Involvement of Dendritic Cells in the Pathogenesis of Inflammatory Bowel Disease
Francisco Leon, Lesley E. Smythies, Phillip D. Smith and Brian L. Kelsall
Dendritic cells (DC) are antigen-presenting cells (APCs) with unique properties that allow them to efficiently process antigens and activate naïve T cells. Mucosal DCs have a particular capacity to induce regulatory T cell differentiation in the steady state, but they are also potent inducers of effector T cell responses, indeed constituting the main APC in the gut. In addition, mucosal DCs may contribute to innate defense by the production of cytokines following direct exposure to pathogens. DCs may also play a role in the maintenance of secondary T cell responses within inflamed mucosa, such as in inflammatory bowel disease (IBD). In contrast, resident intestinal macrophages do not appear to act as APC, or produce inflammatory cytokines, but are specialized in mucosal defense against pathogens by their ability to scavenge, phagocytose, and kill microorganisms. However, during active mucosal inflammation like IBD, fully inflammatory monocytes are recruited from the blood, which can contribute to tissue injury and damage. The present chapter will focus on the role of mucosal APC, mainly dendritic cells in the pathogenesis of IBD. A summary of current concepts of DC biology will be followed by a review of the growing knowledge regarding DC and macrophages in IBD.