Activity of IgG and IgM ABO antibodies against some weak A (A3, Ax, Aend) and weak B (B3, Bx) red cells

The IgG and IgM anti-A and anti-B activities from several immune and non-immune O, A and B sera were tested against a panel of weak (A (A3, AX, AND Aend) and weak B (B3 and Bx) red cells. In all cases it is the IgM which agglutinated optimally Ax (or Bx) cells, while IgG and IgM anti-A (or anti-B) reacted similarly with A3 and Aend (or B3) cells. The agglutinating activity of all these ABO antibodies was found straightly related to their association constant for the A (or the B) receptor.