ABSTRACTNeisseria meningitidiscolonizes the nasopharyngeal mucosa of healthy populations asymptomatically, although the bacterial surface is rich in motifs that activate the host innate immunity. What determines the tolerant host response to this bacterium in asymptomatic carriers is poorly understood. We demonstrated that the conserved meningococcal surface protein NhhA orchestrates monocyte (Mo) differentiation specifically into macrophage-like cells with a CD200Rhiphenotype (NhhA-Mφ). In response to meningococcal stimulation, NhhA-Mφ failed to produce proinflammatory mediators. Instead, they upregulated interleukin-10 (IL-10) and Th2/regulatory T cell (Treg)-attracting chemokines, such as CCL17, CCL18, and CCL22. Moreover, NhhA-Mφ were highly efficient in eliminating bacteria. Thein vivovalidity of these findings was corroborated using a murine model challenged withN. meningitidissystematically or intranasally. The NhhA-modulated immune response protected mice from septic shock; Mo/Mφ depletion abolished this protective effect. Intranasal administration of NhhA induced an anti-inflammatory response, which was associated withN. meningitidispersistence at the nasopharynx.In vitrostudies demonstrated that NhhA-triggered Mo differentiation occurred upon engaged Toll-like receptor 1 (TLR1)/TLR2 signaling and extracellular signal-regulated kinase (ERK) and Jun N-terminal protein kinase (JNK) activation and required endogenously produced IL-10 and tumor necrosis factor alpha (TNF-α). Our findings reveal a strategy that might be adopted byN. meningitidisto maintain asymptomatic nasopharyngeal colonization.IMPORTANCENeisseria meningitidisis an opportunistic human-specific pathogen that colonizes the nasopharyngeal mucosa asymptomatically in approximately 10% of individuals. Very little is known about how this bacterium evades immune activation during the carriage stage. Here, we observed thatN. meningitidis, via the conserved surface protein NhhA, skewed monocyte differentiation into macrophages with a CD200Rhiphenotype. Bothin vivoandin vitrodata demonstrated that these macrophages, upon meningococcal infection, played an important role in forming a homeostatic immune microenvironment through their capacity to eliminate invading bacteria and to generate anti-inflammatory mediators. This work provides novel insight into the mechanisms underlying the commensal persistence ofN. meningitidis.
Evidence for Tyrosine-Linked Glycosaminoglycan in a Bacterial Surface Protein
