Epitope Specificity of Anti–Cardiac Troponin I Monoclonal Antibody 8I-7

To the Editor: The monoclonal antibody (MAb)1 8I-7 (International Point of Care Inc.) has been considered a sensitive tool for the detection of human cardiac troponin I (cTnI) for at least 15 years (1). It has been used in several cTnI assays and in different cTnI studies (1–5). According to the manufacturer's data, 8I-7 is specific to the epitope comprising amino acid residues 137–148 of the cTnI molecule. In the March issue of Clinical Chemistry, Savukoski et al. (2) presented a study dedicated to evaluating the epitope specificity of autoantibodies to cTnI (cTnAAbs). In this study, commercial anti-cTnI MAbs specific to different epitopes were used as capture antibodies in sandwich immunoassays with an anti–troponin C MAb used as a tracer. The authors estimated the inhibition of signal after spiking in cTnAAb-positive and cTnAAb-negative (as a control) samples with a ternary troponin complex. The study showed that the anti-TnI MAbs specific to the region located between residues 65 and 158 were the most sensitive to the presence of autoantibodies. The only exception was MAb 8I-7. The signal inhibition obtained for 8I-7 was markedly lower than the signal inhibition found for the MAbs specific for the neighboring epitopes and was similar to that of MAb 625 (the epitope comprising amino acid residues 169–178).