The antigens Jk^a and Jk^b belong to which blood group system?

• A. Kidd
• B. Duffy
• C. MNS
• D. Kell

Answer: (A)

Jka and Jkb are antigens in the Kidd blood group system. This system is one of the major human blood group systems used in transfusion medicine. The antigens are located on the red cell membrane on the urea transporter protein encoded by the SLC14A1 gene. The common phenotypes involve combinations of the two antigens: Jk(a+b-), Jk(a-b+), and Jk(a+b+), with the rare Jk(a-b-) occurring infrequently. Antibodies to these antigens (anti-Jka or anti-Jkb) can cause clinically significant hemolytic transfusion reactions and may be challenging to detect because they often react at or near body temperature and show dosage effects, being stronger with homozygous antigen expression. Understanding this system helps in accurate antigen typing and safer transfusion practice.