EAST AND CAP SPECIFICITY FOR THE EVALUATION OF IGE AND IGG ANTIBODIESTO DIISOCYANATE-HSA CONJUGATES

Sera of 54 symptomatic workers showing sensitization to isocyanate-hum an serum albumin (HSA) conjugates were subjected to parallel enzyme al lergosorbent test (EAST) and CAP measurements to determine IgE antibod ies to diphenylmethane diisocyanate-HSA, toluene diisocyante-HSA and h examethylene diisocyanate-HSA. Results of both methods correlated rath er well with each other. In comparison to the EAST results, the CAP va lues were twice as high, and 4, 17 and 13% more frequently positive fi ndings were obtained with the three different antigens. Autoinhibition performed with both methods proved the specificity of IgE binding in 92% of sera in EAST and in 89% of sera in CAP if values of greater tha n or equal to 0.35 kU/l were considered. The total IgE level in sera i nfluenced the antibody results. Four of 20 sera studied by autoinhibit ion had a total IgE of >700 kU/l, and two of them did not show signifi cant autoinhibition with all conjugates by CAP and one serum by EAST. In addition, three of these sera showed an elevated binding to control HSA only (0.31-0.5 kU/l), and two revealed only a slightly increased IgE binding when compared with the HSA control (ratio of isocyanate-HS A to HSA, <2). Only 2 of the 16 sera with a total IgE level of <700 kU /l yielded a noninhibitory positive CAP result, whereas all positive E AST values of these sera could be significantly blocked by autoinhibit ion. Therefore, we suggest regarding EAST and CAP IgE results to isocy anate-HSA as positive if they exceed HSA control by 100% and are above 0.35 kU/l. Weak positive CAP results (less than or equal to 1 kU/l), especially of sera with total IgE >700 kU/l, should by confirmed by in hibition experiments. Twelve of 40 symptomatic isocyanate workers exhi bited borderline or weakly increased IgG values for diisocyanate-HSA c onjugates in the CAP system and IgG-EAST. HSA tested in EAST as a refe rence showed nearly the same results as the isocyanate-HSA conjugates. Tn the 23 inhibition experiments, IgG-binding specificity was not con firmed. These findings imply IgG measurement to be of no diagnostic va lue in isocyanate-induced airway disorders.