This might be of big interest for many, found on NATURE Immunology:

The gut mucosa is the largest and most dynamic immunological environment of the body. It's often the first point of pathogen exposure and many microbes use it as a beachhead into the rest of the body. The gut immune system therefore needs to be ready to respond to pathogens but at the same time it is constantly exposed to innocuous environmental antigens, food particles and commensal microflora which need to be tolerated. Misdirected immune responses to harmless antigens are the underlying cause of food allergies and debilitating conditions such as inflammatory bowel disease. This animation introduces the key cells and molecular players involved in gut immunohomeostasis and disease.