Pseudomonas aeruginosa is an opportunistic pathogen known for its immune evasive abilities amongst others by degradation of a large variety of host proteins. Here we show that digestion of thrombin by P. aeruginosa elastase leads to the release of the C-terminal thrombin-derived peptide FYT21, which inhibits pro-inflammatory responses to several pathogen-associated molecular patterns in vitro and in vivo by preventing toll-like receptor dimerization and subsequent activation of down-stream signalling pathways. Thus, P. aeruginosa ‘hijacks' an endogenous anti-inflammatory peptide-based mechanism, thereby enabling modulation and circumvention of host responses.

Interstitial lung diseases such as idiopathic pulmonary fibrosis (IPF) are caused by persistent micro-injuries to alveolar epithelial tissues accompanied by aberrant repair processes. IPF is currently treated with pirfenidone and nintedanib, compounds which slow the rate of disease progression but fail to target underlying pathophysiological mechanisms. The DNA repair protein 8-oxoguanine DNA glycosylase-1 (OGG1) has significant roles in the modulation of inflammation and metabolic syndromes. Currently, no pharmaceutical solutions targeting OGG1 have been utilized in the treatment of IPF. In this study we show Ogg1-targeting siRNA mitigates bleomycin-induced pulmonary fibrosis in male mice, highlighting OGG1 as a tractable target in lung fibrosis. The small molecule OGG1 inhibitor, TH5487, decreases myofibroblast transition and associated pro-fibrotic gene expressions in fibroblast cells. In addition, TH5487 decreases levels of pro-inflammatory mediators, inflammatory cell infiltration, and lung remodeling in a murine model of bleomycin-induced pulmonary fibrosis conducted in male C57BL6/J mice. OGG1 and SMAD7 interact to induce fibroblast proliferation and differentiation and display roles in fibrotic murine and IPF patient lung tissue. Taken together, these data suggest that TH5487 is a potentially clinically relevant treatment for IPF but further study in human trials is required.

Background: Antithrombin III (ATIII), an antiproteinase-inhibiting coagulation, was investigated for roles in host defense. Results: Extensive proteolysis of ATIII by endogenous and bacterial enzymes generated antimicrobial activity, mapped to helix D of the molecule. Conclusion: ATIII harbor "cryptic" host defense epitopes released during proteolysis. Significance: The results explain previously observed antimicrobial and anti-inflammatory effects of ATIII supplementation during infection.

Together, these results indicate that functional epitopes of HCII may have therapeutic potential against bacterial infection.