Development of an enzyme-linked immunosorbent assay for human plasma inter-α-trypsin inhibitor (ITI) using specific antibodies against each of the H₁ and H₂ heavy chains

Inter-α-trypsin inhibitor (ITI) is a serine-proteinase inhibitor of human plasma enzymes. ITI is composed of three polypeptide chains covalently linked: bikunin, responsible for the antiprotease activity and two heavy chains H₁ and H₂. Human plasma also contains other components immunologically related to ITI such as pre-α-trypsin inhibitor (pal), inter-α-like inhibitor (I α LI) and free bikunin. The ELISA procedure we propose exclusively measures native ITI within the range 12.5-200 μg/l. The intra- and interassay coefficients of variation were less than 5.6% and 8.7%, respectively. When ITI was added to plasma samples, full recovery was obtained, EDTA-plasma from 30 healthy individuals revealed a mean level of 241.5 mg/l (range 145.5-506). The high specificity, sensitivity, reproducibility and accuracy of the present assay should facilitate the specific measurement of native ITI in blood and thus might represent a useful tool for further physiopathological studies.