Heterogeneity of IgE response to TDI-HSA conjugates by ELISA in toluene diisocyanate (TDI)-induced occupational asthma (OA) patients

Abstract

Toluene diisocyanate (TDI), a low molecular weight reactive chemical, is known to be a main cause of occupational asthma (OA) in Korea. Although it is thought that inhaled TDI may act as a hapten, the precise mechanisms of TDI-induced OA are unknown. In this study, TDI-human serum albumin (HSA) conjugates (5, 10, 20 and 30 min) were prepared in the range of 1.5 to 5.0 TDI mole/HSA mole. Specific binding of serum IgE to TDI-HSA (30 min) was observed using IgE ELISA as well as ELISA inhibition assay. Around 40% of TDI-induced OA patients were positive for serum specific IgE by ELISA. Degrees of serum IgE binding were different depending on which TDI-HSA conjugate was used as an antigen. Moreover, binding patterns were different depending on the individuals. Interestingly, higher binding of IgE to TDI-HSA (5 min) than to TDI-HSA (30 min) which was more highly substituted was observed in some patients. Probably new antigenic epitopes on carrier proteins were targets of the specific IgE. The results of this study indicated that IgE responses to TDI-HSA conjugates were heterogeneous in TDI-induced OA patients and self-proteins modified by reactive chemicals can become a major target antigen of IgE in certain cases.

Isocyanate vapor-induced antigenicity of human albumin

“…[10][11][12] Antigenicity of isocyanate-albumin conjugates prepared on the basis of the Scheel liquid phase exposure methodology has been reported to vary according to the degree of isocyanate-protein conjugation, with lightly or moderately substituted conjugates better recognized by IgE in limited human studies. [12][13][14] A similar phenomenon has been well-documented in animal models with other low-molecular-weight haptens, in which the degree of substitution affects immune recognition. 15,16 The generation of low substitution ratio isocyanate-albumin conjugates by methods published to date has been challenging because of numerous technical issues, including isocyanate's insolubility in aqueous solutions, reactivity with water, and fast reaction rate with proteins.…”

Cells and mediators in diisocyanate-induced occupational asthma

“…In contrast to classical IgE-mediated allergic responses, most diisocyanates studies show poor correlation between bronchial responses and the presence of specific IgE antibodies to diisocyanates. Only 40% of patients were positive for serum-specific IgE following human serum albumin conjugation [4]. Moreover, various types of inflammatory cells, including eosinophils, are involved in inflammation after diisocyanates binding to airway epithelial cells (AECs) [5].…”

Issues in Diisocyanate Antibody Testing

“…The preferential antigenic site on the conjugate was also considered. Several authors have suggested that hydrophilic groups reacting with the isocyanate might lead to changes in the three-dimensional conformation of the HSA and formation of new antigenic determinants (Wass and Belin, 1989;Son et al, 1998).…”