Experimental model of skin/lung responses

Introduction
Diisocyanates are the leading cause of chemical-induced occupational asthma. However, despite reductions in workplace respiratory exposures, isocyanate asthma continues to occur. This has prompted a focus on the skin as a route of sensitisation. We have produced immunologically mediated respiratory responses in mice after initial dermal sensitization using a respiratory sensitizer - toluene diisocyanate (TDI).

Methods
Mice were dermally sensitized on days 1 and 8. On day 15, the mice receive a single respiratory challenge. Immediately after the challenge, the ‘early’ ventilatory response (40 min) was monitored and 22h later airway hyperreactivity (AHR) upon methacholine provocation was measured. Pulmonary inflammation was assessed by bronchoalveolar lavage (BAL) analysis. Analysed immune related parameters comprised total serum IgE and local draining lymph nodes.

Results
Mice sensitized and challenged with TDI showed immediate respiratory responses after challenge. Twenty two hours later, these mice showed pronounced AHR, compared to the controls, associated with a severe neutrophilic inflammation. TDI-sensitized and challenged mice showed, in the auricular lymph nodes, an increase in total number of T helper (CD4+), activated/regulatory T (CD4+CD25+), T cytotoxic (CD8+) and B (CD19+) lymphocytes together with an increased in vitro secretion of IFN-g, IL-4, IL-10 and IL-13. An increase in total serum IgE was found. These data were confirmed by applying two other respiratory sensitizers in the model – trimelletic anhydride and ammonium persulfate – which both tested positive. If the model (using TDI) was performed in SCID mice (mice lacking T and B lymphocytes), none of the above described responses were found.

Discussion
We have been successful in our attempt to develop a model of chemical-induced asthma, with initial dermal sensitization, followed by a single airway challenge. Thereby confirming the skin/lung hypothesis, that dermal sensitization can lead to asthma-like responses. Furthermore, we showed that these skin/lung responses depend on the presence of lymphocytes.