Why antigen present on red blood cell?

Antigens on red blood cells (RBCs) are molecules that can trigger an immune response if they are recognized as foreign by the immune system. These antigens, such as the ABO and Rh systems, play a crucial role in blood transfusions and organ transplantation, as they determine blood compatibility. The presence or absence of specific antigens on RBCs helps the body identify its own cells versus invaders, ensuring proper immune function and response.