Immunomodulation By Subchronic Low Dose 2,3,7,8-Tetrachlorodibenzo-p-Dioxin in Experimental Autoimmune Encephalomyelitis in the Absence of Pertussis Toxin

Multiple sclerosis (MS) is an autoimmune neurodegenerative disorder, characterized by demyelination of neurons in the central nervous system. To investigate the pathogenicity of various T cell types in MS, especially IFN-gamma- or IL-17-producing CD4(+) cells (T(H)1 or T(H)17 cells, respectively), the mouse model, experimental autoimmune encephalomyelitis (EAE), is commonly used. One method by which EAE is induced is immunization with myelin oligodendrocyte glycoprotein (MOG) peptide (MOG(35-55)) followed by subsequent injections of pertussis toxin (PTX) as an adjuvant. We have an interest in the mechanisms by which EAE occurs in the absence of PTX because it induces a milder disease state more consistent with autoimmune disease onset and PTX inactivates G(i/o) protein-coupled receptors, many of which contribute to immune homeostasis. Another receptor that plays a role in immune homeostasis is the aryl hydrocarbon receptor (AHR). In fact, the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been shown to attenuate EAE pathogenesis by affecting CD4(+) T and regulatory T (Treg) cells in an AHR-dependent manner. However, many of these studies have been conducted with an acute high dose TCDD. Thus, the goal of this work was to investigate the modulation of MOG-specific immune responses with subchronic low dose TCDD (0.1-1.0 mu g/kg/d for 12 days) in EAE without PTX. The results demonstrate that subchronic, low dose exposure of TCDD attenuates the immune responses in EAE development in the absence of PTX, which is due in part to suppression of MOG-specific IL-17A and IFN-gamma responses.