B. pertussis, tracheal cytotoxin biases NOD signaling to suppress IL-1 mediated inflammation and evade adaptive immunity

Abstract

Bordetella pertussis releases the monomeric peptidoglycan (PGN) fragment tracheal cytotoxin (TCT) due to inefficient recycling by the permease AmpG. Releasing this PGN is metabolically costly and potentially immune alarming and the benefits to B. pertussis are unclear. While TCT has been characterized as a potent NOD1 agonist capable of causing the extrusion of ciliated cells, in vitro, the consequences of its release have yet to be studied in vivo. Here we show that selective PGN release by B. pertussis biases host PGN sensing toward NOD1 and away from NOD2, suppressing IL-1{beta}-driven inflammation and blunting adaptive immune recruitment. Mice infected with a TCT over-releasing strain (TCT(+)) exhibit reduced pulmonary immunopathology relative to wild type (WT) and a TCT-under-releasing strain (TCT(-)), despite similar bacterial burdens. NOD reporter assays demonstrate that TCT release enhances NOD1 activation and inversely correlates with NOD2 activation. Bulk transcriptomic analysis of infected lungs shows that B. pertussis PGN release dampens pro-inflammatory transcriptional programs. Single-cell transcriptomic determined Nod2 expression is limited to inflammatory myeloid subsets. IL-1 family genes were highly enriched in Nod2- but not Nod1 expressing alveolar macrophages. Upstream regulator analysis predicted IL-1{beta} as a major driver of B. pertussis inflammation, which was enhanced by the absence of PGN release. Flow cytometry shows that PGN release skews macrophages polarization toward M2 and away from M1 in a NOD1 dependent manner. Finally, extracellular release of PGN and subsequent reduced IL-1 production facilitated the suppression fibroblast chemokine programs (e.g., CXCL13, CCL19), diminished recruitment of B and T cells, reduced iBALT formation, and limited immune memory development. Conversely, IL-1R1 deficiency impairs adaptive recruitment and bacterial clearance despite similar innate infiltration. Together, these data suggest PGN release by B. pertussis is an immune-evasion strategy, favoring NOD1 activation over NOD2, reducing IL-1-dependent fibroblast reprogramming, and curtailing chemokine-driven adaptive responses. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=114 SRC="FIGDIR/small/669383v2_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@ada335org.highwire.dtl.DTLVardef@1b61a0eorg.highwire.dtl.DTLVardef@68c66eorg.highwire.dtl.DTLVardef@bb6e54_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 8.C_FLOATNO Graphic Abstract B. pertussis can produce both NOD1 and NOD2 activating PGNs. Release of TCT promotes NOD1 activation and diminishes NOD2 activation. NOD2 activation in myeloid cells drives M1 polarization of macrophages and IL-1 family cytokine production. IL-1 family cytokines skew fibroblasts towards an inflammatory phenotype, leading to chemokine release, extracellular remodeling, and recruitment of lymphocytes. Therefore, TCT release tempers long-term immunity to B. pertussis. C_FIG