Effect of metal allergens on the DNA synthesis of unsensitized guinea pig lymphoid cells cultured in vitro

Mercury-induced inflammation and autoimmunity

BACKGROUND

Human exposure to mercury leads to a variety of pathologies involving numerous organ systems including the immune system. A paucity of epidemiological studies and suitable diagnostic criteria, however, has hampered collection of sufficient data to support a causative role for mercury in autoimmune diseases. Nevertheless, there is evidence that mercury exposure in humans is linked to markers of inflammation and autoimmunity. This is supported by experimental animal model studies, which convincingly demonstrate the biological plausibility of mercury as a factor in the pathogenesis of autoimmune disease.

SCOPE OF THE REVIEW

In this review, we focus on ability of mercury to elicit inflammatory and autoimmune responses in both humans and experimental animal models.

MAJOR CONCLUSIONS

Although subtle differences exist, the inflammatory and autoimmune responses elicited by mercury exposure in humans and experimental animal models show many similarities. Proinflammatory cytokine expression, lymphoproliferation, autoantibody production, and nephropathy are common outcomes. Animal studies have revealed significant strain dependent differences in inflammation and autoimmunity suggesting genetic regulation. This has been confirmed by the requirement for individual genes as well as genome wide association studies. Importantly, many of the genes required for mercury-induced inflammation and autoimmunity are also required for idiopathic systemic autoimmunity. A notable difference is that mercury-induced autoimmunity does not require type I IFN. This observation suggests that mercury-induced autoimmunity may arise by both common and specific pathways, thereby raising the possibility of devising criteria for environmentally associated autoimmunity.

GENERAL SIGNIFICANCE

Mercury exposure likely contributes to the pathogenesis of autoimmunity.

Hormetic Dose-Response Relationships in Immunology: Occurrence, Quantitative Features of the Dose Response, Mechanistic Foundations, and Clinical Implications

This article provides an assessment of the occurrence of immune-system-related hormetic-like biphasic dose-response relationships. Such dose-response relationships are extensive, with over 90 different immune response-related endpoints reported, induced by over 70 endogenous agonists, over 100 drugs, and over 40 environmental contaminants. Such hormetic responses were reported in over 30 animal models, over a dozen mammalian and human cell lines. These findings demonstrate that immune-system-related hormetic-like biphasic dose-response relationships are common and highly generalizable according to model, endpoint, and chemical class. The quantitative features of the dose response are generally consistent with previously published examples of hormetic dose responses for other biological endpoints. These findings were generally recognized and explicitly discussed by the original authors, often with consideration given to possible mechanistic foundations as well as numerous clinical implications. Despite the recognition by individual authors of the hormetic nature of these observed responses, the overall widespread nature of immune-related hormetic responses has been only little appreciated, with a general lack of insight into the highly generalizable nature of this phenomenon as well as the complex regulatory networks affecting biological switching mechanisms that result in the hormetic responses.

The in vitro proliferation of murine lymphocytes to mercuric chloride is restricted to mature T cells and is interleukin 1 dependent

The aims of this study were to compare the in vitro responses of murine lymphocytes to HgCl2 to determine the requirement for adherent cells, and the contribution that costimulation plays in T cell proliferation. The in vitro proliferative response of murine splenocytes to HgCl2 was found to be both cell concentration- and HgCl2 concentration-dependent with the greatest response occurring with 5 x 10(6) cells/ml in the presence of 10(-5) M HgCl2. Both CD4+ and CD8+ T cells proliferated in response to HgCl2, but B cells and immature T cells (thymocytes) did not. Proliferation required the presence of splenic adherent cells and was inhibited by addition of anti-IL-1 alpha antibodies. Antibodies to the other co-stimulatory molecules CD40 ligand, CD80 (B7-1), and CD86 (B7-2), although inhibitory, were less effective. Xenobiotics such as the heavy metal mercury can elicit a spectrum of immunological responses ranging from immunosuppression to autoimmunity. The most common response, in vivo and in vitro, is lymphoproliferation, which may be a prelude to immune activation. Although a number of the requirements for mercury-induced T cell proliferation in vitro have been described, the role that adherent cells play remains to be explained. The studies described here show that interaction between co-stimulatory molecules of adherent cells and mature T cells contributes to HgCl2-induced T cell proliferation. Among these co-stimulatory molecules, IL-1 appears to play an important role. The requirement for mature T cells, adherent cells, and co-stimulatory molecules argues that HgCl2-induced T cell proliferation possesses the properties of an antigen-induced response.

Effects of arsenic on blast transformation and DNA synthesis of human blood lymphocytes

Effects of inorganic arsenicals on DNA synthesis in unsensitized human blood lymphocytes were biphasic: the chemicals at very low concentrations enhanced blast transformation and DNA synthesis, whereas higher concentrations inhibited the transformation and DNA synthesis. The concentrations of arsenicals at which the maximum stimulating effect was found were 1 x 10(-5) M, 1 x 10(-6) M or 2 x 10(-6) M, and 0.8 x 10(-6) M or 1 x 10(-6) M for sodium arsenite exposure of 1 h, 3 days and 6 days, respectively; for sodium arsenate, 1 x 10(-5) M, 1 x 10(-5) M, and 2 x 10(-6) M or 5 x 10(-6) M, respectively. Arsenicals must be present for the entire 6 days culture period to produce maximum stimulation of blast transformation of human lymphocytes. The longer exposure of the lymphocytes to arsenicals, the lower the concentrations of arsenicals at which the maximum stimulating effect was found. The stimulating effect of trivalent arsenic (sodium arsenite) was stronger than pentavalent arsenic (sodium arsenate).

Immunologic specificity of lymphocyte cell lines from dogs exposed to beryllium oxide

We have reported that dogs exposed twice to aerosols of beryllium oxide (BeO) developed Be-specific immune responses within the lung, along with granulomatous and fibrotic lung lesions. To evaluate the specificity of the immune response, lymphocytes from lungs and blood of BeO-exposed dogs were co-cultured over an irradiated blood monocyte layer, alternately with interleukin 2 and BeSO4. Resultant cell lines were then tested for their response to different metal cations, common canine recall antigens, and BeSO4 in an in vitro cell proliferation assay. The cell lines responded to BeSO4 in a dose-dependent fashion, with mean stimulation indices of 7, 58, 119, and 112 at concentrations of 0.01, 1.0, 10, and 100 microM BeSO4 respectively. Cells not proliferate when incubated with ZnSO4 or NiSO4, or with canine distemper, leptospira, adenovirus 2, parvovirus, or parainfluenza antigens. Lymphocytes from normal vaccinated dogs proliferated markedly when cultured with these antigens. Cells from the cultured cell lines (91%) stained with Thy-1 (a pan T-cell marker) and 96% stained with DT2 (a helper T-cell marker). Furthermore, the Be-induced proliferative response was restricted by major histocompatibility (MHC) class II antigens. These data reinforce the premise that inhalation exposure of dogs to BeO produces lung lesions and MHC class II restricted immunologic responses mediated by Be-specific, helper T-Cells. These data further confirm the hypothesis that antigen localized to the lung results in the recruitment of T-cells to the lung, followed by localized antigen-specific, cell-mediated immune responses.

Effect of mercury on the immune response and mean intensity of Ascaris suum infection in guinea pigs

The subchronic effect of mercury on selected immunological parameters was studied in guinea pigs with experimental Ascaris suum infection. HgC1(2) given for 28 days reduced significantly T- and B-cell populations in the lymphoid organs and the phagocytic ability of peritoneal macrophages. The subsequent infection of HgC1(2)-intoxicated animals elevated the studied immunological parameters, but in comparison with infected non-intoxicated guinea pigs they remained significantly suppressed. The mercury compound in infection stressed animals caused a slight alteration of the complement CH50 and AH50 activity. The specific circulating antibody level in infected and HgC1(2) treated animals rose a little by day 12 p.i. and then again decreased significantly, compared with untreated guinea pigs. The mean intensity of infection with migrating Ascaris larvae in HgC1(2)-treated animals increased by 15%, compared with controls.

Effects of inorganic arsenicals on DNA synthesis in unsensitized human blood lymphocytes in vitro

Effects of inorganic arsenicals on DNA synthesis in unsensitized human blood lymphocytes were biphasic: The chemicals at very low concentrations enhanced DNA synthesis, whereas higher concentrations inhibited DNA synthesis. The concentrations of arsenicals at which the maximum stimulating effect was found were 1 x 10(-5) M, 1 x 10(-6) or 2 x 10(-6) M, and 0.8 x 10(-6) or 1 x 10(-6) M for sodium arsenite exposure of 1 h, 3 d, and 6 d, respectively; for sodium arsenate, 1 x 10(-5) M, 1 x 10(-5) M, and 2 x 10(-6) or 5 x 10(-6) M, respectively. Arsenicals must be present for the entire 6-d culture period to produce maximum stimulation of DNA synthesis in human lymphocytes. The longer exposure of the lymphocytes to arsenicals, the lower the concentrations of arsenicals at which the maximum stimulating effect on DNA synthesis was found. Stimulating effect of trivalent arsenic (sodium arsenite) on DNA synthesis was stronger than pentavalent arsenic (sodium arsenate), and the stronger the effect of trivalent arsenic than pentavalent, the longer exposure of the cells to the chemicals. Both sodium arsenite and sodium arsenate stimulated DNA synthesis in human lymphocytes to a lower degree than phytohemagglutinin (PHA).

Protecting effects of vasoactive intestinal polypeptide on lymphocytes against metal toxicity

The hormonal neuropeptides calcitonin gene-related peptide (CGRP), cholecystokinin (CCK), neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP), were investigated for a potential protective effect on thymocytes after a toxic dose of nickel sulfate, giving an inhibition of DNA synthesis. There was a statistically significant increase in the synthesis of DNA from the level caused by nickel sulfate, with VIP, 10(-4)-10(-5) mol/l, while the slightly stimulating effects obtained with CGRP, CCK and NPY, were statistically non-significant. This indicates that VIP, at least as pharmacological concentrations, might have protective effects on lymphocytes against metal toxicity.

Mercuric chloride inhibition of leucocyte migration

The effects of mercuric chloride, at different concentrations, were tested on polymorphonuclear and mononuclear leucocyte migration by using the sealed capillary migration technique, and these effects were compared to influence on cell number and dye exclusion. A migration inhibition was obtained at 1.1 x 10(-5) M when tested on polymorphonuclear cells, while a concentration of 6.6 x 10(-5) inhibited the migration of mononuclear cells. Polymorphonuclear cells seemed to be more sensitive (were inhibited at a lower dose) to mercuric chloride as regards migration compared to cell number and dye exclusion, while mononuclear cells showed migration inhibition at about the same dose range as that which had effect on dye exclusion and cell number.

Zinc effects on nickel dermatitis in the guinea pig

Prevention of NiSO4 induced allergic contact dermatitis (ACD) using ZnSO4 in drinking water was studied in a guinea pig model. Without ZnSO4 interventions, nickel (Ni)-exposure resulted in significantly higher (p less than 0.05) stimulation indices (SIs) as compared to non-exposed controls, using NiSO4 as an allergen in the lymphocyte transformation test (LTT). Oral intake of ZnSO4 at both 250 micrograms/ml double-distilled deionized water (DDD) and 500 micrograms/ml DDD resulted in lower SIs than those of control guinea pigs drinking only DDD; the 250 micrograms/ml group had significantly lower SIs (p = 0.025) than controls. There was no significant correlation between intradermal test responses and the SI values of individual guinea pigs exposed to NiSO4. Mean zinc (Zn) concentrations in skin and in whole blood were not statistically different between the NiSO4 exposed control and Zn supplemented groups, nor between Ni-sensitive and non-sensitive animals within groups. The rôle of Zn homeostasis, rôle of the Langerhans cell, effect of Zn supplementation on Ni ACD in other species, and possible blocking effects of other metals should be investigated in future studies.