A highly sensitive and specific enzyme immunoassay (EIA) for human lymphotoxin (hLT) has been developed. The assay is based upon a sandwich system employing two kinds of anti-hLT antibodies with neutralizing activity. One of them was mouse monoclonal antibody raised against Escherichiacoli-derived recombinant hLT with a deletion of 20 amino-terminal amino acids and used as labelled antibody. The other was rabbit antibody raised against the carboxyl-terminal portion of hLT and used as solid-phase antibody. The EIA employing such a combination was able to detect less than 50 pg/ml of hLT, showing that this method was approximately 5–10 times higher sensitivity than the conventional bioassay employing L929 cell-lysis. The mean recovery of hLT added to serum specimens was 101% and the coefficients of variation were 3.3-7.8% (intra-assay) and 2.9-17.2% (inter-assay). There was a good correlation between the present EIA and the bioassay (r=0.93). (KEY WORDS: Human Lymphotoxin (hLT), Enzyme Immunoassay (EIA), Carboxyl-Terminal Peptide of hLT, Recombinant hLT Muteins with a Deletion of Amino-Terminal Amino Acids).
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