Which plant-derived reagent is used in ABO typing to detect A1 antigen?

• A. Anti-A1
• B. Anti-A2
• C. Anti-B
• D. Lectin from Dolichos biflorus

Answer: (A)

The key idea is distinguishing the A1 and A2 subtypes of the A antigen in ABO typing. A plant-derived reagent called Dolichos biflorus lectin binds specifically to the A1 form of the antigen on red cells, causing agglutination of A1 cells while usually not reacting with A2 cells. This selective binding allows you to identify A1 status in a mixed population and resolve cases where A1/A2 subtyping is clinically relevant. Other reagents such as anti-A or anti-B detect the presence of antigen broadly, and anti-A2 can help identify A2, but the plant-derived reagent used to detect A1 specifically is the Dolichos biflorus lectin.