Microarray gene expression profiling of peripheral blood mononuclear cells (PBMC) obtained from acute otitis media (AOM) patients. Peripheral blood was isolated from patients before and after the onset of clinical AOM caused by Nontypeable Haemophilus influenzae (NTHi) infection, in children at 6 to 30 months of age (n=4). PBMCs were isolated from blood samples by Ficoll gradient. The diagnosis of AOM was based on symptoms of fever, irritability or ear ache and physical signs of inflammation of the tympanic membrane with the presence of middle ear fluid.