What is one of the primary roles of white blood cells?

White blood cells, also known as leukocytes, play a crucial role in the immune system, which is primarily responsible for protecting the body against infections and diseases. Their main function is to identify and eliminate pathogens, such as bacteria, viruses, and other foreign substances that pose a threat to health. Each type of white blood cell has specific functions; for example, phagocytes engulf and digest microbes, while lymphocytes are involved in the adaptive immune response by recognizing specific antigens.

This protective mechanism is essential for maintaining the body's overall health and preventing illness. While other choices describe important biological functions—oxygen transport is primarily done by red blood cells, blood clotting involves platelets, and body temperature regulation is handled by various systems in the body, including the hypothalamus—none are functions of white blood cells. Thus, their primary role distinctly revolves around immune defense, making the protection against infections the correct choice.