Specific activity of alpha(1) proteinase inhibitor and alpha(2)macroglobulin in human serum: Application to insulin-dependent diabetes mellitus

The shifting balance between proteinases and proteinase inhibitors in blood , a function of their relative affinities and concentrations, has long been hypothesized to influence immune competency. The identification of protein ase-activated receptor responses in cells of the mononuclear phagocyte syst em, suggests a potential explanation. The major serum proteinase inhibitor, alpha(1)proteinase inhibitor (alpha(1)PI, alpha(1)-antitrypsin), has been reported to increase in concentration during inflammation. Quantitative det ermination of serum alpha(1)PI has traditionally been performed nephelometr ically; however, antigenically quantitated levels may not be representative of functional capacity. It has previously been observed that alpha(1)PI in serum exhibits bimodal behavior as the result of various concentrations of proteinase inhibitors, specifically alpha(2)macroglobulin (alpha(2)M) and inter-alpha-trypsin inhibitor, which compete in binding to a panel of serin e proteinases. Consequently, it has not previously been possible to assign a numerical value for the specific activity of these competing proteinase i nhibitors in serum. By applying known constants representing the associatio n of proteinase inhibitors with porcine pancreatic elastase (PPE), the theo retical relationship between the functional and antigenic values for alpha( 1)PI and alpha(2)M has been empirically derived allowing, for the first tim e, the calculation of their specific activities in serum. As predicted, the serum concentration of alpha(1)PI was found to be highly correlated with r esidual uninhibited PPE catalytic activity in healthy individuals, but not in individuals exhibiting fragmented or complexed alpha(1)PI. Using these t echniques, both the antigenic and functional levels of alpha(1)PI were dete rmined in sera from subjects with insulin-dependent diabetes mellitus (IDDM ) who had been clinically diagnosed as having either periodontal disease or gingival health. Determination of quantitative levels by antigen-capture s uggests that the IDDM subjects with periodontitis manifest dramatically inc reased Bevels of fragmented serum alpha(1)PI compared with their orally hea lthy counterparts or normal controls. In contrast, functional analysis of s erum alpha(1)PI revealed no differences between the three subject populatio ns. The elevated levels of antigenically determined serum alpha(1)PI reflec t the inflammatory status of periodontal disease. These results support the importance of and provide methodology for determining the functionally act ive levels of alpha(1)PI allowing reexamination of changes detected during the acute phase of inflammation, replacement therapy, and longitudinal stud ies in relevant disease processes including malignancy and diabetes. (C) 19 98 Academic Press.