Under the hypercapnic challenge: how macrophages react to pneumonia-causing bacteria

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Objective: To evaluate the inflammatory response of macrophage-like THP-1 as a result of infection with Pseudomonas aeruginosa (PA) or Streptococcus pneumoniae (SP) under different CO2 concentrations, and determine the impact of macrophage response in bacterial survival. Methods: Cultures of macrophage-like THP-1 cells were separately infected with PA or SP for 1h at 37°C under normocapnic (5% CO2) or hypercapnic (15% CO2) conditions. Extracellular and intracellular bacterial survival post-infection was evaluated through seeding in blood agar plates. 24h after infection, at 37ºC and 5% or 15% CO2, cell culture supernatant was analysed through ELISA technique for inflammatory cytokines (IL-1β, IFN-γ, CCL-2, IL-8 and IL-10). Results: Under hypercapnic conditions, IL-1β secretion is enhanced in both infections, IL-10 decreases only in PA infection and chemokines are decreased (Fig 1A-E). In PA-infected macrophages the secretion of chemokines is inhibited, in SP infection macrophages could play a pivotal role as recruiters (Fig 1D-E). No differences in post-infection bacterial extracellular survival were determined (Fig 1F). PA could be establishing intracellular niches within macrophages since intracellular growth is detected 24h post-infection (Fig 1G). erj;64/suppl_68/PA5323/F1 F1 F1 Conclusion: Macrophages perform different defensive responses against PA and SP infection. Hypercapnic condition on bacterial-infection response could play a detrimental role.

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