Bacterial secretions in growth medium stimulate the mouse respiratory innate immune response

Introduction. Finding a safe innate immune response stimulator is one of the greatest challenges facing immunologists and vaccine manufacturers.Gap statement. The role of sterile bacterial secretions (SBSs) of Pseudomonas aeruginosa in stimulating the innate immune response was not investigated previously.Aim. The comparative effect of SBSs and bacterial cells of P. aeruginosa isolates isolated from freshwater (PAE) and infected wounds (PAC) on the respiratory tract innate immune response.Methodology. Four test mice groups were instilled intranasally (i.n.) with 10⁶ c.f.u of PAC, 10⁶ c.f.u of PAE, SBS of PAC, and SBS of PAE. Two control groups were given i.n. either LB broth or PBS. Time-course changes in IL-1 beta mRNA, TNF-alpha mRNA, IL-1β and TNF-α, leukocyte count, bacterial uptake, and intracellular bacterial killing by mouse alveolar macrophages (AMs) and histological changes were examined. Lung bacterial burdens were counted in first and second test groups.Results. The maximum level of IL-1β was seen as early as 2 h (1360±180 pg ml^-1) post-instillation (i.n.) with SBS of PAC and 1 h (1910±244 pgml^-1) post-instillation with SBS of PAE. The maximum level of TNF-α was seen as early as 4 h (953±192 pg ml^-1) post-instillation with SBS of PAC and (1197±298 pg ml^-1) post-instillation with SBS of PAE. These values were almost in line with IL-1β and TNF-α gene expression. Moderate infiltration of leukocytes in bronchoalveolar lavage (BAL) and lung sections and moderate activity of AMs (bacterial uptake and bacterial killing) were observed. The above innate immune response parameters in mice instilled i.n. with PAC and PAE were higher (P<0.05) than in the mice groups instilled i.n. with SBSs. The PAC was persistent in the lungs of mice for up to 72 h (3.5±0.22 log₁₀ of c.f.u. g^-1) and up to 48 h (2.05±0.21 log₁₀ of c.f.u. g^-1) for PAE.Conclusion. The administration of mice with SBS i.n. stimulates cellular and molecular arms of the innate immune response in the respiratory tract, opening the door to the possibility of using SBS of P. aeruginosa as an adjuvant.