Specificity of allozyme-absorbed antisera to human placental alkaline phosphatase for individual phenotypes.

Antisera raised against the rare FD phenotype enzyme were exhaustively absorbed with SS and FF phenotype enzyme immobilized on agarose gels. When it was absorbed with the FF phenotype enzyme, the antiserum no longer reacted with the F-variant enzyme, but did with the S-, D-, and I-variants, as determined by electrophoretic retardation experiments and precipitation of antigen-antibody complexes using staphylococcal protein A. When the antiserum was absorbed with SS phenotype enzyme, it no longer reacted with S-, D-, or I-variant enzyme, but did have some reactivity with the F-variant, as seen in the protein A assay. Based upon the IgG concentration, which bound 40% of the appropriate enzyme, 1/20 of the antiserum preparation was specific for the S-, D-, and I-variant shared specificity, and 1/400 was specific for the F-variant alone.