Alcohol impairs J774.16 macrophage-like cell antimicrobial functions in Acinetobacter baumannii infection

Case Report: Severe Community-Acquired Pneumonia in Réunion Island due to Acinetobacter baumannii

Acinetobacter baumannii (Ab) is a well-known nosocomial pathogen that has emerged as a cause of community-acquired pneumonia (CAP) in tropical regions. Few global epidemiological studies of CAP-Ab have been published to date, and no data are available on this disease in France. We conducted a retrospective chart review of severe cases of CAP-Ab admitted to intensive care units in Réunion University Hospital between October 2014 and October 2022. Eight severe CAP-Ab cases were reviewed. Median patient age was 56.5 years. Sex ratio (male-to-female) was 3:1. Six cases (75.0%) occurred during the rainy season. Chronic alcohol use and smoking were found in 75.0% and 87.5% of cases, respectively. All patients presented in septic shock and with severe acute respiratory distress syndrome. Seven patients (87.5%) presented in cardiogenic shock, and renal replacement therapy was required for six patients (75.0%). Five cases (62.5%) presented with bacteremic pneumonia. The mortality rate was 62.5%. The median time from hospital admission to death was 3 days. All patients received inappropriate initial antibiotic therapy. Acinetobacter baumannii isolates were all susceptible to ceftazidime, cefepime, piperacillin-tazobactam, ciprofloxacin, gentamicin, and imipenem. Six isolates (75%) were also susceptible to ticarcillin, piperacillin, and cotrimoxazole. Severe CAP-Ab has a fulminant course and high mortality. A typical case is a middle-aged man with smoking and chronic alcohol use living in a tropical region and developing severe CAP during the rainy season. This clinical presentation should prompt administration of antibiotic therapy targeting Ab.

Immunity on ice: The impact of methamphetamine on peripheral immunity

Methamphetamine (METH) regulation of the dopamine transporter (DAT) and central nervous system (CNS) dopamine transmission have been extensively studied. However, our understanding of how METH influences neuroimmune communication and innate and adaptive immunity is still developing. Recent studies have shed light on the bidirectional communication between the CNS and the peripheral immune system. They have established a link between CNS dopamine levels, dopamine neuronal activity, and peripheral immunity. Akin to dopamine neurons in the CNS, a majority of peripheral immune cells also express DAT, implying that in addition to their effect in the CNS, DAT ligands such as methamphetamine may have a role in modulating peripheral immunity. For example, by directly influencing DAT-expressing peripheral immune cells and thus peripheral immunity, METH can trigger a feed-forward cascade that impacts the bidirectional communication between the CNS and peripheral immune system. In this review, we aim to discuss the current understanding of how METH modulates both innate and adaptive immunity and identify areas where knowledge gaps exist. These gaps will then be considered in guiding future research directions.

Acinetobacter baumannii Strains Deficient in the Clp Chaperone-Protease Genes Have Reduced Virulence in a Murine Model of Pneumonia

Acinetobacter baumannii has emerged as a significant opportunistic Gram-negative pathogen and causative agent of nosocomial pneumonia especially in immunocompromised individuals in intensive care units. Recent advances to understand the contribution and function of A. baumannii virulence factors in its pathogenesis have begun to elucidate how this bacterium interacts with immune cells and its interesting mechanisms for multi-antibiotic resistance. Taking advantage of the availability of the A. baumannii AB5075 transposon mutant library, we investigated the impact of the A. baumannii Clp genes, which encode for a chaperone-protease responsible for the degradation of misfolded proteins, on bacterial virulence in a model of pneumonia using C57BL/6 mice and survival within J774.16 macrophage-like cells. Clp-protease A. baumannii mutants exhibit decreased virulence in rodents, high phagocytic cell-mediated killing and reduced biofilm formation. Capsular staining showed evidence of encapsulation in A. baumannii AB5075 and Clp-mutant strains. Surprisingly, clpA and clpS mutants displayed irregular cell morphology, which may be important in the biofilm structural deficiencies observed in these strains. Interestingly, clpA showed apical-like growth, proliferation normally observed in filamentous fungi. These findings provide new information regarding A. baumannii pathogenesis and may be important for the development of therapies intended at reducing morbidity and mortality associated with this remarkable pathogen.

A Tractable Drosophila Cell System Enables Rapid Identification of Acinetobacter baumannii Host Factors

Acinetobacter baumannii is an important causative agent of nosocomial infections worldwide. The pathogen also readily acquires resistance to antibiotics, and pan-resistant strains have been reported. A. baumannii is widely regarded as an extracellular bacterial pathogen. However, accumulating evidence demonstrates that the pathogen can invade, survive or persist in infected mammalian cells. Unfortunately, the molecular mechanisms controlling these processes remain poorly understood. Here, we show that Drosophila S2 cells provide several attractive advantages as a model system for investigating the intracellular lifestyle of the pathogen, including susceptibility to bacterial intracellular replication and limited infection-induced host cell death. We also show that the Drosophila system can be used to rapidly identify host factors, including MAP kinase proteins, which confer susceptibility to intracellular parasitism. Finally, analysis of the Drosophila system suggested that host proteins that regulate organelle biogenesis and membrane trafficking contribute to regulating the intracellular lifestyle of the pathogen. Taken together, these findings establish a novel model system for elucidating interactions between A. baumannii and host cells, define new factors that regulate bacterial invasion or intracellular persistence, and identify subcellular compartments in host cells that interact with the pathogen.

Carbapenemases: Transforming Acinetobacter baumannii into a Yet More Dangerous Menace

Acinetobacter baumannii is a common cause of serious nosocomial infections. Although community-acquired infections are observed, the vast majority occur in people with preexisting comorbidities. A. baumannii emerged as a problematic pathogen in the 1980s when an increase in virulence, difficulty in treatment due to drug resistance, and opportunities for infection turned it into one of the most important threats to human health. Some of the clinical manifestations of A. baumannii nosocomial infection are pneumonia; bloodstream infections; lower respiratory tract, urinary tract, and wound infections; burn infections; skin and soft tissue infections (including necrotizing fasciitis); meningitis; osteomyelitis; and endocarditis. A. baumannii has an extraordinary genetic plasticity that results in a high capacity to acquire antimicrobial resistance traits. In particular, acquisition of resistance to carbapenems, which are among the antimicrobials of last resort for treatment of multidrug infections, is increasing among A. baumannii strains compounding the problem of nosocomial infections caused by this pathogen. It is not uncommon to find multidrug-resistant (MDR, resistance to at least three classes of antimicrobials), extensively drug-resistant (XDR, MDR plus resistance to carbapenems), and pan-drug-resistant (PDR, XDR plus resistance to polymyxins) nosocomial isolates that are hard to treat with the currently available drugs. In this article we review the acquired resistance to carbapenems by A. baumannii. We describe the enzymes within the OXA, NDM, VIM, IMP, and KPC groups of carbapenemases and the coding genes found in A. baumannii clinical isolates.

Insights into Acinetobacter baumannii: A Review of Microbiological, Virulence, and Resistance Traits in a Threatening Nosocomial Pathogen

Being a multidrug-resistant and an invasive pathogen, Acinetobacter baumannii is one of the major causes of nosocomial infections in the current healthcare system. It has been recognized as an agent of pneumonia, septicemia, meningitis, urinary tract and wound infections, and is associated with high mortality. Pathogenesis in A. baumannii infections is an outcome of multiple virulence factors, including porins, capsules, and cell wall lipopolysaccharide, enzymes, biofilm production, motility, and iron-acquisition systems, among others. Such virulence factors help the organism to resist stressful environmental conditions and enable development of severe infections. Parallel to increased prevalence of infections caused by A. baumannii, challenging and diverse resistance mechanisms in this pathogen are well recognized, with major classes of antibiotics becoming minimally effective. Through a wide array of antibiotic-hydrolyzing enzymes, efflux pump changes, impermeability, and antibiotic target mutations, A. baumannii models a unique ability to maintain a multidrug-resistant phenotype, further complicating treatment. Understanding mechanisms behind diseases, virulence, and resistance acquisition are central to infectious disease knowledge about A. baumannii. The aims of this review are to highlight infections and disease-producing factors in A. baumannii and to touch base on mechanisms of resistance to various antibiotic classes.

Potential Mechanisms of Mucin-Enhanced Acinetobacter baumannii Virulence in the Mouse Model of Intraperitoneal Infection

Porcine mucin has been commonly used to enhance the infectivity of bacterial pathogens, including Acinetobacter baumannii, in animal models, but the mechanisms for enhancement by mucin remain relatively unknown. In this study, using the mouse model of intraperitoneal (i.p.) mucin-enhanced A. baumannii infection, we characterized the kinetics of bacterial replication and dissemination and the host innate immune responses, as well as their potential contribution to mucin-enhanced bacterial virulence. We found that mucin, either admixed with or separately injected with the challenge bacterial inoculum, was able to enhance the tissue and blood burdens of A. baumannii strains of different virulence. Intraperitoneal injection of A. baumannii-mucin or mucin alone induced a significant but comparable reduction of peritoneal macrophages and lymphocytes, accompanied by a significant neutrophil recruitment and early interleukin-10 (IL-10) responses, suggesting that the resulting inflammatory cellular and cytokine responses were largely induced by the mucin. Depletion of peritoneal macrophages or neutralization of endogenous IL-10 activities showed no effect on the mucin-enhanced infectivity. However, pretreatment of mucin with iron chelator DIBI, but not deferoxamine, partially abolished its virulence enhancement ability, and replacement of mucin with iron significantly enhanced the bacterial burdens in the peritoneal cavity and lung. Taken together, our results favor the hypothesis that iron at least partially contributes to the mucin-enhanced infectivity of A. baumannii in this model.

Whole-Genome Sequencing to Differentiate Relapse From Reinfection in Community-Onset Bacteremic Acinetobacter baumannii Pneumonia

Community-onset bacteremic Acinetobacter baumannii pneumonia recurred in 3 of 30 (10%) patients followed prospectively, all with ongoing hazardous alcohol intake, 3-56 months after initial pneumonia. Paired isolates underwent whole-genome sequencing. Phylogenetic analysis showed that recurrence strains were all distinct from preceding strains, indicating reinfection in susceptible individuals rather than relapse.

Compounding effect of vitamin D3 diet, supplementation, and alcohol exposure on macrophage response to mycobacterium infection

Vitamin D₃ is known to be a key component in the defense against Mycobacterium tuberculosis (Mtb) infection through the regulation of cytokine and effector molecules. Conversely, alcohol exposure has been recognized as an immune dysregulator. Macrophages were extracted from D₃ deficient and sufficient diet mice and supplemented with D₃ or exposed to ethanol during ex vivo infection using M. bovis BCG, as a surrogate for Mtb. Results of our study indicate that while exogenous supplementation or alcohol exposure did alter immune response, in vivo diet was the greatest determinant of cytokine and effector molecule production. Alcohol exposure was found to profoundly dysregulate primary murine macrophages, with ethanol-exposed cells generally characterized as hyper- or hyporesponsive. Exogenous D₃ supplementation had a normative effect for diet deficient host, however supplementation was not sufficient to compensate for the effects of diet deficiency. Vitamin D₃ sufficient diet resulted in reduced cell cytotoxicity for the majority of time points. Results provide insight into the ramifications of both the individual and combined health risks of D₃ deficiency or alcohol exposure. Given the clinical relevance of D₃ deficiency and alcohol use comorbidities, outcomes of this study have implications in therapeutic approaches for the treatment of tuberculosis disease.

Acute intraperitoneal infection with a hypervirulent Acinetobacter baumannii isolate in mice

Acinetobacter baumannii infection has become a major cause of healthcare-associated infection and a critical pathogen in the WHO antimicrobial resistance research and development priority list. Catheter-related septicemia is one of the major clinical manifestations of A. baumannii infection associated with high morbidity and mortality. In this study, we used a clinical A. baumannii strain (LAC-4) that is hypervirulent to immunocompetent C57BL/6 and BALB/c mice and established a mouse model of intraperitoneal (i.p.) A. baumannii infection. Our study showed that i.p. LAC-4 infection of C57BL/6 and BALB/c mice induces a lethal or sublethal infection with high bacterial burdens in peritoneal cavity, blood and tissues and the infected mice either succumbed to the infection within 24 hours or completely recovered from the infection. The infection induces acute peritoneal recruitment of neutrophils and other innate immune cells, and the local and systemic production of proinflammatory cytokines and chemokines (IL-1β, IL-5, IL-6, TNF-α, RANTES, MIP-1β, MCP-1, KC and IL-10). Mechanistic studies suggest an important role of macrophages in the host innate defense in this model in that in vitro stimulation of peritoneal macrophages with killed LAC-4 induced a similar pattern of cytokine/chemokine responses to those in the infected mice, and depletion of peritoneal macrophages rendered the mice significantly more susceptible to the infection. Thus, this mouse infection model will provide an alternative and useful tool for future pathogenesis studies of A. baumannii-associated septicemia and identification and characterization of important virulence factors, as well as serve as a surrogate model for rapid evaluation of novel therapeutics and vaccines for this emerging infectious agent.

Genomic epidemiology of severe community-onset Acinetobacter baumannii infection

Acinetobacter baumannii causes severe, fulminant, community-acquired pneumonia (CAP) in tropical and subtropical regions. We compared the population structure, virulence and antimicrobial resistance determinants of northern Australian community-onset A. baumannii strains with local and global strains. We performed whole-genome sequencing on 55 clinical and five throat colonization A. baumannii isolates collected in northern Australia between 1994 and 2016. Clinical isolates included CAP (n=41), healthcare-associated pneumonia (n=7) and nosocomial bloodstream (n=7) isolates. We also included 93 publicly available international A. baumannii genome sequences in the analyses. Patients with A. baumannii CAP were almost all critically unwell; 82 % required intensive care unit admission and 18 % died during their inpatient stay. Whole-genome phylogenetic analysis demonstrated that community-onset strains were not phylogenetically distinct from nosocomial strains. Some non-multidrug-resistant local strains were closely related to multidrug-resistant strains from geographically distant locations. Pasteur sequence type (ST)10 was the dominant ST and accounted for 31/60 (52 %) northern Australian strains; the remainder belonged to a diverse range of STs. The most recent common ancestor for ST10 was estimated to have occurred in 1738 (95 % highest posterior density, 1626–1826), with evidence of multiple introduction events between Australia and Southeast Asia between then and the present day. Virulence genes associated with biofilm formation and the type 6 secretion system (T6SS) were absent in many strains, and were not associated with in-hospital mortality. All strains were susceptible to gentamicin and meropenem; none carried an AbaR resistance island. Our results suggest that international dissemination of A. baumannii is occurring in the community on a contemporary timescale. Genes associated with biofilm formation and the T6SS may not be required for survival in community niches. The relative contributions of host and bacterial factors to the clinical severity of community-onset A. baumannii infection require further investigation.

Intracellular Invasion and Killing Assay to Investigate the Effectsof Binge Alcohol Toxicity in Murine Alveolar Macrophages

Alcohol consumption has diverse and well-documented effects on the human immune system and its ability to defend against infective agents. While pulmonary related infections can occur in healthy humans, binge alcohol use is recognized as a major health risk factor (Nelson et al., 1991). Although binge alcohol consumption has been considered as a risk factor for the development of pulmonary infections, no experimental studies have investigated the outcomes of a single binge alcohol exposure during infection. A key assay to assess the effects of a single binge alcohol exposure on the interactions between bacteria and alveolar macrophage is a binge alcohol intracellular invasion and killing assay. MH-S alveolar macrophages (AMs) are exposed to a single binge alcohol dose prior to infection for 3 h. The macrophage monolayer is then infected to allow for engulfment, followed by removal of extracellular bacteria to assess the intracellular killing capacity of infected macrophages over time. We have utilized this assay to demonstrate that low alcohol exposure significantly suppressed the uptake and killing of less virulent Burkholderia thailandensis (B. thailandensis) by AMs. More recently we found that activated AMs with interferon (IFN)-γ incubated in alcohol (0.08%) for 3 h prior to infection showed significantly lower bacterial uptake at 2 and 8 h post infection, which lead to B. thailandensis survival and a ~2.5-fold replication increase compared to controls (Jimenez et al., 2017). These results provide insights into binge alcohol consumption, a culturally prevalent risk factor, as a predisposing factor for pulmonary bacterial infections. This assay can be adapted to other bacterial species and host cell types to assess tissue specific effects of alcohol during infection.

Severe Community-Acquired Pneumonia due to Acinetobacter baumannii in North America: Case Report and Review of the Literature

Acinetobacter baumannii is a rare but emerging cause of fulminant community-acquired pneumonia (CAP-AB). We describe a patient from a rural area who developed acute respiratory distress syndrome and septic shock. We describe risk factors and characteristics of this syndrome and review published cases of CAP-AB from North America.

An unusual cause of community-acquired pneumonia

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A. baumannii community-acquired pneumonia incidence and prevalence is unknown in temperate regions.

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It potentially has a rapidly progressive course and poor outcome.

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Progression of disease may be due to immune dysfunction in certain hosts.

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Studies are conflicting on the role and regimen of antibiotics on disease progression.

We present a case of fatal community-acquired pneumonia (CAP) due to Acinetobacter baumannii, which is rarely reported in the northeastern United States. Previously reported cases originate from tropical and subtropical climates, and infection tends to have an aggressive course with a poor outcome. Appropriate antimicrobial therapy is crucial; however, the associated systemic inflammatory response may overwhelm host defenses, especially in patients with certain co-morbidities.

Uncovering the mechanisms of Acinetobacter baumannii virulence

Acinetobacter baumannii is a nosocomial pathogen that causes ventilator-associated as well as bloodstream infections in critically ill patients, and the spread of multidrug-resistant Acinetobacter strains is cause for concern. Much of the success of A. baumannii can be directly attributed to its plastic genome, which rapidly mutates when faced with adversity and stress. However, fundamental virulence mechanisms beyond canonical drug resistance were recently uncovered that enable A. baumannii and, to a limited extent, other medically relevant Acinetobacter species to successfully thrive in the health-care environment. In this Review, we explore the molecular features that promote environmental persistence, including desiccation resistance, biofilm formation and motility, and we discuss the most recently identified virulence factors, such as secretion systems, surface glycoconjugates and micronutrient acquisition systems that collectively enable these pathogens to successfully infect their hosts.

Effects of binge alcohol exposure on Burkholderia thailandensis-alveolar macrophage interaction

Alcohol consumption has diverse and well-documented effects on the human immune system and its ability to defend against infective agents. One example is melioidosis, a disease caused by infection with Burkholderia pseudomallei, which is of public health importance in Southeast Asia and Northern Australia, with an expanding global distribution. While B. pseudomallei infections can occur in healthy humans, binge alcohol use is progressively being recognized as a major risk factor. Although binge alcohol consumption has been considered as a risk factor for the development of melioidosis, no experimental studies have investigated the outcomes of alcohol exposure on Burkholderia spp. infection. Therefore, we proposed the use of non-pathogenic B. thailandensis E264 as a useful BSL-1 model system to study the effects of binge alcohol exposure on bacteria and alveolar macrophage interactions. The MH-S alveolar macrophage (AMs) cell line was used to characterize innate immune responses to infection in vitro. Our results showed that alcohol exposure significantly suppressed the uptake and killing of B. thailandensis by AMs. Alveolar macrophages incubated in alcohol (0.08%) for 3 h prior to infection showed significantly lower bacterial uptake at 2 and 8 h post infection. Activated AMs with IFN-γ and pre and post-incubation in alcohol when exposed to B. thailandensis released lower nitric oxide (NO) concentrations, compared to activated AMs with IFN-γ from non-alcoholic controls. As a result, B. thailandensis survival and replication increased ∼2.5-fold compared to controls. The presence of alcohol (1%) also increased bacterial survival within AMs. Alcohol significantly decreased bacterial motility compared to non-alcoholic controls. Increased biofilm formation was observed at 3 and 6 h when bacteria were pre-incubated in (0.08%) alcohol. These results provide insights into binge alcohol consumption, a culturally prevalent risk factor, as a predisposing factor for melioidosis.

Capsular specific IgM enhances complement-mediated phagocytosis and killing of Cryptococcus neoformans by methamphetamine-treated J774.16 macrophage-like cells

Methamphetamine (METH) is a powerful and highly addictive stimulant that affects the central nervous system of users in the United States and worldwide, and its consumption is associated to the acquisition of HIV and AIDS-related infections. METH enhances cryptococcosis in mice, an opportunistic infection caused by the encapsulated fungus Cryptococcus neoformans. Due to its ability to survive within macrophages, C. neoformans is an ideal model to study pathogen-macrophage interactions. METH abrogates normal macrophage function, which might contribute to the higher rate and more rapid progression of infections in drug abusers. Hence, we investigated the role of complement and specific IgM to C. neoformans capsular polysaccharide on the function of J774.16 macrophage-like cells after exposure to METH. We found that complement and IgM significantly promotes complement-mediated phagocytosis of C. neoformans by J774.16 cells in comparison to co-incubation with complement alone. IgM enhances the expression of complement receptor 3 on the surface macrophages treated with the drug. Also, IgM-increased macrophage phagocytosis of C. neoformans may be associated with upregulation of GTPase-RhoA, a key regulator of the actin polymerization signaling cascade. Fungal cells incubated with complement and IgM in the presence of METH demonstrated higher number of cells per aggregate, a possible explanation for their enhanced ingestion by phagocytes. IgM increased killing of yeast cells by macrophages by inhibiting the alkalization of the phagosome and stimulating the intracellular production of nitric oxide. Together, our findings suggest that IgM stimulates the effector functions of macrophages against opportunistic pathogens in the setting of drug abuse.

Malondialdehyde-Acetaldehyde-Adducted Surfactant Protein Alters Macrophage Functions Through Scavenger Receptor A

BACKGROUND

Reactive aldehydes such as acetaldehyde and malondialdehyde generated as a result of alcohol metabolism and cigarette smoke exposure lead to the formation of malondialdehyde-acetaldehyde-adducted proteins (MAA adducts). These aldehydes can adduct to different proteins such as bovine serum albumin and surfactant protein A or surfactant protein D (SPD). Macrophages play an important role in innate immunity, but the effect of MAA adducts on macrophage function has not yet been examined. Because macrophage scavenger receptor A (SRA; CD204) mediates the uptake of modified proteins, we hypothesized that the effects of MAA-modified proteins on macrophage function are primarily mediated through SRA.

METHODS

We tested this hypothesis by exposing SPD-MAA to macrophages and measuring functions. SPD-MAA treatment significantly stimulated pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α) release in the macrophage cell line, RAW 264.7.

RESULTS

A significant reduction in phagocytosis of zymosan particles was also observed. SPD-MAA stimulated a significant dose-dependent increase in TNF-α and interleukin (IL)-6 release from peritoneal macrophages (PMs) of wild-type (WT) mice. But significantly less TNF-α and IL-6 were released from PMs of SRA-/- mice. We observed a significant reduction in phagocytosis of zymosan particles in PMs from WT mice treated with SPD-MAA. No further SPD-MAA-induced reduction was seen in PMs from SRA-/- mice. SPD-MAA treatment significantly increased SRA mRNA expression, but had no effect on surface receptor protein expression. Protein kinase C alpha inhibitor and NF-κB inhibitor significantly reduced pro-inflammatory cytokine release in response to SPD-MAA.

CONCLUSIONS

In conclusion, our data demonstrate that SRA is important for MAA-adducted protein-mediated effect on macrophage functions.

Community-acquired Acinetobacter baumannii: clinical characteristics, epidemiology and pathogenesis

Community-acquired Acinetobacter baumannii (CA-Ab) is a rare but serious cause of community-acquired pneumonia in tropical regions of the world. CA-Ab infections predominantly affect individuals with risk factors, which include excess alcohol consumption, diabetes mellitus, smoking and chronic lung disease. CA-Ab pneumonia presents as a surprisingly fulminant course and is characterized by a rapid onset of fever, severe respiratory symptoms and multi-organ dysfunction, with a mortality rate reported as high as 64%. It is unclear whether the distinct clinical syndrome caused by CA-Ab is because of host predisposing factors or unique bacterial characteristics, or a combination of both. Deepening our understanding of the drivers of overwhelming CA-Ab infection will provide important insights into preventative and therapeutic strategies.

Chronic Ethanol Exposure: Pathogenesis of Pulmonary Disease and Dysfunction

Ethanol (EtOH) is the world’s most commonly used drug, and has been widely recognized as a risk factor for developing lung disorders. Chronic EtOH exposure affects all of the organ systems in the body and increases the risk of developing pulmonary diseases such as acute lung injury and pneumonia, while exacerbating the symptoms and resulting in increased mortality in many other lung disorders. EtOH and its metabolites inhibit the immune response of alveolar macrophages (AMs), increase airway leakage, produce damaging reactive oxygen species (ROS), and disrupt the balance of antioxidants/oxidants within the lungs. In this article, we review the role of EtOH exposure in the pathogenesis and progression of pulmonary disease.

Cannabinoid receptor 1 but not 2 mediates macrophage phagocytosis by G(α)i/o /RhoA/ROCK signaling pathway

Phagocytosis is critical to macrophages linking innate and adaptive immune reaction. Cannabinoid receptor 1 (CB1) and 2 (CB2) mediate immune modulation. However, the role of cannabinoid receptors in macrophage phagocytosis is undefined. In this study, we found that two murine macrophage lines (J774A.1 and RAW264.7) and peripheral blood macrophages all expressed CB1 and CB2 by immunofluorescence-staining, real time RT-PCR and Western blot. Macrophage phagocytic activity was determined by quantifying fluorescent intensity of the engulfed BioParticles or fluorescence-activated cell sorting. mAEA (CB1 agonist) enhanced phagocytosis of macrophages, but JWH133 (CB2 agonist) had no influence. Pharmacological or genetic ablation of CB1 inhibited mAEA-enhanced phagocytosis, while CB2 had no such effects. Meanwhile, activation of CB1 increased GTP-bounding active form of small GTPase RhoA, but not Rac1 or Cdc42. AM281 (CB1 antagonist) and pertussis toxin (PTX, G((α)i/o) protein inhibitor) decreased GTP-bound RhoA protein level with mAEA. In addition, PTX, C3 Transferase (RhoA inhibitor) or Y27632 (Rho-associated kinase ROCK inhibitor) attenuated CB1-mediated phagocytosis. These results confirm that activation of CB1 regulates macrophage phagocytosis through G((α)i/o)/RhoA/ROCK signaling pathway. Moreover, activation of CB1 induced significant up-regulation of CB1 expression by real time RT-PCR and Western blot analysis, but not CB2. It indicated the existence of a positive feedback between CB1 activation and CB1 expression. The up-regulation of CB1 was RhoA-independent but it may contribute to maintaining high phagocytic activity of macrophages for a longer time. In conclusion, CB1 mediates macrophage phagocytosis by G((α)i/o)/RhoA/ROCK signal axis. These data further underline the role of CB1 in macrophage phagocytic process.

Alcohol enhances Acinetobacter baumannii-associated pneumonia and systemic dissemination by impairing neutrophil antimicrobial activity in a murine model of infection

Acinetobacter baumannii (Ab) is a common cause of community-acquired pneumonia (CAP) in chronic alcoholics in tropical and sub-tropical climates and associated with a >50% mortality rate. Using a murine model of alcohol (EtOH) administration, we demonstrated that EtOH enhances Ab-mediated pneumonia leading to systemic infection. Although EtOH did not affect neutrophil recruitment to the lungs of treated mice, it decreased phagocytosis and killing of bacteria by these leukocytes leading to increased microbial burden and severity of disease. Moreover, we determined that mice that received EtOH prior to Ab infection were immunologically impaired, which was reflected in increased pulmonary inflammation, sequential dissemination to the liver and kidneys, and decreased survival. Furthermore, immunosuppression by EtOH was associated with deregulation of cytokine production in the organs of infected mice. This study establishes that EtOH impairs immunity in vivo exacerbating Ab infection and disease progression. The ability of Ab to cause disease in alcoholics warrants the study of its virulence mechanisms and host interactions.