Abstract
Brown Norway rats are widely used as a model of asthma, whereas Sprague Dawley rats do not develop allergic reactions under the same conditions. Given the importance of alveolar macrophages (AM) in down-regulating cellular immune responses in the lung, we postulated that the different susceptibilities in the development of airway allergic reactions in these rat strains may be related to functional differences in their AM. We investigated the production of important mediators in asthma, namely tumour necrosis factor (TNF), interleukin-10 (IL-10), IL-12, IL-13, nitric oxide (NO) and macrophage inflammatory protein-1alpha (MIP-1alpha), by AM of unsensitized Sprague Dawley and Brown Norway rats. AM were purified by adherence and stimulated with OX8 (anti-CD8 antibody) or LPS. OX8 stimulation significantly increased the release of TNF, IL-10 and NO in both strains of rats, whereas MIP-1alpha and IL-12 release were increased in Brown Norway rats only. Interestingly, stimulated AM from Sprague Dawley rats released significantly more TNF and less IL-10, IL-12, IL-13, MIP-1alpha and NO compared with AM from Brown Norway rats. These differences were also observed at the mRNA level, except for TNF. Thus, AM from Brown Norway and Sprague Dawley rats are functionally different. Furthermore, LPS- and OX8-stimulated AM from Brown Norway rats produce more Th2 type cytokines (IL-10 and IL-13) than AM from Sprague Dawley rats, suggesting that these cells may play an important role in creating a cytokine milieu that may favour the development of allergic reactions.