Impairment of antibacterial defense mechanisms of the lung by extrapulmonary infection

Pre-exposure to mechanical ventilation and endotoxemia increases Pseudomonas aeruginosa growth in lung tissue during experimental porcine pneumonia

Background

Immune system suppression during critical care contributes to the risk of acquired bacterial infections with Pseudomonas (P.) aeruginosa. Repeated exposure to endotoxin can attenuate systemic inflammatory cytokine responses. Mechanical ventilation affects the systemic inflammatory response to various stimuli.

Aim

To study the effect of pre-exposure to mechanical ventilation with and without endotoxin-induced systemic inflammation on P. aeruginosa growth and wet-to-dry weight measurements on lung tissue and plasma and bronchoalveolar lavage levels of tumor necrosis factor alpha, interleukins 6 and 10.

Methods

Two groups of pigs were exposed to mechanical ventilation for 24 hours before bacterial inoculation and six h of experimental pneumonia (total experimental time 30 h): A_30h+Etx (n = 6, endotoxin 0.063 μg x kg^-1 x h^-1) and B_30h (n = 6, saline). A third group, C_6h (n = 8), started the experiment at the bacterial inoculation unexposed to endotoxin or mechanical ventilation (total experimental time 6 h). Bacterial inoculation was performed by tracheal instillation of 1x10¹¹ colony-forming units of P. aeruginosa. Bacterial cultures and wet-to-dry weight ratio analyses were done on lung tissue samples postmortem. Separate group comparisons were done between A_30h+Etx vs.B_30h (Inflammation) and B_30h vs. C_6h (Ventilation Time) during the bacterial phase of 6 h.

Results

P. aeruginosa growth was highest in A_30h+Etx, and lowest in C_6h (Inflammation and Ventilation Time both p<0.05). Lung wet-to-dry weight ratios were highest in A_30h+Etx and lowest in B_30h (Inflammation p<0.01, Ventilation Time p<0.05). C_6h had the highest TNF-α levels in plasma (Ventilation Time p<0.01). No differences in bronchoalveolar lavage variables between the groups were observed.

Conclusions

Mechanical ventilation and systemic inflammation before the onset of pneumonia increase the growth of P. aeruginosa in lung tissue. The attenuated growth of P. aeruginosa in the non-pre-exposed animals (C_6h) was associated with a higher systemic TNF-α production elicited from the bacterial challenge.

Risk of Serious Infection, Opportunistic Infection, and Herpes Zoster among Patients with Psoriasis in the United Kingdom

The risk of infection among patients with psoriasis of varying severity in a broadly representative population remains poorly understood. Using The Health Improvement Network (THIN), an electronic medical records database representative of the general UK population, we performed a cohort study to determine the risks of serious infection, opportunistic infection, and herpes zoster among patients with versus without psoriasis and according to psoriasis severity. We identified 187,258 patients with mild and 12,442 patients with moderate to severe psoriasis based on treatment patterns. Using Cox proportional hazards regression, the adjusted hazard ratios (95% confidence intervals) for serious infection were 1.18 (1.16-1.21) and 1.63 (1.52-1.75) for the mild and moderate to severe psoriasis groups, respectively. Among a nested cohort of 8,569 psoriasis patients with disease severity classified by body surface area involvement, similar results were obtained with the exception of an attenuated but significantly increased risk of serious infection among the moderate to severe psoriasis group (1.27 [1.10-1.47]). Overall, the risks of opportunistic infection and herpes zoster were significantly increased only among the moderate to severe psoriasis group and were associated with immunosuppressive therapy. Our analyses suggest that psoriasis is associated with an increased risk of serious infection, and psoriasis severity is a predictor of serious infection risk.

Invited review: Compartmentalization of the inflammatory response in sepsis and SIRS

Sepsis and systemic inflammatory response syndrome (SIRS) are associated with an exacerbated production of both pro- and anti-inflammatory mediators that are mainly produced within tissues. Although a systemic process, the pathophysiological events differ from organ to organ, and from organ to peripheral blood, leading to the concept of compartmentalization. The nature of the insult ( e.g. burn, hemorrhage, trauma, peritonitis), the cellular composition of each compartment ( e.g . nature of phagocytes, nature of endothelial cells), and its micro-environment ( e.g. local presence of granulocyte-macrophage colony stimulating factor [GM-CSF] in the lungs, low levels of arginine in the liver, release of endotoxin from the gut), and leukocyte recruitment, have a great influence on local inflammation and on tissue injury. High levels of pro-inflammatory mediators ( e.g. interleukin-1 [IL-1], tumor necrosis factor [TNF], gamma interferon [IFN-γ], high mobility group protein-1 [HMGB1], macrophage migration inhibitory factor [MIF]) produced locally and released into the blood stream initiate remote organ injury as a consequence of an organ cross-talk. The inflammatory response within the tissues is greatly influenced by the local delivery of neuromediators by the cholinergic and sympathetic neurons. Acetylcholine and epinephrine contribute with IL-10 and other mediators to the anti-inflammatory compensatory response initiated to dampen the inflammatory process. Unfortunately, this regulatory response leads to an altered immune status of leukocytes that can increase the susceptibility to further infection. Again, the nature of the insult, the nature of the leukocytes, the presence of circulating microbial components, and the nature of the triggering agent employed to trigger cells, greatly influence the immune status of the leukocytes that may differ from one compartment to another. While anti-inflammatory mediators predominate within the blood stream to avoid igniting new inflammatory foci, their presence within tissues may not always be sufficient to prevent the initiation of a deleterious inflammatory response in the different compartments.

Decreased Risk of Ventilator-Associated Pneumonia in Sepsis Due to Intra-Abdominal Infection

RATIONALE

Experimental studies suggest that intra-abdominal infection (IAI) induces biological alterations that may affect the risk of lung infection.

OBJECTIVES

To investigate the potential effect of IAI at ICU admission on the subsequent occurrence of ventilator-associated pneumonia (VAP).

METHODS

We used data entered into the French prospective multicenter Outcomerea database in 1997-2011. Consecutive patients who had severe sepsis and/or septic shock at ICU admission and required mechanical ventilation for more than 3 days were included. Patients with acute pancreatitis were not included.

MEASUREMENTS AND MAIN RESULTS

Of 2623 database patients meeting the inclusion criteria, 290 (11.1%) had IAI and 2333 (88.9%) had other infections. The IAI group had fewer patients with VAP (56 [19.3%] vs. 806 [34.5%], P<0.01) and longer time to VAP (5.0 vs.10.5 days; P<0.01). After adjustment on independent risk factors for VAP and previous antimicrobial use, IAI was associated with a decreased risk of VAP (hazard ratio, 0.62; 95% confidence interval, 0.46-0.83; P<0.0017). The pathogens responsible for VAP were not different between the groups with and without IAI (Pseudomonas aeruginosa, 345 [42.8%] and 24 [42.8%]; Enterobacteriaceae, 264 [32.8%] and 19 [34.0%]; and Staphylococcus aureus, 215 [26.7%] and 17 [30.4%], respectively). Crude ICU mortality was not different between the groups with and without IAI (81 [27.9%] and 747 [32.0%], P = 0.16).

CONCLUSIONS

In our observational study of mechanically ventilated ICU patients with severe sepsis and/or septic shock, VAP occurred less often and later in the group with IAIs compared to the group with infections at other sites.

Activation of Hepatic STAT3 Maintains Pulmonary Defense during Endotoxemia

Pneumonia and infection-induced sepsis are worldwide public health concerns. Both pathologies elicit systemic inflammation and induce a robust acute-phase response (APR). Although APR activation is well regarded as a hallmark of infection, the direct contributions of liver activation to pulmonary defense during sepsis remain unclear. By targeting STAT3-dependent acute-phase changes in the liver, we evaluated the role of liver STAT3 activity in promoting host defense in the context of sepsis and pneumonia. We employed a two-hit endotoxemia/pneumonia model, whereby administration of 18 h of intraperitoneal lipopolysaccharide (LPS; 5 mg/kg of body weight) was followed by intratracheal Escherichia coli (10(6) CFU) in wild-type mice or those lacking hepatocyte STAT3 (hepSTAT3(-/-)). Pneumonia alone (without endotoxemia) was effectively controlled in the absence of liver STAT3. Following endotoxemia and pneumonia, however, hepSTAT3(-/-) mice, with significantly reduced levels of circulating and airspace acute-phase proteins, exhibited significantly elevated lung and blood bacterial burdens and mortality. These data suggested that STAT3-dependent liver responses are necessary to promote host defense. While neither recruited airspace neutrophils nor lung injury was altered in endotoxemic hepSTAT3(-/-) mice, alveolar macrophage reactive oxygen species generation was significantly decreased. Additionally, bronchoalveolar lavage fluid from this group of hepSTAT3(-/-) mice allowed greater bacterial growth ex vivo. These results suggest that hepatic STAT3 activation promotes both cellular and humoral lung defenses. Taken together, induction of liver STAT3-dependent gene expression programs is essential to countering the deleterious consequences of sepsis on pneumonia susceptibility.

Septic shock in older people: a prospective cohort study

Background

Septic shock is the first cause of death in Intensive Care Units. Despite experimental data showing increased inflammatory response of aged animals following infection, the current accepted hypothesis claims that aged patients are immunocompromised, when compared to young individuals.

Results

Here, we describe a prospective cohort study designed to analyze the immune profile of this population.

Conclusion

Older people are as immunocompetent as the young individual, regarding the cytokines, chemokines and growth factors response to devastating infection.

Associations between TNF-α polymorphisms and pneumonia: a meta-analysis

BACKGROUND

Several studies evaluated the associations of tumor necrosis factor-α (TNF-α) polymorphisms with pneumonia in different populations. However, the results were conflicting and controversial.

METHODS

Databases including PubMed, Embase, Web of Science, and China National Knowledge Infrastructure (CNKI) were searched to find relevant studies. Data were extracted independently by two investigators. Crude odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were estimated.

RESULTS

Twelve case-control studies and one cohort study were included. Overall, no association between TNF-α -308A/G polymorphism and pneumonia risk was observed for AA +AG vs. GG (OR = 1.13; 95% CI 0.99-1.30; P = 0.07). In addition, TNF-α -308A/G polymorphism was not associated with pneumonia mortality (OR = 1.96; 95% CI 0.94-4.09; P = 0.07). Furthermore, there was no association of TNF-α -238A/G polymorphism with the risk of pneumonia (OR = 1.38; 95% CI 0.84-2.28; P = 0.20).

CONCLUSIONS

TNF-α -308A/G, -238A/G polymorphisms were not associated with pneumonia risk. Moreover, TNF-α -308A/G polymorphism did not play a role in the pneumonia mortality risk.

Pulmonary phagocyte depression induced by an acid or alkaline solution in a rat model of peritonitis

BACKGROUND

Peritonitis is a surgical problem with a high mortality rate attributable to various complications, including respiratory infection. This complication is more common under certain conditions reflective of the origin of peritonitis, suggesting that the composition of the peritoneal fluid exerts an influence on the intensity of the macrophage and peritoneal response. To establish a correlation among macrophage function, absorption of bacteria from the peritoneal cavity, and the pH of the peritoneal fluid, we carried out this study.

METHODS

Thirty female Wistar rats were divided into three equal groups, all of which received infusions of 0.9% saline by parietal puncture. In group A (control), the saline pH was 7.0; in group B, it was 2.5; and in group C, it was 8.5. After 40 min, 0.25 mL of a suspension containing 10(11) colony-forming units of (99m)Tc-labeled Escherichia coli was infused by the same route. After another 40 min, samples of vena caval blood, spleen, liver, and lung were removed; the radioactivity was counted; bacterial absorption was determined; and the proportional radioactivity/g of tissue was calculated. The values were compared among the groups by the Student t-test, with the level of significance set at p < 0.05.

RESULTS

There was significantly greater bacterial absorption in group B than in group C (p = 0.004) but no differences in the numbers of bacteria in the liver and spleen. Bacteria were significantly more numerous in the peripheral blood in group B than in groups A and C (p = 0.04 for both). Pulmonary phagocytosis was significantly reduced in group B compared with group A (p = 0.008) and group C (p = 0.005).

CONCLUSION

Peritonitis associated with acidic conditions in the peritoneal cavity is correlated with a reduction in pulmonary phagocytosis and an increase in the numbers of nonphagocytized bacteria in the peripheral blood, possibly representing a direct or indirect cause of the higher incidence of pneumonia and sepsis in these individuals.

Direct examination and cultures of bronchoalveolar lavage in pneumonia diagnosis: a comparative experimental study

OBJECTIVE

To assess the accuracy of direct examination and quantitative cultures of BAL to diagnose pneumonia with or without antibiotic treatment.

DESIGN

Experimental rat models.

INTERVENTIONS

Pneumonia was induced by intratracheal inoculation of S. pneumoniae (10(9) cfu/ml) or P. aeruginosa (10(8)cfu/ml). Controls (n = 10) received sterile inoculum. Study animals received penicillin (n = 19) or saline (n = 18) (pneumococcal model); amikacin (n = 13), ceftazidime (n = 11), or saline (n = 13) (Pseudomonas model). BAL was assessed 48 h after infection. The animals were killed for histopathological analysis.

RESULTS

All study animals developed pneumonia, which was more extensive in the pneumococcal than in the Pseudomonas model. In pneumococcal pneumonia the sensitivity of BAL cultures (10(3) cfu/ml or higher) was 77.8% with saline and 21.0% with penicillin. In the Pseudomonas ceftazidime group all specimens were negative, precluding diagnosis. The sensitivity of cultures with amikacin was 23.1% vs. 30.8% with saline. In the pneumococcal model intracellular organism (ICO) count of 2% or higher had a sensitivity of 100% for detecting pneumonia with saline and 57.9% with penicillin. In the Pseudomonas model the sensitivity of ICO was 69.2% with both amikacin and saline and 36.3% with ceftazidime. The sensitivity of neutrophil count above 50% in pneumococcal pneumonia was 77.8% and 64.7% with saline and penicillin, respectively, and 69.2%, 61.5%, and 81.8% with saline, amikacin, and ceftazidime, respectively, in Pseudomonas pneumonia.

CONCLUSIONS

BAL-positive intracellular organisms were more accurate than cultures for the diagnosis of recent pneumonia, and were less affected by antibiotic treatment.

Preinfection systemic inflammatory markers and risk of hospitalization due to pneumonia

RATIONALE

Elevated proinflammatory cytokines are associated with severity of pneumonia, but the role of preinfection cytokine levels in the predisposition to pneumonia in humans is less clear.

OBJECTIVE

To ascertain role of preinfection inflammatory markers on susceptibility to community-acquired pneumonia (CAP).

METHODS

Longitudinal analysis over 6.5 yr of a cohort that consisted of 70- to 79-yr-old well-functioning elderly individuals.

MEASUREMENTS

Association between preinfection tumor necrosis factor (TNF), interleukin 6 (IL-6), and C-reactive protein (CRP) levels and CAP requiring hospitalization.

RESULTS

Of the 3,075 participants, 161 (5.2%) developed at least one episode of CAP requiring hospitalization over a median duration of 3.3 yr. The highest tertiles of TNF (> 3.7 pg/ml) and IL-6 (> 2.4 pg/ml) were associated with increased risk of CAP, and the adjusted odds ratios were 1.6 (95% confidence interval [CI], 1.02-2.7) and 1.7 (95% CI, 1.1-2.8), respectively. The adjusted risk of CAP with at least one of these markers in the highest tertile was 1.6 (95% CI, 1.1-2.3). TNF and IL-6 levels in the highest tertile had a synergistic effect (p = 0.01 for interaction), and risk of CAP for both markers in the highest tertile was 2.8 (95% CI, 1.8-4.3). An FEV(1) of 50% or less of predicted was associated with the highest risk of CAP (adjusted odds ratio, 3.6; 95% CI, 2.3-5.6). Furthermore, TNF and IL-6 levels modified risk of CAP in participants with coexisting medical conditions and history of smoking.

CONCLUSION

In the well-functioning elderly subjects, preinfection systemic levels of TNF and IL-6 were associated with higher risk of CAP requiring hospitalization in smokers and those with coexisting medical conditions.

The Lung in Sepsis: Fueling the Fire

Advances in our understanding of the molecular mechanisms underlying the pathophysiology of sepsis have generated considerable efforts in manipulating the host response during this frequently lethal condition. While existing trials of immune modulation have been largely unsuccessful, an appreciation for the roles of individual organ systems in sepsis is important to enable clinicians to discern how each functions as both a target for injury and a contributor to the derangement in homeostasis seen in sepsis. Such awareness will encourage treatment decisions aimed at optimizing conventional therapy while minimizing the adverse effects of supportive care, and it may also guide the incorporation of newer immunomodulatory therapeutics into our existing modalities. This article discusses the lung's response to sepsis, from the standpoint of organ dysfunction related to sepsis as well as its participation in the generation and maintenance of the systemic inflammatory state.

Variation of infected cell count in bronchoalveolar lavage and timing of ventilator-associated pneumonia

OBJECTIVES

The aim of this study was to evaluate and compare the accuracy of the percentage of infected cells (%IC) in bronchoalveolar lavage (BAL) for ventilator-associated pneumonia (VAP) diagnosis according to its onset from the initiation of mechanical ventilation.

PATIENTS

One hundred and eight patients admitted to a surgical ICU were retrospectively included (1999-2001). A total of 171 cases of VAP were diagnosed on clinical, biological, chest X-ray and BAL results (threshold >/=10(4 )cfu/ml).

RESULTS

The %IC significantly decreased with the timing of VAP diagnosis: 12.2+/-12.1% for VAP occurring less than 7 days after the initiation of mechanical ventilation, 7.4+/-9.2% for VAP occurring between 7 and 15 days and 4.8+/-6.4% for VAP after 15 days ( p=0.0002), despite the same number of elements and proportion of polymorphonuclear neutrophils in BAL. In addition, a relationship between the %IC and the pathogen responsible for VAP was observed for P. aeruginosa [higher for VAP <7 days than for VAP 7-15 days ( p=0.01) and VAP >15 days ( p=0.006)] and S. aureus [lower for VAP >15 days than VAP 7-15 days ( p=0.04) and VAP <7 days ( p=0.04)]. Furthermore, the %IC in BAL was lower in patients undergoing antimicrobial therapy than in patients without antibiotics ( p=0.04). Three factors were independently associated with the %IC: quantitative culture of BAL (beta=0.42, p<0.0001), ongoing antimicrobial therapy (beta= -0.21, p=0.003) and onset of VAP (beta= -0.17, p=0.01).

CONCLUSIONS

A relationship between the %IC in BAL, duration of ventilation, quantitative culture of BAL and ongoing antimicrobial therapy has been proved in this study. The %IC for VAP diagnosis may not be accurate in patients with ongoing antibiotics and late onset infections (>7 days).

Intra-abdominal sepsis attenuates local inflammation-mediated increases in microvascular permeability at remote sites in mice in vivo

BACKGROUND

Given that leukocyte delivery to remote sites is diminished in states of systemic inflammation, such as sepsis, and activated leukocytes may be responsible for endothelial injury leading to vascular leakage, we hypothesized that intra-abdominal sepsis would diminish microvascular leakage at remote sites by altering leukocyte-endothelial interactions.

METHODS

Using a murine intravital microscopy model, we examined leukocyte-endothelial interactions and vascular leakage at a peripheral site in the presence of local and/or systemic inflammation. Forty mice were randomized to 1 of 4 study groups: local infection (orchitis), systemic infection (intra-abdominal sepsis by cecal ligation and puncture), local and systemic infection, and control. Postcapillary venules of the cremaster muscle were examined by bright light and fluorescence intravital microscopy. Microvascular leakage was determined after intravenous administration of fluorescent albumin.

RESULTS

Systemic infection attenuated the increases in both leukocyte adherence and local infection-induced microvascular permeability. Neutrophil cell-surface expression of L-selectin, as determined by flow cytometry, diminished with both local and systemic infection, whereas expression of CD11b increased with systemic, but not local, infection.

CONCLUSIONS

These data suggest that systemic (intra-abdominal) sepsis diminishes local inflammation-mediated vascular leakage by attenuating leukocyte adherence.

Regulation of pulmonary and systemic bacterial lipopolysaccharide responses in transgenic mice expressing human elafin

The control of lung inflammation is of paramount importance in a variety of acute pathologies, such as pneumonia, the acute respiratory distress syndrome, and sepsis. It is becoming increasingly apparent that local innate immune responses in the lung are negatively influenced by systemic inflammation. This is thought to be due to a local deficit in cytokine responses by alveolar macrophages and neutrophils following systemic bacterial infection and the development of a septic response. Recently, using an adenovirus-based strategy which overexpresses the human elastase inhibitor elafin locally in the lung, we showed that elafin is able to prime lung innate immune responses. In this study, we generated a novel transgenic mouse strain expressing human elafin and studied its response to bacterial lipopolysaccharide (LPS) when the LPS was administered locally in the lungs and systemically. When LPS was delivered to the lungs, we found that mice expressing elafin had lower serum-to-bronchoalveolar lavage ratios of proinflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha), macrophage inflammatory protein 2, and monocyte chemoattractant protein 1, than wild-type mice. There was a concomitant increase in inflammatory cell influx, showing that there was potential priming of innate responses in the lungs. When LPS was given systemically, the mice expressing elafin had reduced levels of serum TNF-alpha compared to the levels in wild-type mice. These results indicate that elafin may have a dual function, promoting up-regulation of local lung innate immunity while simultaneously down-regulating potentially unwanted systemic inflammatory responses in the circulation.

Soluble L-selectin attenuates tumor necrosis factor-alpha-mediated leukocyte adherence and vascular permeability: a protective role for elevated soluble L-selectin in sepsis

OBJECTIVE

We have previously demonstrated that leukocyte delivery to remote sites is decreased in sepsis and that increased concentrations of soluble L-selectin are, in part, responsible for this finding. Given that leukocytes have been implicated in the pathogenesis of vascular leakage, we hypothesized that the elevated soluble L-selectin concentrations in sepsis may translate into decreased inflammation-mediated leukocyte-endothelial cell interactions and vascular leakage at these sites.

DESIGN

Prospective, controlled animal study.

SETTING

Surgical research laboratory in a university hospital.

SUBJECTS

Swiss white male mice weighing 25-35 g.

INTERVENTIONS

Mice were randomized to one of three study groups: intracremaster tumor necrosis factor-alpha with subsequent intravenous bicarbonate buffered solution; intracremaster tumor necrosis factor-alpha with intravenous soluble L-selectin (10 microg/mL); and intracremaster bicarbonate buffered solution with intravenous bicarbonate buffered solution. The cremaster muscle was prepared for both light and fluorescence intravital microscopy 2 hrs after intracremaster injection, and fluorescein isothiocyanate-labeled albumin was injected intravenously. Leukocyte-endothelial interactions (rolling flux, rolling velocity, and adherence) were counted off-line. Postcapillary venule leakage was determined by the permeability index (perivenular/intravenular fluorescence) after intravenous injection of fluorescent albumin.

MEASUREMENTS AND MAIN RESULTS

Soluble L-selectin significantly attenuated tumor necrosis factor-alpha-mediated increases in leukocyte adherence and vascular leakage. Leukocyte rolling velocity was restored to baseline with soluble L-selectin; however, rolling flux was not altered. Blood pressure, shear rate, and leukocyte counts did not differ between groups.

CONCLUSIONS

Soluble L-selectin decreases local inflammation-mediated leukocyte adherence and vascular leakage in vivo. The increased concentrations of soluble L-selectin in sepsis may represent a protective mechanism by which the host attempts to diminish the deleterious systemic effects of activated leukocytes during sepsis.

Soluble L-selectin at levels present in septic patients diminishes leukocyte-endothelial cell interactions in mice in vivo: a mechanism for decreased leukocyte delivery to remote sites in sepsis

OBJECTIVE

Recent in vivo studies of both septic humans and animals demonstrate that leukocyte delivery is attenuated to sites remote from the primary infection. The mechanisms for this are not entirely clear. L-selectin is integral to rolling, the first step in leukocyte recruitment to an inflammatory site. L-selectin is shed from leukocytes in sepsis, resulting in increased levels of soluble L-selectin in plasma (2.33 microg/mL). This study investigates the effects of soluble L-selectin at levels found in sepsis on leukocyte trafficking in vivo.

DESIGN

Prospective, controlled trial.

SETTING

Surgical research laboratory in a university hospital.

SUBJECTS

Swiss white male mice of 25-35 g.

INTERVENTIONS

Mice were randomized to one of three study groups: soluble L-selectin 2.33, soluble L-selectin 8.0, or albumin. Intravital microscopy was performed on postcapillary venules of 20-40 microm in diameter in the cremaster muscle of mice. Leukocyte-endothelial cell interactions (rolling, adherence, and rolling velocity) were measured pre- and post- (1, 15, 30, and 45 mins) intravenous infusion of human recombinant soluble L-selectin (2.33 and 8.0 microg/mL) or human albumin (8.0 microg/mL).

MEASUREMENTS AND MAIN RESULTS

The intravenous administration of soluble L-selectin to a systemic concentration of 2.33 microg/mL diminished rolling significantly. Soluble L-selectin at 8.0 microg/mL decreased rolling and increased rolling velocity to a greater degree. Injection of albumin did not alter leukocyte-endothelial cell interactions at any time point. No difference between groups in blood pressure, shear rate, or leukocyte counts was detected.

CONCLUSIONS

Soluble L-selectin diminishes leukocyte rolling at levels present in sepsis (2.33 microg/mL). This effect is dose dependent, and could not be explained by differences in blood pressure, shear rate, or leukocyte counts. These findings identify increased soluble L-selectin levels as one of the mechanisms for decreased leukocyte delivery and exudation to remote sites in septic patients.

Temporal sequence of pulmonary and systemic inflammatory responses to graded polymicrobial peritonitis in mice

The lungs are the remote organ most commonly affected in human peritonitis. The major goals of this study were to define the dose- and time-dependent relationship between graded septic peritonitis and systemic and pulmonary inflammatory responses in mice. BALB/c mice were treated with intraperitoneal polymicrobial inoculi and sacrificed at 3, 12, and 24 h. The treatment protocol resulted in distinct groups of animals with respect to mortality rate, kinetics, and concentrations of a broad spectrum of pro- and anti-inflammatory endogenous mediators, intrapulmonary bacterial accumulation, and static lung compliance. In sublethally infected mice, pulmonary bacterial proliferation was controlled. Levels of monocyte chemoattractant protein-1 (MCP-1), interleukin-10, interleukin-6, granulocyte colony-stimulating factor (G-CSF), and tumor necrosis factor (TNF) in plasma were elevated 3 h after infection exclusively. At 3 h, MCP-1, gamma interferon, and TNF were detected in extracts of pulmonary tissue or in bronchoalveolar lavage (BAL) fluid. Static lung compliance (C(st)) was transiently decreased at 12 h. In contrast, in lethally infected mice pulmonary bacterial proliferation was not contained. Concentrations of MCP-1, G-CSF, and TNF in plasma were maximal at 24 h, as were pulmonary MCP-1 levels. Lung myeloperoxidase activity was increased at 3, 12, and 24 h. C(st) was reduced after 3 h and did not reach control values at 24 h. Pulmonary cyclooxygenase-2 mRNA and eicosanoids in BAL fluid and plasma were elevated at 3 and 24 h. This study shows that polymicrobial peritonitis in mice leads to dose-dependent systemic and pulmonary inflammation accompanied by a decrease in lung compliance.

Pulmonary host defenses. Implications for therapy

Pulmonary host defenses comprise a redundant system of protective mechanisms against invasion of the lungs by pathogenic microbes. The upper and lower airways are uniquely suited to contain and remove organisms that gain access to the respiratory mucosa. If the balance between host and organism is disputed, however, microbial clearance may be ineffective, and infection established. Pulmonary host defense mechanisms, which provide the basis for several current therapeutic strategies, are reviewed.

Inhibition of pulmonary neutrophil trafficking during endotoxemia is dependent on the stimulus for migration

In rat models of Gram-negative pneumonia, pulmonary emigration of neutrophils (polymorphonuclear leukocytes [PMNs]) is blocked when rats are made endotoxemic by an intravenous administration of endotoxin (lipopolysaccharide [LPS]). To test whether dysfunctional PMN migratory responses in the endotoxemic rat are specific for airway endotoxin, we gave rats intrapulmonary stimuli known to elicit different adhesion pathways for pulmonary PMN migration. Sprague-Dawley rats were treated intravenously with either saline or LPS and then instilled intratracheally with either sterile saline, LPS from Escherichia coli, interleukin (IL)-1, hydrochloric acid (HCl), zymosan-activated serum (ZAS), or lipoteichoic acid (LTA). Three hours later, accumulation of PMNs and protein in bronchoalveolar lavage fluid (BALF) were assessed. BALF PMN accumulation in response to intratracheal treatment with LPS (100%), IL-1 (100%), ZAS (40%), and LTA (58%) was inhibited by endotoxemia. In rats given intratracheal HCl, BALF PMN numbers were unaffected by intravenous LPS. The pattern of inhibition of migration suggests that intravenous LPS only inhibits migration in response to stimuli for which migration is CD18-dependent. In contrast to PMN migration, BALF protein accumulation was inhibited by intravenous LPS only when IL-1 or LPS was used as the intratracheal stimulus. To characterize further the differential responses to the various airway stimuli, the appearance in BALF of tumor necrosis factor-alpha (TNF-alpha) and the PMN chemokine macrophage inflammatory protein (MIP)-2 was measured. Accumulation of PMNs in BALF correlated with the BALF concentrations of MIP-2 (r = 0.846, P < 0.05) and TNF (r = 0.911; P < 0.05). The ability of intravenous LPS to inhibit pulmonary PMN migration correlated weakly with MIP-2 (r = 0.659; P < 0.05) and with TNF (r = 0.413; P > 0.05) concentrations in BALF. However, this correlation was strengthened for TNF (r = 0.752; P < 0.05) when data from IL-1-treated animals were excluded. Thus, the presence in BALF of inflammatory mediators that are known to promote CD18-mediated migration correlates with endotoxemia-related inhibition of PMN migration. Furthermore, the pattern of inhibition of pulmonary PMN migration during endotoxemia is consistent with the CD18 requirement of each migratory stimulus.

Protective effect of endotoxin instillation on subsequent bacteria-induced acute lung injury in rats

The phagocytic capability afforded by neutrophil influx into the lungs is essential to ward off invading bacteria. The objective of this study was to evaluate the effect of prior neutrophil recruitment induced by alveolar instillation of endotoxin (LPS, 200 micrograms/kg) 16 h before a pulmonary infection caused by instillation of live Pseudomonas aeruginosa ([PYO]: 1.5 x 10(8) colony-forming units [cfu]/kg) in rats. A first series of experiments showed that lipopolysaccharide (LPS) instillation induced recruitment of alveolar neutrophils that were capable, ex vivo, of elastase exocytosis, reactive oxygen species secretion, and PYO killing. In a second set of experiments, LPS followed by PYO was compared with PYO alone (n = 11 surviving rats in each group). Parameters were studied 24 h after the bacterial challenge. As compared with PYO alone, pretreatment with LPS followed by PYO was associated with decreased mortality (0% versus 54%, p < 0.05), decreased protein leakage into bronchoalveolar lavage (BAL) fluid (1.8 +/- 0.4 versus 13.5 +/- 2.2 mg/ml, p < 0.001), and improved bacterial clearance from BAL (4.0 +/- 1.4 x 10(2) versus 1.2 +/- 0.5 x 10(4) cfu/ml, p < 0.05) and from pulmonary parenchyma (8.5 +/- 6.4 x 10(5) versus 1.9 +/- 0.8 x 10(7) cfu/ml, p < 0.05). We conclude that prior alveolar endotoxin instillation induces local recruitment of functionally active neutrophils, and that this is associated with resistance to subsequent experimental pneumonia.

Ventilator-associated pneumonia due to Pseudomonas aeruginosa

OBJECTIVE

Ventilator-associated pneumonia (VAP) caused by Pseudomonas aeruginosa has been associated with higher case fatality rates than VAP caused by other bacterial etiologies. The causes of this excess mortality are unclear.

DESIGN

Retrospective review of 38 consecutive ventilated patients with Pseudomonas pneumonia, documented by highly reliable methods. Charts of five additional patients were unavailable for review.

SETTING

Medical ICUs of a university-affiliated Veterans Affairs Medical Center and a university-affiliated municipal hospital.

MEASUREMENTS

Prospectively collected hospital admission acute physiologic and chronic health examination (APACHE) II scores and cause of ICU admission. Retrospectively calculated organ failure and APACHE scores, VAP score. Clinical and microbiologic variables. Antibiotic treatment and outcome. Direct cause of death by standard definitions.

RESULTS

Overall mortality was 69% (26/38), significantly higher than the APACHE II predicted mortality of 42.6% (p=0.037). At least 38% (10/26) of deaths were directly attributable to Pseudomonas VAP. Multivariate analysis of factors associated with death found infectious cause for ICU admission (odds ratio [OR]=8.67; 95% confidence interval [CI], 0.86 to 85.94) and number of organ dysfunctions on the day of diagnosis (OR=1.73, 95% CI, 1.02 to 2.92) were significant. Septic shock from Pseudomonas VAP, septic shock from subsequent infection, and multiple organ dysfunction syndrome were the most common immediate causes of death. Mortality increased linearly with increasing APACHE III score on the day of diagnosis. Of initial antibiotic regimens, 67% (26/36) were considered failures. Persistent pneumonia occurred in 35% of patients while recurrent pneumonia was unusual (1/38).

CONCLUSIONS

Development of Pseudomonas pneumonia results in a mortality rate in excess of that due to the presenting illness. The attributable mortality determined by several means appears to approach 40%. The excess mortality appears to be related to the host defense response to the pneumonia rather than any characteristic of the pneumonia. Even standard antibiotic regimens fail frequently and do not prevent the excess mortality. Since at least 38% of deaths can be directly attributable to the Pseudomonas pneumonia, improvement in therapy is needed.

Endotoxin-induced suppression of pulmonary antibacterial defenses against Staphylococcus aureus

In order to evaluate the effect of endotoxin on lung host defenses, Sprague-Dawley rats were intravenously injected with either placebo or 5 mg/kg of Escherichia coli lipopolysaccharide B. Two hours after treatment, animals were challenged with Staphylococcus aureus by either low dose aerosol inhalation or high dose intratracheal instillation of the bacteria into the lungs. Quantitative lung bacteriologic examination and bronchoalveolar lavage (BAL) for total and differential cell counts were performed immediately (zero hour) and at 4 h after bacterial challenge. Lung phagocytic defenses against aerosolized S. aureus challenges are provided solely by the alveolar macrophage (AM) in the absence of inflammation. In aerosol-challenged control rats, 20.6 +/- 2.0% of the initial deposited bacterial challenge remained viable in the lung at 4 h. Animals pretreated with endotoxin, however, showed a significant decrease in pulmonary bactericidal activity (31.3 +/- 3.4% bacteria remaining at 4 h), indicating a defect in alveolar macrophage (AM) function. Further assessment of the bactericidal oxidative metabolism of endotoxin-treated AM by luminol-enhanced chemiluminescence indicated an increased production of free radical oxygen species when compared with control nontreated cells in both the unstimulated (66 +/- 4 versus 38 +/- 7 x 10(3) cpm in control) and stimulated (250.5 +/- 17.1 versus 147.1 +/- 6.2 x 10(3) cpm in control) states. Total and differential cell counts in both control and endotoxin-treated aerosol-challenged rats were similar.(ABSTRACT TRUNCATED AT 250 WORDS)