Cyanobacterium Brasilonema sp. LPS Induces Neutrophil Infiltration and Lung Inflammation in a TLR4-Dependent Manner and Exacerbates Th2-Dependent Lung Inflammation.

backgroundChronic airway inflammation can be induced by both chemical and environmental factors. Airway inflammation can be induced through different immune pathways, including allergic Th2-dependent activation of eosinophils and mast cells, Th1/Th17-dependent neutrophil recruitment, or a combination of both mast cell and neutrophil recruitment, that is extremely difficult to treat. An environmental factor that we have shown to induce neutrophil-mediated lung inflammation is cyanobacterium lipopolysaccharide (LPS). The study has two main objectives: first to determine whether TLR4 is required for cyanobacterium LPS-induced lung inflammation, given our prior findings that it signals differently from other LPS types, and second to test if cyanobacterium LPS exacerbates lung inflammation in a Th2-dependent mouse model of airway hypersensitivity.

methodsLPS from the cyanobacterium strain, Brasilonema sp., was purified and used for both in vivo and in vitro assays. For in vitro assays, the TLR4 inhibitor, SPA-4, was assessed in its ability to block Brasilonema sp.-dependent IL-6 and IL-8 induction in lung epithelial cell lines, and in vivo, the ability of Brasilonema sp. LPS to induce lung inflammation was assessed in TLR4-deficient mice in comparison to controls. Finally, Th2-driven lung inflammation was established using ovalbumin and then these mice were exposed to Brasilonema sp. LPS intranasally to assess if Brasilonema sp. LPS resulted in the exacerbation of Th2-dependent airway inflammation.

resultsOur results indicate that Brasilonema sp. LPS stimulates the production of cytokines both in vitro and in vivo in a TLR4-dependent manner, since the addition of the SPA-4 peptide blocks Brasilonema sp. LPS-dependent increases in IL-6 and IL-8 in vitro and TLR4-deficient mice were refractory to Brasilonema sp. LPS-mediated induction of lung inflammation in vivo. Additionally, both E. coli and Brasilonema sp. LPS exacerbated airway inflammation in a Th2-dependent model of lung inflammation. However, Brasilonema sp. LPS exacerbated Th2-dependent lung inflammation without significant neutrophil infiltration.

conclusionsDespite the altered signaling through TLR4 by cyanobacterium LPS, these data demonstrate that lung inflammation induced by LPS from the cyanobacterium strain, Brasilonema sp., requires TLR4 and exacerbates Th2-dependent lung inflammation. Therefore, novel interventions that target TLR4 may be beneficial in the treatment of LPS-induced lung inflammation from environmental exposure.