Therapeutic effect of surfactant protein D in allergic inflammation of mite-sensitized mice

Summary Background Surfactant protein D (SP‐D) is involved in the innate immunity within the lung and may have important roles in modulating the inflammatory process of asthma. Objective To examine the potential immunomodulating role of SP‐D on the allergic response in mice, and its interaction with the alveolar macrophages (AMs) during allergic inflammation. Methods A recombinant 60 kDa fragment of human SP‐D (rfh SP‐D), Survanta, and budesonide were administrated, respectively, to Der p‐sensitive BALB/c mice before or after allergen challenge (AC). Total and differential cell counts, levels of cytokines in bronchoalveolar lavage fluids(BALFs), and levels of Der p‐specific IgE and IgG1 antibodies in sera, were assayed. The production of nitric oxide (NO), and inducible NO synthase (iNOS) expression, in AMs, were determined by ELISA and RT‐PCR, respectively. Results Instillation of rfh SP‐D to sensitized mice 6 h after AC (therapeutic), but not 24 h before AC (preventive), markedly reduced infiltration of eosinophils, and also reduced levels of IL‐4, IL‐5, eotaxin, and TNF‐α but elevated levels of IFN‐γ in the BALF. These effects were comparable with those obtained with budesonide treatment, whereas Survanta did not have a suppressive effect, either before or after AC. There was significant inhibition of NO production in the rfh SP‐D pre‐treated AMs of allergen‐sensitized mice, but not in naïve mice. Conclusions These results indicate that rfh SP‐D has a therapeutic effect on allergen‐induced bronchial inflammation, and that this might be because of its inhibitory effect on NO and TNF‐α production by AMs, and it thus prevents the development of T‐helper type 2 cytokine response.