Red cell membrane antigens determine blood groups.
Blood group antigens are either sugars, proteins, lipids or a combination.1
Some induce clinically significant immune responses when transfused into mismatched recipients.
In the past, the blood antigens responsible for these immune responses have been identified by immunologic methods.
In recent years, the genes that encode these proteins have been cloned and sequenced, allowing their structure and sometimes function to be established.
Reference
https://www.ncbi.nlm.nih.gov/books/NBK2264/
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