The Toxicologist - Society of Toxicology

IDO2. Similar effect by TCDD and LPS were found in inflammatory bone marrow
derived DC (BMDC). These data indicate that the cross-talk between AhR and
NF-κB is not limited to chemokines and cytokines but also affects significantly the
expression of surface markers critical for the differentiation and function of DC.
Data also show that AhR activation may drastically change the regular NF-κB-mediated
inflammatory response in a gene target dependent manner. For instance the
usually transient effect of LPS can be significantly increased and prolonged through
the activation of AhR.
1131 AH RECEPTOR ACTIVATION GENERATES REGULATORY
DENDRITIC CELLS CAPABLE OF INDUCING CD4+
CD25+ FOXP3+ REGULATORY T CELLS.
T. Simones, J. Bankoti and D. M. Shepherd. Center for Environmental Health
Sciences, University of Montana, Missoula, MT.
The Aryl hydrocarbon Receptor (AhR) mediates the toxic effects of various environmental
and dietary compounds and has recently been shown to contribute to
the generation of regulatory T cells (Tregs). However, the mechanisms underlying
Treg induction and immunomodulation following AhR activation remain to be defined.
Within the immune system, dendritic cells (DCs) express high levels of the
AhR and are sensitive to AhR activation. We hypothesized that AhR activation in
DCs leads to the generation of regulatory DCs and subsequent Treg induction. To
test this hypothesis, murine GM-CSF bone marrow-derived DCs (BMDCs) were
generated in the presence of TCDD or a vehicle control. AhR activation significantly
increased the expression of the regulatory genes, TGFβ3 and indoleamine
2,3-dioxygenase-1 and -2 (IDO1, IDO2) but not IL-27, OX40L or Aldh1a2 in unstimulated
BMDCs. Additionally, TGFβ1, TGFβ2, IDO1 and IDO2 expression
increased, while IL-27, OX40L and Aldh1a2 levels remained unchanged in LPSstimulated
AhR-activated BMDCs. Under antigen-specific conditions, AhR-activated
BMDCs generated an increased frequency of CD4+ CD25+ FoxP3+ Tregs
after three days in culture with media alone or IL-2/TGFβ supplemented media,
thereby demonstrating the functional capacity of AhR-induced regulatory DCs. In
the absence of antigen, TCDD-treated regulatory BMDCs led to a sustained maintenance
of Tregs. Conversely, production of effector T cell cytokines including IL-
2, IFN-γ and IL-10 was inhibited in these cultures. Overall, AhR activation induces
regulatory DCs capable of directly inducing CD4+ CD25+ FoxP3+ Tregs in vitro.
Studies are ongoing to determine the specific mechanisms (i.e. cell contact, TGFβ
and/or IDO dependency) of Treg induction by AhR-activated regulatory DCs. This
novel research significantly advances our understanding of AhR-induced immunomodulation
and provides a foundation for the generation of AhR-targeted,
antigen-specific therapeutics.
1132 ALL AHR LIGANDS ARE NOT CREATED EQUAL: THE
DURATION OF AHR ACTIVATION IS A KEY
PARAMETER IN MODULATING THE IMMUNE
RESPONSE TO INFLUENZA VIRUS INFECTION.
J. Head 1 and B. Lawrence 1, 2 . 1 Environmental Medicine, University of Rochester,
Rochester, NY and 2 Microbiology and Immunology, University of Rochester,
Rochester, NY.
It is apparent that the aryl hydrocarbon receptor (AhR) plays a role in a variety of
immunological pathways via multiple targets. While many studies have traditionally
utilized 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to activate the receptor,
other AhR ligands have also been shown to affect various immune endpoints.
Interestingly, activation of the AhR can have either host-beneficial or detrimental
consequences depending on the type of AhR ligand used. One significant difference
between many AhR agonists is the duration of time in which they activate the
receptor. Our laboratory set out to examine whether the duration of AhR activation
is responsible for differentially impacting AhR-sensitive immunological endpoints
using two different AhR agonists: TCDD and the tryptophan degradation product
6-formylindolo[3,2-b]carbazole (FICZ). Although FICZ has a similar affinity for
the AhR as TCDD, it has a much shorter half-life in vivo. We used FICZ to examine
the contribution of duration of AhR activation on the immune response to influenza
virus infection, a system with well-characterized, AhR-induced changes in
mice treated with TCDD. We show here that transient AhR activation caused by a
single dose of FICZ did not have the same impact on the immune response to influenza
virus as a single dose of TCDD. Interestingly, even when AhR activation
was prolonged during infection using constant delivery of FICZ with mini-osmotic
pumps, the immunomodulatory changes observed with a single dose of TCDD
were not replicated. These findings suggest that although duration of activation
242 SOT 2011 ANNUAL MEETING
may contribute to the AhR’s effects on immune function, it is likely that additional
ligand-specific parameters also play an integral part in dictating how the AhR modulates
immune function. Determining these specific parameters is key to fully understanding
the physiological role the AhR plays as well as detailing the varied molecular
mechanisms by which the AhR perturbs immune pathways.
1133 TCDD AMELIORATES COLITIS IN MICE BY
INDUCTION OF REGULATORY T CELLS (TREGS) VIA
AHR ACTIVATION.
N. P. Singh 1 , U. Singh 1 , B. Singh 2 , L. Hofseth 3 , M. Nagarkatti 1 and P.
Nagarkatti 1 . 1 Pathology, Microbiology, and Immunology, University of South
Carolina School of Medicine, Columbia, SC, 2 Primate Research Center, Emory
University, Atlanta, GA and 3 South Carolina College of Pharmacy, University of
South Carolina, Columbia, SC.
TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is a potent environmental pollutant
that activates aryl hydrocarbon receptor (AhR), which in turn regulates T cell differentiation.
Inflammatory bowel diseases (IBD), such as ulcerative colitis (UC),
are associated with chronic inflammation of the intestinal tract. In the current
study, we investigated the effect of AhR activation on Dextran Sodium Sulphate
(DSS)-induced colitis in mice. Colitis was generated in mice (C57BL/6) administering
3% DSS in water by ad libitum. The mice were treated with vehicle (corn
oil) or TCDD in corn oil (25 micro gram/kg body weight) and development of
clinical symptoms was followed for two weeks. AhR activation suppressed the clinical
score of colitis as well as various pathological markers, including the loss of
body weight. AhR activation during colitis also caused decreased levels of inflammatory
cytokines (IL-6 and TNF-alpha) and chemokines (MCP-1, KC, and
Eotaxin) in the sera. Also, percentage of CXCR3+ T cells in lamina propria (LP) decreased
while the percentage of myeloid derived suppressor cells (MDSCs) increased
both in spleen and LP. We also noted induction of both systemic and mucosal
FoxP3+ regulatory T cells (Tregs). AhR activation in vitro also led to increased
differentiation of Tregs. Furthermore, antigen-specific activated T cells also showed
significant differentiation into Tregs in the presence of TCDD. Together, these results
suggested that TCDD via AhR activation in vivo decreases CXCR3+ T cells,
induces FoxP3+Tregs, and increases mucosal MDSC expression which in turn may
inhibit inflammatory Th1 cells and suppress the intestinal inflammation. Together,
the current study demonstrates that AhR activation may serve as a novel therapeutic
target for the treatment of chronic inflammatory bowel disease (Supported in
part by NIH grants R01ES09098, P01AT003961, R01ES019313).
1134 ARYL HYDROCARBON RECEPTOR ACTIVATION
SUPPRESSES INTESTINAL INFLAMMATION.
J. M. Benson and D. M. Shepherd. Biomedical and Pharmaceutical Sciences,
University of Montana, Missoula, MT.
Exaggerated T cell-mediated immune responses to commensal bacteria arise from
both genetic and environmental factors and ultimately lead to Crohn’s disease, a
chronic inflammatory disease of the gastrointestinal tract. 2,3,7,8-tetrachlorodibenzo-p-dioxin
(TCDD), the potent ligand of the aryl hydrocarbon receptor
(AhR), has been shown to generate regulatory T cells (Tregs) that suppress immune
responses. We hypothesized that AhR activation reduces disease severity and
inflammation in the gut. The 2,4,6-trinitrobenzenesulfonic acid (TNBS) model of
colitis was used to test this hypothesis. Mice were gavaged with TCDD prior to colitis
induction with TNBS, which included peripheral sensitization before enema
administration to elicit efficient effector T cell responses. The extent of colonic inflammation
was determined by assessing severity of clinical symptoms, tissue damage,
and inflammatory cell infiltration in the colon and surrounding lymph tissue.
TCDD-treated mice recovered more rapidly, experienced less colonic inflammation,
and decreased pro-inflammatory mediator production compared to vehicletreated
mice. Increased frequencies of Foxp3+ Tregs were also observed in the gut of
TNBS-exposed Foxp3egfp mice. In these mice, the CD103+ regulatory dendritic
cell (DC) population was also increased. Regulatory genes, such as idoleamine-2,3,dioxygenase,
were elevated while levels of pro-inflammatory genes, such as IL-17,
were reduced in the colon. Furthermore, in vitro studies conducted on intestinal
epithelial cells and bone marrow-derived DCs demonstrated that TCDD suppresses
LPS-induced immune responses suggesting that these cells may be critical to
suppressing gut inflammation in vivo. Collectively, these results indicate that AhR
activation by TCDD generates a regulatory environment in the gut that decreases
inflammation in a murine model of colitis. This research was supported by the
grants P20RR017670 (NCRR), P20RR015583(NCRR), ESO13784(NIH), and
F31AT005557(NCCAM).