Graduation Year

2006

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Molecular Medicine

Major Professor

Thomas W. Klein, Ph.D.

Keywords

THC, DCs, Th, Legionella, Infection, Immunity

Abstract

Cannabinoids suppress Th1 immunity in a variety of models including infection with the intracellular pathogen Legionella pneumophila (Lp). To examine the cellular mechanism of this effect, mouse bone marrow-derived dendritic cells (DCs) were studied following infection and drug treatment. DCs produced high levels of IL-12p40 following Lp infection. THC suppressed this cytokine response in a concentration-dependent manner and the endocannabinoids 2-arachidonoyolglycerol and virodhamine less potently suppressed cytokine production. DCs expressed mRNA for cannabinoid receptor 1 (CB1), CB2, and transient receptor potential vanilloid type 1 (TRPV1); furthermore, inhibition of Gi signaling by adding pertussis toxin completely attenuated the suppression induced by low concentrations of THC but not at high concentrations.

In addition, the THC suppression was partially attenuated in DC cultures from CB1 and CB2 knockout mice and in cultures from normal mice co-treated with THC and cannabinoid receptor antagonists. Cytokine suppression was not attenuated by pretreatment with the TRPV1 antagonist capsazepine, suggesting that Gi signaling and cannabinoid receptors, but not TRPV1, are involved in THC-induced suppression of DC potential to polarize the development of naïve T cells to be Th1 cells. Besides IL-12, THC suppressed other DC polarizing characteristics such as the expression of MHC class II and co-stimulatory molecules CD86 and CD40, as well as the Notch ligand Delta 4. However, THC treatment did not affect other DC functions such as intracellular killing of Lp and Lp-induced apoptosis.

Testing the capacity of THC to suppress DC polarizing function with T cells showed that DCs infected in vitro with Lp were able to immunize mice when injected prior to a lethal Lp infection; however, the immunization potential along with Th1 cytokine production was attenuated by THC treatment of the cells at the time of in vitro infection. In addition, THC-treated and Lp-infected DCs poorly stimulated primed splenic CD4 T cells in culture to produce IFN-gamma (IFN-y); however, this stimulating deficiency was reversed by adding recombinant IL-12p40 protein to the cultures. In conclusion, the data suggest that THC inhibits Th1 polarization by targeting essential DC functions such as IL-12p40 secretion and the maturation and expression of co-stimulatory and polarizing molecules.

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