Mercury induces inflammatory mediator release from human mast cells

Abstract

Background: Mercury is known to be neurotoxic, but its effects on the immune system are less well known. Mast cells are involved in allergic reactions, but also in innate and acquired immunity, as well as in inflammation. Many patients with Autism Spectrum Disorders (ASD) have "allergic" symptoms; moreover, the prevalence of ASD in patients with mastocytosis, characterized by numerous hyperactive mast cells in most tissues, is 10-fold higher than the general population suggesting mast cell involvement. We, therefore, investigated the effect of mercuric chloride (HgCl2) on human mast cell activation.

Methods: Human leukemic cultured LAD2 mast cells and normal human umbilical cord blood-derived cultured mast cells (hCBMCs) were stimulated by HgCl2 (0.1-10 microM) for either 10 min for beta-hexosaminidase release or 24 hr for measuring vascular endothelial growth factor (VEGF) and IL-6 release by ELISA.

Results: HgCl2 induced a 2-fold increase in beta-hexosaminidase release, and also significant VEGF release at 0.1 and 1 microM (311 +/- 32 pg/106 cells and 443 +/- 143 pg/106 cells, respectively) from LAD2 mast cells compared to control cells (227 +/- 17 pg/106 cells, n = 5, p < 0.05). Addition of HgCl2 (0.1 microM) to the proinflammatory neuropeptide substance P (SP, 0.1 microM) had synergestic action in inducing VEGF from LAD2 mast cells. HgCl2 also stimulated significant VEGF release (360 +/- 100 pg/106 cells at 1 microM, n = 5, p < 0.05) from hCBMCs compared to control cells (182 +/- 57 pg/106 cells), and IL-6 release (466 +/- 57 pg/106 cells at 0.1 microM) compared to untreated cells (13 +/- 25 pg/106 cells, n = 5, p < 0.05). Addition of HgCl2 (0.1 microM) to SP (5 microM) further increased IL-6 release.

Conclusions: HgCl2 stimulates VEGF and IL-6 release from human mast cells. This phenomenon could disrupt the blood-brain-barrier and permit brain inflammation. As a result, the findings of the present study provide a biological mechanism for how low levels of mercury may contribute to ASD pathogenesis.

Figure 1

Effects of HgCl₂ on (A) LAD2 mast cells and (B) hCBMCs viability assayed by supravital staining with Trypan blue. LAD2 mast cells and hCBMCs were incubated with HgCl₂ one hour or 24 hours at 37°C and the viability was assayed (n = 3).

Figure 2

Effects of HgCl₂ on (A) β-hexosaminidase and (B) VEGF release from LAD2 mast cells. LAD2 mast cells were incubated with HgCl₂ and/or SP as indicated for 10 min for β-hexosaminidase and 24 hours for VEGF release at 37°C. The cells were then centrifuged and the supernatant fluid was collected. VEGF release was assayed by ELISA, while β-hexosaminidase release was assayed spectrophotometrically (n = 5, *p < 0.05).

Figure 3

Effects of HgCl₂ on VEGF release from hCBMCs. Mast cells were incubated with HgCl₂ and/or SP as indicated for 24 hours at 37°C. The cells were then centrifuged and the supernatant fluid was collected. VEGF (A) and IL-6 (B) release from hCBMCs was assayed by ELISA (n = 5, *p < 0.05).