Where in the body are white blood cells, which protect against infections, found?

White blood cells, or leukocytes, are crucial components of the immune system that help defend the body against infections. While they are produced in the bone marrow, their primary function in fighting infections occurs in the bloodstream. This is where white blood cells circulate throughout the body, allowing them to reach areas where they are needed to combat pathogens.

In addition to being found in blood, white blood cells can also reside in other areas such as lymph nodes and certain tissues. However, when focusing on their presence and role in actively defending against infections, blood is the immediate medium through which they travel to reach infected sites. This makes it essential to recognize blood as the correct answer, as it highlights the transportation and functional aspects of white blood cells in the immune response.