Saccharomyces cerevisiae β-glucan improves the response of trained macrophages to severe P. aeruginosa infections.

OBJECTIVE P. AERUGINOSA: (PA), the major pathogen of lung cystic fibrosis (CF), polarizes macrophages into hyperinflammatory tissue damaging phenotype. The main aim of this study was to verify whether training of macrophages with β-glucan might improve their response to P. aeruginosa infections.

Methods: To perform this task C57BL/6 mice sensitive to infections with P. aeruginosa were used. Peritoneal macrophages were trained with Saccharomyces cerevisiae β-glucan and exposed to PA57, the strong biofilm-forming bacterial strain isolated from the patient with severe lung CF. The release of cytokines and the expression of macrophage phenotypic markers were measured. A quantitative proteomic approach was used for the characterization of proteome-wide changes in macrophages. The effect of in vivo β-glucan-trained macrophages in the air pouch model of PA57 infection was investigated. In all experiments the effect of trained and naïve macrophages was compared.

Results: Trained macrophages acquired a specific phenotype with mixed pro-inflammatory and pro-resolution characteristics, however they retained anti-bacterial properties. Most importantly, transfer of trained macrophages into infected air pouches markedly ameliorated the course of infection. PA57 bacterial growth and formation of biofilm were significantly suppressed. The level of serum amyloid A (SAA), a systemic inflammation biomarker, was reduced.

Conclusions: Training of murine macrophages with S. cerevisiae β-glucan improved macrophage defense properties along with inhibition of secretion of some detrimental inflammatory agents. We suggest that training of macrophages with such β-glucans might be a new therapeutic strategy in P. aeruginosa biofilm infections, including CF, to promote eradication of pathogens and resolution of inflammation.