What substance do white blood cells primarily combat in the body?

White blood cells, also known as leukocytes, primarily combat pathogens in the body. These cells play a crucial role in the immune system, helping to identify and attack various infectious agents such as bacteria, viruses, fungi, and parasites. When pathogens invade the body, white blood cells are mobilized to respond by either directly attacking these invaders or by coordinating a more complex immune response.

The function of white blood cells goes beyond simple combat; they also help to remember specific pathogens and contribute to immune memory, making the body more efficient at responding to future infections. This is vital for maintaining health and preventing illness. While oxygen, nutrients, and toxins do play significant roles in the body, they are not the primary targets of white blood cells. Instead, it is the pathogens that pose an immediate threat to health, making them the focus of the immune response facilitated by white blood cells.