Graduation Year


Document Type




Degree Granting Department

Molecular Medicine

Major Professor

Thomas W. Klein, Ph.D.


Dendritic cells, EGCG, TNFa, Toll-like Receptors, MHC, CD86, CD40, IL-12


Dendritic cells (DCs) are a migratory group of bone-marrow-derived leukocytes specialized for uptake, transport, processing and presentation of antigens to T cells. Exposure of DCs to bacterial pathogens can induce DC maturation characterized by cytokine production, up-regulation of co-stimulatory molecules and an increased ability to activate T cells. DCs have the ability to restrict growth of L. pneumophila (Lp), an intracellular Gram-negative bacillus that causes a severe form of pneumonia known as Legionnaires' disease, in murine ER-derived organelles (121) but replicate in human DCs (145). Even in human cells, however, lysis of the DCs does not occur for at least 24 hours which may allow DCs time to participate in the transition from innate to adaptive immunity (145).

The primary polyphenol in green tea extract is the catechin (-)-epigallocatechin-3-gallate (EGCG) which accounts for most of the numerous reported biological effects of green tea catechins, including anti-bacterial, anti-tumor, and neuroprotective effects. Primary murine bone marrow derived DCs from BALB/c mice were treated in vitro with Lp, or stimulated for comparison with Escherichia coli lipopolysaccharide (LPS). CD11c, considered an important marker of mouse DCs, and surface expression of co-stimulatory molecules CD40, CD80, CD86, as well as class I/ II MHC molecules was determined by flow cytometry. Treatment of the cells with EGCG inhibited the microbial antigen induced up-regulation of CD11c, CD40, CD80, CD86 and MHC I/ II molecules. EGCG also inhibited, in a dose dependent manner, induced production of the Th1 helper cell activating cytokine, IL-12, and the chemokines RANTES, MIP1a, and MCP-1. However, EGCG upregulated TNFa production.

In addition, EGCG inhibited both Lp and LPS induced expression of both TLR2 and TLR4 as well as LPS-induced NF-kB activation; all of which are important mediators of DC maturation. The modulation of phenotype and function of DCs by EGCG has implications for host interaction with microbial pathogens like Lp, which involve TLR interaction.