What do leukocytes primarily function as in the body?

Leukocytes, also known as white blood cells, primarily function in the immune system as defenders against infections and diseases. Their main role is to identify and eliminate pathogens such as bacteria, viruses, and other foreign invaders. Different types of leukocytes have specialized functions; for example, some can engulf and digest pathogens, while others produce antibodies that help to neutralize these threats. This immune response is crucial for maintaining the body's overall health and protecting against disease.

In contrast to the other options, which represent different components of the blood, the role of leukocytes is distinct. Red blood cells are primarily responsible for transporting oxygen throughout the body, while platelets play a key role in blood clotting. Clotting factors, also not linked to immune response, assist in various processes essential for stopping bleeding. Thus, the unique function of leukocytes in fighting infections makes them a vital part of the body's defense mechanism.