The Toxicologist - Society of Toxicology

numbers of IFN-γ producing cells were observed when EL-4 gp120
clones were used
as target cells compared to parental EL-4 cells, and the response was modulated by
Δ 9 -THC when introduced in the elicitation phase. Collectively, these results suggest
that DC2.4gp120 clones are capable of eliciting a gp120-specific CTL response,
and Δ 9 -THC can modulate the elicitation of CTL. Supported by NIH
DA07908
1529 TARGETING CANNABINOID RECEPTORS AS A NOVEL
TREATMENT MODALITY AGAINST LIVER INJURY
AND CHRONIC INFLAMMATION INDUCED BY
CHEMICAL TOXICANTS.
S. Kanada, M. Nagarkatti and P. Nagarkatti. Department of Pathology,
Microbiology, and Immunology, University of South Carolina School of Medicine,
Columbia, SC.
Liver diseases are one of the main causes of mortality in the world. Especially,
chronic hepatitis leading to the development of liver cirrhosis or liver cancer is a severe
clinical problem. There are several conditions known to cause chronic hepatitis
including viral infections, intake of toxin, or autoimmunity. Previous studies
from our laboratory and elsewhere have shown that natural cannabinoids such as
Δ 9 -tetrahydrocannabinol (THC) exhibit immunosuppressive and anti-inflammatory
properties. In this study, we investigated the effect of THC on chronic hepatitis
caused by repeated toxic insult. For the induction of chronic hepatitis, ConA or
carbon tetrachloride (CCl 4
) was administered i.v. or i.p., respectively, to the
C57BL/6 mice once a week for 6 weeks. THC was injected i.p. 30 minutes after
toxic insult. Blood serum was collected 24 hours after every weekly injection of
ConA or CCl 4
to measure the serum aminotransferase (ALT and AST) levels. One
week after sixth injection of ConA or CCl 4
, livers were collected for the histological
assessment and hepatic mononuclear cells were harvested from livers for flow cytometric
analysis to characterize the nature of hepatic inflammatory cells. Fibrosis related
genes expression in injured liver was investigated by real time PCR. The results
showed that blood serum level of both AST and ALT were significantly
suppressed in acute phase in the THC-treated group when compared to the vehicle
control group. In the chronic phase, the mRNA expression of liver fibrosis marker
FGF2 and α-SMA were significantly suppressed by THC treatment. Flow cytometric
analysis suggested that THC treatment decreased the inflammatory cell accumulation
in the liver. These results demonstrate that THC can suppress chronic
hepatitis and indicate that cannabinoids or cannabinoid receptors can be the new
therapeutic targets preventing immune cell-mediated liver injury (Supported in
part by NIH grants R01ES09098, R01AI058300, R01DA016545,
P01AT003961).
1530 2, 3, 7, 8-TETRACHLORODIBENZO-P-DIOXIN (TCDD)
SUPPRESSES LPS-ACTIVATED BINARY SWITCHING OF
B CELLS TO PLASMA CELLS.
D. E. Kline 1 , Q. Zhang 2 , S. Bhattacharya 2 , M. E. Andersen 2 , R. B. Conolly 3 ,
R. B. Crawford 4 and N. E. Kaminski 1, 4 . 1 Center for Integrative Toxicology,
Michigan State University, East Lansing, MI, 2 Hamner Institutes for Health Sciences,
Research Triangle Park, NC, 3 National Center for Computational Toxicology, U.S.
Environmental Protection Agency, Research Triangle Park, NC and 4 Pharmacology &
Toxicology, Michigan State University, East Lansing, MI.
Impairment of B cell differentiation by TCDD is well established. Based on the
gene regulatory network that underlies B cell differentiation, we hypothesized that
a transcriptional bistable switch underlies B cell activation and TCDD disrupts the
switching process. A computational model of the network shows that this switch
can generate the two mutually exclusive transcriptional profiles corresponding to
the B cell and plasma cell states. Using flow cytometry lipopolysaccharide (LPS)-activation
yields two distinct cell subsets (a bimodal distribution), supporting the idea
of an underlying biological switch. The cells exhibited either a resting B cell-like
phenotype with low intracellular IgM (IgM low ), or a plasma-cell like phenotype
with high intracellular IgM (IgM high ). The average IgM levels in these two populations
differed by two orders of magnitude. Fewer than 5% of total B cells exhibited
intermediate intracellular IgM. This nearly binary IgM response to LPS was both
concentration- and time-dependent, with maximal number of IgM high cells observed
at ≥ 5μg/ml LPS at 72 h post activation. Suppression by TCDD of the IgM
response in LPS-activated B cells occurred through a reduction in the total number
of IgM high cells rather than a reduction in intracellular IgM levels. The reduction in
the number of LPS-stimulated IgM high cells was TCDD concentration-dependent
and was up to 50% of the control. In summary, we confirmed that conversion from
a naïve B cell phenotype into a plasma cell phenotype is a discrete, switch-like
process, and that by disrupting this process, TCDD suppresses the probability with
which B cells differentiate to plasma cells. (Supported by NIH P42E504911 and
R01 ES02520)
1531 INSIGHT INTO AHR-MEDIATED INCREASES IN
NEUTROPHILIA DURING INFECTION: INOS AS A
POTENTIALLY NEW AHR TARGET GENE.
J. Head 1, 3 and B. Lawrence 1, 2, 3 . 1 Environmental Medicine, University of Rochester,
Rochester, NY, 2 Microbiology & Immunology, University of Rochester, Rochester, NY
and 3 Toxicology Training Program, University of Rochester, Rochester, NY.
Respiratory viral infections, such as influenza virus, remain one of the leading
causes of morbidity worldwide. The innate immune response to influenza virus infection
is critical, and perturbation of this response can have significant consequences.
Many factors exist which can affect immune responses to infections, including
exposure to environmental contaminants. Our laboratory has shown that
activation of the aryl hydrocarbon receptor (AhR) by the persistent environmental
contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) enhances the recruitment
of neutrophils to the lungs of influenza virus-infected mice. Interestingly, we
have found that AhR activation does not affect the known mechanisms of neutrophil
recruitment, suggesting that an as-of-yet undiscovered mechanism is responsible
for increased neutrophilia. Separate studies in our laboratory suggest that
AhR-mediated increases in inducible nitric oxide synthase (iNOS) during infection
may be this link. We show here that in iNOS-deficient mice infected with influenza
virus, AhR activation does not result in enhanced neutrophil recruitment to the
lung. This suggests that not only are these AhR-mediated events related, but that
increased iNOS expression could be a novel mechanism underlying exacerbated
neutrophil migration the lung. Additionally, we show here that depleting neutrophils
during viral infection does not abrogate AhR-mediated increases in iNOS
expression, demonstrating that neutrophil recruitment is downstream of elevated
iNOS. These studies implicate iNOS as both a novel AhR target gene and a potential
regulator of inflammation in the lung. Moreover, these findings suggest the
AhR plays a unique role as a fulcrum, regulating the balance between sufficient and
excessive inflammation during viral infection.
1532 ARYL HYDROCARBON RECEPTOR MODULATES
DENDRITIC CELL FUNCTION DURING RESPIRATORY
VIRAL INFECTION.
G. Jin, J. L. Head, A. J. Moore and B. Lawrence. Environmental Medicine,
University of Rochester, Rochester, NY.
The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that
plays a critical role in the development and function of the immune system.
Activation of the AhR by high-affinity ligands such as the pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin
(TCDD) has been shown to suppress immune responses
and impair host resistance to infection. However, the mechanisms by which AhR
ligands modulate immune function remain poorly understood. The overall goal of
our present study is to better understand how AhR activation modulates dendritic
cell (DC) function in a physiological setting. DCs are unique antigen-presenting
cells that capture antigen in the periphery and migrate to draining lymph nodes,
where they play a key role in the priming of antigen-specific naïve T cells. We have
previously reported that AhR activation reduces the proliferation and differentiation
of influenza virus-specific CD8+ T cells through an indirect mechanism. In
this study, we examined how AhR activation alters DC phenotype in the lung, and
DC trafficking to and function in the mediastinal lymph nodes (MLN) in influenza
virus-infected mice. We show that AhR activation by TCDD alters the phenotypic
profile of DCs in the lung and impairs lung DC migration to MLN.
Moreover, AhR activation reduces the ability of DCs to activate naïve CD8+ T
cells. Using novel AhR mutant mice, in which the AhR protein lacks its DNA binding
domain, we show that the suppressive effects of TCDD require that the activated
AhR complex bind to DNA. Our results indicate that AhR activation by
TCDD reduces DC function, and suggest that environmental factors may contribute
to differential susceptibilities and responses to respiratory viral infections.
(Supported by NIH Grants K02-ES012409 and R01-ES013958 to BPL, EHSC
P30-ES01247, and T32-ES07026 to JLH).
1533 CHARACTERIZATION OF 2, 3, 7, 8-
TETRACHLORODIBENZO-P-DIOXIN EFFECT ON THE
CD40L-INDUCED IGM ANTIBODY RESPONSES IN
PRIMARY MOUSE AND HUMAN B LYMPHOCYTES.
H. Lu 1, 2 , R. B. Crawford 2 , B. F. Kaplan 1, 2 and N. E. Kaminski 1, 2 . 1 Center for
Integrative Toxicology, Michigan State University, East Lansing, MI and
2
Pharmacology and Toxicology, Michigan State University, East Lansing, MI.
Previous studies using rodent models established the B cell as a direct cellular target
of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in suppression of the primary antibody
response, a sensitive endpoint of TCDD-mediated immune dysfunction.
However, data concerning TCDD effects on human B cells remain limited, preventing
a comprehensive evaluation of human risk posed by TCDD exposure on
SOT 2010 ANNUAL MEETING 325