MMP9 and infectious otitis media: RNA-seq analyses showed that the expression of S100a9 and its downstream target molecules, such as Cxcl1, Cxcl2, Tnfα, Il6, Saa3, Mmp7, Mmp9, and Lcn2 (14, 31–35), were significantly increased in the AOM/DSS group (i.e., AOM/DSS + IgG Ab vs Control), which was consistent with our previous findings in the gene expression profile of CAC mouse model (13).