What is the main function of the immune system?

The main function of the immune system is to protect against infectious diseases. This system serves as the body's defense mechanism, identifying and combating pathogens such as bacteria, viruses, fungi, and parasites. When foreign invaders enter the body, the immune system recognizes them as threats and activates various white blood cells and antibodies to eliminate them. This response not only helps to prevent illness but also supports healing and recovery from infections that do occur.

In addition to directly fighting off infections, the immune system is crucial for memory response, which allows the body to remember previous encounters with pathogens and respond more effectively if re-exposed. This capability is the basis for how vaccines work, training the immune system to recognize and react to specific pathogens without causing disease.

The other options do not describe the primary function of the immune system: digestion of food is handled by the gastrointestinal system, energy provision is a role of metabolic processes primarily involving the digestive and circulatory systems, and production of red blood cells occurs in the bone marrow, part of the hematologic system, rather than the immune system itself.