Ranulfo Lemus

Isocyanate-conjugated human lung epithelial cell proteins: A link between exposure and asthma?

BACKGROUND Isocyanates are a group of highly reactive cross-linking chemicals that cause airway inflammation and asthma in exposed individuals. Isocyanates have been detected along the airway epithelia of exposed workers and animals, prompting the hypothesis that isocyanates can directly bind to epithelial cell proteins. OBJECTIVE We tested the hypothesis that hexamethylene diisocyanate (HDI) binds directly to lung epithelial cell proteins and initiated studies to evaluate the immunostimulatory potential of HDI-conjugated lung epithelial cell proteins. METHODS Human lung epithelial cell lines were exposed to vapor- and liquid-phase HDI, and the cellular proteins were analyzed for HDI conjugation by Western blotting and tested for the ability to induce lymphocyte proliferation in vitro. RESULTS A number of epithelial cell polypeptides, ranging from 25 to 110 kd in apparent molecular weight, were conjugated with HDI after exposure of the human lung epithelial cell lines (A549 and NCI-H292) to HDI concentrations greater than 0.005% (vol/vol) in the liquid phase. Vapor-phase HDI exposure resulted in a more restricted HDI conjugation pattern, with major HDI-conjugated polypeptides migrating at 47, 71, and 91 kd. HDI-conjugated epithelial cell proteins specifically stimulated proliferation of PBMCs from subjects with isocyanate-induced asthma but not HDI-exposed nonasthmatic individuals or atopic subjects with nonisocyanate-related asthma. CONCLUSIONS The data demonstrate that epithelial cell proteins readily react with HDI and that HDI-conjugated epithelial cell proteins can stimulate lymphocyte proliferation. Further characterization and evaluation of HDI-conjugated epithelial cell proteins will elucidate their potential role in the pathogenesis of isocyanate-induced asthma.

Importance of inflammatory and immune components in a mouse model of airway reactivity to toluene diisocyanate (TDI)

Background Nearly 9 million individuals are exposed to agents in the workplace associated with asthma, and isocyanates represent the most common cause of occupationally induced asthma.

Isolated airway exposure to toluene diisocyanate results in skin sensitization

Toluene diisocyanate (TDI), a highly reactive industrial chemical is a leading cause of occupational asthma in westernized countries. It has also been reported to be a skin sensitizer in mice and guinea pigs although instances of skin sensitivity in humans are rare. It is uncertain if skin-contact is necessary to initiate the dermal sensitization. This study sought to determine if exclusive airway exposure to TDI could result in skin sensitivity. A group of guinea pigs was administered 50 microl of 0.6% TDI intratracheally (it.), another group received intranasal (in.) application of 0.6, 1.2, or 1.8% TDI. Eighty percent (4/5) of the it.-dosed animals, and 92% (11/12) of in.-dosed animals exhibited skin sensitivity. None of 14 control animals gave a positive reaction to patch challenge with TDI. These findings indicate that exclusive exposure of the airways to TDI can result in skin sensitivity and suggest that such events may be possible in TDI workers and should be considered in all workers exposed via the airways to chemical sensitizers.

Conjugation of Haptens

Many naturally occurring proteins, peptides, carbohydrates, nucleic acids, and lipids, as well as synthetic peptides, are successful immunogens. To elicit an immune response, a compound must contain an antigenic determinant or epitope and must be of sufficient size to initiate lymphocyte activation necessary for an antibody response. In practice, small chemical compounds (haptens) are generally not good immunogens. However, when attached to macromolecules (carriers), they can become immunogenic. An immunogen must have epitopes that can be recognized by antigen-presenting cells and a T-cell receptor, and it must be degradable. Haptens and corresponding hapten-carrier conjugates have been essential to the development of sensitive quantitative and qualitative immunoassays. In the design of hapten conjugates, consideration must be given to the hapten, the carrier, the coupling strategy, and the hapten density because the amount of hapten attached to the carrier influences the strength of the immune response directed toward the newly created antigenic determinant. Hence the haptenic density of the conjugate is also important in the development of immunoassays. The optimal epitope density of a conjugate to elicit either a strong immune response or provide the best immunoassay is dependent on the structure of the epitope and the nature of the immunoassay. The aim of this chapter is to describe the diverse techniques used to couple haptens to carriers and provide guidance in the selection of the most appropriate procedure for a particular hapten.