Metal-specific lymphocyte reactivity is down-regulated after dental amalgam replacement


Metal-specific lymphocyte reactivity is down-regulated after dental metal replacement

Neuroendocrinology Letters 1999

Jenny Stejskal, Vera DM Stejskal


OBJECTIVES: This study was done to evaluate the results and clinical relevance of an optimized lymphocyte proliferation test, MELISA®, for metal-induced inflammation in patients with CFS-like symptoms. The treatment of patients consisted of the replacement of incompatible dental materials (RID) together with supportive anti-oxidant therapy.


513 patients were tested by MELISA® at the beginning of the study. Out of this group, 248 patients were available for follow-up MELISA® after RID.


In MELISA®, lymphocytes are isolated from the blood and cultivated with different metal salts in tissue culture medium containing 10% inactivated human AB+ serum or autologous serum. After 5 days, the presence of metal-reactive lymphocytes are measured by isotope labelling of newly formed DNA in growing lymphoblasts and evaluated by calculating the Stimulation Index. 


Nickel was the most common sensitizer, followed by inorganic mercury, thimerosal, lead, cadmium, palladium and gold. After RID treatment, a decrease of metal-specific lymphocyte responses in patients who reacted to metals at the beginning of the study could be observed. The cultivation of lymphocytes in autologous and homologous serum did not significantly affect the results. Simultaneous, the health status of patients improved as well.


Replacement of incompatible dental materials resulted in downregulation of metal-induced lymphocyte sensitivity in vitro, as well as in the improvement of health status of majority of patients with unspecific CFS-like symptoms.


Dental amalgam, which is composed of at least 50% metallic mercury together with silver, copper, tin, palladium and zinc, has been used by dentists to restore decayed teeth for over 150 years.

When amalgam interacts with saliva, it will slowly corrode [7, 8]. Dental amalgam fillings were thought to be safe in vivo based on the erroneous belief that mercury, once bound to other metals, became an inert compound. It is now firmly established that mercury is continuously released into the oral cavity and consequently inhaled, absorbed and ingested [18, 16].

With the help of radioactive 203Hg it has been shown that mercury is deposited in many organs, including the brain [13, 14, 11, 12, 10, 33]. Mercury and other heavy and transition metals, such as gold or silver, strongly bind to SH groups in autologous proteins and therefore have potential to elicit allergic and autoimmune reactions. 

Inorganic mercury and gold induce autoimmunity in genetically susceptible rats and mice, and susceptibility or resistance to autoimmunity is dependent on genetic haplotypes [3]. Metals may also induce allergy in genetically susceptible individuals [19, 20, 22]. Allergic reactions are mostly of type 4 (delayed-type hypersensitivity, such as contact dermatitis) but immediate-type reactions are sometimes also observed [2, 17]. Cell-mediated reactions operate in parts of the body different from those where metals are deposited [12, 28]. 

Metal-induced hypersensitivity in man is based upon the reaction of the allergen with the surface of memory T- lymphocytes previously sensitized to a specific allergen.

Upon contact with the allergen, memory cells become activated and produce lymphokines. The interaction of memory cells with the antigen forms the basis of the Lymphocyte Stimulation Test (LST), also called Lymphocyte Transformation Test (LTT). MELISA® (MEmory Lymphocyte Immuno Stimulation Assay) is an optimization of LST.

With MELISA®, it is possible to measure immunological sensitization induced by mercury, gold, palladium, and other metals included in dental amalgam and in other metal alloys [25, 26, 27]. Additional sources of metals are metal pigments such as titanium dioxide (TiO2, E171), a white colouring agent used e.g. in composites, dental cements, and different pharmaceuticals [27]. Phenylmercury has been used together with lead and arsenic in certain root fillings [6]. Thimerosal, an organic mercury preservative, was used in nose and eye drops, vaccines, and in cleaning solutions for soft contact lenses in the past and is still used as a preservative in certain vaccines. Nickel was also tested, as it is the most common sensitizer among the metals.

In this study we performed the MELISA® test on patients with health problems suspected to be related to amalgam and other dental metal alloys. Lymphocyte reactivity was studied prior to and after the replacement of biological incompatible dental restorations. In addition, lymphocytes were cultured in homologous or in autologous serum (patient’s own serum) in order to see if the latter might contain factors which might change the reactivity of lymphocytes. It was found that replacement of incompatible dental materials down-regulated metalspecific responses in sensitized individuals. 


A significant number of patients with CFS-like symptoms had metal-specific lymphocytes in the blood. Nickel was the most frequent sensitizer, followed by inorganic mercury, thimerosal, and other metals. The high prevalence of nickel hypersensitivity in some patients was due to wearing earrings and other jewellery which contained nickel. About two thirds of the patients studied were females [28].

Inorganic mercury is the second most common sensitizer which implies the role of mercury from dental amalgam as a possible causative agent for different health problems related to amalgam.

According to Svare [30] and WHO criteria [34], amalgam is the main source of inorganic mercury exposure in man. The main exposure paths for mercury from amalgam fillings are absorption by the lungs from intra-oral air; vapor absorbed by saliva or swallowed; amalgam particles which may be ingested, and membrane, olfactory, venous and neural path transfer of mercury absorbed by oral mucosa, gums, etc [1, 32, 4, 9]. The response of lymphocytes to thimerosal was very much expected since thimerosal was previously used in Sweden and worldwide as a preservative in vaccines, soft contact-lens fluids and immunoglobulin preparations.

Sensitization to gold, palladium, and titanium was also expected from the frequent use of different metal alloys in dental restorative materials. Sensitization to phenylmercury may be due to use of phenylmercury salts as preservatives in eye drops and cosmetics. Phenylmercury may induce allergic reactions [16]. In dentistry, phenylmercury has been used as a component of N2, a widely used root canal filling material [6]. Between 10–20% of the patients have been previously reported to respond to methylmercury [28], and this have been confirmed by our findings.

The main source of methylmercury is fish and Swedish fish meal is also used as a source of protein in feed for poultry and swine [24], in addition to fish, meat and eggs from animals fed on fish products are likely to contribute to the exposure to methylmercury in the general population.

After replacement of dental metals in patients, there was a general decrease in patients’ responses to metals in the follow-up MELISA® test. A significant decrease in positive responses to inorganic mercury in patients after amalgam replacement indicates that this lymphocyte reactivity is allergenic in nature. These results corroborate the data previously published [28]. 

Regarding methodology, MELISA® is one of the two few validated LTT tests [31], the other being beryllium- specific LTT used in US as a golden standard for the evaluation of beryllium allergy in occupationally exposed workers [23]. The use of patient’s own serum (autologous) has theoretically the advantage that it might better reflect the actual situation of accelerators and inhibitors of lymphocyte  metal reactivity in the individual patient compared with homologous serum.

During evaluation of the results, no significant differences have been noticed in lymphocytes reactivity regarding the use of homologous or autologous serum in the MELISA® test. In addition to the replacement of incompatible dental metals, the patients were informed about their existing metal sensitivity and avoided future exposure to metals as a precaution. The efficacy of a low nickel diet for the treatment of CFS has been published previously [21]. A similar reduction in metal exposure can be achieved by quitting smoking or avoiding cigarette smoke. It has been reported that cigarette smoke contains manganese, mercury, cadmium and lead [5]. In recent publications, the prognosis of improvement of multiple sclerosis and other autoimmune diseases following amalgam removal has been inversely correlated to the exposure to nickel and other metals from cigarette use [2]. Thus for patients who are genetically susceptible to metal pathology, the strict avoidance of metal exposure is strongly recommended.


The replacement of incompatible dental restorations in sensitized patients together with anti-oxidant supplementation resulted in the down-regulation of metalinduced lymphocyte responses in vitro. The reduced ability of lymphocytes to respond to metals in vitro after dental metal replacement might reflect the decrease of chronic inflammation in vivo. Thus, in vitro testing is not only improving diagnosis but is also useful for further monitoring of the outcome of the treatment.

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