LAP-TLR2 Axis Drives Inflammatory Pathology during Listeria monocytogenes Gastroenteritis

Listeria monocytogenes (Lm) causes acute gastroenteritis that precedes systemic invasive listeriosis, yet the molecular mechanisms coordinating bacterial virulence with host inflammatory responses during the enteric phase remain poorly understood. We show that Lm-associated gastroenteritis is dose-dependent, and a high infectious dose (~1x10^10 CFU/mouse), reflecting epidemic cases, recapitulates hallmark features of gastroenteritis in a mouse model, including early onset, epithelial erosion, and profound inflammatory cell infiltration. We identify Listeria adhesion protein (LAP), rather than classical virulence factors such as internalin A and listeriolysin O, as the primary mediator of enteric pathology, driving epithelial cell death and neutrophil recruitment. Transcriptomic (mRNA-seq) profiling implicates LAP-driven engagement of the TLR2-MyD88 pathway. Using the HEK-Dual hTLR2 (NF-kB) reporter cell line and TLR2 knockout mice, we show that LAP engages TLR2 to activate TNFalpha; NF-kB signaling and compromises the gut epithelial barrier. Disease severity correlates with myeloid hyperactivation and intestinal ion channel dysregulation, as CD11b-; mice exhibit attenuated diarrhea despite elevated bacterial tissue loads. Finally, studies in MLCK knock-out mice confirm that this myeloid-driven pathology requires MLCK-dependent tight junction opening for paracellular neutrophil migration, which works in concert with LAP-TLR2 signaling during Lm-induced gastroenteritis.