Bilirubin is a waste product of which type of blood cells?

Bilirubin is primarily a waste product that results from the breakdown of hemoglobin, which is found in red blood cells. When red blood cells reach the end of their lifespan, they are broken down in the liver and spleen, leading to the release of hemoglobin. This hemoglobin is then processed into bilirubin. It is important to understand that bilirubin is a critical component in the body's method of disposing of the byproducts of red blood cell degradation.

The other types of blood cells involved in the body's immune response, such as mast cells, white blood cells, and platelets, do not produce bilirubin as they do not contain hemoglobin. Mast cells primarily play roles in inflammatory responses and allergic reactions, white blood cells are involved in fighting infections, and platelets are essential for clotting. Thus, the key association between bilirubin and red blood cells makes the choice regarding red blood cells the appropriate answer.