Mechanisms of isocyanate sensitisation. An in vitro approach.

Although there is an abundance of clinical evidence which suggests that the inhalation of isocyanates can induce occupational asthma, the immunological basis for the disease is not understood. We have investigated immune cell responses to isocyanate using the cell line mono-mac-6, by measuring the production of hydrogen peroxide, and the expression of ICAM-1 following challenge with isocyanates and their corresponding amines. We observed an increase in the levels of intracellular peroxide, in addition to an upregulation of ICAM-1 expression (P<0.05), following cell stimulation with isocyanates, which was not apparent following stimulation with amines. From the results of this study we hypothesise that the production of reactive oxygen species (ROS) by monocytic cells at the site of exposure to an isocyanate may have two potential outcomes. The first is that the ROS may contribute to tissue damage at the site of inflammation, and then secondly, it is possible this production of hydrogen peroxide may also induce the upregulation of adhesion markers on monocytic cells, specifically ICAM-1, which may potentiate the infiltration and adhesion of cells at the site of inflammation.

Colophony: an in vitro model for the induction of sensitization.

BACKGROUND: The potential of colophony fumes from soldering flux to induce asthma has been known since the 1970s, however, no direct in vitro or in vivo evidence has been reported. The present study investigated the potential of colophony to stimulate human phagocytic cells to produce reactive oxygen species. METHODS: The human cell line HL-60 was differentiated to produce cells with a monocyte-like and a neutrophil-like phenotypes. A number of procedures were used to confirm the phenotype of these differentiated cells including morphology, esterase activity, flow cytometry and phagocytosis. The potential of colophony to stimulate human phagocytic cells to produce reactive oxygen species was monitored using flow cytoenzymology. RESULTS: We were able to show that intracellular peroxide levels were increased in both monocyte-like and neutrophil-like cells, but not in undifferentiated HL-60 cells following the addition of colophony. CONCLUSIONS: The resin acid epoxides and hydroperoxides which have been suggested to be sensitizers in contact allergy, are degraded during the soldering process. However, conditions for the oxidation of colophony may occur in vivo as a result of the colophony-induced oxidative burst from neutrophils and monocytes. These oxidation products may then interact with body proteins to further initiate immune responses. Therefore for the preparation of low molecular weight chemical (LMWC)-protein conjugates, consideration must be taken to determine whether the LMWC is undergoing a reaction in vivo before it is interacting with body proteins.