Pneumococcal pneumonia suppresses allergy development but preserves respiratory tolerance in mice.

Colonization with Streptococcus pneumoniae (S. pneumoniae) is associated with an increased risk for recurrent wheeze and asthma. Killed S. pneumoniae showed some potential as an effective immunomodulatory therapy in a murine model of asthma. Murine studies demonstrated protection against allergic asthma by symbiotic bacteria via triggering regulatory T cell response: treatment with killed S. pneumoniae resulted in suppressed levels of allergen-specific Th2 cytokines, while early immunization generated a protective Th1 response. We investigated the impact of lung infection with live S. pneumoniae on both the development and maintenance of allergic airway inflammation and respiratory tolerance in mice. BALB/c mice were infected intratracheally with S. pneumoniae either prior to or after tolerance or allergy were induced, using ovalbumin (OVA) as model allergen. Infection of mice with S. pneumoniae prior to sensitization or after manifestation of allergic airway inflammation suppressed the development of an allergic phenotype as judged by reduced eosinophil counts in bronchoalveolar lavage fluid, decreased IgE serum levels and Th2 cytokines, relative to non-infected allergic control mice. In contrast, infection of mice with S. pneumoniae after manifestation of allergic airway inflammation combined with late mucosal re-challenge did not affect the allergic response. Moreover, induction and maintenance of respiratory tolerance to OVA challenge were not altered in S. pneumoniae-infected mice, demonstrating that mice remained tolerant to the model allergen and were protected from the development of allergic airway inflammation regardless of the time point of infection. Our results suggest that a bacterial infection may decrease the manifestation of an allergic phenotype not only prior to sensitization but also after manifestation of allergic airway inflammation in mice, whereas both, induction and maintenance of respiratory tolerance are not affected by pneumococcal pneumonia. These data may point to a role for undisturbed development and maintenance of mucosal tolerance for the prevention of allergic inflammation also in humans.

TNF-related apoptosis-inducing ligand (TRAIL) exerts therapeutic efficacy for the treatment of pneumococcal pneumonia in mice.

Apoptotic death of alveolar macrophages observed during lung infection with Streptococcus pneumoniae is thought to limit overwhelming lung inflammation in response to bacterial challenge. However, the underlying apoptotic death mechanism has not been defined. Here, we examined the role of the TNF superfamily member TNF-related apoptosis-inducing ligand (TRAIL) in S. pneumoniae-induced macrophage apoptosis, and investigated the potential benefit of TRAIL-based therapy during pneumococcal pneumonia in mice. Compared with WT mice, Trail(-/-) mice demonstrated significantly decreased lung bacterial clearance and survival in response to S. pneumoniae, which was accompanied by significantly reduced apoptosis and caspase 3 cleavage but rather increased necrosis in alveolar macrophages. In WT mice, neutrophils were identified as a major source of intraalveolar released TRAIL, and their depletion led to a shift from apoptosis toward necrosis as the dominant mechanism of alveolar macrophage cell death in pneumococcal pneumonia. Therapeutic application of TRAIL or agonistic anti-DR5 mAb (MD5-1) dramatically improved survival of S. pneumoniae-infected WT mice. Most importantly, neutropenic mice lacking neutrophil-derived TRAIL were protected from lethal pneumonia by MD5-1 therapy. We have identified a previously unrecognized mechanism by which neutrophil-derived TRAIL induces apoptosis of DR5-expressing macrophages, thus promoting early bacterial killing in pneumococcal pneumonia. TRAIL-based therapy in neutropenic hosts may represent a novel antibacterial treatment option.

Hepatic induction of cholesterol biosynthesis reflects a remote adaptive response to pneumococcal pneumonia.

Community-acquired pneumonia presents a spectrum of clinical phenotypes, from lobar pneumonia to septic shock, while mechanisms underlying progression are incompletely understood. In a transcriptomic and metabolomic study across tissues, we examined serotype-specific regulation of signaling and metabolic pathways in C57BL/6 mice intratracheally instilled with either serotype 19F Streptococcus pneumoniae (S19; causing lobar pneumonia), or serotype 2 S. pneumoniae (S2; causing septic pneumococcal disease,) or vehicle (Todd-Hewitt broth). Samples of lung, liver, and blood were collected at 6 and 24 h postinfection and subjected to microarray analysis and mass spectrometry. Results comprise a preferential induction of cholesterol biosynthesis in lobar pneumonia at low-infection doses (10(5) colony forming units/mouse) leading to increased plasma cholesterol (vehicle: 1.8±0.12 mM, S2: 2.3±0.10 mM, S19: 2.9±0.15 mM; P<0.05, comparing S19 to vehicle and S2). This induction was pneumolysin dependent, as a pneumolysin-deficient strain of serotype 19F failed to induce cholesterol biosynthesis (S19ΔPLY: 1.9±0.03 mM). Preincubation of pneumolysin with purified cholesterol or plasma from hypercholesterolemic mice prior to intratracheal instillation protected against lung barrier dysfunction and alveolar macrophage necrosis. Cholesterol may attenuate disease severity by neutralizing pneumolysin in the alveolar compartment and thus prevent septic disease progression.

Evaluation of biophotonic imaging to estimate bacterial burden in mice infected with highly virulent compared to less virulent Streptococcus pneumoniae serotypes.

Bioluminescence imaging is an innovative, noninvasive tool to analyze infectious disease progression under real-life conditions in small laboratory animals. However, the relevance of bioluminescence imaging to monitor invasive compared to noninvasive bacterial infections of the lung has not been examined so far. In the current study, we systematically evaluated the importance of bioluminescence imaging to monitor pneumococcal disease progression by correlating biophotonic signals with lung bacterial loads in two mouse strains (BALB/c, C57BL/6) infected with either self-glowing, bioluminescent serotype 19 Streptococcus pneumoniae causing focal pneumonia or serotype 2 S. pneumoniae causing invasive pneumococcal disease. The best correlations between bioluminescence signals and lung CFU counts were observed in BALB/c mice compared to C57BL/6 mice just on day 3 after infection with invasive serotype 2 S. pneumoniae, while excellent correlations between photon counts and bacterial loads were observed in isolated lungs of BALB/c and C57BL/6 mice, irrespective of the employed pneumococcal serotype. Moreover, good correlations between biophotonic signals and CFU counts were also observed in mice upon infection with serotype 19 S. pneumoniae causing focal pneumonia in mice, again with best correlation values obtained for BALB/c mice at day 3 postinfection. Collectively, we show that the relevance of biophotonic imaging to monitor S. pneumoniae-induced lung infections in mice is largely influenced by the disease model under investigation. The provided data may be important for studies of infectious diseases.

Efficacy profiles of daptomycin for treatment of invasive and noninvasive pulmonary infections with Streptococcus pneumoniae.

Daptomycin is a novel lipopeptide antibiotic with excellent activity against Gram-positive bacterial pathogens, but its therapeutic value for the treatment of invasive pneumococcal disease compared to that for the treatment of pneumococcal pneumonia is incompletely defined. We investigated the efficacy of daptomycin in two models of Streptococcus pneumoniae-induced lung infection, i.e., pneumococcal pneumonia and septic pneumococcal disease. Mice were infected with a bioluminescent, invasive serotype 2 S. pneumoniae strain or a less virulent serotype 19 S. pneumoniae strain and were then given semitherapeutic or therapeutic daptomycin or ceftriaxone. Readouts included survival; bacterial loads; and septic disease progression, as determined by biophotonic imaging. Semitherapeutic daptomycin treatment fully protected the mice against the progression of septic disease induced by serotype 2 S. pneumoniae, while therapeutic treatment of the mice with daptomycin or ceftriaxone led to approximately 70% or approximately 60% survival, respectively. In contrast, mice infected with serotype 19 S. pneumoniae developed severe pneumonia and lung leakage even in the presence of increased intra-alveolar daptomycin levels, resulting in only 40% survival, whereas the ceftriaxone-treated mice had 100% survival. Together, although daptomycin demonstrates little efficacy in the treatment of pneumococcal pneumonia, daptomycin is highly effective in preventing S. pneumoniae-induced septic death, thus possibly offering a therapeutic option for patients with life-threatening septic pneumococcal disease.

Pharmacodynamic consequences of P-glycoprotein-dependent pharmacokinetics of risperidone and haloperidol in mice.

Efflux transporters, like P-glycoprotein (P-gp), may limit the access of drugs to the brain via the blood-brain barrier. The antipsychotic drug risperidone and its active metabolite 9-hydroxyrisperidone (paliperidone) are substrates of P-gp. Motor behavior of P-gp deficient mice (mdr1a/1b (-/-, -/-)) and wild type animals on a rotarod after acute doses of risperidone or haloperidol, a nonsubstrate of P-gp, were analysed aiming to show that P-gp substrate properties of an antipsychotic drug have functional consequences. Behavioral tests revealed dose-dependent effects of 0.3-3 mg/kg risperidone in wild type animals 0.5-12 h after i.p. injection of the drug. In knockout mice the 0.3 mg/kg dose of risperidone was as effective as the 3 mg/kg dose in wild type mice. A dose of 0.3 mg/kg haloperidol, however, exhibited similar pharmacodynamic effects in both genotypes. Brain concentrations of risperidone plus 9-hydroxyrisperidone were 10-fold higher in knockout than in wild type animals whereas brain concentrations of haloperidol did not differ between the two genotypes. P-gp-dependent brain distribution kinetics and behavioral effects of risperidone give evidence that the expression of P-gp has an impact on psychotropic drug actions when treating patients with drugs that are substrates of P-gp.