Characteristics of the complex between alkaline phosphatase and immunoglobulin A in human serum.

An abnormal band of alkaline phosphatase (ALP) activity was detected by electrophoresis in the serum of a patient with liver cirrhosis, and was shown to be a complex between ALP and immunoglobulin A (IgA) of the lambda type. Physicochemical studies of ALP in the patient's serum showed properties of liver and bone isozymes. The patient's IgA and its F(ab')2 fragment were prepared by column chromatography, and used in in-vitro reconstitution studies with various ALP isozymes. It was found that only the liver and bone ALP attached to the IgA, while the placental and intestinal ALP did not. The ALP was attached to the F(ab')2 fragment of IgA. It is concluded that this complex is the result of an antibody-antigen reaction. Molecular weights of the two complexes, ALP-IgA and ALP-IgA-F(ab')2, suggest that two molecules of monovalent ALP associated with one molecule of divalent IgA.