What is the primary function of white blood cells?

The primary function of white blood cells, also known as leukocytes, is to fight infections. These cells are a crucial component of the immune system, which protects the body against both infectious disease and foreign invaders. White blood cells identify, attack, and neutralize pathogens such as bacteria, viruses, and other microorganisms that can cause illness. They can also produce antibodies, which help to specifically target and remember these pathogens for faster response during future exposures.

In contrast, the other options describe functions associated with different types of cells or biological processes. The production of hormones is primarily the role of endocrine cells; red blood cells are responsible for transporting oxygen in the bloodstream; and the digestion of food is chiefly carried out by enzymes and digestive organs rather than by white blood cells.