What function do white blood cells primarily serve?

White blood cells, also known as leukocytes, play a critical role in the immune system by defending the body against both infectious disease and foreign invaders. Their primary function is to identify, attack, and eliminate pathogens such as bacteria, viruses, and fungi. White blood cells can be categorized into different types, each with specialized roles in immune response; for instance, lymphocytes (such as T cells and B cells) are pivotal for recognizing specific pathogens and formulating an adaptive immune response.

The other functions listed, such as clotting blood or transporting oxygen and hormones, are handled primarily by other types of cells. Platelets and certain proteins in plasma are involved in blood clotting, while red blood cells are responsible for carrying oxygen throughout the body. Hormones are transported by the bloodstream, often carried by plasma and specific transport proteins, not by white blood cells. Therefore, the correct focus on the role of white blood cells in fighting infections highlights their essential contribution to maintaining health and the body's overall defense mechanisms.