Impaired Host Defense Research Articles

“Deepening” Insight on Skin Aging and Anti-microbial Immunity

Skin aging is of considerable interest from various perspectives, ranging from aesthetics to cancer development. Zhang etal. (2019) elucidate an immunological consequence of aging in the adipose layer of skin. Age-dependent increases in TGF-β signaling impair fibroblast adipogenic potential that results in impaired anti-bacterial host defense.

Decreased IL-17RB expression impairs CD11b+CD11c\u2212 myeloid cell accumulation in gastric mucosa and host defense during the early-phase of Helicobacter pylori infection

Interleukin-17 receptor B (IL-17RB), a member of the IL-17 receptor family activated by IL-17B/IL-17E, has been shown to be involved in inflammatory diseases. However, the regulation and function of IL-17RB in Helicobacter pylori (H. pylori) infection, especially in the early-phase is still unknown. Here, we found that gastric IL-17RB mRNA and protein were decreased in gastric mucosa of both patients and mice infected with H. pylori. In vitro experiments show that IL-17RB expression was down regulated via PI3K/AKT pathway on gastric epithelial cells (GECs) stimulated with H. pylori in a cagA-involved manner, while in vivo studies showed that the effect was partially dependent on cagA expression. IL-17E was also decreased during the early-phase of H. pylori infection, and provision of exogenous IL-17E resulted in increased CD11b+CD11c− myeloid cells accumulation and decreased bacteria colonization within the gastric mucosa. In the early-phase of H. pylori infection, IL-17E-IL-17RB promoted gastric epithelial cell-derived CXCL1/2/5/6 to attract CD11b+CD11c− myeloid cells, and also contributed to host defense by promoting the production of antibacterial protein Reg3a. This study defines a negative regulatory network involving IL-17E, GECs, IL-17RB, CD11b+CD11c− myeloid cells, and Reg3a in the early-phase of H. pylori infection, which results in an impaired host defense within the gastric microenvironment, suggesting IL-17RB as a potential early intervening target in H. pylori infection.

A pathologic two-way street: how innate immunity impacts lung fibrosis and fibrosis impacts lung immunity.

Lung fibrosis is characterised by the accumulation of extracellular matrix within the lung and is secondary to both known and unknown aetiologies. This accumulation of scar tissue limits gas exchange causing respiratory insufficiency. The pathogenesis of lung fibrosis is poorly understood, but immunologic‐based treatments have been largely ineffective. Despite this, accumulating evidence suggests that innate immune cells and receptors play important modulatory roles in the initiation and propagation of the disease. Paradoxically, while innate immune signalling may be important for the pathogenesis of fibrosis, there is also evidence to suggest that innate immune function against pathogens may be impaired, leading to dysregulated and/or impaired host defence. This review summarises the evidence for this pathologic two‐way street, highlights new concepts of pathogenesis and recommends future directions for research emphasis.

Relationships between phagocytosis, mucoid phenotype, and genetic characteristics of Klebsiella pneumoniae clinical isolates.

The relationships between phagocytosis, and mucoid phenotype, plasmid profile and virulence, and resistance genetic characteristics of Klebsiella pneumoniae clinical isolates were evaluated. Thirty isolates were used to determine the mucoid aspect. Four were selected for analysis of phagocytosis by alveolar macrophages. Thirty percent of the samples presented the mucoid phenotype. The phagocytosis rate ranged from 21.5% to 43.43%. Phagocytosis was not correlated with the plasmid profile, but was apparently correlated with mucoid phenotype and antibiotic susceptibility. Several virulence factors act in parallel in K. pneumoniae to impair host defense.

New primary immunodeficiency diseases: context and future.

Primary immunodeficiency diseases (PIDs) are genetic disorders classically characterized by impaired host defense and an increased susceptibility to infections. It is now appreciated that these conditions broadly include variations in the genetic code that cause dysregulated immune function. This review highlights the newly defined PIDs in the 2017 International Union of Immunologic Societies (IUIS) report, current approaches to diagnosing PIDs, and the implications for the future management of PIDs. With the advances in and increased commercial availability of genetic testing and the adoption of the TREC assay into the US Newborn Screening program, the number of identified PIDs has exponentially risen in the past few decades, reaching over 350 disorders. The IUIS Inborn Errors of Immunity committee acknowledged at least 50 new disorders between 2015 and 2017. Furthermore, given the greater recognition of disorders with primarily immune dysregulation, the committee proposed a more inclusive term of 'inborn errors of immunity' to encompass primary immunodeficiencies and immune dysregulation disorders. This latest IUIS report underscores the rapid expansion in the PID field with technologic advancements in immunogenetics and clinical screening discovering new genetic diseases, and therefore, paving the way to novel therapeutics and precision medicine.

Thrombocytopenia Impairs Host Defense Against Burkholderia pseudomallei (Melioidosis).

Infection with the gram-negative bacillus Burkholderia pseudomallei (melioidosis) is an important cause of pneumosepsis in Southeast Asia and has a mortality of up to 40%. We aimed to assess the role of platelets in the host response against B. pseudomallei infection. Association between platelet counts and mortality was determined in 1160 patients with culture-proven melioidosis. Mice treated with (low- or high-dose) platelet-depleting antibody were inoculated intranasally with B. pseudomallei and killed. Additional studies using functional glycoprotein Ibα-deficient mice were conducted. Thrombocytopenia was present in 31% of patients at admission and predicted mortality in melioidosis patients even after adjustment for confounders. In our murine-melioidosis model, platelet counts decreased, and mice treated with a platelet-depleting antibody showed enhanced mortality and higher bacterial loads compared to mice with normal platelet counts. Low platelet counts had a modest impact on early-pulmonary neutrophil influx. Reminiscent of their role in hemostasis, platelet depletion impaired vascular integrity, resulting in early lung bleeding. Glycoprotein Ibα-deficient mice had reduced platelet counts during B. pseudomallei infection together with an impaired local host defense in the lung. Thrombocytopenia predicts mortality in melioidosis patients and, during experimental melioidosis, platelets play a protective role in both innate immunity and vascular integrity.

Nbeal2 Deficiency Increases Organ Damage but Does Not Affect Host Defense During Gram-Negative Pneumonia-Derived Sepsis.

Objective- Nbeal2-/- mice, a model of human gray platelet syndrome, have reduced neutrophil granularity and impaired host defense against systemic Staphylococcus aureus infection. We here aimed to study the role of Nbeal2 deficiency in both leukocytes and platelets during gram-negative pneumonia and sepsis. Approach and Results- We studied the role of Nbeal2 in platelets and leukocytes during murine pneumonia and sepsis by Klebsiella pneumoniae. Apart from platelet α-granule deficiency and reduced neutrophil granularity, also monocyte granularity was reduced in Nbeal2-/- mice, whereas plasma levels of MPO (myeloperoxidase), elastase, NGAL (neutrophil gelatinase-associated lipocalin), and MMP-9 (matrix metalloproteinase 9), and leukocyte CD11b expression were increased. Nbeal2-/- leukocytes showed unaltered in vitro antibacterial response and phagocytosis capacity against Klebsiella, and unchanged reactive nitrogen species and cytokine production. Also during Klebsiella pneumonia and sepsis, Nbeal2-/- mice had similar bacterial growth in lung and distant body sites, with enhanced leukocyte migration to the bronchoalveolar space. Despite similar infection-induced inflammation, organ damage was increased in Nbeal2-/- mice, which was also seen during endotoxemia. Platelet-specific Nbeal2 deficiency did not influence leukocyte functions, indicating that Nbeal2 directly modifies leukocytes. Transfusion of Nbeal2-/- but not of Nbeal2+/+ platelets into thrombocytopenic mice was associated with bleeding in the lung but similar host defense, pointing at a role for platelet α-granules in maintaining vascular integrity but not host defense during Klebsiella pneumosepsis. Conclusions- These data show that Nbeal2 deficiency-resulting in gray platelet syndrome-affects platelets, neutrophils, and monocytes, with intact host defense but increased organ damage during gram-negative pneumosepsis.

CXCL-1/KC collaborates with CXCL-2/MIP2 to regulate granulopoiesis and recruitment in pneumococcal pneumonia

Abstract Streptococcus pneumoniae remains as a leading cause of community-acquired pneumonia in the U.S. and world. Leukocytes (neutrophils) recruitment to the lungs is critical step in the host defense against pneumococcal infections. CXCL-1/KC is sufficient to induce neutrophil influx in numerous bacterial lung infections, but precise mechanism of how it regulates recruitment to the lungs remains unexplored. Here, we used a mouse model of pneumococcal pneumonia to investigate the role of CXCL-1 in neutrophil granulopoiesis, recruitment, and host defense. CXCL-1 knockout and their wild type controls were infected intratracheally with S. pneumoniae. Survival, leukocyte influx, cytokines/chemokines in bronchoalveolar lavage fluid, and bacterial burdens in lungs and other organs were quantified. Flow cytometry was performed to study different stages of neutrophil granulopoiesis according to their levels of c-Kit and Ly6G expression. Recombinant CXCL-2/MIP2 was administered to rescue neutrophil recruitment in CXCL-1 knockout mice. We here demonstrate that CXCL-1 modulates rapid neutrophil influx, restricts bacterial burden in lungs, regulates production of cytokines/chemokines, and improves host survival. Flow cytometry analysis revealed CXCL-1 is involved in efficient amplification of early neutrophil precursor and release of mature neutrophils from bone marrow. Furthermore, CXCL-2 treatment post-pneumonia corrected the impairment in host defense through increased neutrophil influx in CXCL -1 knockout mice. These results suggest CXCL-1 mediates granulopoiesis and recruitment of neutrophil, and modulation of its activity presents a promising avenue for development of therapeutics against pneumococcal pneumonia.

Next-generation sequencing for identifying genetic mutations in adults with bronchiectasis.

Defective airway host-defense (e.g., altered mucus properties, ciliary defects) contributes to the pathogenesis of bronchiectasis. This study aims to determine whether genetic mutations associated with defective airway host-defense are implicated in the pathogenesis of bronchiectasis. Based on the systematic screening of 32 frequently reported bronchiectasis-associated genes, we performed next-generation sequencing (NGS) on peripheral blood samples from 192 bronchiectasis patients and 100 healthy subjects. The variant distribution frequency and pathogenicity of mutations were analyzed. We identified 162 rare variants in 192 bronchiectasis patients, and 85 rare variants among 100 healthy subjects. Among bronchiectasis patients, 25 (15.4%), 117 (72.2%) and 18 (11.1%) rare variants were associated with cystic fibrosis transmembrane receptor (CFTR), epithelial sodium channel, and primary ciliary dyskinesia genes, respectively. Biallelic CFTR variants were detected in four bronchiectasis patients but none of the healthy subjects. Carriers of homozygous p.M470 plus at least one CFTR rare variant were detected in 6.3% of bronchiectasis patients (n=12) and in 1.0% of healthy subjects (n=1, P=0.039). Twenty-six patients (16 with idiopathic and 6 with post-infectious bronchiectasis) harbored biallelic variants. Bronchiectasis patients with biallelic DNAH5 variants, or biallelic CFTR variants plus an epithelial sodium channel variant, tended to have greater disease severity. Genetic mutations leading to impaired host-defense might have implicated in the pathogenesis of bronchiectasis. Genetic screening may be a useful tool for unraveling the underlying causes of bronchiectasis, and offers molecular information which is complementary to conventional etiologic assessment for bronchiectasis.

English

INTRODUCTION : Infections caused by the yeasts of the genus candida are common in clinical practice. They may involve the mucous membranes and / or skin or spread internally to produce systemic infections. Superficial infections of the mucous membranes and skin are numerically most important but more serious involvement of the internal organs as in septicemia, endocarditis, meningitis, can also occur. Candida albicans is an oval yeast 2-6 x 3-9 μm in size, which can produce budding cells, pseudohyphae and true hyphae. The ability to simultaneously display several morphological forms is known as polymorphism. Although hyphae are likely to be produced during the process of tissue invasion, yeasts without hyphae may also occur in invasive disease, particularly in infections caused by non-albicans candida species. AIM AND OBJECTIVE OF THE STUDY : The term immunocompromised host is used to define a patient with impaired host defences who is at the risk of developing an opportunistic infection. This includes patients with immunodeficiency because of the disease perse such as patients with ‘Acquired Immune Deficiency Syndrome’ (AIDS) or induced iatrogenically as a result of chemotherapy. Susceptibility to infection is increased when normal host defence mechanisms are compromised by underlying disease states, therapeutic interventions or iatrogenic manipulations. Frequently all the three factors play a role in creating an immunocompromised state, in which infection is likely. Candida species are the most common cause of systemic fungal infections in the immunocompromised patients (Hawkins, 1984). This study has been designed, 1. To isolate, culture and subculture thereby identify the subspecies of candida from the mucosal lesions of immunocompromised individuals. 2. To study the age and sex distribution of immunosuppressed patients suffering from candidiasis. 3. To study the morphological pattern of lesions in the background of immunosuppression. 4. To identify the subspecies of candida causing various types of lesions in immunosuppressed patients. 5. To study the dose and duration of the immunosuppressive therapy that predisposed to candidasis. CONCLUSIONS : * Candidiasis is the commonest mycosis in patients on systemic immunosuppressive therapy and immunosuppressive status like HIV infection. * Majority of the affected victims of candidiasis, were in the age group between 31-50 years. Incidence of candidiasis was found to be more in male patients than female patients. (Males → 62%). (Females → 38%). However the age and sex distribution is also related to the patients screened. * Acute pseudomembranous glossitis was the commonest morphological type of the lesion encountered in this study (35%), to be followed by, chronic erythematous candidiasis (22%), Angular cheilitis (21%), acute erythematous glossitis (19%), balanoposthitis (2%) & Median rhomboid glossitis (1%). * Among the various immunosuppressive drugs taken into account for this study, Tab.Prednisolone was the commonest drug predisposing to candidiasis (28%) followed by Inj. Dexamethasone (22%). Thus systemic steroids accounted for 50% of drugs predisposing to candidosis, remaining 50% being contributed by cytotoxic drugs like methotrexate, cyclophosphamide, azathioprine etc; * Of all the various bullous dermatoses screened, pemphigus vulgaris was the commonest bullous disorder predisposing to candidosis (40%) followed by bullous pemphigoid (16.6%), Pemphigus foliaceus (8.3%), Dermatitis Herpetiformis (1.6%) and Pemphigus vegetans (5%). * Candida albicans was the commonest species isolated (52%). Other species isolated include, Candida tropicalis (22%), Candida glabrata (21%), Candida krusei (3%) and Candida dubliniensis (2%). * Patients with O+ve Blood group are considered to have high carriage of candidia species. * Even in HIV infected individuals, candida albicans was the commonest species isolated, in our study; candida dubliniensis is said to be exclusively common in the oral lesions of HIV patients, which however accounted only for (2%) in our study. Probably the sample size had still been larger. * The minimum time duration of systemic immunosuppressive therapy required for predisposition to oral candidosis was found to be 10 (Ten) days in our study in Non-HIV infected individuals, which was found to be still shorter in known cases of HIV infection (around 1 week); probably due to CD4 cell count depletion, and other associated opportunistic infections. * Inspite of heroic measures to avoid contaminants, and adhering to very strict aseptic protocols, it was found in our study that the maximum keeping time of primary candida culture in SDA with chloramphenicol and subcultures in Himedia CHROMagar was just 72 hours, after which saprophytic bacteria and various moulds and concomitant pathogens spoil the culture media.

Platelet HMGB1 is required for efficient bacterial clearance in intra-abdominal bacterial sepsis in mice

AbstractThrombocytopenia impairs host defense and hemostasis in sepsis. However, the mechanisms of how platelets regulate host defense are not fully understood. High-mobility group box 1 (HMGB1), a danger-associated molecular pattern protein, is released during infection and contributes to the pathogenesis of sepsis. Platelets express HMGB1, which is released on activation and has been shown to play a critical role in thrombosis, monocyte recruitment, and neutrophil extracellular trap (NET) production. However, the contribution of platelet HMGB1 to host defense is unknown. To determine the role of platelet HMGB1 in polymicrobial sepsis, platelet-specific HMGB1 knockout (HMGB1 platelet factor 4 [PF4]) mice were generated and were subjected to cecal ligation and puncture (CLP), a clinically relevant intra-abdominal sepsis model. Compared with HMGB1 Flox mice and wild-type (WT) mice, HMGB1 PF4 mice showed significantly higher bacterial loads in the peritoneum and blood, an exaggerated systemic inflammation response, and significantly greater mortality after CLP. Deletion of HMGB1 in platelets was associated with lower platelet-derived chemokines (PF4 and RANTES) in the peritoneal cavity, and a decrease of platelet-neutrophil interaction in the lung after CLP. In vitro, neutrophils cocultured with activated HMGB1 knockout platelets showed fewer platelet-neutrophil aggregates, reduced reactive oxygen species (ROS) burst as compared with control. Taken together, these data reveal an unrecognized role of platelet HMGB1 in the regulation of neutrophil recruitment and activation via modulation of platelet activation during sepsis.

Neutropenia in adults – significant diagnostic issue

Abstract Introduction. Neutropenia, a disorder quite commonly encountered in blood tests, is defined as a decrease in the absolute neutrophil count below 1500/µl. Neutropenia may not be clinically significant, whereas it sometimes indicates serious haematological, infectious or rheumatic diseases. The reduction of the number of neutrocytes below 500/µl is referred to as ’agranulocytosis’. Such decrease in neutrophil count impairs host defense and makes the patient more vulnerable to bacterial and fungal infections, which may lead to life-threatening sepsis. Aim. This review presents the causes of congenital and acquired neutropenia, with particular attention to drug-induced neutropenia, which may occur due to the intake of the broad spectrum of drugs, including over-the-counter drugs. The article also attempts to answer the question of how the neutropenia and agranulocytosis should be diagnosed and treated. Methods. The publication is based on the analysis of the literature (PubMed database). Results. It has to be emphasized that a thorough physical examination and appropriate additional tests make it possible to diagnose a disease that causes neutropenia. This allows for the implementation of appropriate therapeutic procedures, and consequently, leads to avoidance of serious infections.

Transformation of Fonsecaea pedrosoi into sclerotic cells links to the refractoriness of experimental chromoblastomycosis in BALB/c mice via a mechanism involving a chitin-induced impairment of IFN-γ production.

Fonsecaea pedrosoi (F. pedrosoi) is the most common agent of chromoblastomycosis. Transformation of this fungus from its saprophytic phase into pathogenic sclerotic cells in tissue is an essential link to the refractoriness of this infection. Experimental studies in murine models have shown that the absence of CD4+ T cells impairs host defense against F. pedrosoi infection. Clinical research has also suggested that a relatively low level of the Th1 cytokine INF-γ and inefficient T cell proliferation are simultaneously present in patients with severe chromoblastomycosis upon in vitro stimulation with ChromoAg, an antigen prepared from F. pedrosoi. In the present study, we show that in mice intraperitoneally infected with F. pedrosoi-spores, -hyphae or in vitro-induced sclerotic cells respectively, the transformation of this causative agent into sclerotic cells contributes to a compromised Th1 cytokine production in the earlier stage of infection with impaired generation of neutrophil reactive oxygen species (ROS) and pan-inhibition of Th1/Th2/Th17 cytokine production with disseminated infection in the later stage by using a CBA murine Th1/Th2/Th17 cytokine kit. In addition, we have further demonstrated that intraperitoneal administration of recombinant mouse IFN-γ (rmIFN-γ) effectively reduces the fungal load in the infected mouse spleen, and dampens the peritoneal dissemination of F. pedrosoi-sclerotic cells. Meanwhile, exogeneous rmIFN-γ contributes to the formation and maintenance of micro-abscess and restores the decrease in neutrophil ROS generation in the mouse spleen infected with F. pedrosoi-sclerotic cells. Of note, we have once again demonstrated that it is a chitin-like component, but not β-glucans or mannose moiety, that exclusively accumulates on the outer cell wall of F. pedrosoi-sclerotic cells which were induced in vitro or isolated from the spleens of intraperitoneally infected BALB/c mice. In addition, our results indicate that decreased accumulation of chitin on the surface of live F. pedrosoi-sclerotic cells after chitinase treatment can be self-compensated in a time-dependent manner. Importantly, we have for the first time demonstrated that exclusive accumulation of chitin on the transformed sclerotic cells of F. pedrosoi is involved in an impaired murine Th1 cytokine profile, therefore promoting the refractoriness of experimental murine chromoblastomycosis.

Thrombospondin-1 protects against pathogen-induced lung injury by limiting extracellular matrix proteolysis.

Acute lung injury is characterized by excessive extracellular matrix proteolysis and neutrophilic inflammation. A major risk factor for lung injury is bacterial pneumonia. However, host factors that protect against pathogen-induced and host-sustained proteolytic injury following infection are poorly understood. Pseudomonas aeruginosa (PA) is a major cause of nosocomial pneumonia and secretes proteases to amplify tissue injury. We show that thrombospondin-1 (TSP-1), a matricellular glycoprotein released during inflammation, dose-dependently inhibits PA metalloendoprotease LasB, a virulence factor. TSP-1-deficient (Thbs1-/-) mice show reduced survival, impaired host defense, and increased lung permeability with exaggerated neutrophil activation following acute intrapulmonary PA infection. Administration of TSP-1 from platelets corrects the impaired host defense and aberrant injury in Thbs1-/- mice. Although TSP-1 is cleaved into 2 fragments by PA, TSP-1 substantially inhibits Pseudomonas elastolytic activity. Administration of LasB inhibitor, genetic disabling of the PA type II secretion system, or functional deletion of LasB improves host defense and neutrophilic inflammation in mice. Moreover, TSP-1 provides an additional line of defense by directly subduing host-derived proteolysis, with dose-dependent inhibition of neutrophil elastase from airway neutrophils of mechanically ventilated critically ill patients. Thus, a host matricellular protein provides dual levels of protection against pathogen-initiated and host-sustained proteolytic injury following microbial trigger.

Submucosal gland mucus strand velocity is decreased in chronic rhinosinusitis.

Chronic rhinosinusitis (CRS) may be initiated by innately impaired host defense mechanisms that predispose the upper airways to infection. Recent evidence suggests tethering of submucosal gland mucus strands represents an inciting event within cystic fibrosis (CF) airways, occurring prior to onset of chronic infection. Submucosal gland hypertrophy and defective mucociliary clearance (MCC) are present in actively inflamed sinuses, but mucus strand velocity may also be affected as a secondary event, further contributing to chronic disease. The objective of this study is to assess whether mucus strand velocity is decreased in patients with CRS. Mucosal explants from patients with and without CRS were submerged in Ringer's solution mixed with fluorescent nanospheres. Methacholine was then added, and videos demonstrating strand growth and detachment were generated from a time-lapse of Z-stack images using a multiphoton confocal microscope. Dynamic mucus strands were identified and individual velocities quantified with the MTrackJ plug-in of ImageJ. Fifteen patients met criteria for ex vivo analysis of mucus strand velocities (CRS, n = 9 vs controls, n = 6). Mucus strands were recorded (pixels/second) streaming from the submucosal gland openings. Average mucus strand velocities were significantly decreased in patients with CRS (1.53 ± 0.67 vs controls, 4.86 ± 1.68 pixels/second; p < 0.001). This study is the first to report evidence of abnormal mucus strand velocity from submucosal glands in diseased sinonasal mucosa. Future pharmacologic studies targeting this critical component of MCC are warranted.

Viral DNAemia and Immune Suppression in Pediatric Sepsis.

Demonstrate that DNA viremia is common in pediatric sepsis and quantitate its associations with host immune function and secondary infection risk. Retrospective analysis of a prospective cohort study. Seventy-three children admitted with sepsis-induced organ failure. None. This study was performed as an ancillary investigation to a single-center prospective study of children with severe sepsis. Longitudinally collected, batched, frozen plasma was examined using real time-polymerase chain reaction for the presence of cytomegalovirus, Epstein-Barr virus, herpes simplex virus, human herpes virus-6, torque teno virus, and adenovirus DNA. Innate immune function was also measured longitudinally via quantification of ex vivo lipopolysaccharide -induced tumor necrosis factor-α production capacity. Viral DNAemia with a virus other than torque teno virus was detected in 28 of 73 subjects (38%) and included cytomegalovirus 5%, Epstein-Barr virus 11%, herpes simplex virus 4%, human herpes virus-6 8%, and adenovirus 26%. In addition, torque teno virus was detected in 89%. Epstein-Barr virus DNAemia was associated with preexisting immune suppression (p = 0.007) Viral DNAemia was associated with preexisting immune suppression and high risk for the subsequent development of secondary infection (p < 0.05 for both). Subjects with viral DNAemia had lower innate immune function over time compared with those who were virus negative (p < 0.05). DNAemia from multiple viruses can be detected in septic children and is strongly associated with preexisting immune suppression and secondary infection risk. The role of DNA viruses in the perpetuation of impaired host defense in this setting should be the subject of prospective study.

Nominal carbonic anhydrase activity minimizes airway-surface liquid pH changes during breathing.

The airway‐surface liquid pH (pHASL) is slightly acidic relative to the plasma and becomes more acidic in airway diseases, leading to impaired host defense. CO 2 in the large airways decreases during inspiration (0.04% CO 2) and increases during expiration (5% CO 2). Thus, we hypothesized that pHASL would fluctuate during the respiratory cycle. We measured pHASL on cultures of airway epithelia while changing apical CO 2 concentrations. Changing apical CO 2 produced only very slow pHASL changes, occurring in minutes, inconsistent with respiratory phases that occur in a few seconds. We hypothesized that pH changes were slow because airway‐surface liquid has little carbonic anhydrase activity. To test this hypothesis, we applied the carbonic anhydrase inhibitor acetazolamide and found minimal effects on CO 2‐induced pHASL changes. In contrast, adding carbonic anhydrase significantly increased the rate of change in pHASL. Using pH‐dependent rates obtained from these experiments, we modeled the pHASL during respiration to further understand how pH changes with physiologic and pathophysiologic respiratory cycles. Modeled pHASL oscillations were small and affected by the respiration rate, but not the inspiratory:expiratory ratio. Modeled equilibrium pHASL was affected by the inspiratory:expiratory ratio, but not the respiration rate. The airway epithelium is the only tissue that is exposed to large and rapid CO 2 fluctuations. We speculate that the airways may have evolved minimal carbonic anhydrase activity to mitigate large changes in the pHASL during breathing that could potentially affect pH‐sensitive components of ASL.

Leukotriene B4-Mediated Neutrophil Recruitment Causes Pulmonary Capillaritis during Lethal Fungal Sepsis

Candida albicans bloodstream infection causes fungal septicaemia and death in over half of afflictedpatients. Polymorphonuclear leukocytes (PMN) mediate defense against invasive candidiasis, but their role in protection versus tissue injury and sepsis is unclear. We observe PMN intravascular swarming and subsequent clustering in response to C.albicans yeast in a lethal septic mouse and human pulmonary circulation model. Live C.albicans sequester to the endothelium and are immediately captured by complement-dependent PMN chemotaxis, which is required for host survival. However, complement activation also leads to Leukotriene B4 (LTB4)-mediated intravascular PMN clustering and occlusion, resulting in capillaritis with pulmonary hemorrhage and hypoxemia. This clustering is unique to fungi and triggered by fungal cell wall components. PMN clustering is absent in mice lacking LTB4-receptor, and capillaritis is attenuatedupon pharmacological LTB4 blockade without affecting phagocytosis. Therefore, therapeutically disrupting infection-induced capillaritis may limit organ injury without impairing host defense during fungal sepsis.

ASC and NLRP3 impair host defense during lethal pneumonia caused by serotype 3 Streptococcus pneumoniae in mice.

Streptococcus (S.) pneumoniae is the most common cause of community-acquired pneumonia. The Nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, consisting of NLRP3, ASC (the adaptor apoptosis-associated speck-like protein containing a CARD) and caspase-1, has been implicated in protective immunity during pneumonia induced by high doses of S. pneumoniae serotype 2. Here we investigated the role of the NLRP3 inflammasome in the host response during lethal airway infection with a low dose of serotype 3 S. pneumoniae. Mice were euthanized at predefined endpoints for analysis or observed in survival studies. In additional studies, Tlr2-/- /Tlr4-/- mice and Myd88-/- mice incapable of Toll-like receptor signaling were studied. In stark contrast with existing literature, both Nlrp3-/- and Asc-/- mice showed a strongly improved host defense, as reflected by a markedly reduced mortality rate accompanied by diminished bacterial growth and dissemination. Host defense was unaltered in Tlr2-/- /Tlr4-/- mice and Myd88-/- mice. These results show that the NLRP3 inflammasome impairs host defense during lethal pneumonia caused by serotype 3 S. pneumoniae. Our findings challenge the current paradigm that proximal innate detection systems are indispensable for an adequate host immune response against bacteria.

Gaseous Mediators and Mitochondrial Function: The Future of Pharmacologically Induced Suspended Animation?

The role of nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) as poisonous gases is well-established. However, they are not only endogenously produced but also, at low concentrations, exert beneficial effects, such as anti-inflammation, and cytoprotection. This knowledge initiated the ongoing debate, as to whether these molecules, also referred to as “gaseous mediators” or “gasotransmitters,” could serve as novel therapeutic agents. In this context, it is noteworthy, that all gasotransmitters specifically target the mitochondria, and that this interaction may modulate mitochondrial bioenergetics, thereby subsequently affecting metabolic function. This feature is of crucial interest for the possible induction of “suspended animation.” Suspended animation, similar to mammalian hibernation (and/or estivation), refers to an externally induced hypometabolic state, with the intention to preserve organ function in order to survive otherwise life-threatening conditions. This hypometabolic state is usually linked to therapeutic hypothermia, which, however, comes along with adverse effects (e.g., coagulopathy, impaired host defense). Therefore, inducing an on-demand hypometabolic state by directly lowering the energy metabolism would be an attractive alternative. Theoretically, gasotransmitters should reversibly interact and inhibit the mitochondrial respiratory chain during pharmacologically induced suspended animation. However, it has to be kept in mind that this effect also bears the risk of cytotoxicity resulting from the blockade of the mitochondrial respiratory chain. Therefore, this review summarizes the current knowledge of the impact of gasotransmitters on modulating mitochondrial function. Further, we will discuss their role as potential candidates in inducing a suspended animation.