Defensive proteins are better known as antibodies. These are a key part of the immune system. Antibodies are formed in the white blood cells and fight off infections and viruses.
Defense proteins such as antibodies, which are also known as immunoglobulin, are designed to be able to tell when a foreign body has entered the bloodstream. The antibodies set off a reaction inside the human body that works to fight off the offending organism. Often, people believe the antibodies actually destroy viruses and bacteria, but the direct reaction is usually more along the lines of rendering the invading organism harmless.