CXCL9 and inflammatory response: Previous reports (30) concerning experimental models of lower respiratory tract infection with M. pneumoniae have indicated that lung disease severity is directly associated with Th1-type cellular immunity; tigecycline treatment significantly reduced the levels of IFN-γ, tumor necrosis factor-α, and IL-1β, CXCL9, and other inflammatory mediators, thereby significantly reducing histological lung inflammation and disease severity.