STAT3 Deficiency Alters the Macrophage Activation Pattern and Enhances Matrix Metalloproteinase 9 Expression during Staphylococcal Pneumonia.

Staphylococcus aureus is a significant cause of morbidity and mortality in pulmonary infections. Patients with autosomal-dominant hyper-IgE syndrome due to STAT3 deficiency are particularly susceptible to acquiring staphylococcal pneumonia associated with lung tissue destruction. Because macrophages are involved in both pathogen defense and inflammation, we investigated the impact of murine myeloid STAT3 deficiency on the macrophage phenotype in vitro and on pathogen clearance and inflammation during murine staphylococcal pneumonia. Murine bone marrow-derived macrophages (BMDM) from STAT3 LysMCre+ knockout or Cre- wild-type littermate controls were challenged with S. aureus, LPS, IL-4, or vehicle control in vitro. Pro- and anti-inflammatory responses as well as polarization and activation markers were analyzed. Mice were infected intratracheally with S. aureus, bronchoalveolar lavage and lungs were harvested, and immunohistofluorescence was performed on lung sections. S. aureus infection of STAT3-deficient BMDM led to an increased proinflammatory cytokine release and to enhanced upregulation of costimulatory MHC class II and CD86. Murine myeloid STAT3 deficiency did not affect pathogen clearance in vitro or in vivo. Matrix metalloproteinase 9 was upregulated in Staphylococcus-treated STAT3-deficient BMDM and in lung tissues of STAT3 knockout mice infected with S. aureus. Moreover, the expression of miR-155 was increased. The enhanced inflammatory responses and upregulation of matrix metalloproteinase 9 and miR-155 expression in murine STAT3-deficient as compared with wild-type macrophages during S. aureus infections may contribute to tissue damage as observed in STAT3-deficient patients during staphylococcal pneumonia.

Virus-Induced Changes of the Respiratory Tract Environment Promote Secondary Infections With Streptococcus pneumoniae.

Secondary bacterial infections enhance the disease burden of influenza infections substantially. Streptococcus pneumoniae (the pneumococcus) plays a major role in the synergism between bacterial and viral pathogens, which is based on complex interactions between the pathogen and the host immune response. Here, we discuss mechanisms that drive the pathogenesis of a secondary pneumococcal infection after an influenza infection with a focus on how pneumococci senses and adapts to the influenza-modified environment. We briefly summarize what is known regarding secondary bacterial infection in relation to COVID-19 and highlight the need to improve our current strategies to prevent and treat viral bacterial coinfections.

Capillary leakage provides nutrients and antioxidants for rapid pneumococcal proliferation in influenza-infected lower airways.

Influenza A virus (IAV)-related mortality is often due to secondary bacterial infections, primarily by pneumococci. Here, we study how IAV-modulated changes in the lungs affect bacterial replication in the lower respiratory tract (LRT). Bronchoalveolar lavages (BALs) from coinfected mice showed rapid bacterial proliferation 4 to 6 h after pneumococcal challenge. Metabolomic and quantitative proteomic analyses demonstrated capillary leakage with efflux of nutrients and antioxidants into the alveolar space. Pneumococcal adaptation to IAV-induced inflammation and redox imbalance increased the expression of the pneumococcal chaperone/protease HtrA. Presence of HtrA resulted in bacterial growth advantage in the IAV-infected LRT and protection from complement-mediated opsonophagocytosis due to capsular production. Absence of HtrA led to growth arrest in vitro that was partially restored by antioxidants. Pneumococcal ability to grow in the IAV-infected LRT depends on the nutrient-rich milieu with increased levels of antioxidants such as ascorbic acid and its ability to adapt to and cope with oxidative damage and immune clearance.

Proton Motive Force Disruptors Block Bacterial Competence and Horizontal Gene Transfer.

Streptococcus pneumoniae is a commensal of the human nasopharynx that can also cause severe antibiotic-resistant infections. Antibiotics drive the spread of resistance by inducing S. pneumoniae competence, in which bacteria express the transformation machinery that facilitates uptake of exogenous DNA and horizontal gene transfer (HGT). We performed a high-throughput screen and identified potent inhibitors of S. pneumoniae competence, called COM-blockers. COM-blockers limit competence by inhibiting the proton motive force (PMF), thereby disrupting export of a quorum-sensing peptide that regulates the transformation machinery. Known chemical PMF disruptors and alterations in pH homeostasis similarly inhibit competence. COM-blockers limit transformation of clinical multi-drug-resistant strains and HGT in infected mice. At their active concentrations, COM-blockers do not affect growth, compromise antibiotic activity, or elicit detectable resistance. COM-blockers provide an experimental tool to inhibit competence and other PMF-involved processes and could help reduce the spread of virulence factors and antibiotic resistance in bacteria. VIDEO ABSTRACT.

In Vivo Mouse Models to Study Pneumococcal Host Interaction and Invasive Pneumococcal Disease.

Animal models are fundamental tools to study the biology of physiological processes and disease pathogenesis. To study invasive pneumococcal disease (IPD), many models using mice in particular have been established and developed during recent years. Thanks to the advances of the research in the pneumococcal field, nowadays, there is the possibility to use defined mouse models to study each disease caused by the pneumococcus. In this chapter mouse models for pneumonia, bacteremia, and meningitis are described. Since pneumococci are commensal pathogens found to a high extent in healthy individuals. Hence, we also describe a mouse model for nasopharyngeal colonization.

Factor H binding proteins protect division septa on encapsulated Streptococcus pneumoniae against complement C3b deposition and amplification.

Streptococcus pneumoniae evades C3-mediated opsonization and effector functions by expressing an immuno-protective polysaccharide capsule and Factor H (FH)-binding proteins. Here we use super-resolution microscopy, mutants and functional analysis to show how these two defense mechanisms are functionally and spatially coordinated on the bacterial cell surface. We show that the pneumococcal capsule is less abundant at the cell wall septum, providing C3/C3b entry to underlying nucleophilic targets. Evasion of C3b deposition at division septa and lateral amplification underneath the capsule requires localization of the FH-binding protein PspC at division sites. Most pneumococcal strains have one PspC protein, but successful lineages in colonization and disease may have two, PspC1 and PspC2, that we show affect virulence differently. We find that spatial localization of these FH-recruiting proteins relative to division septa and capsular layer is instrumental for pneumococci to resist complement-mediated opsonophagocytosis, formation of membrane-attack complexes, and for the function as adhesins.

Analysis of IAV Replication and Co-infection Dynamics by a Versatile RNA Viral Genome Labeling Method.

Genome delivery to the proper cellular compartment for transcription and replication is a primary goal of viruses. However, methods for analyzing viral genome localization and differentiating genomes with high identity are lacking, making it difficult to investigate entry-related processes and co-examine heterogeneous RNA viral populations. Here, we present an RNA labeling approach for single-cell analysis of RNA viral replication and co-infection dynamics in situ, which uses the versatility of padlock probes. We applied this method to identify influenza A virus (IAV) infections in cells and lung tissue with single-nucleotide specificity and to classify entry and replication stages by gene segment localization. Extending the classification strategy to co-infections of IAVs with single-nucleotide variations, we found that the dependence on intracellular trafficking places a time restriction on secondary co-infections necessary for genome reassortment. Altogether, these data demonstrate how RNA viral genome labeling can help dissect entry and co-infections.

Influenza A Virus Infection Predisposes Hosts to Secondary Infection with Different Streptococcus pneumoniae Serotypes with Similar Outcome but Serotype-Specific Manifestation.

Influenza A virus (IAV) and Streptococcus pneumoniae are major causes of respiratory tract infections, particularly during coinfection. The synergism between these two pathogens is characterized by a complex network of dysregulated immune responses, some of which last until recovery following IAV infection. Despite the high serotype diversity of S. pneumoniae and the serotype replacement observed since the introduction of conjugate vaccines, little is known about pneumococcal strain dependency in the enhanced susceptibility to severe secondary S. pneumoniae infection following IAV infection. Thus, we studied how preinfection with IAV alters host susceptibility to different S. pneumoniae strains with various degrees of invasiveness using a highly invasive serotype 4 strain, an invasive serotype 7F strain, and a carrier serotype 19F strain. A murine model of pneumococcal coinfection during the acute phase of IAV infection showed a significantly increased degree of pneumonia and mortality for all tested pneumococcal strains at otherwise sublethal doses. The incidence and kinetics of systemic dissemination, however, remained bacterial strain dependent. Furthermore, we observed strain-specific alterations in the pulmonary levels of alveolar macrophages, neutrophils, and inflammatory mediators ultimately affecting immunopathology. During the recovery phase following IAV infection, bacterial growth in the lungs and systemic dissemination were enhanced in a strain-dependent manner. Altogether, this study shows that acute IAV infection predisposes the host to lethal S. pneumoniae infection irrespective of the pneumococcal serotype, while the long-lasting synergism between IAV and S. pneumoniae is bacterial strain dependent. These results hold implications for developing tailored therapeutic treatment regimens for dual infections during future IAV outbreaks.

Toll-Like Receptor 3/TRIF-Dependent IL-12p70 Secretion Mediated by Streptococcus pneumoniae RNA and Its Priming by Influenza A Virus Coinfection in Human Dendritic Cells.

UNLABELLED: A functional immune response is crucial to prevent and limit infections with Streptococcus pneumoniae. Dendritic cells (DCs) play a central role in orchestrating the adaptive and innate immune responses by communicating with other cell types via antigen presentation and secretion of cytokines. In this study, we set out to understand how pneumococci activate human monocyte-derived DCs to produce interleukin-12 (IL-12) p70, an important cytokine during pneumococcal infections. We show that IL-12p70 production requires uptake of bacteria as well as the presence of the adaptor molecule TRIF, which is known to transfer signals of Toll-like receptor 3 (TLR3) or TLR4 from the endosome into the cell. While TLR4 is redundant for IL-12p70 production in DCs, we found that TLR3 is required to induce full IL-12p70 secretion. Influenza A virus (IAV) infection of DCs did not induce IL-12p70 but markedly upregulated TLR3 expression that during coinfection with S. pneumoniae significantly enhanced IL-12p70 secretion. Finally, we show that pneumococcal RNA can act as a bacterial stimulus for TLR3 and that it is a key signal to induce IL-12p70 production during challenge of DCs with pneumococci. IMPORTANCE: Streptococcus pneumoniae, a common colonizer of the nose, is the causative agent of severe and deadly diseases. A well-orchestrated immune response is vital to prevent and limit these diseases. Dendritic cells (DCs) reside in the mucosal linings of the lungs and sample antigens. They are activated by pathogens to present antigens and secrete cytokines. While many studies focus on murine models, we focused our work on human monocyte-derived DCs. We found that pneumococcal RNA is an important stimulus in DCs to activate the endosomal receptor TLR3, a receptor previously not identified to sense pneumococci, and its adaptor molecule TRIF. This leads to secretion of the cytokine interleukin-12 (IL-12). Severe pneumococcal pneumonia occurs closely after influenza A virus (IAV) infection. We show that IAV infection upregulates TLR3 in DCs, which sensitizes the cells to endosomal pneumococcal RNA. This new insight contributes to unlock the interplay between pneumococci, IAV, and humans.

Lung cell-specific modulation of LPS-induced TLR4 receptor and adaptor localization.

Lung infection by Gram-negative bacteria is a major cause of morbidity and mortality in humans. Lipopolysaccharide (LPS), located in the outer membrane of the Gram-negative bacterial cell wall, is a highly potent stimulus of immune and structural cells via the TLR4/MD2 complex whose function is sequentially regulated by defined subsets of adaptor proteins. Regulatory mechanisms of lung-specific defense pathways point at the crucial role of resident alveolar macrophages, alveolar epithelial cells, the TLR4 receptor pathway, and lung surfactant in shaping the innate immune response to Gram-negative bacteria and LPS. During the past decade intracellular spatiotemporal localization of TLR4 emerged as a key feature of TLR4 function. Here, we briefly review lung cell type- and compartment-specific mechanisms of LPS-induced TLR4 regulation with a focus on primary resident hematopoietic and structural cells as well as modifying microenvironmental factors involved.

Surfactant protein-A modulates LPS-induced TLR4 localization and signaling via ß-arrestin 2.

The soluble C-type lectin surfactant protein (SP)-A mediates lung immune responses partially via its direct effects on alveolar macrophages (AM), the main resident leukocytes exposed to antigens. SP-A modulates the AM threshold of lipopolysaccharide (LPS) activity towards an anti-inflammatory phenotype both in vitro and in vivo through various mechanisms. LPS responses are tightly regulated via distinct pathways including subcellular TLR4 localization and thus ligand sensing. The cytosolic scaffold and signaling protein ß-arrestin 2 acts as negative regulator of LPS-induced TLR4 activation. Here we show that SP-A neither increases TLR4 abundancy nor co-localizes with TLR4 in primary AM. SP-A significantly reduces the LPS-induced co-localization of TLR4 with the early endosome antigen (EEA) 1 by promoting the co-localization of TLR4 with the post-Golgi compartment marker Vti1b in freshly isolated AM from rats and wild-type (WT) mice, but not in ß-arrestin 2(-/-) AM. Compared to WT mice pulmonary LPS-induced TNF-α release in ß-arrestin 2(-/-) mice is accelerated and enhanced and exogenous SP-A fails to inhibit both lung LPS-induced TNF-α release and TLR4/EEA1 positioning. SP-A, but not LPS, enhances ß-arrestin 2 protein expression in a time-dependent manner in primary rat AM. The constitutive expression of ß-arrestin 2 in AM from SP-A(-/-) mice is significantly reduced compared to SP-A(+/+) mice and is rescued by SP-A. Prolonged endosome retention of LPS-induced TLR4 in AM from SP-A(-/-) mice is restored by exogenous SP-A, and is antagonized by ß-arrestin 2 blocking peptides. LPS induces ß-arrestin 2/TLR4 association in primary AM which is further enhanced by SP-A. The data demonstrate that SP-A modulates LPS-induced TLR4 trafficking and signaling in vitro and in vivo engaging ß-arrestin 2.

Pulmonary surfactant protein A enhances endolysosomal trafficking in alveolar macrophages through regulation of Rab7.

Surfactant protein A (SP-A), the most abundant pulmonary soluble collectin, modulates innate and adaptive immunity of the lung, partially via its direct effects on alveolar macrophages (AM), the most predominant intra-alveolar cells under physiological conditions. Enhanced phagocytosis and endocytosis are key functional consequences of AM/SP-A interaction, suggesting a SP-A-mediated modulation of small Rab (Ras related in brain) GTPases that are pivotal membrane organizers in both processes. In this article, we show that SP-A specifically and transiently enhances the protein expression of endogenous Rab7 and Rab7b, but not Rab5 and Rab11, in primary AM from rats and mice. SP-A-enhanced GTPases are functionally active as determined by increased interaction of Rab7 with its downstream effector Rab7 interacting lysosomal protein (RILP) and enhanced maturation of cathepsin-D, a function of Rab7b. In AM and RAW264.7 macrophages, the SP-A-enhanced lysosomal delivery of GFP-Escherichia coli is abolished by the inhibition of Rab7 and Rab7 small interfering RNA transfection, respectively. The constitutive expression of Rab7 in AM from SP-A(-/-) mice is significantly reduced compared with SP-A(+/+) mice and is restored by SP-A. Rab7 blocking peptides antagonize SP-A-rescued lysosomal delivery of GFP-E. coli in AM from SP-A(-/-) mice. Activation of Rab7, but not Rab7b, by SP-A depends on the PI3K/Akt/protein kinase Cζ (PKCζ) signal transduction pathway in AM and RAW264.7 macrophages. SP-A induces a Rab7/PKCζ interaction in these cells, and the disruption of PKCζ by small interfering RNA knockdown abolishes the effect of SP-A on Rab7. The data demonstrate a novel role for SP-A in modulating endolysosomal trafficking via Rab7 in primary AM and define biochemical pathways involved.

Preclinical analysis of treosulfan in combination with total body irradiation as conditioning regimen prior to bone marrow transplantation in rats.

Treosulfan (Treo) and total body irradiation (TBI) demonstrate a high therapeutic activity in treatment of acute leukemia and lymphoma. We investigated the combination of Treo and TBI prior to bone marrow transplantation (BMT) in rats. Female Lewis rats were treated with Treo on 3 consecutive days followed by TBI with either 5 Gy (n = 28) or 7.5 Gy (n = 48). After conditioning animals received 4 x 10E7 bone marrow cells (BC) from female Lewis rats. Additional 16 rats were transplanted with 4 x 10E7 BC and 1.5 x 10E7 spleen T-cells from female Brown-Norway (BN) rats. Animals were examined daily for clinical signs and toxicity was investigated by necropsy and histology in all animals. Gastrointestinal toxicity was the dose-limiting factor of Treo in combination with TBI. The highest tolerable dose of Treo in combination with 7.5 Gy TBI was 3 x 0.5 g/kg and the highest tolerable dose of Treo in combination with 5 Gy TBI was 3 x 0.6 g/kg. Allogeneic BMT from BN donors resulted in engraftment and survival of 12 out of 16 animals. Gastrointestinal toxicity is the dose-limiting factor in the treatment with Treo and TBI. Furthermore, Treo possesses certain characteristics of a radiosensitizer.