Acridinium ester labelled cytokines: receptor binding studies with human interleukin-1 alpha, interleukin-1 beta and...

As a consequence of environmental protection and legal restrictions, increasing efforts are made to avoid radioactivity. One alternative is the labelling of ligands with chemiluminescent acridinium esters such as 2,6-dimethyl-4-(N-succinimidyloxy-carbonyl)phenyl 10-methylacridinium-9-carboxylate methosulphate (DMAE-NHS). When exposed to hydrogen peroxide in a basic solution, the DMAE-moiety decays with emission of a short-lasting chemiluminescent flash. With the goal of replacing the radioactive label in protein ligands with a DMAE label, and of increasing the efficiency by using microtitre plate technology for DMAE detection, we compared the receptor binding properties of iodinated interleukin-1 alpha (125I-IL-1 alpha), interleukin-1 beta (125I-IL-1 beta) and interferon-gamma (125I-IFN-gamma) with the corresponding DMAE-labelled ligands. The luminescence signal was assessed in a single-tube luminometer and in the prototype of a chemiluminescent microtitre plate reader. Derivatization of the three proteins with DMAE-N-hydroxy-succinimide resulted in photon yields of up to 100,000 counts per femtomole. As shown by Scatchard analysis, no significant loss of receptor binding affinity was observed, which might have been expected as a consequence of the chemical modification of the proteins. The use of DMAE labelling of proteins has the following advantages as compared to iodination: (i) the coupling reaction and binding assay can be performed in a normal laboratory, (ii) since there is no radiolysis, the DMAE-labelled proteins remain stable, (iii) the detection sensitivity may be improved as a consequence of higher specific activity of the DMAE label.(ABSTRACT TRUNCATED AT 250 WORDS)