Characterization of nucleotide-binding oligomerization domain (NOD) protein expression in primary murine microglia.

We demonstrate that primary microglia express nucleotide-binding oligomerization domain (NOD) proteins that are thought to serve as novel pattern recognition receptors for bacterial peptidoglycan motifs. NOD2 is constitutively present in microglia and is upregulated following exposure to Borrelia burgdorferi or Neisseria meningitidis. Its expression is also elevated following exposure to Toll-like receptor (TLR) ligands and muramyl dipeptide (MDP), a putative ligand for NOD2. Microglia express essential downstream effector molecules for NOD2-mediated cell responses, and MDP augments TLR ligand-induced inflammatory cytokine production. Together these data suggest that NOD2 may contribute to microglial immune responses to bacterial pathogens.