Acid sphingomyelinase regulates TH2‐cytokine release and bronchial asthma

BACKGROUND: Allergic diseases and especially allergic asthma are widespread diseases with high prevalence in childhood, but also in adults. Acid sphingomyelinase (ASM) is a key regulator of the sphingolipid pathway. Previous studies defined the association of ASM with the pathogenesis of TH 1-directed lung diseases like cystic fibrosis and acute lung injury. Here, we define the role of ASM in TH 2-regulated allergic bronchial asthma. METHODS: To determine the role of Asm under baseline conditions, wild-type (WT) and Asm(-/-) mice were ventilated with a flexiVent setup and bronchial hyperresponsiveness was determined using acetylcholine. Flow cytometry and cytokine measurements in bronchoalveolar lavage fluid and lung tissue were followed by in vitro TH 2 differentiations with cells from WT and Asm(-/-) mice and blockade of Asm with amitriptyline. As proof of principle, we conducted an ovalbumin-induced model of asthma in WT- and Asm(-/-) mice. RESULTS: At baseline, Asm(-/-) mice showed better lung mechanics, but unaltered bronchial hyperresponsiveness. Higher numbers of Asm(-/-) T cells in bronchoalveolar lavage fluid released lower levels of IL-4 and IL-5, and these results were paralleled by decreased production of typical TH 2 cytokines in Asm(-/-) T lymphocytes in vitro. This phenotype could be imitated by incubation of T cells with amitriptyline. In the ovalbumin asthma model, Asm(-/-) animals were protected from high disease activity and showed better lung functions and lower levels of eosinophils and TH 2 cytokines. CONCLUSION: Asm deficiency could induce higher numbers of TH 2 cells in the lung, but those cells release decreased TH 2 cytokine levels. Hereby, Asm(-/-) animals are protected from bronchial asthma, which possibly offers novel therapeutic strategies, for example, with ASM blockade.