Molecular distribution of elastase between its two main inhibitors: direct quantitation of elastase-alpha 2-macroglobulin complex with a novel ELISA technique

Antibody binding to alpha 2-macroglobulin facilitates direct quantitation of elastase-alpha 2-macroglobulin complexes by a simple ELISA technique

In order to investigate the effect which the binding of anti-alpha 2-macroglobulin (anti-A2M) antibody has on subsequent antigen-antibody reaction between the complexed elastase and the solid phase anti-elastase antibody, elastase alpha 2-macroglobulin complex (EMC) was incubated with anti-A2M antibody and then extracted by a solid-phase bound rabbit anti-elastase antibody. A doubling dilution series of EMC generated dose related absorbance values. The critical factor permitting the immunological detection of A2M-bound elastase is the pre-incubation of anti-A2M antibody with EMC in solution. The assay exhibited a lower detection limit of 0.5 ng bound elastase per ml and EMC levels in serum samples from ten volunteers were significantly higher than in plasma (28 vs. 21 ng/ml, p < 0.05, Student's t test for paired samples). The EMC levels measured with this assay were essentially identical to those obtained when phenyl methyl sulfonyl fluoride (PMSF) was added to the assay buffer solution.

Increase in lactoferrin and elastase alpha-1-proteinase inhibitor complexes but lack of complement activation and IL-6 response following thoracic surgery

Polymorphonuclear neutrophil (PMN) stimulation and degranulation can be mediated by the cytokines and by complement activation. The aim of the present study was to measure TNF alpha, IL-1 alpha, IL-6 and C3d in relation to postoperative increase in lactoferrin and elastase alpha-1-proteinase inhibitor (E alpha-1-PI) levels. Eleven patients undergoing thoracic surgery took part in the study. Blood leucocytes, E alpha-1-PI, lactoferrin and C3d were measured preoperatively, at the end of surgery and postoperatively, at 4 h and on day 1, 2, 3 and 5. TNF alpha, IL-1 alpha and IL-6 were measured preoperatively, at the end of surgery and postoperatively, at 4 h, and on days 1 and 5. The leucocyte count, lactoferrin and E alpha-1-PI levels increased significantly postoperatively (P < 0.01). There was no significant change in C3d values. Plasma IL-6 levels were unchanged in the postoperative period. Plasma TNF alpha and IL-1 alpha were detectable at low levels in only two and four patients, respectively.

CONCLUSION

The postoperative increase in blood levels of PMN lactoferrin and E alpha-1-PI complexes observed in the present study was not accompanied by complement activation, or increased blood levels of IL-6.

Aspects of preanalytical variation of lactoferrin and elastase/alpha 1-protease inhibitor complexes

A number of interesting applications of plasma elastase/alpha 1-protease inhibitor complexes (ELA-PI) and lactoferrin (LAC) have recently been suggested. However, the clinical utility of these components often seems to be low. This might be improved by minimizing the preanalytical variation, if possible. Therefore, we have evaluated the influence of various aspects of sampling and handling conditions on the results obtained when measuring ELA-PI and LAC. Blood samples from both healthy persons as well as patients, who had undergone laparotomy the day before, were investigated. We confirmed the previous observations of higher concentrations of ELA-PI and LAC in serum compared to plasma. This was more pronounced in patients than in healthy adults. In EDTA-blood the most important change was seen in samples from patients when stored at room temperature. In this situation increases of LAC concentrations of 50% and 100% following 2 and 5 h, respectively were found. This in vitro release of LAC was abolished when samples were stored on ice until centrifugation within 5 h. In contrast, a statistically significant increase in ELA-PI of 10% was observed following storage on ice for 2 h of blood specimens drawn from healthy persons. EDTA-plasma obtained by venous puncture following minimal stasis contained 10% higher concentrations of LAC compared to samples drawn from intravenous catheters, while no difference was observed in the case of ELA-PI. However, in one individual prolonged venous stasis resulted in larger differences of both LAC and ELA-PI. Different centrifugation conditions (1500 vs. 3000 x g; room temperature vs. 4 degrees C) did not influence concentrations of LAC or ELA-PI measured, neither did eating a normal meal nor moderate physical activity (30 min walk). In conclusion, ELA-PI and LAC should be measured in EDTA-plasma. Blood must be drawn by venous puncture applying minimal stasis or from indwelling venous catheters. Samples for measuring LAC must be stored on ice until centrifugation. Separation of plasma from cells should be performed as fast as possible, but storage for up to 5 h can be accepted.

An ELISA for elastase alpha 1-protease inhibitor complexes in human plasma and serum

An ELISA for neutrophil elastase (ELA) in complex with alpha 1-protease inhibitor (PI) (alpha 1-antitrypsin) was developed in microtitre plates and compared to the ELISA kit from MERCK (2-h version). Recovery of ELA-PI was good in both assays. The detection limits were 4.4 micrograms l-1 and 7.7 micrograms l-1 of the in-house and MERCK assay, respectively, while limits of quantitation were estimated to 7.7 micrograms l-1 (5.5-9.9 micrograms l-1) and 28.9 micrograms l-1 (14.6-44.3 micrograms l-1) for the two assays. Furthermore, as dilution curves of normal plasma were parallel with the calibration curve in the in-house assay over a wide range of dilutions, it is feasible to assay plasma in dilutions of only 1:6, resulting in a limit of quantitation of only 1.1 micrograms l-1. The total analytical coefficient of variation for samples measured in double determinations was 10.5%-12.5% in the in-house assay and 13.9%-14.6% in the MERCK assay. One-hundred-and-eight plasma samples covering a wide range of ELA-PI concentrations were analysed in both assays. A proportional difference between the two methods was detected, the mean ratio (in-house/MERCK) with 95% confidence limits was 1.115 (1.070-1.160). The cause of the difference was probably due to difference calibration of the assays. Until this problem is solved, method specific reference intervals are needed. A reference interval for the in-house method based on plasma samples from 123 healthy adults; median age 36 years (range: 19-65 years) was estimated to 16.5-48.5 micrograms l-1.