Biology Regents Practice Exam

Organ transplant recipients need medications to decrease immune responses primarily because transplanted organs contain foreign antigens that can trigger the recipient's immune system. The immune system is designed to identify and attack anything it perceives as foreign, including cells from transplanted tissues that do not belong to the recipient. This immune reaction can lead to transplant rejection, where the body attacks the new organ, seeing it as a threat.

By using immunosuppressive medications, transplant recipients can reduce the activity of their immune system, allowing the transplanted organ to function properly without being attacked. These medications prevent the activation of white blood cells that would typically respond to the foreign antigens present in the donor organ, thus increasing the chances of successful transplantation and long-term organ acceptance.

Other options do not accurately describe the role of antigens in organ transplants or the need for immunosuppressive therapy. Therefore, understanding the presence of foreign antigens in transplanted organs is critical for comprehending why immune suppression is necessary in these patients.