What is the primary function of white blood cells?

White blood cells, also known as leukocytes, play a crucial role in the immune system and are primarily responsible for fighting infection. They identify, target, and eliminate pathogens such as bacteria, viruses, and other foreign invaders that can cause disease. Different types of white blood cells, including lymphocytes, neutrophils, and monocytes, have specialized functions in recognizing and responding to these threats, thereby helping to maintain the body's health.

The other functions listed in the options are attributed to other components of the body. For instance, transporting oxygen is primarily the role of red blood cells, regulating body temperature is managed through mechanisms in the skin and circulatory system, and the promotion of healing is more related to platelets and growth factors rather than the direct function of white blood cells.