The Indian blood group system

The Indian blood group system (ISBT: IN/023) consists of two antithetical antigens: In^a(IN1), which is present in approximately 10 percent of some Arab populations and in 3 percent of Bombay Indians, and its allelic antigen In^b(IN2), an antigen of high incidence in all populations. In 2007, two new high-incidence antigens were identified as belonging to the IN blood group system, namely IN3 (INFI) and IN4 (INJA). The antigens in this system are located on CD44, a single-pass membrane glycoprotein that is encoded by the CD44gene on chromosome 11 at position p13. The biologic function of CD44 is as a leukocyte homing receptor and cellular adhesion molecule. The In^aand In^bpolymorphism represents a 252G>C substitution of CD44,encoding R46P, and lack of IN3 and IN4 results from homozygosity for mutations encoding H85Q and T163R in the CD44gene. The high-frequency antigen AnWj (901009) has not been assigned to the Indian system, but either is located on an isoform of CD44 or is closely associated with it. Immunohematology2011;27:89–93.