Final answer:
Proteins are considered part of the body's defense mechanism because they play several important roles in the immune system, such as fighting off infections and regulating cellular activities.
Step-by-step explanation:
Proteins are considered part of the body's defense mechanism because they play several important roles in the immune system. Antibodies, which are proteins, help fight off infections by recognizing and neutralizing pathogens. Proteins also regulate cellular activities and contribute to the immune response. Additionally, proteins are used in cellular repair and the formation of blood cells. Overall, proteins are essential for the body's defense against foreign invaders.