Endosomal recognition of Lactococcus lactis G121 and its RNA by dendritic cells is key to its allergy-protective effects

J Allergy Clin Immunol. 2017 Feb;139(2):667-678.e5. doi: 10.1016/j.jaci.2016.06.018. Epub 2016 Jul 15.

Abstract

Background: Bacterial cowshed isolates are allergy protective in mice; however, the underlying mechanisms are largely unknown. We examined the ability of Lactococcus lactis G121 to prevent allergic inflammatory reactions.

Objective: We sought to identify the ligands and pattern recognition receptors through which L lactis G121 confers allergy protection.

Methods: L lactis G121-induced cytokine release and surface expression of costimulatory molecules by untreated or inhibitor-treated (bafilomycin and cytochalasin D) human monocyte-derived dendritic cells (moDCs), bone marrow-derived mouse dendritic cells (BMDCs), and moDC/naive CD4+ T-cell cocultures were analyzed by using ELISA and flow cytometry. The pathology of ovalbumin-induced acute allergic airway inflammation after adoptive transfer of BMDCs was examined by means of microscopy.

Results: L lactis G121-treated murine BMDCs and human moDCs released TH1-polarizing cytokines and induced TH1 T cells. Inhibiting phagocytosis and endosomal acidification in BMDCs or moDCs impaired the release of TH1-polarizing cytokines, costimulatory molecule expression, and T-cell activation on L lactis G121 challenge. In vivo allergy protection mediated by L lactis G121 was dependent on endosomal acidification in dendritic cells (DCs). Toll-like receptor (Tlr) 13-/- BMDCs showed a weak response to L lactis G121 and were unresponsive to its RNA. The TH1-polarizing activity of L lactis G121-treated human DCs was blocked by TLR8-specific inhibitors, mediated by L lactis G121 RNA, and synergistically enhanced by activation of nucleotide-binding oligomerization domain-containing protein (NOD) 2.

Conclusion: Bacterial RNA is the main driver of L lactis G121-mediated protection against experimentally induced allergy and requires both bacterial uptake by DCs and endosomal acidification. In mice L lactis G121 RNA signals through TLR13; however, the most likely intracellular receptor in human subjects is TLR8.

Keywords: Allergy protection; Lactococcus lactis G121; Toll-like receptor 13; Toll-like receptor 8; bacterial RNA; dendritic cells; endosomal acidification; pattern recognition receptor.

MeSH terms

  • Animals
  • Antigens, Bacterial / immunology*
  • Cattle
  • Cells, Cultured
  • Cytokines / metabolism
  • Dendritic Cells / immunology*
  • Disease Models, Animal
  • Endosomes / metabolism*
  • Female
  • Humans
  • Lactococcus lactis / immunology*
  • Lung / immunology*
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Milk Hypersensitivity / immunology*
  • Milk Hypersensitivity / prevention & control
  • Nod2 Signaling Adaptor Protein / metabolism
  • RNA, Bacterial / immunology*
  • Th1 Cells / immunology
  • Toll-Like Receptor 8 / antagonists & inhibitors
  • Toll-Like Receptors / genetics

Substances

  • Antigens, Bacterial
  • Cytokines
  • NOD2 protein, human
  • Nod2 Signaling Adaptor Protein
  • RNA, Bacterial
  • TLR8 protein, human
  • Tlr13 protein, mouse
  • Toll-Like Receptor 8
  • Toll-Like Receptors