Effects of mercury and fluoride on human immune cells : elucidation of mechanisms

Abstract

Mercury, from dental amalgam, and fluoride, administered to prevent dental caries, have been argued to cause adverse health effects. The aims of this thesis have been to examine in what manner the fluoride and mercuric ions interact with human immune cells and, in the case of mercury, if it would be possible to monitor a tentative in vivo effect by in vitro assays.

Effects of NaF on the mitogen or antigen induced lymphocyte response were examined with respect to cytokine (IL-6 and IFN-[gamma]) and soluble IL-2 receptor release in an in vitro whole blood cell system. It was revealed that 0.6 mM NaF has the ability to increase both the mitogen- and the antigen-induced IFN-[gamma] release from blood lymphocytes. However, the concentration required for an effect was 10 - 50 times higher than the concentration reached in blood after dental treatment.

Ten healthy individuals, had all their amalgam fillings removed on one occasion to examine if an acute low dose of mercury would influence the immunocompetent cells. The B- and T-cells in blood; including the CD4+ and CD8+ subsets, the spontaneous lymphocyte proliferation in vitro as well as serum levels of the proinflammatory cytokine interleukin-6 were monitored for 48 hours after intervention. Plasma levels of C-reactive protein were followed for seven days. Despite a transient increase of mercury in blood and plasma during the first 48 hours after amalgam removal, no effect on the immunologic parameters was detected except for an increased level of serum IL-6, 7 hours after amalgam removal. However, the IL-6 levels were still within the normal range.

Mercuric chloride (HgCl2) has been proposed to be a mitogen for human blood lymphocytes in vitro. We found that HgCl2 (1 - 4 µg/ml) has the ability to preferentially stimulate CD4+ T-cells to blast transformation and DNA synthesis. The reaction, when monitored during days 2 - 6, was maximal at day 6 and the majority of lymphoblasts expressed the interleukin-2 receptor. CD8+ T-cells were not affected to the same extent. HgCl2 induced lymphocyte reactivity was dependent on CD14+ accessory cells. Furthermore, the activated CD4+ lymphoblasts were selectively TCRVb2+ (15-40 % of the blasts). If cells were pre-activated with HgCl2 for 5 days after which IL-2 in fresh medium was added, the TCRVb7+ subset was also stimulated to blast transformation. Thus, HgCl2 has the characteristics of being a superantigen.

Two different lymphocyte proliferation assays were used to evaluate if patients with oral contact lesions to amalgam have a higher in vitro lymphocyte reactivity to HgCl2 than controls. In addition, the release of interferon-[gamma] was measured in cell supernatants. The phenotypes of peripheral lymphocyte subsets, the frequency of circulating cells expressing the IL-2 receptor, spontaneous lymphocyte proliferation and serum levels of interleukin-6 were analyzed in patient and control samples. No differences were recorded in lymphocyte reactivity between patients and controls in any of the variables studied. Thus, there are at present no in vitro tests available that reveal a selective reactivity in patients with presumed mercury allergy.