Inflammasomes in Pneumococcal Infection: Innate Immune Sensing and Bacterial Evasion Strategies
Streptococcus pneumoniae frequently colonizes the upper respiratory tract of healthy individuals, but also commonly causes severe invasive infections such as community-acquired pneumonia and meningitis. One of the key virulence factors of pneumococci is t
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Abstract Streptococcus pneumoniae frequently colonizes the upper respiratory tract of healthy individuals, but also commonly causes severe invasive infections such as community-acquired pneumonia and meningitis. One of the key virulence factors of pneumococci is the pore-forming toxin pneumolysin which stimulates cell death and is involved in the evasion of some defense mechanisms. The immune system, however, employs different inflammasomes to sense pneumolysin-induced pore formation, cellular membrane damage, and/or subsequent leakage of bacterial nucleic acid into the host cell cytosol. Canonical inflammasomes are cytosolic multiprotein complexes consisting of a receptor molecule such as NLRP3 or AIM2, the adapter ASC, and caspase-1. NLRP3 and AIM2 inflammasomes mediate cell death and production of important IL-1 family cytokines to recruit leukocytes and defend against S. pneumoniae. Here, we review recent evidence that highlights inflammasomes as critical sensors of S. pneumoniae-induced cellular perturbations, summarize their role in pneumococcal infections, and discuss potential evasion strategies of some emerging pneumococcal strains.
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Introduction.......................................................................................................................... Brief Overview of the Innate Immune Response to S. Pneumoniae Infection.................. Sensing of S. Pneumoniae by Inflammasomes................................................................... Role of Inflammasomes in Pneumococcal Infections......................................................... Evasion of Inflammasome-Dependent Sensing by Emerging Strains ................................ Concluding Remarks ...........................................................................................................
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A. Rabes N. Suttorp B. Opitz (&) Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany e-mail: [email protected] © Springer International Publishing Switzerland 2016 S. Backert (ed.), Inflammasome Signaling and Bacterial Infections, Current Topics in Microbiology and Immunology 397, DOI 10.1007/978-3-319-41171-2_11
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1 Introduction The family Streptococcaceae comprises several clinically important species of which Streptococcus pneumoniae (the pneumococcus) is of particular importance. Similar to group A and B streptococci, S. pneumoniae can be classified as pathobiont, as it colonizes the oro—and nasopharynx of up to 60 % of healthy small children and 10 % of adults (Henriques-Normark and Tuomanen 2013). This colonization is in most cases temporary and asymptomatic; however, it is also a prerequisite of local and life-threatening invasive infections as well as transmission to new susceptible hosts
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