GENOTYPING OF KEL1 AND KEL2 OF THE HUMAN KELL BLOOD-GROUP SYSTEM BY THE POLYMERASE CHAIN-REACTION WITH SEQUENCE-SPECIFIC PRIMERS

Background: Kell is a major antigenic system in human red cells, with more than 20 identified antigens. KEL1 and KEL2 are two opposing low- and high-frequency alleles. Immunization to KEL1 is clinically signifi cant, because anti-KEL1 can cause severe reactions to transfusion of i ncompatible blood, as well as hemolytic disease of the newborn. At the nucleotide level, the difference between the KEL2 and KEL1 alleles is a single-base change within exon 6 that results in the substitution o f methionine (ATG) for threonine (ACG) at position 193. Study Design a nd Methods: An assay using polymerase chain reaction and sequence-spec ific primers to genotype for the KEL1 and KEL2 alleles has been develo ped. It uses two allele-specific forward primers for either KEL2 or KE L2 and a single reverse-consensus primer. Results: A validation study of 42 serologically typed samples (5 KEL:1,-2 [K+k-]; [K+k+]; 23 KEL:1 ,2 [K+k+]; and 14 KEL:-1,2 [K-k+]) was performed. A concordance rate o f 100 percent (42/42 samples) was observed between polymerase chain re action with sequence-specific primers and serologic typing. Conclusion : This rapid, nonradioactive, Kell system genotyping assay does not re quire the additional steps of probe hybridization or restriction enzym e digestion. This application of polymerase chain reaction with sequen ce-specific primers should prove particularly useful in Kell system ge notyping of amniotic cells to identify pregnancies at risk for hemolyt ic disease of the newborn.