TDI-specific IgG and IgE levels in serum samples from each worker at baseline, 6-, and 12- months post-employment were measured using previously described enzyme-linked immunosorbent assays (ELISA) [Ye, et al. 2006]. Briefly, TDI-albumin conjugates (10 μg/ml) prepared by mixed phase (vapor/liquid) exposure methods were used to coat 96-well NUNC Maxisorp ELISA plates (Thermo Fisher Scientific Inc., Waltham, MA), followed by blocking with 3% dry milk in phosphate buffered saline (PBS). Workers’ sera were diluted in 3% milk + PBS + 0.05% Tween 20 and TDI-specific IgG was detected with horseradish peroxidase linked anti-human IgG antibodies from Pharmingen (San Jose, CA), and expressed as an end-titer. For detecting TDI-specific IgE, plates were developed with biotinylated goat anti-human IgE (Bethyl; Montgomery, TX) followed by alkaline phosphatase conjugated streptavidin, and pNPP substrate from Thermo Fisher Scientific Inc.