Activation of pulmonary and lymph node dendritic cells during chronic Pseudomonas aeruginosa lung infection in mice

Pseudomonas aeruginosa in chronic lung disease: untangling the dysregulated host immune response

Pseudomonas aeruginosa is a highly adaptable opportunistic pathogen capable of exploiting barriers and immune defects to cause chronic lung infections in conditions such as cystic fibrosis. In these contexts, host immune responses are ineffective at clearing persistent bacterial infection, instead driving a cycle of inflammatory lung damage. This review outlines key components of the host immune response to chronic P. aeruginosa infection within the lung, beginning with initial pathogen recognition, followed by a robust yet maladaptive innate immune response, and an ineffective adaptive immune response that propagates lung damage while permitting bacterial persistence. Untangling the interplay between host immunity and chronic P. aeruginosa infection will allow for the development and refinement of strategies to modulate immune-associated lung damage and potentiate the immune system to combat chronic infection more effectively.

Effect of examining lymph nodes count on mortality risk in resected T1 non-small-cell lung cancer

OBJECTIVES

This study aims to estimate the effect of the examined lymph node count (ELNC) on the cancer-related mortality risk and non-cancer-related mortality risk in patients with resected T1 non-small-cell lung cancer (NSCLC).

METHODS

Patients diagnosed as primary T1 NSCLC between 2000 and 2017 were extracted from the Surveillance, Epidemiology and End Results database. Patients were divided into 2 groups according to the ELNC cutoff value, which was calculated based on overall survival outcomes. Propensity score matching was used to equalize the differences in baseline characteristics between groups.

RESULTS

A total of 38 242 resected T1 NSCLC patients were extracted from the database with the ELNC cutoff value of 8. After propensity score matching, 27 676 patients were included in this study. Examining ≥8 ELNC was associated with a more accurate assessment of lymph node (LN) metastasis and significantly improving the prognosis. These trends remained consistent in subgroup analysis by histology type. In competing risk mode, examining ≥8 LNs could significantly reduce the risk of death from lung cancer, risk of death from chronic obstructive pulmonary disease, and risk of death from cardiac diseases. In the subgroup analysis, these trends were consistent.

CONCLUSIONS

Given the mortality risk associated with lung cancer, chronic obstructive pulmonary disease, and cardiac diseases, at least 8 LNs should be examined in surgery for T1 NSCLC.

Advances in immune response to pulmonary infection: Nonspecificity, specificity and memory

The lung immune response consists of various cells involved in both innate and adaptive immune processes. Innate immunity participates in immune resistance in a nonspecific manner, whereas adaptive immunity effectively eliminates pathogens through specific recognition. It was previously believed that adaptive immune memory plays a leading role during secondary infections; however, innate immunity is also involved in immune memory. Trained immunity refers to the long-term functional reprogramming of innate immune cells caused by the first infection, which alters the immune response during the second challenge. Tissue resilience limits the tissue damage caused by infection by controlling excessive inflammation and promoting tissue repair. In this review, we summarize the impact of host immunity on the pathophysiological processes of pulmonary infections and discuss the latest progress in this regard. In addition to the factors influencing pathogenic microorganisms, we emphasize the importance of the host response.

Immune Response to Biofilm Growing Pulmonary Pseudomonas aeruginosa Infection

Biofilm infections are tolerant to the host responses and recalcitrance to antibiotic drugs and disinfectants. The induced host-specific innate and adaptive immune responses by established biofilms are significantly implicated and contributes to the course of the infections. Essentially, the host response may be the single one factor impacting the outcome most, especially in cases where the biofilm is caused by low virulent opportunistic bacterial species. Due to the chronicity of biofilm infections, activation of the adaptive immune response mechanisms is frequently experienced, and instead of clearing the infection, the adaptive response adds to the pathogenesis. To a high degree, this has been reported for chronic Pseudomonas aeruginosa lung infections, where both a pronounced antibody response and a skewed Th1/Th2 balance has been related to a poorer outcome. In addition, detection of an adaptive immune response can be used as a significant indicator of a chronic P. aeruginosa lung infection and is included in the clinical definitions as such. Those issues are presented in the present review, along with a characterization of the airway structure in relation to immune responses towards P. aeruginosa pulmonary infections.

Tracking the response to Pseudomonas aeruginosa infection in ozone-induced chronic obstructive pulmonary disease mouse models

Pseudomonas aeruginosa (P. aeruginosa) is commonly isolated from the sputum of COPD patients. However, the precise role of P. aeruginosa infection in the progression of COPD, especially its role in altering inflammation remains unclear. Here, we designed mice models of COPD infected with P. aeruginosa (PA) and observed dynamic changes of lung structure, lung inflammatory microenvironment, lung function. After infection, the level of mucus secretion peaked on day 3 and remained higher throughout the study period, and the airway remodeling and emphysema was starkly apparent on day 14 and 21. On day 3, interferon-γ and interleukin (IL)- 5 levels increased rapidly, accompanied by elevated T-bet mRNA expression and CD4⁺T-bet⁺ cells; at the late stage of infection (days 14 and 21), consistent with increased GATA3 mRNA expression and CD4⁺GATA3⁺ cells, IL-4 and IL-13 levels significantly increased; IL-17A level, Foxp3 mRNA expression, CD4⁺ROR-γt⁺ cells and CD4⁺FOXP3⁺ cells remained at higher levels throughout the course of the infection. Small-airway function showed a decline from day 3 to day 21; large airway function showed a decline on day 14 and 21. Overall, P. aeruginosa infection contributed to the progression of COPD. During the infection, an early Th1-related inflammation gradually shifted to a later Th2-related inflammation, and small-airway function decline occurred earlier than that of large-airway function. On the basis of infection control, the appropriate use of glucocorticoid might slow disease progression by mitigating the enhanced Th2-related inflammation, and small airways could be also an important treatment target in P. aeruginosa -infected COPD patients.

Animal models of chronic and recurrent Pseudomonas aeruginosa lung infection: significance of macrolide treatment

Animal models of human diseases are invaluable and inevitable elements in identifying and testing novel treatments for serious diseases, including severe infections. Planning and conducting investigator-initiated human trials are generally accepted as being enormously challenging. In contrast, it is often underestimated how much planning, including background and modifying experiments, is needed to establish a relevant infectious disease animal model. However, representative animal infectious models, well designed to test generated hypotheses, are useful to improve our understanding of pathogenesis, virulence factors and host response and to identify novel treatment candidates and therapeutic strategies. Such results can subsequently proceed to clinical testing if suitable. The present review aims at presenting all the pulmonary Pseudomonas aeruginosa infectious models we have knowledge of and the detailed descriptions of established animal models in our laboratory focusing on macrolide therapy are presented.

Immune Responses to Pseudomonas aeruginosa Biofilm Infections

Pseudomonas aeruginosa is a key pathogen of chronic infections in the lungs of cystic fibrosis patients and in patients suffering from chronic wounds of diverse etiology. In these infections the bacteria congregate in biofilms and cannot be eradicated by standard antibiotic treatment or host immune responses. The persistent biofilms induce a hyper inflammatory state that results in collateral damage of the adjacent host tissue. The host fails to eradicate the biofilm infection, resulting in hindered remodeling and healing. In the present review we describe our current understanding of innate and adaptive immune responses elicited by P. aeruginosa biofilms in cystic fibrosis lung infections and chronic wounds. This includes the mechanisms that are involved in the activation of the immune responses, as well as the effector functions, the antimicrobial components and the associated tissue destruction. The mechanisms by which the biofilms evade immune responses, and potential treatment targets of the immune response are also discussed.

Immunomodulatory activity and protective effects of chokeberry fruit extract on Listeria monocytogenes infection in mice

Chokeberry (Aronia melanocarpa) fruit extracts (CE) are rich in polyphenols and usually exhibit immunomodulatory, anti-viral and anti-bacterial effects. We have previously shown that the CE used in this study activated macrophages and stimulated effector T cell differentiation in vitro. When applied orally to healthy mice, CE increased the proportion of CD11c+ dendritic cells in the gut-associated lymphoid tissue. CE-pretreated BALB/c mice readily eradicated orally ingested Listeria monocytogenes as evidenced by a slighter decrease in body weight and number of bacteria recovered from the spleen and reduced spleen size compared to the control infected mice. CE pretreatment in infected mice resulted in higher proportions of CD11b+ macrophages and CD8+ cytotoxic T cells both in the gut and the spleen. Phagocytosis, reactive oxygen species production and the proportions of activated CD86+ macrophages (CD11b+) and dendritic cells (CD11c+) were also enhanced in CE-pretreated infected mice. Furthermore, the expression of inducible nitric oxide synthase and IL-6 was increased in CE-pretreated infected mice and similar results were obtained in peritoneal macrophages in vitro. This effect of CE was associated with increased phosphorylation of IκB and Notch1 production. Finally, CE pretreatment elevated the proportion of perforin-producing cells in the spleen compared to control infected mice. This study demonstrates that prophylactic treatment with CE leads to more rapid eradication of bacterial infection with L. monocytogenes predominantly through increased activity of myeloid cells in the gut and in the spleen.

Pseudomonas aeruginosa Biofilms: Host Response and Clinical Implications in Lung Infections

Pseudomonas aeruginosa is a major health challenge that causes recalcitrant multidrug-resistant infections, especially in immunocompromised and hospitalized patients. P. aeruginosa is an important cause of nosocomial and ventilator-associated pneumonia characterized by high prevalence and fatality rates. P. aeruginosa also causes chronic lung infections in individuals with cystic fibrosis. Multidrug- and totally drug-resistant strains of P. aeruginosa are increasing threats that contribute to high mortality in these patients. The pathogenesis of many P. aeruginosa infections depends on its ability to form biofilms, structured bacterial communities that can coat mucosal surfaces or invasive devices. These biofilms make conditions more favorable for bacterial persistence, as embedded bacteria are inherently more difficult to eradicate than planktonic bacteria. The molecular mechanisms that underlie P. aeruginosa biofilm pathogenesis and the host response to P. aeruginosa biofilms remain to be fully defined. However, it is known that biofilms offer protection from the host immune response and are also extremely recalcitrant to antimicrobial therapy. Therefore, development of novel therapeutic strategies specifically aimed at biofilms is urgently needed. Here, we review the host response, key clinical implications of P. aeruginosa biofilms, and novel therapeutic approaches to treat biofilms relevant to lung infections. Greater understanding of P. aeruginosa biofilms will elucidate novel avenues to improve outcomes for P. aeruginosa pulmonary infections.

Progression of Cystic Fibrosis Lung Disease from Childhood to Adulthood: Neutrophils, Neutrophil Extracellular Trap (NET) Formation, and NET Degradation

Genetic defects in cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene cause CF. Infants with CFTR mutations show a peribronchial neutrophil infiltration prior to the establishment of infection in their lung. The inflammatory response progressively increases in children that include both upper and lower airways. Infectious and inflammatory response leads to an increase in mucus viscosity and mucus plugging of small and medium-size bronchioles. Eventually, neutrophils chronically infiltrate the airways with biofilm or chronic bacterial infection. Perpetual infection and airway inflammation destroy the lungs, which leads to increased morbidity and eventual mortality in most of the patients with CF. Studies have now established that neutrophil cytotoxins, extracellular DNA, and neutrophil extracellular traps (NETs) are associated with increased mucus clogging and lung injury in CF. In addition to opportunistic pathogens, various aspects of the CF airway milieux (e.g., airway pH, salt concentration, and neutrophil phenotypes) influence the NETotic capacity of neutrophils. CF airway milieu may promote the survival of neutrophils and eventual pro-inflammatory aberrant NETosis, rather than the anti-inflammatory apoptotic death in these cells. Degrading NETs helps to manage CF airway disease; since DNAse treatment release cytotoxins from the NETs, further improvements are needed to degrade NETs with maximal positive effects. Neutrophil-T cell interactions may be important in regulating viral infection-mediated pulmonary exacerbations in patients with bacterial infections. Therefore, clarifying the role of neutrophils and NETs in CF lung disease and identifying therapies that preserve the positive effects of neutrophils, while reducing the detrimental effects of NETs and cytotoxic components, are essential in achieving innovative therapeutic advances.

Widespread alterations in the peripheral blood innate immune cell profile in cystic fibrosis reflect lung pathology

Cystic fibrosis (CF) is caused by mutations to the CF transmembrane conductance regulator (CFTR) gene. CFTR is known to be expressed on multiple immune cell subtypes, dendritic cells, monocytes/macrophages, neutrophils and lymphocytes. We hypothesized that the lack of CFTR expression on peripheral blood innate immune cells would result in an altered cell profile in the periphery and that this profile would reflect lung pathology. We performed a flow cytometric phenotypic investigation of innate immune cell proportions in peripheral blood collected from 17 CF patients and 15 age-matched healthy controls. We observed significant differences between CF patients and controls in the relative proportions of natural killer (NK) cells, monocytes and their subsets, with significant correlations observed between proportions of NK and monocyte cell subsets and lung function (forced expiratory volume in 1 sec, % predicted; FEV1% predicted) in CF patients. This study demonstrates the widespread nature of immune dysregulation in CF and provides a basis for identification of potential therapeutic targets. Modulation of the distinct CF-related immune cell phenotype identified could also be an important biomarker for evaluating CFTR-targeted drug efficacy.

Biofilms and host response - helpful or harmful

Biofilm infections are one of the modern medical world's greatest challenges. Probably, all non-obligate intracellular bacteria and fungi can establish biofilms. In addition, there are numerous biofilm-related infections, both foreign body-related and non-foreign body-related. Although biofilm infections can present in numerous ways, one common feature is involvement of the host response with significant impact on the course. A special characteristic is the synergy of the innate and the acquired immune responses for the induced pathology. Here, we review the impact of the host response for the course of biofilm infections, with special focus on cystic fibrosis, chronic wounds and infective endocarditis.

Inflammation: A Double-Edged Sword in the Response to Pseudomonas aeruginosa Infection

The Gram-negative opportunistic pathogen Pseudomonas aeruginosa exploits failures of barrier defense and innate immunity to cause acute infections at a range of anatomic sites. We review the defense mechanisms that normally protect against P. aeruginosa pulmonary infection, as well as the bacterial products and activities that trigger their activation. Innate immune recognition of P. aeruginosa is critical for pathogen clearance; nonetheless, inflammation is also associated with pathogen persistence and poor host outcomes. We describe P. aeruginosa adaptations that improve this pathogen's fitness in the inflamed airway, and briefly discuss strategies to manipulate inflammation to benefit the host. Such adjunct therapies may become increasingly important in the treatment of acute and chronic infections caused by this multi-drug-resistant pathogen.