BelTox Annual Meeting location:Namur, Belgium date:28 November 2007
To validate a mouse model of chemical induced asthma we compared a single with a multiple challenge protocol.
On day 1 and 8 BALB/c mice where dermally sensitized with 0.3% TDI (20 µl/ear) or vehicle (acetone/olive oil). From day 15 on the mice received 1 to 6 intranasal instillations (challenges) with 0.1% TDI (10 µl/nostril) or vehicle, with 1 week interval between instillations. The airway responses were measured (Penh and pulmonary resistance) after the last challenge. Mice where sacrificed 24 hours later. Total and differential cell counts were performed in the broncho-alveolar lavage (BAL) fluid and TNF- and MIP-2 concentrations were measured. Total serum IgE, IgG1 and IgG2a levels were measured. Lymphocyte subpopulations (CD4+, CD8+, CD19+) were determined in the auricular (ALN) and cervical (CLN) lymph nodes. IL-4 and IFN- release, in vitro, after concanavalin A (ConA) stimulation, was assessed.
After 1, 2 or 3 challenges with TDI a significant increase in airway hyperreactivity was found in TDI sensitized mice. This response diminished with further challenges. An increase in the total cell count and percent neutrophils (15-20 %) was found in BAL fluid, but this decreased with increasing TDI challenges. There was a decrease in the percent of CD4+ and CD8+ cells and an increase in the percent of CD19+ cells in the ALN and CLN, which was restored to control values with increasing TDI challenges. Increased levels of IL-4 were found in CLN cells in vitro. The total serum IgE levels in TDI sensitized mice were always significantly increased compared to control mice.
Ventilatory responses and lung inflammation diminish after multiple challenges with 1 week interval between challenges. It is likely that this ‘fading out’ is due to the acquisition of tolerance. Nevertheless, some immunologic parameters are still increased after 6 challenges with TDI.