In vivo effect of adhesion inhibitor heparin on Legionella pneumophila pathogenesis in a murine pneumonia model

Prospective, controlled experimental study.

University research laboratory.

A/J mice received 5 μg of sulfated heparin intratracheally co-instilled with 10⁶ or 10⁸ colony-forming units (CFU) of a virulent isolate of L. pneumophila.

ALI was assessed in control groups (PBS and PBS-heparin) and on days 1, 2 and 3 post-infection, in terms of the lung wet-to-dry (W/D) weight ratios and of lung endothelial permeability to radio-labeled albumin (Perm-I¹²⁵). Lung bacterial loads were measured and systemic spread was assessed by blood and target organ culture. The alveolar inflammatory response was evaluated by measuring the cytokine levels (TNF-α, IFN-γ, IL-6 and IL-12p70) in bronchoalveolar lavage fluids (BALF). Co-instilled heparin improved mouse survival after the 10⁸ CFU challenge (p < 0.01). On day 2, heparin co-instillation significantly reduced the W/D ratio and Perm-I¹²⁵ (p < 0.01 and p < 0.001 respectively), improved lung bacterial clearance (p < 0.001), prevented systemic dissemination (blood, liver, spleen, kidneys and brain cultures, all p < 0.05) and significantly increased IFN-γ and IL-12p70 levels in BALF (p < 0.05).

Heparin co-instillation during intratracheal L. pneumophila challenge has a protective effect on the alveolar–capillary barrier and prevents bacterial dissemination. These results tend to confirm the competitive inhibition by heparin of L. pneumophila attachment to lung epithelium in vivo, and point to the possible involvement of a heparan-sulfate adhesin in L. pneumophila binding to pneumocytes.