The Kidd blood group system has been recognized as clinically important in red blood cell (RBC) serology since its identification in 1951. Forty years later, the JK glycoprotein was determined to be a product of SCL14A1 and was identical to the urea transport protein UT-B produced by HUT11A. The functional role of the protein as a urea transporter in RBCs and kidney has been well documented. The polymorphism responsible for the antithetical antigens Jka and Jkb was identified in 1994 as c.838G>A (p. Asp280Asn). Recent discoveries have expanded the system to include 23 variant alleles recognized by the International Society of Blood Transfusion that silence the protein expression and 7 variant alleles presumably producing weak or partial JK antigens. Null phenotypes have been identified in individuals of several populations including those of African, Indian, and Chinese decent, in addition to the well-documented findings in the Polynesian and Finnish populations. This review will examine the historical information about the antigens and antibodies of the JK system as well as catalog the variations of the JK gene. Immunohematology2015;31:29–35.
