What does the immune system primarily help the body to combat?

The immune system primarily helps the body to combat infections. Its fundamental role is to identify and neutralize pathogens, including viruses, bacteria, fungi, and parasites, which can cause disease. The immune response involves a complex network of cells, tissues, and organs that work together to detect foreign invaders and mount a defense against them. This includes the production of antibodies, activation of immune cells, and various other mechanisms designed to eliminate threats and protect the body from illness.

While external injuries and autoimmune disorders can affect the body's health, they are not the primary combatants that the immune system is designed to fight. Fatigue, on the other hand, is more of a symptom of various conditions and isn't directly addressed by the immune system. Thus, the immune system's main focus remains on protecting the body from infections, making it the correct answer to the question.