Molecular genotyping of Indian blood group system antigens in Indian blood donors

Haemagglutination has been the gold standard for defining the blood group status. However, these tests depend upon the availability of specific and reliable antisera. Potent antisera for extended phenotyping are very costly, weakly reacting or available in limited stocks and unavailable for some blood group systems like Indian, Dombrock, Coltan, Diego etc. The Indian blood group system consists of two antithetical antigens, In^a and In^b. The In^a /In^b polymorphism arises from 252C > G missense mutation in the CD44 gene. This knowledge has allowed the development of molecular methods for genotyping IN alleles.

Blood samples were collected from 715 blood donors from Mumbai. DNA was extracted using phenol-chloroform method and genotyping for Indian (In^a/IN*01, In^b /IN*02) blood group alleles was done by Sequence Specific PCR.

Seventeen donors among 715 were heterozygous for In^a antigen i.e. In (a+b+). The In^a antigen positivity was confirmed serologically, using anti-In^a prepared in-house and the genotype-phenotype results were concordant. The frequency of In^a (2.37%) was higher than Caucasians and comparable to those reported among Indians of Bombay.

This is the first study reporting molecular screening of Indian blood group antigens in Indian population. The frequency of In^a and In^b antigens was found to be 2.37% and 100% respectively. Red cells of In^a positive donors can be used as in-house reagent red cells for screening and identification of corresponding antibodies. Thus, DNA based methods will help in large scale screening of donors to identify rare blood groups, when commercial antisera are unavailable.