Microbiota and the immune system

Venue: Edificio Povo 1, via Sommarive nr. 5, Povo (Tn) - Room A105
 At 2:00 p.m.

• Maria Rescigno - Dendritic cell biology and immunotherapy Unit - European Institute of Oncology and University of Milan, Milan, Italy

The intestinal microbiota has several functions in our organism and is required for the breakdown of complex macromolecules ingested with the food. Hence, it has to be tolerated by our mucosal immune system but at the same time it has to be kept at bay. A complex immune system has developed tools to tolerate the microbiota and this is achieved primarily via the division of labour among immune cells and in particular antigen presenting cells. In the gut there are two major types of antigen presenting cells: dendritic cells and macrophages. In addition there is a subset of antigen presenting cells that shares characteristics of both macrophages and dendritic cells. Macrophages are ideally located to take up antigens and bacteria and to handle this material to dendritic cells via a gap junction mediated mechanism. Dendritic cells can then migrate into mesenteric lymph nodes for the induction of T regulatory cells that are required to induce oral tolerance towards food antigens. Hence, there is a division of labour between macrophages that take up antigens and dendritic cells which migrate out of the gut to establish oral tolerance. During infection or inflammation a new wave of antigen presenting cells is generated after recruitment of inflammatory monocytes. These allow the induction of immunity rather than tolerance. What happens however if bacteria can accidentally cross the first line of defense that is provided by the mucus layer and the epithelial cells? Then we have a second layer of protection that is mediated by a vascular barrier that resembles the blood brain barrier.