Acute inhibition of inducible nitric oxide synthase but not its absence suppresses asthma-like responses Richardt G. Landgraf, Momtchilo Russo, Sonia Jancar * Department of Immunology, Institute of Biomedical Sciences, University of Sa ˜o Paulo, Sa ˜o Paulo, Brazil Received 28 October 2004; received in revised form 26 April 2005; accepted 29 April 2005 Available online 14 July 2005 Abstract In the present study we investigated the lymphocytes infiltration and other parameters of allergic lung inflammation comparing mice submitted to acute suppression of nitric oxide synthesis with mice deficient in inducible nitric oxide synthase (NOS2 À/À ) gene. At weekly intervals C57Bl/6 mice, wild type and NOS2 À/À were sensitized twice with ovalbumin-alumen and challenged twice with ovalbumin aerosol and lungs examined 24 h later. In wild type mice, treatment with nitric oxide synthase inhibitor, N N -nitro-l-arginine-methyl-ester (l-NAME) or aminoguanidine (i.p., 30 min before each ovalbumin challenge) caused a significant decrease in bronchoalveolar lavage cell number: eosinophils (90%), lymphocytes NK1.1 + (70%), Tgy + (50%), CD4 + (55%), CD8 + (60%) and B220 + (65%). Both inhibitors abolished airway hyperreactivity and significantly reduced mucus secretion (l-NAME 64%; aminoguanidine 58%). Surprisingly, in NOS2 À/À mice these parameters of allergic lung inflammation were not significantly different when compared with wild type mice. In addition, treatment of NOS2 À/À mice with l-NAME or aminoguanidine did not affect these parameters. Thus, acute inhibition of NOS2 activity inhibits asthma- like responses but absence of NOS2 has no affect. D 2005 Elsevier B.V. All rights reserved. Keywords: Nitric oxide; Eosinophil; Airway inflammation; Asthma; Hyperreactivity 1. Introduction Asthma is a chronic inflammatory disease of the airways characterized by lymphocytes and eosinophil infiltration, where Th2-dependent mechanisms play a central role in eosinophil recruitment to the airways, mucus hyper secre- tion and airway hyperreactivity. The involvement of NK1.1 + and gy T cells in allergic lung inflammation has been previously documented. We have shown a clear increase in the number of gy and NK1.1 T cells as well as of eosinophils in the bronchoalveolar lavage of immunized mice after ovalbumin challenge (Gama Landgraf et al., 2003). It was also demonstrated that depletion or absence of NK1.1 + cells before immunization inhibits lung eosinophilia in a mouse model of asthma (Korsgren et al., 1999; Lisbonne et al., 2003) and that gy T cells appear to be required for development of a Th2 mediated lung inflam- mation in mice (Zuany-Amorim et al., 1998). Nitric oxide seems to have an important role in amplifying and perpetuating Th2 mediated inflammatory responses. It has been speculated that the large amount of nitric oxide generated in the asthmatic airways may result in suppression of Th1 cells and a concomitant reduction of interferon-g (IFN-g) levels, leading to proliferation of Th2 cells (reviewed by Ricciardolo, 2003). Exhaled nitric oxide was found in pediatric (Colon- Semidey et al., 2000) and adult asthmatics (Alving et al., 1993; Kharitonov et al., 1994). Nitric oxide can be generated enzymatically by three distinct isoforms of nitric oxide synthases: NOS1, NOS2 and NOS3 expressed by different cell types present in normal or inflamed lung tissue. NOS1 and NOS3 isoforms are expressed constitu- tively and produce low levels of nitric oxide whereas NOS2 0014-2999/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ejphar.2005.04.047 * Corresponding author. Universidade de Sa ˜o Paulo, Instituto de Cie ˆncias Biome ´dicas, Departamento de Imunologia, Av. Prof. Lineu Prestes, 1730, Sa ˜o Paulo-SP-Brazil, CEP: 05508-900. Tel./fax: +55 11 3091 7744. E-mail address: sojancar@icb.usp.br (S. Jancar). European Journal of Pharmacology 518 (2005) 212 – 220 www.elsevier.com/locate/ejphar