Co-infection subverts mucosal immunity in the upper respiratory tract

► Host responses elicited by a pathogen affect other microbes including other pathogens. ► Effective host responses can be rendered ineffective by co-infection, and vice versa. ► H. influenzae enhances PMN clearance of S. pneumoniae colonization but promotes virulence. ► Influenza increases pneumococcal carriage levels and risk of invasive disease via IFN. ► S. pneumoniae may reduce the risk of S. aureus carriage via adaptive immunity.