Kidd antigen system

The Jk antigen is found on a protein responsible for urea transport in the red blood cells and the kidney.

[4] Kidd comprises three antigens on a glycoprotein with 10 transmembrane spanning domains, cytoplasmic N- and C-termini and one extracellular N-glycosylation site.

[citation needed] Jka and Jkb are the products of alleles with Asp280 and Asn280 in the fourth external loop of the Kidd glycoprotein.

[5] In Polynesians the null allele contains a splice site mutation in intron 5 causing a loss of exon 6 from the mRNA product.

[citation needed] A rare null phenotype in Japanese individuals results from heterozygosity for an inhibitor gene.

[citation needed] Very weak expression of Jka and/or Jkb can be detected on In(Jk) red blood cells in adsorption/elution tests.

[citation needed] Kidd antibodies can be difficult to detect by direct agglutination testing and generally require addition of antihuman globulin after a warm incubation period.

[citation needed] Kidd antibodies are dangerous as they are capable of causing severe acute hemolytic transfusion reactions.

[4] Kidd antibodies are capable of behaving as histocompatibility antigens in renal transplants and may be responsible for allograft rejection in some cases.