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Chapter 78 : Legionella Infection of Bone Marrow Dendritic Cells Induces Modulation by Catechins
In this chapter, primary murine (BALB/c) bone marrow-derived dendritic cells (DCs), a phagocytic monocytic cell essential for innate immunity to intracellular microorganisms like Legionella, were infected in vitro with the bacteria. In related studies, it was recently reported that epigallocatechin gallate (EGCG) inhibited interleukin-12 (IL-12) production by lipopolysaccaride-treated DCs. EGCG has also been reported to decrease LPS-induced TNF- α production in a dose-dependent manner in the murine macrophage cell line RAW 264.7 and to similarly inhibit LPS-induced TNF- α production in elicited BALB/c mouse peritoneal macrophages, effects attributed in part through blocking NF- κ activation. In cultured human peripheral blood mononuclear cells, EGCG was also reported to stimulate production of TNF- α. All of these reports suggest that cytokine modulatory effects of catechins have varied effects depending upon the immune cell subpopulation studied. However, it is likely that concentrations of catechins at tissue sites are higher than in the blood. The short half-life of catechins in vivo might be overcome, however, by repeated administration, which is feasible given the reported low toxicity of this catechin and given that even high doses, such as 1,600 mg, are well tolerated by human subjects. In conclusion, authors present evidence that EGCG can inhibit IL-12 production while enhancing TNF- α production in bone marrow-derived DCs infected with Legionella.