Which part of the blood participates primarily in the immune response?

The part of the blood that primarily participates in the immune response is white blood cells. These cells, also known as leukocytes, play a crucial role in identifying and combating pathogens such as bacteria, viruses, and other foreign substances that threaten the body's health.

White blood cells are divided into several types, including lymphocytes, neutrophils, monocytes, eosinophils, and basophils, each having specific functions in immune defense. For instance, lymphocytes include T cells and B cells, which are vital for adaptive immunity. T cells help to directly attack infected cells, while B cells produce antibodies that neutralize pathogens.

In contrast, other components of the blood have different primary functions. Plasma serves as the liquid medium that transports cells, nutrients, and waste products, but it does not directly engage in the immune response. Red blood cells are responsible for oxygen transport and do not have a role in immunity. Platelets are essential for blood clotting and wound healing, playing no direct part in immune responses. Thus, white blood cells are the key players in protecting the body against infections and ensuring a well-functioning immune system.