Chronic glucocorticosteroid therapy impairs staphylococcal clearance from murine lungs

Inhaled fluticasone propionate impairs pulmonary clearance of Klebsiella pneumoniae in mice

Background

Recent trials demonstrate increased pneumonia risk in chronic obstructive pulmonary disease patients treated with the inhaled corticosteroid (ICS) fluticasone propionate (FP). There is limited work describing FP effects on host defenses against bacterial pneumonia.

Methods

C57BL/6 mice received daily, nose-only exposure to nebulized FP or vehicle for 8 days, followed by pulmonary challenge with Klebsiella pneumoniae. Bacterial burden, phagocytosis, leukocyte recruitment, cytokine expression, nitric oxide release, and survival were measured.

Results

Inhaled FP increased bacterial burden in lungs and blood 48 h after infection but affected neither in vivo phagocytosis of bacteria by alveolar macrophages (AM) nor alveolar neutrophil recruitment. AM from FP-treated mice showed impaired expression of infection induced TNF-alpha, IP-10 (CXCL-10), and interleukin 6 (IL-6), and AM also showed a trend towards impaired intracellular pathogen control following in vivo infection. In vitro FP treatment resulted in a dose-dependent impairment of cytokine expression by AM. Furthermore, infection-induced nitric oxide (but not hydrogen peroxide) production was impaired by FP in vivo and in vitro. FP decreased survival in this model.

Conclusions

Exposure to inhaled FP impairs pulmonary clearance of K. pneumoniae in mice, an effect associated with greater systemic bacteremia and death. Decreased AM cytokine and nitric oxide expression parallel the failure to control infection. These results support the study of ICS effects on human pulmonary host defenses.

Intrapulmonary growth of Staphylococcus aureus in rats during induced atelectasis

Intrinsic pulmonary antibacterial defenses are mediated by alveolar macrophages and by noncellular factors. Mechanical ventilation in the resting tidal volume range leads to alterations in the physical characteristics of alveolar surfactant, alveolar instability, regional hypoxia, and systemic hypoxemia. While a number of experimental manipulations diminish the activity of the intrinsic antibacterial defense system, the effects of mechanical ventilation per se have not been systematically evaluated previously. We found that normal rats ventilated without sighing (periodic large breaths) manifested severe defects in pulmonary clearance of Staphylococcus aureus during 6-h experiments, such that growth of the inoculum occurred. Addition of a timer-controlled mechanism to cause the animals to sigh every 2 min, without other modifications in the experimental conditions, caused significant improvement in clearance. Analysis of cellular response, compartmentalization of viable bacteria, surfactant quantities and sedimentation characteristics, and protein influx indicated that the defect in clearance paralleled alterations in the physical state of surfactant and alveolar stability but was not strongly correlated with alterations in the other parameters we measured. The data show that defective pulmonary bacterial clearance is rapidly induced by measures which alter alveolar stability and suggest that intrinsic pulmonary defenses require maintenance of normal air-liquid interfaces for optimal function.

Methylprednisolone impairs the bactericidal activity of alveolar macrophages

Corticosteroid treatment of patients following acid aspiration has been reported to increase the incidence of bacterial pneumonia, with Staphylococcus aureus being a common isolate. We hypothesized that administration of methylprednisolone (MP) to mice with acid-injured lungs would impair pulmonary clearance of S. aureus by compromising the bactericidal oxidative metabolism of pulmonary phagocytes. Using an inhalational bacterial challenge, we established that MP decreased pulmonary clearance of S. aureus. In mice with normal lungs and without MP treatment 14 +/- 2% of all initially deposited Staphylococci remained at 4 hr compared to 28 +/- 2% remaining in the lungs of mice with MP treatment. In mice with acid-injured lungs, MP caused a greater impairment of S. aureus clearance at 4 hr with 44 +/- 10% of all initially deposited bacteria remaining in the lungs of control mice and 210 +/- 24% remaining in the lungs of MP-treated mice. After it was demonstrated that there was no difference in the numbers of phagocytic cells obtained by lung lavage from mice with or without MP treatment, the bactericidal oxidative metabolism of these cells was quantitated using luminol-amplified chemiluminescence. Phagocytic cells from mice not exposed to S. aureus displayed minimal chemiluminescence whether they were treated with saline (22 +/- 14 mV) or MP (14 +/- 8 mV). In contrast, phagocytes from saline-treated mice exposed to S. aureus showed a significant increase in chemiluminescence (159 +/- 22 mV). Pretreatment with MP, however, prevented this response to S. aureus (21 +/- 13 mV), indicating that bactericidal oxidative metabolism of these phagocytic cells had been suppressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of pulmonary clearance of bacteria by antioxidants

To further delineate the mechanisms underlying murine pulmonary defenses against bacterial infection, we studied the effects of antioxidant enzymes and hydroxyl radical scavengers on pulmonary clearance processes. Intratracheal injection of catalase and superoxide dismutase resulted in prolonged intraalveolar residence of the enzymes, but caused no decrease in rates of clearance of either Staphylococcus aureus 502A or Pseudomonas aeruginosa PAO1. In contrast, dimethylsulfoxide and dimethylthiourea caused significant depression of clearance of P. aeruginosa without altering clearance of S. aureus. These results provide further differentiation between clearance processes affecting gram-negative and gram-positive bacteria and suggest that murine clearance of gram-negative organisms may be in part mediated by reactions which generate hydroxyl anion. In vivo administration of agents which inhibit hydrogen peroxide-, superoxide-, or hydroxyl anion-mediated reactions do not alter normal clearance of S. aureus.

Interaction between the legionnaires' disease bacterium (Legionella pneumophila) and human alveolar macrophages. Influence of antibody, lymphokines, and hydrocortisone

We have studied the interaction between virulent Legionella pneumophila and human alveolar macrophages, the resident phagocytes at the site of infection in Legionnaires' disease. L. pneumophila multiplied 2.5-5 logs within 3 d, as measured by colony forming units, when incubated with freshly explanted alveolar macrophages in monolayer culture. At the peak of bacterial multiplication, the alveolar macrophage monolayers were destroyed. L. pneumophila multiplied more rapidly in 4-d-old than in freshly explanted alveolar macrophages. Inside alveolar macrophages, L. pneumophila were located within membrane-bound vacuoles whose cytoplasmic sides were studded with ribosomes. Alveolar macrophages that were incubated with concanavalin A (Con A) stimulated human mononuclear cell supernatants (cytokines), inhibited L. pneumophila multiplication, and the degree of inhibition was proportional to the concentration of Con A supernatant added. Anti-L. pneumophila antibody in conjunction with complement promoted phagocytosis of L. pneumophila by alveolar macrophages. By electron microscopy, most (75%) of the phagocytized L. pneumophila were intracellular. However, freshly explanted alveolar macrophages were able to kill only 0-10% of an innoculum of L. pneumophila even in the presence of antibody and complement. At the same time, alveolar macrophages also killed opsonized Escherichia coli poorly. Increasing the ratio of macrophages to bacteria, adhering the macrophages to microcarrier beads, or preincubating the macrophages for 24 or 48 h with Con A supernatants failed to augment alveolar macrophage killing of opsonized E. coli. Corticosteroids appear to increase patient susceptibility to Legionnaires' disease. However, pretreatment of alveolar macrophages and monocytes with hydrocortisone had no influence on intracellular multiplication of L. pneumophila or on the inhibition of that multiplication by activated alveolar macrophages or monocytes. Hydrocortisone did impair cytokine-induced aggregation of alveolar macrophages. These findings demonstrate that L. pneumophila multiplies in human alveolar macrophages and that they do so within a ribosome-lined phagosome; that freshly explanted alveolar macrophages kill few L. pneumophila even in the presence of antibody and complement; that activated alveolar macrophages inhibit L. pneumophila multiplication; and that steroids do not exert a direct suppressive effect on the anti-L. pneumophila activity of activated or nonactivated alveolar macrophages. Our findings indicate that alveolar macrophages may play a central role in both the pathogenesis of Legionnaires' disease and in host defense against it. This paper shows that human resident macrophage can be activated to a higher state of antimicrobial capacity and that the human alveolar macrophage can serve as an effector call in call-mediated immunity.

The possible role of stress in the induction of pneumonic pasteurellosis

Five groups of range bred calves (four calves per group) were used to investigate the effect of stress on susceptibility to aerosol exposures with bovine herpesvirus-1 or Pasteurella haemolytica. Twelve calves were weaned, transported, processed at a commercial feedlot and transported to isolation facilities three days later. An aerosol challenge of either 10 colony forming units of P. haemolytica or 10 plaque forming units of bovine herpesvirus-1 virus was given to two groups of calves and the third group was not challenged. The fourth group was transported directly to the isolation facilities after weaning and aerosol challenged with P. haemolytica. The fifth group remained at the farm after weaning and was not challenged. All transported animals had elevated plasma cortisol levels which remained above normal for at least three days postchallenge. The blastogenic response of all calves was depressed after leaving the farm and remained depressed throughout the experiment. The suppression correlated well with elevated serum cortisol levels. Calves processed through the feedlot encountered bovine herpesvirus-1 because eight out of 12 animals seroconverted to this antigen. Most calves seroconverted to P. haemolytica whether they were experimentally challenged or not. Where the unchallenged calves encountered P. haemolytica is unknown. Calves challenged with bovine herpesvirus-1 but not with P. haemolytica, had significant clinical signs of pneumonia and two animals died due to bovine herpesvirus-1 infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Pseudomonas aeruginosa clearance in mice: comparison of tissue, strain, and corticosteroid effects

We used a murine model to determine whether chronic corticosteroid therapy has uniform effects on bacterial clearance processes in different tissues. After a 2-week regimen of oral prednisolone, Swiss Webster mice were challenged with Pseudomonas aeruginosa strain PAO1 or virulent derivatives of PAO1 (IP-8 and IT-10). Chronic corticosteroid therapy delayed the clearance of strain PAO1 from the peritoneal cavity. However, steroid treatment did not reduce the neutrophil influx, did not reduce the in vivo phagocytic capacity of neutrophils, and did not alter bactericidal activity of peritoneal exudate cells in vitro. Virulent isolates (IP-8 and IT-10) replicated in the peritoneal cavity in steroid-treated mice even though the neutrophil influx was similar to control mice. In contrast to the abnormal peritoneal clearance, all strains were rapidly cleared from the lungs of control and steroid-treated mice after aerosol challenge. Neutrophil influx into bronchoalveolar spaces was greater in steroid-treated mice than in control mice. All mice (control and steroid treated) survived these challenges, except for some steroid-treated mice infected intraperitoneally with IP-8. These results demonstrate that chronic steroid therapy alters bacterial clearance processes on the peritoneal surfaces to a greater extent than in the lower respiratory tract. The explanation for this altered clearance in the peritoneum is unclear, but cannot be explained by reductions in neutrophil migration to inflammatory stimuli. Therefore, the infectious risk associated with chronic corticosteroid therapy appears to depend on both the tissue and the virulence of the bacterial strain and may reflect alterations in clearance processes other than neutrophil migration.