Adjuvant Activity of Ambient Particulate Matter in Macrophage Activity-Suppressed, N-Acetylcysteine-Treated, iNOS- and IL-4-Deficient Mice

Abstract

In previous studies, we have shown strong adjuvant activity for Ottawa dust (EHC-93) after coexposure of the BALB/c mouse to EHC-93 and ovalbumin. Mice were intranasally sensitized at days 0 and 14 with 200 μg ovalbumin and 150 μg EHC-93, and challenged with ovalbumin at days 35, 38, and 41 with 200 μg ovalbumin. Mice were autopsied at day 42. This adjuvant activity was shown for the antibody response to ovalbumin (immunoglobulins E, G₁, and G_2a), histopathological lesions in the lung, cytokines, and the numbers of eosinophils in lung lavages. To study the mechanisms of this adjuvant activity, mice (BALB/c C.D2-Vil6) with natural-resistance-associated macrophage protein (Nramp1^s), BALB/c mice pretreated with the antioxidant N-acetylcysteine (NAC), mice (B6.129P2-Nos2tmLau) deficient in inducible nitric oxide synthase (iNOS), and mice with interleukin-4 (IL-4) deficiency (BALB/cIl4< tm2Nnt) were coexposed to ovalbumin and EHC-93. Our studies have shown that the adjuvant activity induced after such coexposure does not change if the macrophage activation of the mice is disturbed or if the mice have been pretreated with N-acetylcysteine. In addition, the adjuvant activity does not develop through the pathway in which inducible nitric oxide synthase is involved. Because the histopathological lesions are statistically significant less in the IL-4 knockout strain in comparison with the wild type, we conclude that interleukin-4 might play an important role in the adjuvant activity caused by EHC-93.

The authors thank D. Kegler, H. Strootman, D. Elberts, P. van Schaaik, and C. Moolenbeek for skilful biotechnical assistance, and B. Nagarajah, J. P. Vermeulen, and S. G. P. M. de Waal-Jacobs for histotechnical assistance. This investigation was performed within the European Union study entitled “Respiratory Allergy and Inflammation Due to Ambient Particles” (RAIAP, CLRT-2000-00792).