REGULATORY ROLES FOR NATURAL KILLER T CELLS AND TOLL-LIKE RECEPTORS IN MERCURY-INDUCED AUTOIMMUNITY

Abstract

The development of autoimmune diseases is frequently linked to exposure to environmental factors such as chemicals, drugs or infections. In the experimental model of metal-induced autoimmunity, administration of subtoxic doses of mercury (a common environmental pollutant) to genetically susceptible mice induces an autoimmune syndrome with rapid anti-nucleolar antibody production and immune system activation. Regulatory components of the innate immune system such as NKT cells and TLRs can also modulate the autoimmune process. We examined the interplay among environmental chemicals and NKT cells in the regulation of autoimmunity. Additionally, we studied NKT and TLR ligands in a tolerance model where pre-administration of a low dose of mercury in the steady state renders animals tolerant to metal-induced autoimmunity. We also studied the effect of Sphingomonas capsulata, a bacterial strain that carries both NKT cell and TLR ligands, on metal-induced autoimmunity. Overall, NKT cell activation by synthetic ligands enhanced the manifestations of metal-induced autoimmunity. Exposure to S. capsulata exacerbated autoimmunity elicited by mercury. Although the synthetic NKT cell ligands that we used are reportedly similar in their ability to activate NKT cells, they displayed pronounced differences when co-injected with environmental agents or TLR ligands. Individual NKT ligands differed in their ability to prevent or break tolerance induced by low-dose mercury treatment. Likewise, different NKT ligands either dramatically potentiated or inhibited the ability of TLR9 agonistic oligonucleotides to disrupt tolerance to mercury. Our data suggest that these differences could be mediated by the modification of cytokine profiles and regulatory T cell numbers. The mechanisms by which a heavy metal with an elementary chemical structure induces autoimmunity are unknown. Herein we show that mercury administration results in release of endogenous ligands that activate TLR7, an innate immune receptor implicated in the development of systemic autoimmunity. Moreover, our results suggest that fine specificity of autoantibodies recognizing RNA-containing snoRNPs could be a consequence of TLR7 activation.