from II - Dendritic cells and innate immune responses to bacteria
Published online by Cambridge University Press: 12 August 2009
INTRODUCTION
Pathogenic bacteria have evolved several strategies to gain access across epithelial surfaces particularly those lining the mucosae. After their epithelial transcytosis bacteria find a first line of immune defense represented by professional phagocytes, including macrophages and dendritic cells. These cells are particularly apt at bacterial uptake, killing and processing for the initiation/maintenance of adaptive immune responses. Furthermore, intracellular bacteria can induce by epithelial cells the release of inflammatory mediators and cytokines that will recruit other immune cells, particularly neutrophils. Dendritic cells are not simply passive players waiting for possible invaders, they can actively participate to bacterial sampling by intercalating between epithelial cells. This mechanism is not restricted to pathogenic bacteria. Since gut dendritic cells have been thoroughly studied, in this chapter we will focus on dendritic cells located in the intestinal mucosa and on their role in the uptake and handling of luminal bacteria.
THE ANATOMY OF THE INTESTINAL MUCOSAL EPITHELIUM AND THE GUT ASSOCIATED LYMPHOID TISSUE (GALT)
The intestinal epithelium is the first line of defense toward dangerous microorganisms. It opposes a physical, electric and chemical barrier against luminal bacteria. The permeability of the barrier is regulated by the presence of both tight junctions (TJ) between epithelial cells (ECs) and a negatively charged mucous glycocalix. TJ seal adjacent ECs to one another and regulate solute and ion flux between cells. The glycocalix sets the size of macromolecules that can reach the apical membrane of ECs and opposes an electric barrier to bacteria.
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