SPN and infection: Immunofluorescence staining for the complement component deposition on the middle ear epithelium on day 1 post Spn infection showed increased C3, C5aR (Fig. 6A), and C5b-9 (Fig. 6B) deposition on the inflammatory middle ear epithelium in the cohorts infected with both IAV and Spn compared to those infected with either pathogen alone.