Landsteiner realized that “natural” antibodies develop that are directed against antigens not present on the red cells. Individuals with “A” antigens on their red cells had sera containing the “anti-B” antibody. Individuals with “B” antigens had sera containing “anti-A," and “O” individuals’ sera contained “anti-A” and “anti-B.”
Subsequent researchers determined that “AB” individuals had sera with no ABO antibodies present, and sera from group O individuals may also contain a separate antibody, “anti-A,B.” Anti-A,B possesses serologic activity not found in mixtures of anti-A and anti-B. Anti-A,B sera will agglutinate A, B, and AB cells. (This is particularly useful in detecting weak A and B antigens).
The table on the following page summarizes the antigens and antibodies for each blood type.
