SPP1 and asthma: Thus, the aims of this work were, firstly, to compare the protective effects of wild-type mice versus OPN knockout mice on airway inflammation in asthma, secondly, to analyze if knockout of OPN could disorder the gut/lung microbiome and the intestinal epithelial barrier function to aggravate asthma, and thirdly, to assess whether the protective effect of OPN on asthma is mediated by the gut microbiota, thereby elucidating the association of protective effects of OPN with the microbiota and the mechanisms.