SO2-induced bronchopathy decreases airway sensitization with intratracheal ovalbumin in the rat

We investigated in this study the effect of SO2-induced bronchopathy on airway sensitization to ovalbumin in the rat. Sprague-Dawley rats were immunized with a single intratracheal injection of ovalbumin (OA) 100 micrograms in 0.1 ml PBS or 0.1 ml Bordetella pertussis (BP) heat-killed vaccine (6.5 X 10(9) cells X ml-1). The rats were primed immediately after SO2 exposure (60 h, 200 ppm; group I, n = 16) and three months after exposure was achieved (group II, n = 24), then compared to a control group exposed to air (group III, n = 30). Airway sensitization was evaluated by the in vitro contractile response to antigen challenge using paired tracheal rings. Specific IgE level was determined with PCA reactions. No significant difference was found in the maximal contractile responses to carbamyl choline within and between each group. Excepted in animals of group III, OA alone was not found able to sensitize the airways. When OA was used in association with BP, sensitization of the airways occurred, but this occurrence was found to depend upon a previous SO2 exposure: 73.3% in group III, 41.7% in group II and 25% in group I were sensitized. In addition, only five animals (BP + OA injected rats of group III) displayed a PCA positive reaction. It is concluded that: 1) the concomitant intratracheal injection of BP with OA increased the occurrence of specific airway sensitization, 2) a previous chronic exposure to SO2 decreased the specific tracheal smooth muscle sensitization to intratracheal ovalbumin. This decrease persisted, although slighter, when immunization was done three months after the exposure to SO2 was stopped.