Conversion of the human blood group H antigen to A antigen in vitro.

A-transferase (N-acetylgalactosaminyl transferase) was purified from human group A plasma using Sepharose 4B affinity chromatography. Human anti-A antibodies were purified from human serum by adsorption to an immunosorbent column and heat elution in order to detect the A antigen. Conditions appropriate for the development of the A antigen on O red cells were examined and several buffer systems were found to be equally effective. Expression of the developed A antigen was found to be similar to that on group A red cells, indicating that the system in vitro has similar activity to the system in vivo. The H antigen from human saliva was coupled to Sepharose 4B or adsorbed to a nitrocellulose membrane. The A antigen was able to be developed on these materials by the action of group A-transferase. The procedures enabled the identification in vitro of sugar-transferase activities which can be useful in studies within the A,B,H antigen system or other carbohydrate antigen system.