Inter-alpha-inhibitor as marker for neutrophil proteinase activity: An in vitro investigation

Human neutrophil proteinases have been implicated in the pathogenesis of a wide variety of inflammatory diseases. The degradation of plasma proteins such as coagulation and fibrinolysis factors has been attributed to the excessive release of elastase in septicemia and in other conditions in which heightened proteolysis occurs. Inter-alpha-inhibitor (l alpha l) is particularly sensitive to cleavage by leukocyte proteinases. For this reason, the determination of I alpha I has been proposed as a method for evaluating plasma protein proteolysis by neutrophil enzymes. In this article we provide evidence that intact residual I alpha I can be accurately quantified by enzyme-linked immunosorbent assay (ELISA) determination without interference from fragments released from I alpha I by incubation with triggered neutrophils. We demonstrate that under these conditions I alpha I was quickly and steadily proteolyzed in a cell dose-dependent manner. alpha-1 proteinase inhibitor (alpha 1PI) partially protected I alpha I; however, the proteolysis persisted when I alpha I was incubated with stimulated neutrophils in the presence of a large relative excess of alpha 1PI over the amount of elastase theoretically present in cells. For the same amount of alpha 1PI, serum provided a better protection than alpha 1PI atone but did not completely inhibit the I alpha I degradation, Therefore, ELISA determination of I alpha I might be useful for monitoring the in vivo activity of neutrophil proteinases in systemic proteolytic states.