What is the primary function of leukocytes?

Leukocytes, also known as white blood cells, play a crucial role in the body's immune response. Their primary function is to fight infections and diseases by identifying and attacking pathogens such as bacteria, viruses, fungi, and parasites. These cells are an essential component of the immune system and work in various ways, including producing antibodies, engulfing harmful microorganisms, and coordinating the immune response.

In contrast, the other options relate to functions performed by different types of cells or systems within the body. Hormone production is primarily the role of endocrine cells, while the transportation of nutrients is mainly the function of red blood cells and the circulatory system. Regulating body temperature involves various mechanisms, including sweating and blood flow adjustments, rather than a direct function of leukocytes. Thus, the involvement of leukocytes in fighting infections clearly establishes their primary role in maintaining health and combating diseases.