Neutrophils Directly Recognize Group B Streptococci and Contribute to Interleukin-1β Production during Infection

PLoS One. 2016 Aug 10;11(8):e0160249. doi: 10.1371/journal.pone.0160249. eCollection 2016.

Abstract

Previous studies have shown that the pro-inflammatory cytokine IL-1β has a crucial role in host defenses against group B streptococcus (GBS), a frequent human pathogen, by recruiting neutrophils to infection sites. We examined here the cell types and mechanisms involved in IL-1β production during infection. Using a GBS-induced peritonitis model in mice, we first found that a large proportion of exudate cells contain intracellular IL-1β by immunofluorescence. Of the IL-1β positive cells, 82 and 7% were neutrophils and macrophages, respectively, suggesting that the former cell type might significantly contribute to IL-1β production. Accordingly, depletion of neutrophils with anti-Ly6G antibodies resulted in a significant reduction in the levels of IL-1β, but not of TNF-α or IL-6. We next found that neutrophils are capable of releasing mature IL-1β and TNF-α directly in response to in vitro stimulation with GBS. The production of pro-IL-1β and TNF-α in these cells required the Toll-like receptor (TLR) adaptor MyD88 and the chaperone protein UNC93B1, which is involved in mobilization of a subfamily of TLRs to the endosomes. Moreover, pro-IL-1β processing and IL-1β release was triggered by GBS hemolysin and required components of the canonical inflammasome, including caspase-1, ASC and NLRP3. Collectively our findings indicate that neutrophils make a significant contribution to IL-1β production during GBS infection, thereby amplifying their own recruitment. These cells directly recognize GBS by means of endosomal TLRs and cytosolic sensors, leading to activation of the caspase-1 inflammasome.

MeSH terms

  • Animals
  • Antibodies / immunology
  • Antigens, Ly / immunology
  • Bacterial Proteins / immunology
  • Bacterial Proteins / metabolism
  • Caspase 1 / deficiency
  • Caspase 1 / genetics
  • Caspase 1 / metabolism
  • Disease Models, Animal
  • Female
  • Hemolysin Proteins / immunology
  • Hemolysin Proteins / metabolism
  • Interleukin-1beta / analysis
  • Interleukin-1beta / metabolism*
  • Interleukin-6 / analysis
  • Interleukin-6 / metabolism
  • Membrane Transport Proteins / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Myeloid Differentiation Factor 88 / metabolism
  • NLR Family, Pyrin Domain-Containing 3 Protein / metabolism
  • Neutrophils / immunology
  • Neutrophils / metabolism*
  • Peritonitis / immunology
  • Peritonitis / microbiology
  • Peritonitis / pathology
  • Serogroup
  • Streptococcal Infections / immunology
  • Streptococcal Infections / microbiology
  • Streptococcal Infections / pathology
  • Streptococcus / isolation & purification
  • Streptococcus / physiology*
  • Toll-Like Receptors / metabolism
  • Tumor Necrosis Factor-alpha / analysis
  • Tumor Necrosis Factor-alpha / metabolism

Substances

  • Antibodies
  • Antigens, Ly
  • Bacterial Proteins
  • Hemolysin Proteins
  • Interleukin-1beta
  • Interleukin-6
  • Ly6G antigen, mouse
  • Membrane Transport Proteins
  • Myeloid Differentiation Factor 88
  • NLR Family, Pyrin Domain-Containing 3 Protein
  • Nlrp3 protein, mouse
  • Toll-Like Receptors
  • Tumor Necrosis Factor-alpha
  • UNC93B1 protein, mouse
  • streptococcal group B hemolysin
  • Caspase 1

Grant support

Scylla Biotech Srl, a spin-off company of the University of Messina, provided support in the form laboratory reagents and consumables. C. Beninati and GT own Scylla Biotech Srl and Charybdis Vaccines. The specific roles of these authors are articulated in the ‘author contributions’ section. Scylla Biotech Srl and Charybdis Vaccines did not have any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Work described here was supported by funds granted to Scylla Biotech Srl by the Ministero dell’Università e della Ricerca Scientifica of Italy (Project n. 4/13 ex art. 11 D.M. n. 593).