Why is an individual with blood type O considered a universal donor?

An individual with blood type O is considered a universal donor because their red blood cells do not have A or B antigens on their surface. This absence of antigens means that when blood type O is transfused to a person of any other blood type, the recipient's immune system cannot recognize the O blood as foreign, since it lacks the antigens that typically trigger an immune response.

In the context of blood transfusions, if a person with blood type A, B, or AB were to receive blood that carries those specific antigens, their immune system could potentially recognize those cells as invaders and mount an attack, which could lead to serious complications. However, since type O blood has neither antigen, it is compatible with all other blood types, making it safe for transfusion across different blood groups.

The other options relate to the presence of antigens and the immune response associated with different blood types, but they do not provide the rationale necessary to understand why type O blood is universally acceptable as a donor.