Rationale: The Toll-like receptor 3 Leu412Phe (TLR3 L412F) polymorphism attenuates cellular anti-viral responses and is associated with accelerated disease progression in IPF. The role of TLR3 L412F in bacterial infection in IPF or in acute exacerbations (AE) has not been reported. Objective: To characterize the association between TLR3 L412F and AE-related death in IPF. To determine the effect of TLR3 L412F on the lung microbiome and on anti-bacterial TLR-responses of primary lung fibroblasts from IPF patients. Methods: TLR-mediated anti-bacterial and anti-viral responses were quantitated in L412F-wild-type and 412F-heterozygous primary lung fibroblasts from IPF patients using ELISA, western blot analysis and qPCR. Hierarchical heatmap analysis was employed to establish bacterial and viral clustering in nasopharyngeal lavage (NPL) samples from AE-IPF patients. 16S rRNA qPCR and pyrosequencing were used to determine the effect of TLR3 L412F on the IPF lung microbiome. Measurements and Main Results: A significant increase in AE-related death in 412F-variant IPF patients was reported. We established that 412F-heterozygous IPF lung fibroblasts have reduced anti-bacterial TLR responses to LPS (TLR4), Pam3CYSK4 (TLR1/2), flagellin (TLR5) and FSL-1 (TLR6/1) and have reduced responses to live Pseudomonas aeruginosa infection. Using 16S rRNA sequencing, we demonstrated that 412F-heterozygous IPF patients have a dysregulated lung microbiome with increased frequencies of Streptococcus and Staphylococcus spp. Conclusions: This study reveals that TLR3 L412F dysregulates the IPF lung microbiome and reduces the responses of IPF lung fibroblasts to bacterial TLR-agonists and live bacterial infection. These findings identify a candidate role for TLR3 L412F in viral- and bacterial-mediated AE-death.