A patient carries the A antigen on the erythrocyte membrane. Which antibody circulates in that patient's plasma?

1. An antibody attacks what the body reads as nonself. 2. This patient carries the A antigen, so A is self and cannot be attacked. 3. The B antigen is absent from these erythrocytes, so B is nonself. 4. The ABO group is unusual in that the antibody is preformed, without any prior exposure to incompatible blood. 5. A type A individual therefore has preformed anti-B antibodies circulating in the plasma. 6. Anti-A would agglutinate the patient's own cells, which is why that option is self-defeating. 7. Carrying both antibodies belongs to type O and carrying neither belongs to type AB, so each of those options names a different type. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 18 "The Cardiovascular System: Blood", section 18.6 Blood Typing_