Studies on the blood group antigen Ina

Anti-Ina antibodies have been observed in 30 of the 41 anti-Rh donors hyperimmunised with group O Ror In(a+) blood. They have also been found in four of 60 Rh immunised women. In three of these the husbands and previous children were In(a+). However, there was no evidence of haemolytic disease of the newborn due to anti-Ina antibodies alone. The Ina antigen is developed at birth though it is weaker than in adults. The strength of the Ina antigen decreases during pregnancy and returns to the previous level three months afer termination of pregnancy. The Ina antigen is affected by papain, trypsin, bromelin and neuraminidase. The antibodies in all the donors, even though their sera were preserved for more than 10 years at -20 degrees C, reacted in saline and albumin milieux and in the indirect antiglobulin procedure using anti-IgG reagents. These antibodies are complement binding as shown by the two-stage complement binding test. Treatment with 2-mercaptoethanol and DEAE-column chromatography suggested the anti-Ina antibodies were of the IgG class. Anti-Ina antibodies could possibly cause a transfusion reaction since In(a+) red cells when transfused into individuals possessing anti-Ina antibodies are eliminated from the circulation within 20 minutes.