Determination of tumor necrosis factor-α (TNF-α) in serum by a highly sensitive enzyme amplified lanthanide luminescence immunoassay

Abstract Objectives: To develop a highly sensitive enzyme amplified lanthanide luminescence (EALL) immunoassay for tumor necrosis factor-α (TNF-α). Methods: The method is based on the use of two monoclonal antibodies against TNF-α, one “capture” antibody and one labeled with biotin, in a “sandwich type” assay format. Alkaline phosphatase (ALP) conjugated to an antibiotin-polyclonal antibody is used as the enzyme label. ALP cleaves phosphate from diflunisal phosphate (DIFP) to produce diflunisal (DIF). The detection system is based on the combination of enzymatic amplification introduced by ALP and the formation of a highly fluorescent terbium complex that can be monitored by time resolved or conventional fluorimetry. Results: By using 50 μL of sample, the dynamic range of the assay extends up to 2000 ng/L of TNF-α, with a detection limit of 1 ng/L, within-run CVs ranging from 3 to 15% and recoveries of 97 ± 2%. By using 100 μL of sample the dynamic range of the assay extends up to 1000 ng/L of TNF-α with a detection limit of 0.2 ng/L, recoveries of 94 ± 13%, within-run CVs ranging from 2 to 6.5% and between-run CVs ranging from 5 to 15%, in a total incubation time of 3h. No interference by the presence of other cytokines (IL-1β, IL-2, IL-4, IL-6, IFN-γ) or by rheumatoid factors has been observed. The results obtained by the proposed method and by a commercially available kit (Medgenix TNF-α EASIA) correlated well (n = 26, r = 0.934). Conclusion: The proposed method is highly sensitive, simple and rapid and can reliably measure TNF-α in the ng range in biological specimens.