The interaction of particulate and gaseous
pollutants in their effects on the severity of allergic
inflammation and airway responsiveness are not well understood. We assessed the effect of exposure to NO(2) in the presence or absence of repetitive treatment with
carbon nanoparticle (CNP) during
allergen sensitization and challenges in Brown-Norway (BN) rat, in order to assess their interactions on lung function and airway responses (AR) to
allergen and
methacholine (MCH), end-expiratory lung volume (EELV), bronchoalveolar lavage fluid (BALF) cellular content, serum and BALF
cytokine levels and histological changes. Animals were divided into the following groups (n = 6): Control; CNP (Degussa-FW2): 13 nm, 0.5 mg/kg instilled intratracheally ×3 at 7-day intervals; OVA:
ovalbumin-sensitised; OVA+CNP: both sensitized and exposed to CNP. Rats were divided into equal groups exposed either to air or to NO(2), 10 ppm, 6 h/d, 5d/wk for 4 weeks. Exposure to NO(2), significantly enhanced
lung inflammation and airway reactivity, with a significantly larger effect in animals sensitized to
allergen, which was related to a higher expression of TH1 and TH2-type
cytokines. Conversely, exposure to NO(2) in animals undergoing repeated tracheal instillation of CNP alone, increased BALF neutrophilia and enhanced the expression of TH1
cytokines: TNF-α and IFN-γ, but did not show an additive effect on airway reactivity in comparison to NO(2) alone. The exposure to NO(2) combined with CNP treatment and
allergen sensitization however, unexpectedly resulted in a significant decrease in both airway reactivity to
allergen and to
methacholine, and a reduction in TH2-type
cytokines compared to
allergen sensitization alone. EELV was significantly reduced with sensitization, CNP treatment or both. These data suggest an immunomodulatory effect of repeated tracheal instillation of CNP on the proinflammatory effects of NO(2) exposure in sensitized BN rat. Furthermore, our findings suggest that NO(2), CNP and OVA sensitization may significantly slow overall lung growth in parenchymally mature animals.