Pulmonary bacterial clearance in lipopolysaccharide-induced tolerance vs. shock murine models

RODRIGUEZ RODRIGUES N ; MARTIRE-GRECO D; LANDONI V; CHIARELLA P; SCHIERLOH P; REARTE B; MEISS R. ; ISTURIZ M; FERNÁNDEZ G.

Mar del Plata

Congreso; LXII Reunión Científica Anual de la Sociedad Argentina de Inmunología; 2014

Sociedad Argentina de Inmunología

Repeated inoculation of bacterial lipopolysaccharide (LPS) in mice generates a refractory state, where animals survive lethal doses of LPS and have low amounts of LPS-induced TNF. This state is also associated with defects in antibody responses. Our aim was to compare how the exposure to LPS affects pulmonary bacterial clearance as a measure of innate immune function. For this purpose, we used two models of LPS exposure. In the LPS-tolerance model, tolerance was induced by daily i.v. injections of increasing doses of LPS (5-100 µg/day/mouse) for 7 days. In the LPS-shock model a single high dose of LPS (50 µg/mouse) was administered i.v. Then the animals were challenged intratracheally with intestinal bacteria (5x106 CFU) and the number of remaining bacteria in the lung or bronchoalveolar lavage (BAL) was evaluated 4h post-infection on McConkey agar plates. In the LPS-tolerance model the bacterial clearance was higher compared to Control mice (Total CFU. Lung: C= 3,94x106 ± 1,02x106, Tol= 1,34x106 ± 0,90x106. BAL: C= 5,85x105 ± 0,57x105, Tol= 6,66x104 ± 2,22x104, p<0.0001). In contrast, in the LPS-shock model bacterial clearance in the lung was decreased (Total CFU. Lung: C= 7,86x104 ± 0,24x104, Tol= 1,23x105 ± 0,25x105, p<0.05. BAL: C= 2,19x104 ± 0,42x104, Tol= 2,15x104 ± 0,31x104). No differences in the number of neutrophils (PMN) and alveolar macrophages in BAL or Lung after the bacterial challenge were observed. To determine the functional state of PMN that may explain the increased clearance observed in the LPS-tolerance model, an in vitro phagocytosis assay was performed using lung isolated PMN (Gr-1+) and FITC-labeled bacteria. The amount of ingested bacteria determined by flow cytometry (Mean fluorescence intensity, MFI) was higher in Tol Gr-1+ cells (MFI FITC: C= 518 ± 39, Tol= 745 ± 70, p<0.05). These data indicate that sustained exposure to LPS increases the functionality of PMN, perhaps to compensate the functional decline of the adaptive immune system.