Immunoreactive Granulocyte Elastase in Human Serum

Abstract

A specific radioimmunoassay was developed for determination of human granulocyte elastase in blood. The granulocyte elastase employed as radioiodinated tracer in the assay was inactivated with DFP to prevent binding of the tracer to the serum inhibitors .alpha.2-macroglobulin and .alpha.1-antitrypsin, while still retaining its immunoreactivity. The labeled tracer showed a pronounced tendency to nonspecific binding to serum proteins such as albumin and .alpha.2-macroglobulin and also to the Sephadex particles. The binding of the labeled tracer to .alpha.2-macroglobulin caused a false increase in the immunoreactive granulocyte elastase in serum. But the binding of the labeled tracer and its consequences could be circumvented by increasing the NaCl concentration of the reaction mixtures and/or gel filtration buffers. Freshly drawn normal human serum contained about 135 .mu.g granulocyte elastase/l measured as DFP-inactivated granulocyte elastase. The results of experiments in which serum was fractionated by Sephadex G-100 gel filtration suggested that essentially all of the immunoreactive material in normal human serum was granulocyte elastase bound by .alpha.1-antitrypsin. Granulocyte elastase is apparently released from the cells in an active form and then rapidly bound by the inhibitors.