Type I Interferons in Immune Defense Against Streptococci

Infections with Streptococcus pneumoniae, Group A Streptococcus (GAS), and Group B Streptococcus (GBS) are among the most frequent bacterial infections in humans and major causes of diseases. Immune responses against streptococci include the induction of type I interferons (IFNs), which are immunomodulatory cytokines with well-established antiviral functions, but ambiguous roles in bacterial infections. Studies of streptococcal infections further highlight the importance of type I IFN signaling in host defense against bacterial pathogens. We discuss the complexity of type I IFN induction by streptococcal ligands and their engagement in stimulating innate immune receptors. Furthermore, we elaborate on the broad physiological role and different impacts of type I IFN signaling on the outcome of streptococcal infections and influenza virus coinfections.