Capsular polysaccharide and O-specific antigen divergently modulate pulmonary neutrophil influx in an Escherichia coli model of gram-negative pneumonitis in rats.

Enteric gram-negative bacilli cause a severe, often life-threatening pneumonia. An improved understanding of the pathogenesis of this infection may lead to improved treatment. Nearly all of the responsible gram-negative bacilli possess capsular polysaccharides and/or an O-specific antigen as part of their lipopolysaccharide (LPS). We hypothesized that these surface polysaccharides may modulate the pulmonary host response. To investigate this, a rat pneumonitis model was used, and pulmonary neutrophil influx, a critical aspect of host defense, was measured. To assess for the effect of the capsule and O-specific antigen on this host response, three proven, isogenic derivatives that are deficient in capsular polysaccharide alone (CP9.137), the O-specific antigen moiety of the LPS alone (CP921), and both the capsular polysaccharide and O-specific antigen (CP923), as well as their wild-type parent (CP9), were used as challenge strains at various intratracheal challenge inocula (CI). Total lung myeloperoxidase (MPO), a surrogate marker for neutrophils, was measured for 15 h post-bacterial challenge. To determine the effect of capsule and the O-specific antigen on the measured MPO levels, a mathematical model was developed and used to describe the MPO levels as a function of time for each CI of each of the four strains. The results from this analysis demonstrated that in the absence of the K54 capsule, 80.7 times the CI is necessary to achieve the same maximum MPO level relative to K54 positive strains (P < 0.0001). In contrast, a diametric effect was observed in the absence of the O-specific antigen, where 0.13 times the CI was necessary to achieve the same maximum MPO level relative to O4-positive strains (P = 0.0032). No interactive effect was observed between the capsule and the O-specific antigen. These findings demonstrate that these surface polysaccharides modulate pulmonary neutrophil influx and suggest that the K54 capsular polysaccharide is a proinflammatory mediator and that the O4-specific antigen attenuates the proinflammatory response. If these speculations are substantiated, an understanding of how the capsule and the O-specific antigen modulate host response could have significant therapeutic implications. The potential use of biologic modulators directed against the host response, as well as approaches based on inactivating bacterial components (e.g., surface polysaccharides) in attempts to modify sepsis syndromes, could be developed.

The role of tumor necrosis factor-alpha in the pathogenesis of aspiration pneumonitis in rats.

BACKGROUND: Aspiration pneumonitis is characterized by proteinaceous pulmonary edema and acute infiltration of neutrophils into the alveolar space. This study examined the role of the proinflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), on the pathogenesis of the injury produced by the different components that may be present in the aspirate, acid, or gastric particles. METHODS: Rats were injured by intratracheal instillation of a vehicle containing acid or gastric particles. TNF-alpha concentration of bronchoalveolar lavage fluid was determined using a bioassay. upregulation of lung TNF-alpha mRNA was also measured. The effect of intratracheal anti-rat TNF-alpha treatment was assessed by lung protein permeability, blood gases, and lung myeloperoxidase activity. RESULTS: Injury vehicle alone and acid injury resulted in a small TNF-alpha peak 1-2 h after injury in the lavage fluid. Both particulate and acidic particulate groups produced a much more robust TNF-alpha signal that reached a plateau at 2-4 h after injury and declined at 8 h. Upregulation of TNF-alpha mRNA was only detected in the particulate-containing groups. Acidic particulate exposure yielded a synergistic increase in protein permeability and decrease in blood oxygenation. Anti-TNF-alpha treatment reduced protein permeability and myeloperoxidase activity and increased blood oxygenation in the groups exposed to only acid. Such treatment had no effect on either of the particulate containing injuries. CONCLUSIONS: TNF-alpha is differentially manifested according to the components that make up the aspirate but the levels of TNF-alpha expression do not correlate with the severity of the resultant injury. However, the reduction in acid-induced lung injury by anti-TNF-alpha treatment indicates that TNF-alpha plays a role in the pathogenesis of aspiration pneumonitis.

Effect of dietary fat on glomerular lipid composition and angiotensin II receptors.

Nutritional factors are major etiologic determinants which may affect the incidence or severity of hypertension. Since angiotensin II (Ang II) has a role in some forms of hypertension, the influence of dietary lipid composition on glomerular lipid content and on Ang II receptor parameters was determined. Three groups of rats were fed diets containing 14% by weight of 1) beef fat (saturated fatty acid rich), 2) safflower oil (n-6 fatty acid rich), or 3) fish oil (n-3 fatty acid rich), each supplemented with 2% corn oil. A fourth group of rats was fed rat chow which contained 6.5% fat. At the end of 7 weeks, the rats were sacrificed, the kidneys removed, and renal glomeruli isolated using a sieving technique. Feeding diets which varied in the quantity and composition of fatty acids altered glomerular fatty acid composition of n-6 and n-3 fatty acids and the unsaturation indices of glomeruli. The cholesterol content, but not the phospholipid content, was decreased in glomeruli of animals fed the high fat diets. This resulted in a lower cholesterol/phospholipid ratio, indicative of an increase in membrane fluidity. Glomerular binding was determined using 125I-Ang II in a radioreceptor assay. Binding was proportional to glomerular protein and was time dependent. Receptor affinity (Ka) and number were determined by Scatchard analysis of binding inhibition data. Glomerular Ka was significantly lower for animals fed the rat chow as compared to the semisynthetic diets. There was no significant difference in the concentration of Ang II receptors in glomeruli of animals fed the different diets. The data indicate that the induced alteration in glomerular lipid composition is associated with alteration in the binding affinity of glomerular Ang II receptors.