A radioimmunoassay for pancreatic elastase 1: use of alpha 1-antitrypsin-elastase 1 conjugate as both standard and tracer to eliminate the influence of anti-elastase 1 autoantibodies.

We have recently reported the occurrence of anti-elastase 1 autoantibodies in human sera (Asada et al., Biochim Biophys Acta, 1991;1080:34-39). The usual radioimmunoassay of elastase 1 in autoantibody-positive sera gave abnormally high levels of elastase 1 and low recoveries of elastase 1 added to the sera. Now we have established a new radioimmunoassay system for determining pancreatic elastase 1 in serum, in which alpha 1-antitrypsin elastase 1 conjugate, the major conjugation form of elastase 1 in serum, is used as standard and alpha 1-antitrypsin-[125I]elastase 1 as tracer, because we found that the conjugate could bind to the elastase 1 specific antiserum but not to the autoantibodies. Thus the new assay system completely eliminate the unfavorable effects of the autoantibodies. The elastase 1 levels determined by the new assay method exhibited a good correlation with those obtained by a commercial assay kit in the autoantibody-negative sera, while no correlation was observed in the autoantibody-positive sera.