Hyperamylasemia from the Binding of Serum Amylase by an 11S IgA Globulin

Abstract

A patient with persistent hyperamylasemia and a low renal clearance of amylase was found to have an abnormally large serum amylase (11S). This large amylase, as shown by preparative ultracentrifugation and gel filtration, comprised 95 per cent of amylase in serum and 5 per cent of that in fasting small-bowel contents. Remaining amylases in serum, intestinal fluid, urine and saliva were of normal size (4–5S). The abnormal amylase was specifically precipitated with anti-IgA antiserum. Mercaptoethanol reduced the sedimentation coefficient of the large amylase to 7–8S; treatment at pH 3.4 reduced its sedimentation coefficient to normal (4–5S). Gel filtration at pH 3.4 resulted in the separation of an amylase that was normal in size and enzyme kinetics. The globulins isolated by acid dissociation bound amylase present in normal serum and increased its size to 11S. These observations are consistent with the hypothesis that hyperamylasemia and large-sized amylase result from the binding of normal amylase by an abnormal 11S IgA globulin in a unique autoimmune reaction.