Which of the following describes the role of the immune system?

The immune system primarily functions to protect the body against infections and diseases caused by pathogens such as bacteria, viruses, and fungi. It detects and identifies harmful microorganisms and responds through various mechanisms, including the activation of white blood cells, antibodies, and other immune responses, to eliminate these threats before they can cause harm.

In addition to its defensive role, the immune system also plays a crucial part in monitoring the body's own cells for any signs of abnormality, such as cancer cells or cells infected with a virus, thus preventing disease progression. This protective aspect of the immune system is vital for maintaining overall health and preventing illnesses.

The other options describe functions that are not directly related to the immune system. Regulating body temperature relates to the body's thermoregulation processes, while transporting nutrients is managed primarily by the circulatory and digestive systems. Supporting digestion involves the digestive system, which breaks down food and absorbs nutrients, rather than the immune system's main responsibilities.