A COMPARATIVE-STUDY OF DIFFERENT ENZYME IMMUNOSORBENT ASSAYS FOR HUMAN TUMOR-NECROSIS-FACTOR-ALPHA

Enzyme immunosorbent assays (ELISA) for human tumor necrosis factor-al pha (TNF-alpha) are available from many companies. Although this cytok ine is meanwhile well established in scientific work, its detection in human blood still leads often to conflicting results. We studied the analytical performance of three different commercial ELISA (Amersham, Immunotech and Medgenix Diagnostics) in plasma samples of 30 human imm unodeficiency virus (HIV) infected individuals. All kits showed signif icantly different mean concentrations of TNF-alpha in the study popula tion (p < 0.05). Kit A: 30.9 pg/ml +/- 46.6 vs. kit B: 46.9 pg/ml +/- 24.8 vs. kit C: 11.8 pg/ml +/- 11.6. Results of assays A and B (r = 0. 34) as well as A and C (r = 0.31) were not significantly correlated. A good statistical relation between values was only found for assay B a nd assay C (r = 0.80, p < 0.001). Three plasma samples were spiked wit h TNF-alpha standard of the corresponding kit to a final concentration of 200 pg/ml. The detection results of these samples were compared wi th the variation conceded by the manufacturer. Assay A detected two sa mples above the corresponding coefficient of intra-assay variation (re covery: 81.8% and 89.2%). All three values obtained with assay B were markedly out of its variation range (recovery: 88.7%, 84.6% and 89.0%) while assay C showed again two results above the intra-assay variatio n (recovery. 92.1% and 89.6%), In our observations we found relevant d ifferences between commercial ELISA kits of different manufacturers, w hich made interpretation of TNF-alpha in human plasma samples difficul t. Additionally, it should be taken into consideration that plasma spe cimen may contain cytokine-binding proteins or autoantibodies which ar e capable of blocking epitopes of TNF-alpha. This may lead to the loss of the necessary immunoreactivity which prevents detection antibodies from recognizing these molecules.