Protein has a function in organisms: protective and enzymatic. Why does protein enter the body with food does

Protein has a function in organisms: protective and enzymatic. Why does protein enter the body with food does not cause protective reactions (the formation of antibodies)?

Protein in food has a quaternary structure, getting into the digestive system, it undergoes a series of breakdown stages under the influence of perchloric acid and enzymes of the liver and pancreas. As a result, the quaternary structure turns into a primary structure, and then into peptides – short AA sequences. In this form, they are absorbed in the small intestine and in the blood do not cause “suspicion” from the immune system.