Direct chemiluminescence immunoassay (CLIA) for muramyl tripeptide phosphatidyl-ethanolamine in plasma

A competitive chemiluminescent immunoassay for quantitation of muramyl tripeptide phosphatidyl-ethanolamine (MTP-PE) in plasma has been developed. The assay is based on the use of an acridinium ester-labelled analogue of muramyl tripeptide and a rabbit antiserum. It includes an overnight incubation and a separation with a second antibody covalently coupled to paramagnetic particles. The sensitivity of detection is 0.012 nmol/l, the assay working range is 0.1-5 nmol/l, and the inter-assay CVs are less than or equal to 10%. Using up to 6000-fold sample dilutions, a wide working range (0.1-30,000 nmol/l) is obtained. Rat plasma samples were collected during and one day after intravenous infusion of MTP-PE. Following infusion, the concentrations in plasma declined multiphasically. Half-life time was 0.37 h +/- 0.03 (mean +/- SD, alpha phase) and 1.76 h +/- 0.08 (mean +/- SD, beta phase), clearance and volume of distribution were 0.09 +/- 0.02 l/h x kg (mean +/- SD) and 0.06 +/- 0.01 l/kg (mean +/- SD) respectively. The use of an acridinium ester as a chemiluminescent (CL) label overcomes the problems associated with reagents of limited shelf-life.