ABSTRACT

The gastrointestinal (GI) tract is a highly evolved anatomical and functional structure that encounters a vast array of antigens, food particles and microorganisms on a daily basis. The intestine has to perform the daunting function of absorbing nutrients essential for human life, while keeping us protected from luminal antigens, particles and pathogens. The adult human intestine is home to an enormous number of microorganisms that is extraordinarily complex, collectively known as intestinal microbiota. Understanding our relationship with commensal flora has gained more depth in recent years; new data demonstrate that gastro-intestinal microbiota plays an important role in defense against pathogenic organisms. Since it is only a thin monolayer of epithelial cells that separates us from the intestinal flora and pathogens, the intestine has acquired specialized cells organized in complex structures that have to perform the function of defending us against pathogens by initiating innate and adaptive immune responses. By constant signaling and communication, intestinal immune cells are organized in a vast and complex network that contributes to maintenance of homeostasis.