IL-9 promotes methicillin-resistant Staphylococcus aureus pneumonia by regulating the polarization and phagocytosis of macrophages

In this study, we examined the effect of Il9 deletion on macrophages in methicillin-resistant Staphylococcus aureus (MRSA) infection. MRSA-infected mice were employed for the in vivo experiments, and RAW264.7 cells were stimulated with MRSA for the in vitro experiments. Macrophage polarization was determined by flow cytometry and quantitative real-time PCR; macrophage phagocytosis was assessed by flow cytometry and laser scanning confocal microscopy; cell apoptosis was assessed by flow cytometry and western blotting. Il9 deletion markedly elevated macrophage phagocytosis and M2 macrophages in MRSA infection, which was accompanied by elevated expression of Il10 and Arg1 and reduced expression of Inos, tumor necrosis factor-α (Tnfα), and Il6. Il9 deletion also inhibited macrophage apoptosis in MRSA infection, which was manifested by elevated B-cell lymphoma 2 (BCL-2) protein level and reduced protein levels of cleaved cysteine protease 3 (CASPASE-3) and BCL2-Associated X (BAX). Both the in vivo and in vitro experiments further showed the activation of phosphoinositide 3-kinase (PI3K)/AKT (also known as protein kinase B, PKB) signaling pathway in MRSA infection and that the regulation of Il9 expression may be dependent on Toll-like receptor (TLR) 2/PI3K pathway. The above results showed that Il9 deletion exhibited a protective role against MRSA infection by promoting M2 polarization and phagocytosis of macrophages and the regulation of Il9 partly owing to the activation of TLR2/PI3K pathway, proposing a novel therapeutic strategy for MRSA-infected pneumonia.

NLRP6 negatively regulates pulmonary host defense in Gram-positive bacterial infection through modulating neutrophil recruitment and function

Gram-positive bacteria, including Staphylococcus aureus are endemic in the U.S., which cause life-threatening necrotizing pneumonia. Neutrophils are known to be critical for clearance of S. aureus infection from the lungs and extrapulmonary organs. Therefore, we investigated whether the NLRP6 inflammasome regulates neutrophil-dependent host immunity during pulmonary S. aureus infection. Unlike their wild-type (WT) counterparts, NLRP6 knockout (KO) mice were protected against pulmonary S. aureus infection as evidenced by their higher survival rate and lower bacterial burden in the lungs and extrapulmonary organs. In addition, NLRP6 KO mice displayed increased neutrophil recruitment following infection, and when neutrophils were depleted the protective effect was lost. Furthermore, neutrophils from the KO mice demonstrated enhanced intracellular bacterial killing and increased NADPH oxidase-dependent ROS production. Intriguingly, we found higher NK cell-mediated IFN-γ production in KO mouse lungs, and treatment with IFN-γ was found to enhance the bactericidal ability of WT and KO neutrophils. The NLRP6 KO mice also displayed decreased pyroptosis and necroptosis in the lungs following infection. Blocking of pyroptosis and necroptosis in WT mice resulted in increased survival, reduced bacterial burden in the lungs, and attenuated cytokine production. Taken together, these novel findings show that NLRP6 serves as a negative regulator of neutrophil-mediated host defense during Gram-positive bacterial infection in the lungs through regulating both neutrophil influx and function. These results also suggest that blocking NLRP6 to augment neutrophil-associated bacterial clearance should be considered as a potential therapeutic intervention strategy for treatment of S. aureus pneumonia.

Secondary Bacterial Pneumonia by Staphylococcus aureus Following Influenza A Infection Is SaeR/S Dependent

Staphylococcus aureus is a predominant cause of fatal pneumonia following influenza A virus (IAV) infection. Herein we investigate the influence of antecedent IAV infection on S. aureus virulence gene expression. Using a murine model, comparing the USA300 and USA300ΔsaeR/S strains, we demonstrate that S. aureus pathogenesis following IAV infection is SaeR/S dependent. Furthermore, we show that IAV modulates the lung environment to rapidly up-regulate S. aureus virulence factors containing the SaeR-binding domain. Data demonstrate that the pathogen response to IAV infection impacts host outcome and provides evidence that the ability of S. aureus to sense and respond to the lung environment determines severity of pneumonia.

Humanized Mice Exhibit Increased Susceptibility to Staphylococcus aureus Pneumonia

Staphylococcus aureus is a highly successful human pathogen that has evolved in response to human immune pressure. The common USA300 methicillin-resistant S. aureus (MRSA) strains express a number of toxins, such as Panton-Valentine leukocidin and LukAB, that have specificity for human receptors. Using nonobese diabetic (NOD)-scid IL2Rγnull (NSG) mice reconstituted with a human hematopoietic system, we were able to discriminate the roles of these toxins in the pathogenesis of pneumonia. We demonstrate that expression of human immune cells confers increased severity of USA300 infection. The expression of PVL but not LukAB resulted in more-severe pulmonary infection by the wild-type strain (with a 30-fold increase in the number of colony-forming units/mL; P < .01) as compared to infection with the lukS/F-PV (Δpvl) mutant. Treatment of mice with anti-PVL antibody also enhanced bacterial clearance. We found significantly greater numbers (by 95%; P < .05) of macrophages in the airways of mice infected with the Δpvl mutant compared with those infected with the wild-type strain, as well as significantly greater expression of human tumor necrosis factor and interleukin 6 (84% and 51% respectively; P < .01). These results suggest that the development of humanized mice may provide a framework to assess the contribution of human-specific toxins and better explore the roles of specific components of the human immune system in protection from S. aureus infection.

Mechanical Ventilation Alters the Development of Staphylococcus aureus Pneumonia in Rabbit

Ventilator-associated pneumonia (VAP) is common during mechanical ventilation (MV). Beside obvious deleterious effects on muco-ciliary clearance, MV could adversely shift the host immune response towards a pro-inflammatory pattern through toll-like receptor (TLRs) up-regulation. We tested this hypothesis in a rabbit model of Staphylococcus aureus VAP. Pneumonia was caused by airway challenge with S. aureus, in either spontaneously breathing (SB) or MV rabbits (n = 13 and 17, respectively). Pneumonia assessment regarding pulmonary and systemic bacterial burden, as well as inflammatory response was done 8 and 24 hours after S. aureus challenge. In addition, ex vivo stimulations of whole blood taken from SB or MV rabbits (n = 7 and 5, respectively) with TLR2 agonist or heat-killed S. aureus were performed. Data were expressed as mean±standard deviation. After 8 hours of infection, lung injury was more severe in MV animals (1.40±0.33 versus [vs] 2.40±0.55, p = 0.007), along with greater bacterial concentrations (6.13±0.63 vs. 4.96±1.31 colony forming units/gram, p = 0.002). Interleukin (IL)-8 and tumor necrosis factor (TNF)-αserum concentrations reached higher levels in MV animals (p = 0.010). Whole blood obtained from MV animals released larger amounts of cytokines if stimulated with TLR2 agonist or heat-killed S. aureus (e.g., TNF-α: 1656±166 vs. 1005±89; p = 0.014). Moreover, MV induced TLR2 overexpression in both lung and spleen tissue. MV hastened tissue injury, impaired lung bacterial clearance, and promoted a systemic inflammatory response, maybe through TLR2 overexpression.

Trace Levels of Staphylococcal Enterotoxin Bioactivity Are Concealed in a Mucosal Niche during Pulmonary Inflammation

Pathogen and cellular by-products released during infection or trauma are critical for initiating mucosal inflammation. The localization of these factors, their bioactivity and natural countermeasures remain unclear. This concept was studied in mice undergoing pulmonary inflammation after Staphylococcal enterotoxin A (SEA) inhalation. Highly purified bronchoalveolar lavage fluid (BALF) fractions obtained by sequential chromatography were screened for bioactivity and subjected to mass spectrometry. The Inflammatory and inhibitory potentials of the identified proteins were measured using T cells assays. A potent pro-inflammatory factor was detected in BALF, and we hypothesized SEA could be recovered with its biological activity. Highly purified BALF fractions with bioactivity were subjected to mass spectrometry. SEA was the only identified protein with known inflammatory potential, and unexpectedly, it co-purified with immunosuppressive proteins. Among them was lactoferrin, which inhibited SEA and anti-CD3/-CD28 stimulation by promoting T cell death and reducing TNF synthesis. Higher doses of lactoferrin were required to inhibit effector compared to resting T cells. Inhibition relied on the continual presence of lactoferrin rather than a programming event. The data show a fraction of bioactive SEA resided in a mucosal niche within BALF even after the initiation of inflammation. These results may have clinical value in human diagnostic since traces levels of SEA can be detected using a sensitive bioassay, and may help pinpoint potential mediators of lung inflammation when molecular approaches fail.

Intestinal Microbiota of Mice Influences Resistance to Staphylococcus aureus Pneumonia

Th17 immunity in the gastrointestinal tract is regulated by the intestinal microbiota composition, particularly the presence of segmented filamentous bacteria (sfb), but the role of the intestinal microbiota in pulmonary host defense is not well explored. We tested whether altering the gut microbiota by acquiring sfb influences the susceptibility to staphylococcal pneumonia via induction of type 17 immunity. Groups of C57BL/6 mice which differed in their intestinal colonization with sfb were challenged with methicillin-resistant Staphylococcus aureus in an acute lung infection model. Bacterial burdens, bronchoalveolar lavage fluid (BALF) cell counts, cell types, and cytokine levels were compared between mice from different vendors, mice from both vendors after cohousing, mice given sfb orally prior to infection, and mice with and without exogenous interleukin-22 (IL-22) or anti-IL-22 antibodies. Mice lacking sfb developed more severe S. aureus pneumonia than mice colonized with sfb, as indicated by higher bacterial burdens in the lungs, lung inflammation, and mortality. This difference was reduced when sfb-negative mice acquired sfb in their gut microbiota through cohousing with sfb-positive mice or when given sfb orally. Levels of type 17 immune effectors in the lung were higher after infection in sfb-positive mice and increased in sfb-negative mice after acquisition of sfb, as demonstrated by higher levels of IL-22 and larger numbers of IL-22(+) TCRβ(+) cells and neutrophils in BALF. Exogenous IL-22 protected mice from S. aureus pneumonia. The murine gut microbiota, particularly the presence of sfb, promotes pulmonary type 17 immunity and resistance to S. aureus pneumonia, and IL-22 protects against severe pulmonary staphylococcal infection.

mCLCA3 modulates IL-17 and CXCL-1 induction and leukocyte recruitment in murine Staphylococcus aureus pneumonia

The human hCLCA1 and its murine ortholog mCLCA3 (calcium-activated chloride channel regulators) are exclusively expressed in mucus cells and linked to inflammatory airway diseases with increased mucus production, such as asthma, cystic fibrosis and chronic obstructive pulmonary disease. Both proteins have a known impact on the mucus cell metaplasia trait in these diseases. However, growing evidence points towards an additional role in innate immune responses. In the current study, we analyzed Staphylococcus aureus pneumonia, an established model to study pulmonary innate immunity, in mCLCA3-deficient and wild-type mice, focusing on the cellular and cytokine-driven innate inflammatory response. We compared clinical signs, bacterial clearance, leukocyte immigration and cytokine responses in the bronchoalveolar compartment, as well as pulmonary vascular permeability, histopathology, mucus cell number and mRNA expression levels of selected genes (mClca1 to 7, Muc5ac, Muc5b, Muc2, Cxcl-1, Cxcl-2, Il-17). Deficiency of mCLCA3 resulted in decreased neutrophilic infiltration into the bronchoalveolar space during bacterial infection. Only the cytokines IL-17 and the murine CXCL-8 homolog CXCL-1 were decreased on mRNA and protein levels during bacterial infection in mCLCA3-deficient mice compared to wild-type controls. However, no differences in clinical outcome, histopathology or mucus cell metaplasia were observed. We did not find evidence for regulation of any other CLCA homolog that would putatively compensate for the lack of mCLCA3. In conclusion, mCLCA3 appears to modulate leukocyte response via IL-17 and murine CXCL-8 homologs in acute Staphylococcus aureus pneumonia which is well in line with the proposed function of hCLCA1 as a signaling molecule acting on alveolar macrophages.

Protective or deleterious role of scavenger receptors SR-A and CD36 on host resistance to Staphylococcus aureus depends on the site of infection

Staphylococcus aureus is a major human opportunistic pathogen responsible for a broad spectrum of infections ranging from benign skin infection to more severe life threatening disorders (e.g. pneumonia, sepsis), particularly in intensive care patients. Scavenger receptors (SR-A and CD36) are known to be involved in S. aureus recognition by immune cells in addition to MARCO, TLR2, NOD2 and α5β1 integrin. In the present study, we further deciphered the contribution of SR-A and CD36 scavenger receptors in the control of infection of mice by S. aureus. Using double SR-A/CD36 knockout mice (S/C-KO) and S. aureus strain HG001, a clinically relevant non-mutagenized strain, we showed that the absence of these two scavenger receptors was protective in peritoneal infection. In contrast, the deletion of these two receptors was detrimental in pulmonary infection following intranasal instillation. For pulmonary infection, susceptible mice (S/C-KO) had more colony-forming units (CFU) in their broncho-alveolar lavages fluids, associated with increased recruitment of macrophages and neutrophils. For peritoneal infection, susceptible mice (wild-type) had more CFU in their blood, but recruited less macrophages and neutrophils in the peritoneal cavity than resistant mice. Exacerbated cytokine levels were often observed in the susceptible mice in the infected compartment as well as in the plasma. The exception was the enhanced compartmentalized expression of IL-1β for the resistant mice (S/C-KO) after peritoneal infection. A similar mirrored susceptibility to S. aureus infection was also observed for MARCO and TLR2. Marco and tlr2 -/- mice were more resistant to peritoneal infection but more susceptible to pulmonary infection than wild type mice. In conclusion, our results show that innate immune receptors can play distinct and opposite roles depending on the site of infection. Their presence is protective for local pulmonary infection, whereas it becomes detrimental in the peritoneal infection.

Influenza A exacerbates Staphylococcus aureus pneumonia by attenuating IL-1β production in mice

Pneumonia is a leading cause of death worldwide. Staphylococcal aureus can be a cause of severe pneumonia alone or a common pathogen in secondary pneumonia following influenza. Recently, we reported that preceding influenza attenuated the Type 17 pathway, increasing the lung's susceptibility to secondary infection. IL-1β is known to regulate host defense, including playing a role in Th17 polarization. We examined whether IL-1β signaling is required for S. aureus host defense and whether influenza infection impacted S. aureus-induced IL-1β production and subsequent Type 17 pathway activation. Mice were challenged with S. aureus (USA 300), with or without preceding Influenza A/PR/8/34 H1N1 infection. IL-1R1(-/-) mice had significantly higher S. aureus burden, increased mortality, and decreased Type 17 pathway activation following S. aureus challenge. Coinfected mice had significantly decreased IL-1β production versus S. aureus infection alone at early time points following bacterial challenge. Preceding influenza did not attenuate S. aureus-induced inflammasome activation, but there was early suppression of NF-κB activation, suggesting an inhibition of NF-κB-dependent transcription of pro-IL-1β. Furthermore, overexpression of IL-1β in influenza and S. aureus-coinfected mice rescued the induction of IL-17 and IL-22 by S. aureus and improved bacterial clearance. Finally, exogenous IL-1β did not significantly rescue S. aureus host defense during coinfection in IL-17RA(-/-) mice or in mice in which IL-17 and IL-22 activity were blocked. These data reveal a novel mechanism by which Influenza A inhibits S. aureus-induced IL-1β production, resulting in attenuation of Type 17 immunity and increased susceptibility to bacterial infection.

Engineering a soluble high-affinity receptor domain that neutralizes staphylococcal enterotoxin C in rabbit models of disease

Superantigens (SAgs) are a class of immunostimulatory exotoxins that activate large numbers of T cells, leading to overproduction of cytokines and subsequent inflammatory reactions and systemic toxicity. Staphylococcal enterotoxin C (SEC), a SAg secreted by Staphylococcus aureus, has been implicated in various illnesses including non-menstrual toxic shock syndrome (TSS) and necrotizing pneumonia. SEC has been shown to cause TSS illness in rabbits and the toxin contributes to lethality associated with methicillin-resistant S.aureus (MRSA) in a rabbit model of pneumonia. With the goal of reducing morbidity and mortality associated with SEC, a high-affinity variant of the extracellular variable domain of the T-cell receptor beta-chain for SEC (~14 kDa) was generated by directed evolution using yeast display. This protein was characterized biochemically and shown to cross-react with the homologous (65% identical) SAg staphylococcal enterotoxin B (SEB). The soluble, high-affinity T-cell receptor protein neutralized SEC and SEB in vitro and also significantly reduced the bacterial burden of an SEC-positive strain of MRSA (USA400 MW2) in an infective endocarditis model. The neutralizing agent also prevented lethality due to MW2 in a necrotizing pneumonia rabbit model. These studies characterize a soluble high-affinity neutralizing agent against SEC, which is cross-reactive with SEB, and that has potential to be used intravenously with antibiotics to manage staphylococcal diseases that involve these SAgs.

A multiplex assay for the quantification of antibody responses in Staphylococcus aureus infections in mice

Staphylococcus aureus causes a variety of infections. Knowledge about the physiological role of most S. aureus antigens in colonization and infection is only limited. This can be studied by measuring antigen-specific antibody responses. In this study, we optimized the multiplex microsphere bead-based flow cytometry technique for mouse serum samples. We analysed immunoglobulin G (IgG) levels directed against 26 S. aureus proteins in a single small-volume mouse serum sample. We assessed possible cross reactivity. Furthermore, we analysed serum samples from mice with different types of S. aureus infections caused by different S. aureus strains. The results show that cross reactivity between proteins on microspheres and serum antibodies towards other proteins was limited. We found that lung-infected mice had a higher and broader IgG response than skin-infected mice. Clearly, the site of infection influences the IgG profile. Next, we compared sera from mice with intravenously-induced bacteraemia caused by different S. aureus strains. We showed different IgG responses depending on the causing S. aureus strain. It is concluded that the bead-based multiplex S. aureus antibody assay can be successfully applied to determine the immunogenicity of different S. aureus proteins in relation to the site of infection and the S. aureus strain causing the infection.

An antidote for Staphylococcus aureus pneumonia?

Methicillin-resistant Staphylococcus aureus (MRSA) is the leading cause of bacterial infections in the United States. Severe invasive MRSA infections, which include pneumonia, are difficult to treat because the bacteria are resistant to antibiotics. A new report now shows that immunization against alpha-hemolysin (Hla), a cytolytic toxin secreted by most S. aureus strains, protects mice against lethal pneumonia. This finding represents the first successful vaccine strategy for the treatment of staphylococcal pneumonia.

Effect of laparotomy on clearance and cytokine induction in Staphylococcus aureus infected lungs

RATIONALE

Staphylococcus aureus is a major pathogen complicating postsurgical care.

OBJECTIVES

To test the effect of sterile laparotomy (LAP) on pulmonary clearance of S. aureus in a murine model.

METHODS

Control and LAP mice were infected intranasally with 10(8) cfu of S. aureus. Microbial clearance, pulmonary leukocyte recruitment, and cytokine profiles were compared between the groups. Antibody neutralization or cytokine gene knockout mice were used to evaluate the role of cytokines.

MEASUREMENTS AND MAIN RESULTS

Laparotomy resulted in a 10-fold increase in S. aureus lung colony-forming units on Days 2 and 3 postinfection. Both groups cleared the infection by Day 4. No defect in leukocyte recruitment into the lungs was observed in infected LAP animals; however, an increase in the number of Mac-3-positive cells and a significant decrease of cells with high surface expression of Fc-gammaR suggest suboptimal activation of leukocytes in the lungs of infected LAP animals. Infected LAP mice had decreased expression of interferon (IFN)-gamma and increased expression of mRNA for IL-13 in the lungs on Day 1 postinfection and decreased levels of IL-6, keratinocyte-derived chemokine (KC), and macrophage inflammatory protein-2 (MIP-2) in bronchoalveolar lavage at Day 2 postinfection. Neutralization of IFN-gamma mimicked the effect of LAP with impaired clearance on Day 2.

CONCLUSIONS

Sterile LAP induced temporary deactivation of innate immune responses to pulmonary S. aureus challenge. Impaired microbial clearance was accompanied by altered cytokine expression and suboptimal activation of pulmonary leukocytes. Lack of early IFN-gamma induction in the infected lungs of LAP animals is a likely mechanism contributing to the observed phenotype.

Effects of murine endotoxemia on lymphocyte subsets and clearance of staphylococcal pulmonary infection

In a model of staphylococcal pneumonia initiated during systemic endotoxemia in BALB/c mice, a significant reduction of the number of circulating CD4+ and CD8+ T-lymphocytes, B-lymphocytes, and NK cells, as well as lung-resident total T- and CD4+ T-lymphocytes was demonstrated. Staphylococcus aureus exposure only induced a similar decrease of lymphocyte subsets in the blood. However, the number of lung-resident total T- and CD4+ T-lymphocytes was increased. More viable bacteria were recovered from the lungs of S. aureus-infected mice than from those animals previously treated with lipopolysaccharide (LPS) followed by a staphylococcal challenge. These results indicate that LPS-induced reduction in the number of circulating lymphocyte subsets and lung-resident total T- and CD4+ T-lymphocytes do not increase susceptibility to staphylococcal respiratory infection. Moreover, LPS challenge prior to S. aureus exposure significantly improves clearance of the bacteria in the lung.

Hypertonic saline dextran after burn injury decreases inflammatory cytokine responses to subsequent pneumonia-related sepsis

The present study examined the hypothesis that hypertonic saline dextran (HSD), given after an initial insult, attenuates exaggerated inflammation that occurs with a second insult. Adult rats (n = 15 per group) were divided into groups 1 (sham burn), 2 [40% total body surface area burn + 4 ml/kg isotonic saline (IS) + 4 ml.kg(-1).% burn(-1) lactated Ringer solution (LR)], and 3 (burn + 4 ml/kg HSD + LR), all studied 24 h after burns. Groups 4 (sham burn), 5 (burn + IS + LR), and 6 (burns + HSD + LR) received intratracheal (IT) vehicle 7 days after burns; groups 7 (burn + IS + LR) and 8 (burn + HSD + LR) received IT Streptococcus pneumoniae (4 x 10(6) colony-forming units) 7 days after burn. Groups 4-8 were studied 8 days after burn and 24 h after IT septic challenge. When compared with sham burn, contractile defects occurred 24 h after burn in IS-treated but not HSD-treated burns. Cardiac inflammatory responses (pg/ml TNF-alpha) were evident with IS (170 +/- 10) but not HSD (45 +/- 5) treatment vs. sham treatment (80 +/- 15). Pneumonia-related sepsis 8 days after IS-treated burns (group 7) exacerbated TNF-alpha responses/contractile dysfunction vs. IS-treated burns in the absence of sepsis (P < 0.05). Sepsis that occurred after HSD-treated burns (group 8) had less myocyte TNF-alpha secretion/better contractile function than IS-treated burns given septic challenge (group 7, P < 0.05). We conclude that an initial burn injury exacerbates myocardial inflammation/dysfunction occurring with a second insult; giving HSD after the initial insult attenuates myocardial inflammation/dysfunction associated with a second hit, suggesting that HSD reduces postinjury risk for infectious complications.

Fatal Community-Associated Methicillin-Resistant Staphylococcus aureus Pneumonia in an Immunocompetent Young Adult

Severe pneumonia caused by community-associated methicillin-resistant Staphylococcus aureus (MRSA) was reported in children soon after this pathogen emerged in the United States in the 1990s. Genes for Panton Valentine leukocidin, which are present in the majority of community-associated MRSA, are thought to enhance the ability of S aureus to cause necrotizing pneumonia. Despite the rapid spread throughout the United States of community-associated MRSA and related skin and soft-tissue infections, reports of severe pneumonia in adults have been rare. We describe a case of a healthy young adult who initially was treated as an outpatient with levofloxacin for what appeared to be typical community-acquired pneumonia. He soon returned to the emergency department (ED) with rapidly fatal necrotizing pneumonia, associated with hemoptysis, leukopenia, and sepsis syndrome, that was caused by community-associated MRSA carrying genes for Panton Valentine leukocidin. This case highlights the typical features of this form of pneumonia and the need to consider MRSA when evaluating and treating severe pneumonia in the ED. It also raises the question of whether the incidence of this form of pneumonia might be increasing in communities with a high prevalence of community-associated MRSA and whether current pneumonia treatment guidelines should be modified.

Lipoteichoic acid and peptidoglycan from Staphylococcus aureus synergistically induce neutrophil influx into the lungs of mice

Staphylococcus aureus is an important pathogen in nosocomial pneumonia. Lipoteichoic acid (LTA) and peptidoglycan (PepG) are part of the staphylococcal cell wall. Here we show that LTA and PepG act in synergy to cause polymorphonuclear cell recruitment in the pulmonary compartment during S. aureus pneumonia.

Protection with antibody to tumor necrosis factor differs with similarly lethal Escherichia coli versus Staphylococcus aureus pneumonia in rats

BACKGROUND

Differing factors may alter the effects of antibody to tumor necrosis factor (TNF) in infection and sepsis. The authors tested whether bacteria type or treatment route alters antibody to TNF in a rat model of bacterial pneumonia.

METHODS

Rats (n = 231) received similarly lethal doses of either intratracheal Escherichia coli or Staphylococcus aureus followed by treatment with either intratracheal or intraperitoneal antibody to TNF or control serum. Animals received antibiotics (cefotiam daily dose, 100 mg/kg) starting 4 h after inoculation and were studied for up to 96 h.

RESULTS

Compared with S. aureus, E. coli increased serum TNF and interleukin-6 concentrations, lung lavage TNF concentrations, neutrophil counts, and alveolar-to-arterial oxygen gradients and decreased circulating neutrophils and lymphocytes (P > or = 0.05 for all). Compared with controls, with both bacteria, except for lung lavage TNF concentrations (which decreased with intratracheal but not with intraperitoneal antibody to TNF), treatment route did not alter the effects of antibody to TNF on any parameter (P = not significant for all). Antibody to TNF reduced mortality rates (relative risk of death +/- SEM) with both E. coli (-1.6 +/- 0.6; P = 0.006) and S. aureus (-0.5 +/- 0.04; P = 0.185), but these reductions were greater with E. coli than with S. aureus in a trend approaching statistical significance (P = 0.09). Compared with controls, similarly (P = not significant) with both bacteria, antibody to TNF decreased lung lavage and tissue bacteria concentrations (both P < 0.05) and serum TNF concentration (P < 0.09) and increased circulating neutrophils and lymphocytes (both P < or = 0.01). Compared with S. aureus, with E. coli antibody to TNF decreased alveolar-to-arterial oxygen gradients (P = 0.04) and increased serum interleukin-6 concentrations (P = 0.003).

CONCLUSION

Antibody to TNF improved host defense and survival rates with both lethal E. coli and S. aureus pneumonia, but protection was greater with E. coli, where TNF concentrations were higher than with S. aureus. The efficacy of antiinflammatory agents in sepsis may be altered by bacteria type.

Pulmonary infiltrates in patients receiving long-term glucocorticoid treatment: etiology, prognostic factors, and associated inflammatory response

BACKGROUND

Glucocorticoid treatment alters immunoregulatory defense mechanisms and may therefore favor the development of different pulmonary infections.

METHODS

The etiology, prognostic factors, and associated inflammatory response of pulmonary infiltrates in 33 patients receiving long-term glucocorticoid treatment (LTGCT) were prospectively evaluated.

RESULTS

Aspergillus spp (n = 9, 31%) and Staphylococcus spp (n = 6, 21%) were the most common causative agents. Using different diagnostic techniques, we obtained a specific diagnosis in 28 of 33 episodes (85%) of pulmonary infiltrates. Bronchoscopic techniques provided the diagnosis in 64% of the cases. Crude mortality was 45%. Variables associated with mortality were as follows: age > 64 years, bilateral radiographic involvement, delay in diagnosis, inappropriate empirical treatment, Simplified Acute Physiology Score (SAPS) II > or = 25, and requirement for mechanical ventilation (MV). SAPS II > or = 25 (odds ratio [OR], 16; 95% confidence interval, 1 to 260) and MV requirement (OR, 50; 95% confidence interval, 2 to 360) were also significant on multivariate analysis. Pulmonary infections were associated with an increase in the concentration of relevant inflammatory cytokines such as tumor necrosis factor-alpha and interleukin-6 both in serum and BAL. This local and systemic inflammatory response was attenuated when compared with the response observed in patients with pulmonary infections but without glucocorticoid treatment or receiving glucocorticoids for a short period of time (< 9 days).

CONCLUSIONS

Pulmonary infiltrates in patients receiving LTGCT are often caused by fungi and Gram-positive cocci, and are associated with attenuated local and systemic inflammatory response. Although in most cases, sputum cultures and bronchoscopic techniques are diagnostic, the associated mortality is high, particularly in those requiring MV.

Differential role of interleukin-6 in lung inflammation induced by lipoteichoic acid and peptidoglycan from Staphylococcus aureus

Lipoteichoic acids (LTA) and peptidoglycans (PepG) are major components of the cell walls of gram-positive bacteria that trigger inflammatory responses in vitro. To study the in vivo effects of LTA and PepG from Staphylococcus aureus in lungs and to determine the role of interleukin (IL)-6 herein, these compounds were intranasally administered to IL-6 gene deficient (IL-6(-/-)) and wild type (IL-6(+/+)) mice. In IL-6(+/+) mice, LTA and PepG induced acute pulmonary inflammation in a dose-dependent way, characterized by neutrophilic influx and IL-6 production in the bronchoalveolar lavage fluid. Endogenously produced IL-6 attenuated inflammation induced by 10 microg LTA, as reflected by enhanced neutrophil influx, and increased tumor necrosis factor-alpha, macrophage inflammatory protein-1-alpha, and cytokine-induced neutrophil chemoattractant (KC) release into bronchoalveolar lavage fluid of IL-6(-/-) mice, compared with IL-6(+/+) mice. By contrast, pulmonary inflammation induced by 100 microg LTA was similar (neutrophil influx) or even tended to be attenuated (cytokine and chemokine release) in IL-6(-/-) mice. Endogenous IL-6 increased inflammation induced by PepG, as reflected by decreased neutrophil influx into lungs of IL-6(-/-) mice, compared with IL-6(+/+) mice. These data suggest that IL-6 plays an anti-inflammatory role during LTA-induced pulmonary inflammation, which is dependent on the severity of the inflammatory challenge, and a proinflammatory role in peptidoglycan-induced acute lung inflammation. Thus, the contribution of IL-6 to lung inflammation may vary with the stimulus used.

Staphylococcus aureus agr and sarA functions are required for invasive infection but not inflammatory responses in the lung

Staphylococcus aureus strains lacking agr- and sarA-dependent gene products or specific MSCRAMM (microbial surface components recognizing adhesive matrix molecules) adhesins were compared for the ability to activate inflammatory responses in the lung. The mutants were evaluated for virulence in a mouse model of pneumonia and by quantifying their ability to stimulate interleukin-8 (IL-8) and granulocyte-macrophage colony-stimulating factor (GM-CSF) expression in respiratory epithelial cells. In a neonatal mouse, only strains with intact agr and sarA loci were consistently associated with invasive, fatal pulmonary infection (P < 0.001) and sarA was specifically required to cause bacteremia (P < 0.001). The agr and/or sarA mutants were, nonetheless, fully capable of producing pneumonia and were as proficient as the wild-type strain in stimulating epithelial IL-8 expression, a polymorphonuclear leukocyte chemokine, in airway cells. In contrast, agr and especially sarA mutants induced less epithelial GM-CSF expression, and MSCRAMM mutants lacking fibronectin binding proteins or clumping factor A, a ligand for fibrinogen, were unable to stimulate epithelial GM-CSF production. The ability to induce IL-8 expression was independent of the adherence properties of intact bacteria, indicating that shed and/or secreted bacterial components activate epithelial responses. While conserved staphylococcal components such as peptidoglycan are sufficient to evoke inflammation and cause pneumonia, the agr and sarA loci of S. aureus are critical for the coordination of invasive infection of the lungs.

Fas/Fas ligand system mediates epithelial injury, but not pulmonary host defenses, in response to inhaled bacteria

The Fas/Fas ligand (FasL) system has been implicated in alveolar epithelial cell apoptosis during pulmonary fibrosis and acute respiratory distress syndrome. However, Fas ligation can also lead to cell activation and cytokine production. The goal of this study was to determine the role of the Fas/FasL system in host defenses against Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae. We administered bacteria by aerosolization into the lungs of Fas-deficient (lpr) mice and wild-type (C57BL/6) mice and measured bacterial clearance at 6 and 12 h. One hour prior to euthanasia, the mice received an intraperitoneal injection of human serum albumin (HSA) for alveolar permeability determinations. At all times after bacterial challenges, the lungs of the lpr mice contained similar or lower numbers of bacteria than those of the C57BL/6 mice. Alveolar permeability changes, as determined by bronchoalveolar lavage fluid HSA concentrations, were less severe in the lpr mice 6 h after the challenges. In response to E. coli, the lpr mice had significantly more polymorphonuclear leukocytes (PMN) and macrophage inflammatory protein 2 in the lungs, whereas histopathologic changes were less severe. In contrast, in response to the gram-positive cocci, the lpr animals had similar or lower numbers of PMN. We conclude that the Fas/FasL system contributes to the development of permeability changes and tissue injury during-gram negative bacterial pneumonia. The Fas/FasL system did not have a major role in the clearance of aerosolized bacteria from the lungs at the bacterial doses tested.

[Detection of Staphylococcus aureus and Staphylococcus epidermis species specific antigens and antibodies to alpha-toxin in the blood of patients with pneumonia]

Test systems for indirect hemagglutination (IHA) test for detection of S. aureus and S. epidermidis teichoic acids and S. aureus alpha-toxin in patients' sera have been developed on the basis of immunoglobulins isolated from monospecific sera. Test system for IHA test for detection of antitoxin in donor and patients' sera has been created on the basis of highly purified alpha-toxin. Thirty donor sera and 61 sera from patients with pneumonia were analyzed. Low antibody levels in the patients may be due to the fact that the sera were collected during the first days of disease. Group of patients with high content of staphylococcal antigens and antitoxin in the blood was particularly interesting. These patients developed severe pneumonia, among whose etiological agents were S. aureus and S. epidermidis. Diagnostic analysis of patients' sera by IHA test for detection of staphylococcal antigens was more effective, accurate, and rapid in comparison with the bacteriological method; moreover, it confirmed the significance of staphylococci in the pathogenesis of pneumonia.

Bacterial superantigen staphylococcal enterotoxin B induces interstitial pneumonia in SCID mice reconstituted with peripheral blood mononuclear cells from collagen vascular disease patients

To investigate whether superantigens induce interstitial pneumonia associated with collagen vascular disease (CVD), staphylococcal enterotoxin B (SEB) was intratracheally administered to SCID mice reconstituted with peripheral blood mononuclear cells (PBMCs) from CVD patients that suffered lung complications. Although a slight accumulation of inflammatory cells into the perivascular area was seen in the lungs of SCID mice injected with PBMCs from CVD patients or healthy donors, SEB administration significantly increased the severity of inflammation in the lungs of SCID mice that received CVD patient PBMCs. Furthermore, human leukocytes were detected by immunohistochemistry in the lungs of SCID mice that received SEB after reconstitution with PBMCs from CVD patients but not in other groups of SCID mice. CD45RO(+) memory T cells comprised the majority of infiltrating human leukocytes. These results suggest the possibility that external superantigens may induce the development of interstitial pneumonia in patients that have a genetic background predisposition to autoimmune disease.

Factors affecting the course and severity of transnasally induced Staphylococcus aureus pneumonia in mice

In order to examine several factors that may affect the course and severity of transnasally induced Staphylococcus aureus pneumonia in mice, bacteria were prepared in a free suspension or bound to fetal mouse cells. Immunosuppression was induced in five strains of mice (ICR, C57BL/6, BALB/c, C3H/He and CBA/J) by injection of cyclophosphamide (200 mg/kg body weight), 2 days before infection. Impairment of mucociliary clearance was induced by intranasal instillation of formalin. Mice were then infected with various doses and strains of the organism. Although no significant differences were observed between either form of inoculum, pretreatment with formalin plus cyclophosphamide was associated with a significant increase in lung bacterial counts. In particular, cyclophosphamide treatment was associated with a high mortality in mice infected with several strains of S. aureus irrespective of their toxin production profiles. Histopathological examination demonstrated that in mice treated with formalin plus cyclophosphamide, clusters of bacteria were observed in lung parenchyma, associated with a mild accumulation of inflammatory cells at day 2 and extensive cell infiltration at day 7. CBA/J mice represented the most susceptible strain among those examined, with 10(4)- and 10(2)-fold higher bacterial counts in the lungs at days 3 and 5, respectively. These results indicate that neutropenia and impaired mucociliary clearance are major factors that influence the severity of S. aureus pneumonia in mice. Analysis of the role of genetic background in enhancement of vulnerability to infection is warranted in future studies.

Immunoglobulin A levels in bronchial samples during mechanical ventilation and onset of nosocomial pneumonia in critically ill patients

Local immunoglobulins play a key role in host defense against lung infection. We investigated the pattern of evolution of bronchial albumin, IgA, and IgG levels in ventilated ICU patients in relation to nosocomial pneumonia. Immunocompetent, critically ill patients underwent serial blood and bronchial protein determinations on Day 1 (intubation day), and on Days 3, 7, 10, and 14. The variations in proteins levels were compared with corresponding Day 1 values in the whole population, and between patients who developed lung infections (Group A) and the remaining population (Group B). Forty-four patients were included into the study. In the whole population, when compared with the baseline value, bronchial IgA/albumin ratio increased significantly (Day 3, +58%, p = 0.04); Day 14, +171%, p < 0.01), but serum IgA/albumin and serum and bronchial IgG/albumin ratios did not change significantly. In Group A, the increase in the IgA/albumin ratio was less than in Group B (Day 3, +15% versus +87%, p = 0.04; Day 14, +29% versus +210%, p < 0.01). No significant differences were observed between the two groups for bronchial and plasma albumin and IgG levels and for bronchial polymorphonuclear elastase levels. Bronchial IgA production was enhanced in ventilated patients. A reduction in this enhanced bronchial IgA production might account for the development of nosocomial pneumonia.

[Studies on MRSA pneumonia as a complication of hematopoietic malignancies]

Recently, the progress of chemotherapy has improved the clinical outcome of chemotherapy for hematopoietic malignancies considerably. However, the incidence of MRSA infections has increased in patients with hematopoietic malignancies, since preventive, multi-drug administration of antibiotics is frequently used in these patients. Moreover, patients with hematopoietic malignancies complicated by MRSA pneumonia have a poor prognosis. We examined lymphocyte subpopulations in bronchoalveolar lavage fluid (BALF) in MRSA pneumonia-complicated patients with hematopoietic malignancies and studied their relationship with the clinical features. We also discuss the cause of their poor prognosis. Of 223 patients with hematopoietic malignancies, 18 (8.1%) were complicated by MRSA pneumonia. Many of those patients had lymphoid malignancies. MRSA pneumonia occurred when neutrophil count was decreased. Most patients had been treated with chemotherapy containing anticancer drugs or with corticosteroid therapy. They had also been treated with third generation cefem antibiotics. We studied lymphocyte subsets in BALF in MRSA pneumonia-complicated patients with non-Hodgkin's lymphoma (NHL) and observed the local changes of the pulmonary immunological system due to NHL itself and due to anti-lymphoma chemotherapy. Our findings suggest the possibility that these immunological changes may play a role in the susceptibility to MRSA pneumonia.

Passive local immunotherapy of experimental staphylococcal pneumonia with human intravenous immunoglobulin

Staphylococcus aureus remains a life-threatening agent of nosocomial pneumonia in immunocompromised patients. The increasing incidence of strains exhibiting wide-spectrum resistance to antibiotics, such as methicillin-resistant S. aureus (MRSA), requires new therapeutic strategies. There is renewed interest in passive immunization with human plasma-derived immunoglobulins (IVIG) as antiinfective agents. The efficacy of IVIG was tested in an experimental model of staphylococcal pneumonia, using both an MRSA clinical isolate and reference strain Cowan III, in mice immunosuppressed with cyclophosphamide. Efficient antistaphylococcal activities were obtained with IVIG administered intravenously or intranasally. IVIG saturated with protein A or its F(ab')2 fragments were as efficient as intact IVIG, suggesting that protection did not require opsonization through IgG Fc-phagocyte Fc gamma-receptor interactions. Thus, topical administration of IVIG may replace a local antibody response to S. aureus in an immunocompromised host and may be useful in prophylaxis and treatment of nosocomial S. aureus pneumonia.

Complications of varicella pneumonia in adults

Varicella is predominantly a disease of children, in whom it typically has a benign course and outcome. However, when the disease affects adults, the complications can be life-threatening. Varicella pneumonia, secondary bacterial infection, and opportunistic infection in the immunocompromised host are the most common complications in the adult. Surveillance for these complications is mandatory because appropriate therapy may be life-saving. The introduction of specific antiviral agents may be useful in certain clinical circumstances. The authors describe two representative patients and discuss the diagnosis and treatment. They also discuss this infection in adulthood in general.

Clinical significance of HIV DNA in polymorphonuclear neutrophils from patients with HIV infection

HIV DNA was detected by the polymerase chain reaction technique in polymorphonuclear neutrophils (PMNs) in 11 of 37 (29.7%) HIV-infected patients. A detectable level of HIV DNA in PMNs was more common in symptomatic than asymptomatic HIV infected patients (46.7% and 18.2%, respectively; p < 0.05). HIV DNA in PMNs was detected most frequently in patients with recurrent bacterial pneumonia or Pneumocystis carininii pneumonia. An association between HIV DNA in PMNs and a low CD4/8 ratio as well as high levels of immunoglobulins in the sera was noted. Detectable HIV DNA was found more frequently in patients with neutropenia than in those with a normal level of neutrophils in peripheral blood (44.4% and 28.0%, respectively; p < 0.05). These data suggest that infection of PMNs by HIV may be associated with PMN impairment during HIV infection.

[Immunologic criteria of severity of suppurative infections in patients on programmed hemodialysis]

Certain parameters of the immune system were studied in patients under programmed hemodialysis with and without pyo-inflammatory complications. It was found that patients without pyo-inflammatory diseases are characterized by the state of immune deficiency while in patients with purulent infection the degree of inhibition of immune response of the organism correlates with spread of the suppurative process.

[Phagocytosis of Staphylococcus aureus and Pseudomonas aeruginosa by pulmonary neutrophilic granulocytes]

The elimination of Staphylococcus aureus (S. a.) and Pseudomonas aeruginosa (P. a.) by pulmonary neutrophilic granulocytes was investigated in vitro. The elimination rate of P. a. is appreciably smaller than that of S. a.. The reason for this is apparently a reduced degree of phagocytosis of P. a. in consequence of the slight adherence to the granulocyte membrane. The liberation of oxidants differs only to a negligible degree.

[Clinico-immunologic effectiveness of chlorophyllypt in the treatment of acute destructive pneumonia]

An attempt has been made to replace antibiotics by chlorophyllypt (0.25 per cent solution in physiological sodium chloride solution administered by intravenous drip). The clinical, laboratory and X-ray parameters in 22 patients treated by this drug normalized in earlier terms than those in 19 patients who received the traditional antibiotic therapy. Chlorophyllypt was found to have the immunocorrective effect manifested by the normalization of the T-lymphocyte number and their theophylline-resistant subpopulation. No such an effect was achieved when broad-action antibiotics were used.

The quantity and function of pulmonary alveolar macrophages after splenectomy and Corynebacterium parvum

We have previously shown that Corynebacterium parvum (C. parvum), a nonspecific immunomodulator, partially protects splenectomized and nonsplenectomized mice when challenged with aerosolized pneumococci. We report here the effects of both splenectomy and C. parvum on the phagocytic function of the lavageable pulmonary alveolar macrophage (PAM). Groups of young adult male Sprague Dawley rats underwent splenectomy or sham operation 3 weeks before injection of C. parvum 1.5 mg IP (or saline) per animal. One week postinjection PAM's were harvested. The in vitro phagocytic indices (PI) for PAM incubated with tritiated thymidine-labeled S. aureus or Streptococcus pneumoniae, type 14, opsonized with normal rat serum, were determined. Splenectomy had no effect on lung weights, PAM yield, or PAM phagocytic activity. C. parvum administration significantly increased spleen weight in sham-operated animals, but had no effect on lung weights, PAM yield, or phagocytic activity of either control or splenectomized animals. Splenectomy in the adult rat did not induce a phagocytic defect in the PAM and thus the lavageable PAM cannot be considered a significant site of the postsplenectomy defect. Since C. parvum protects animals from respiratory challenge with Streptococcus pneumoniae but does not alter the number or activity of lavageable alveolar macrophages, we hypothesize that C. parvum protection is more likely related to our previous finding of an increased clearance of blood-borne bacteria by the expanded and enhanced reticuloendothelial system.

Comparative role of complement in pneumococcal and staphylococcal pneumonia

To evaluate the role of complement in pneumococcal and staphylococcal pneumonia, we decomplemented rats with cobra venom factor and inoculated them intratracheally with Staphylococcus aureus or type 25 pneumococci. S. aureus produced a patchy bronchopneumonia in normal Sprague-Dawley or Lewis rats, and decomplementation did not increase the severity of staphylococcal infection in either rat strain as judged by quantitative cultures of the lungs and blood at 6, 24, and 48 h after inoculation. In contrast, decomplementation markedly increased the severity of pneumonia caused by type 25 pneumococci in Sprague-Dawley and Lewis rats. In Sprague-Dawley rats, decomplementation significantly increased the number of bacteria in the lungs at 3, 6, and 24 h of infection. Bacteremia developed early in decomplemented Sprague-Dawley rats, but the higher pulmonary bacterial counts did not appear to be caused by bacteremic seeding of the lungs. Decomplemented Sprague-Dawley rats inoculated intravenously with pneumococci failed to develop the very high levels of bacteria in the lungs that were observed when the rats were inoculated intratracheally. Moreover, decomplemented Lewis rats inoculated intratracheally with pneumococci developed significantly increased numbers of pneumococci in the lungs early in infection (3 and 6 h) when they had no detectable bacteremia. These data indicate that in murine models complement plays a major protective role against type 25 pneumococci in the lung, whereas complement is not important to host defense in staphylococcal pneumonia.

Effects of bacterial pneumonitis on development of pneumocystosis in rats

Disease caused by the protozoan parasite Pneumocystis carinii complicates management of patients with a variety of defects in immune function and is most commonly observed in patients who receive long-term therapy with glucocorticoids. In the rat, disease is readily induced by chronic administration of glucocorticoids. However, rats that have had polymorphonuclear leukocytic pneumonitis induced by Pseudomonas are protected from development of pneumocystosis, whereas rats that have received an intratracheal injection of Staphylococcus, which does not induce a polymorphonuclear leukocytic alveolar exudate, are not protected. It is possibly that accidental contact of polymorphonuclear leukocytes with dormant Pneumocystis is an important element of control of the organism in healthy animals, and suppression of polymorphonuclear leukocytic inflammatory response underlies glucocorticoid-induced and spontaneous activation of the disease.

Immunodiagnosis of invasive pulmonary aspergillosis in rabbits. Fungal antigen detected by radioimmunoassay in bronchoalveolar lavage fluid

To improve antemortem diagnosis of invasive pulmonary aspergillosis, we used a radioimmunoassay to detect an Aspergillus fumigatus antigen in bronchoalveolar lavage fluid (BALF) and evaluated this technique in a model of disseminated aspergillosis. Antigen was detected in 91% of BALF samples obtained from 11 rabbits with major pulmonary aspergillosis. In an additional 10 rabbits with only minor pulmonary involvement, antigen was detected in 40% of concentrated lavage samples. In contrast, antigenlike activity was found in only 1 of 17 BALF samples from control animals with systemic candidiasis, in none of 9 control animals with staphylococcal pneumonia and in none of 10 normal control animals. Although antigen was present in the serum of 76% of animals infected with Aspergillus, 27% of those with major pulmonary involvement had antigen detected in BALF alone. We found that an extracellular microbial antigen can be detected in BALF and that this technique in the disseminated aspergillosis model is both sensitive and specific for invasive pulmonary disease.

[Immunocytoadherence indices in evaluating the specificity and activity of an inflammatory process]

A method for determination of specificity and activity of the inflammatory process is described. The method is based on the reaction of immunocytoadherence between granulocytes with the round nucleus (nuclei) and microorganisms. The method is sensitive, as the phagocytic reaction is inhibited and the patient's blood cells interact with microbial cells due to the presence of immunoglobulins or receptors of the immunoglobulin nature, active against the causative agent of the disease, on the blood cell surface. The values of immunocytoadherence in tuberculosis, brucellosis and pneumonia are presented.