Which cells are referred to as defenders against infections in the bloodstream?

White blood cells, also known as leukocytes, play a crucial role in the immune response and act as defenders against infections in the bloodstream. They are responsible for identifying and attacking pathogens such as bacteria, viruses, and other foreign invaders. There are several types of white blood cells, including neutrophils, lymphocytes, monocytes, eosinophils, and basophils, each with specific functions in the immune defense process.

In contrast, red blood cells primarily transport oxygen throughout the body and do not have a role in immune defense. Plasma cells are a type of white blood cell that specifically produce antibodies, but they aren't solely on the front lines against all infections. Platelets are involved in blood clotting and do not protect against infections either. Thus, the designation of white blood cells as the defenders against infections highlights their essential function in maintaining the body's health and combating infectious agents.