What is the primary role of the immune system in the body?

The primary role of the immune system is to protect against pathogens. This includes a wide range of harmful substances such as bacteria, viruses, fungi, and parasites that can invade the body and cause disease. The immune system identifies these invaders and mounts a response to eliminate them, using various types of white blood cells and antibodies that target specific pathogens. This protective function is essential for maintaining the body's overall health and preventing infections.

While other systems in the body contribute to digestion, homeostasis, and hormonal regulation, these functions do not reflect the immune system's main purpose. Digestive processes involve the gastrointestinal system, and maintaining homeostasis is a broader biological function that encompasses various systems, including the nervous and endocrine systems. Therefore, the correct choice highlights the unique and crucial role of the immune system in safeguarding health by combatting infectious agents.