Enzyme immunoassay of 2'-5'-oligoadenylates at the femtomole level

We have developed a competition enzyme immunoassay (EIA) for 2'-5'-oligoadenylates [p kappa(A2'p5')nA; 0 less than or equal to kappa less than or equal to 3; 1 less than or equal to n] based on an anti-A2'p5' A monoclonal antibody coated onto 96-well polystyrene plates and A2'p5' A peroxidase as a marker. It permits measurement of 5'OH(A2'p5')nA as such and p kappa(A2'p5')nA after alkaline phosphatase hydrolysis, with a detection threshold of 5 X 10(-12) M. All 2'-5'-oligomers were assayed with similar sensitivity. ATP and adenosine did not interfere at concentrations up to 10(6)-fold higher than those of 2'-5'-oligoadenylates. Reproducibility, stability of reagents and correlation with the radioimmunoassay were good. As such, this EIA is a suitable tool for studying the 2-5A system, particularly, in clinical investigations: the initial velocity of 2-5A synthetase can be determined on 10,000 cells without purification and the level of 2'-5'-oligoadenylates can be assayed on less than 1 ml of blood.