Final answer:
An antigen is a substance that the immune system identifies as self or nonself, potentially eliciting an immune response. These are found on the surface of cells, including red blood cells, and can be composed of proteins, carbohydrates, glycoproteins, or glycolipids. The specific response involves the production of antibodies by B cells that recognize and bind to these antigens.
Step-by-step explanation:
An antigen is a macromolecule that the immune system identifies as either self or nonself. If recognized as nonself, the immune system may react by forming antibodies. Antigens can be proteins, carbohydrates, glycoproteins, or glycolipids, which are found on the surfaces of cells, including red blood cells. These antigens have specific motifs called epitopes, which are recognized and bound by antibodies, thus playing a crucial role in the body's immune response.
Antigens such as those on red blood cells signify to the immune system that the cells are part of the body. However, when foreign red blood cells with different antigens are encountered, they may be attacked by antibodies. The specific digestion of antigens results in a humoral immune response with B cells producing antibodies that bind with the antigen.