Role of Macrophages in Internalization and Early Clearance of Pseudomonas Aeruginosa from the Mouse Lung

This study aimed to evaluate the role of alveolar macrophages (AMs) in the internalisation and early clearance of Pseudomonas aeruginosa in the lung. AMs were depleted by intranasal administration of liposome-encapsulated clodronate disodium. At 24 h following the instillation of liposomes, a sublethal dose of P. aeruginosa (1 X 104 cfu) was inoculated intratracheally. Lung tissue was then evaluated for survival, viable bacteria and for histopathology 4 and 24 h post-infection. AM depletion of 90% did not affect the survival rate of infected mice but the clearance of P. aeruginosa was reduced at 24 h (P<0.05). While at 4 h AM-depleted and control mice showed similar level of PMN recruitment in the distal lung, 24 h post-infection tickening of interstitial spaces was more marked in AM-depleted mice. To evaluate the integrity of the epithelial barrier, the presence of bacteria in the spleen was assessed at 4 and 24 h. AM-depleted mice presented equal numbers of colonies as compared to control mice. At 4 h post-infection, the total and internalized numbers of bacteria were not different from the control group following a high-dose bacterial challenge (1 X 107 cfu). Our study show that AMs do not influence bacterial internalisation by airway epithelial cells.

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