatic increase in the percentage of these double negative cells at the level of peripheral lymphoid tissues does not appear to be due to higher thymic output, since there was a decrease in the percentage of TCR+Thy1+ cells, a phenotype that is associated with recent thymic emigrants. Finally, we have demonstrated that 100% of HgCl2-treated BN rats had circulating antibodies that reacted with both mouse and rat laminin 1, i.e. are autoantibodies to laminin 1. These autoantibodies were predominantly of the IgG1 and IgG2a isotype, possibly as the result of a polarized autoimmune response driven by Type 2 cytokines. A kinetic investigation showed that significant levels of IgG1 and IgG2a autoantibodies to laminin 1 were first presentin the circulation by day 11. The inverse correlation between levels of RT6.2+ T lymphocytes and autoantibodies to laminin 1 suggests that mercury may induce autoimmune responses in BN rats by its effects on these immunoregulatory cells.