wow!! an awesome contribution. These peptidase enzymes cannot differentiate between the protein content of food and the body's own tissue. But the Stomach has a mechanics of preventing the digestion of body tissue. how does it do this?
1- the stomach produces a mucus substance that overlays the inner surface of the stomach. this layer of mucus (alkaline in pH) serve as a barrier between the food and the gastric tissue.
2- the peptidase found in the stomach is Pepsin, and it is first secreted in an inactive form called pepsinogen. this pepsinogen is only activated by the acidic pH of the stomach content and not the stomach itself. therefore an active pepsin is not found in the gastric tissue.

By this the stomach is able to prevent digestion of its tissue.