Crucial Role of Nucleic Acid Sensing via Endosomal Toll-Like Receptors for the Defense of Streptococcus pyogenes in vitro and in vivo

Abstract

Streptococcus pyogenes is a major human pathogen causing a variety of diseases ranging from common pharyngitis to life-threatening soft tissue infections and sepsis. Microbial nucleic acids, especially bacterial RNA, have recently been recognized as a major group of pathogen-associated molecular patterns (PAMPs) involved in the detection of Streptococcus pyogenes via endosomal Toll-like receptors (TLRs) in vitro . However, the individual contribution and cooperation between TLRs as well as cell-type and strain specific differences in dependency on nucleic acid detection during S. pyogenes infection in vitro have not been clarified in detail. Moreover, the role of particularly bacterial RNA for the defense of S. pyogenes infection in vivo remains poorly defined. In this study, we report that in all investigated innate immune cells involved in the resolution of bacterial infections, including murine macrophages, dendritic cells and neutrophils, recognition of S. pyogenes strain ATCC12344 is almost completely dependent on nucleic acid sensing via endosomal TLRs at lower MOIs, whereas at higher MOIs, detection via TLR2 plays an additional, yet redundant role. We further demonstrate that different S. pyogenes strains display a considerable inter-strain variability with respect to their nucleic acid dependent recognition. Moreover, TLR13-dependent recognition of S. pyogenes RNA is largely non-redundant in bone marrow-derived macrophages (BMDMs), but less relevant in neutrophils and bone marrow-derived myeloid dendritic cells (BMDCs) for the induction of an innate immune response in vitro . In vivo , we show that a loss of nucleic acid sensing blunts early recognition of S. pyogenes , leading to a reduced local containment of the bacterial infection with subsequent pronounced systemic inflammation at later time points. Thus, our results argue for a crucial role of nucleic acid sensing via endosomal TLRs in defense of S. pyogenes infection both in vitro and in vivo .

Inflammatory Joint Disease Is a Risk Factor for Streptococcal Sepsis and Septic Arthritis in Mice

“…Although neutrophils are unconditionally indispensable for reducing the bacterial load during infection, they are also suspected to be involved in the pathogenesis of SA (36). They express high densities of pattern recognition receptors and these receptors may be rapidly activated upon encounter with streptococcal components (37)(38)(39). Receptor activation leads to the discharge of inflammatory mediators, thereby attracting further cells and feeding into the derailment of the immune response in SA (40,41).…”

Toll-like Receptors and the Control of Immunity

“…Sensing of bacterial ribosomal RNA may be most important during encounters with microbes whose cell walls are modified in ways that render them poorly immunostimulatory. An example of such a microbe is group B Streptococcus, where TLR13 is the near-exclusive driver of inflammatory responses (Hafner et al, 2019;Hidmark et al, 2012). In the next sections, we will shift focus to the downstream consequences of PAMP detection by TLRs.…”

TLR8 and complement C5 induce cytokine release and thrombin activation in human whole blood challenged with Gram-positive bacteria

“…In murine macrophages TLR13 has a similar function as human TLR8, and deficiency in endosomal TLR signaling impaired early S. pyogenes recognition in a murine model of subcutaneous infection. Loss of endosomal TLR function led to local bacterial overgrowth and hyperinflammation, impaired bacterial containment, and systemic inflammation 42 . Analogous, human TLR8 may be important for early detection of bacteria in the tissue, induction of inflammation, and leukocyte recruitment to the focus of infection.…”