However, we are clearly able to absorb food antigens through our gut into our blood stream with no obvious ill effects. Some of us may be intolerant to certain food antigens such as lactose in milk or wheat gluten but for the most part foreign food molecules pass through our bodies unnoticed by our immune system. We don't understand the details but it would seem that the Peyers patches are involved in monitoring food antigens. The Peyers patches decide what are dangerous gut pathogens to which the body should respond, and which are food antigens which the body should accept. The lymphoid tissue is somehow capable of telling the lymphocytes that they should not respond to food antigens.
Oral tolerance is a growing area of research.
As you may be aware it is a mechanism that has been suggested could be manipulated to combat autoimmune disease. The hypothesis is that if we knew the antigenic target in an autoimmune disease then an individual could be given purified antigenic material to eat. Presenting the purified antigen to the gut associated lymphoid tissue could promote tolerance of the immune system towards this antigen. This mechanism has been successful in some animal models of autoimmune disease and human trials of eating purified chicken collagen to reduce rheumatoid arthritis inflammation has met with some success. Appendix So, you were probably told that the appendix is a vestigial organ that has no function in humans.