Role of Macrophages in Early Host Resistance to Respiratory Acinetobacter baumannii Infection

Acinetobacter baumannii is an emerging bacterial pathogen that causes nosocomial pneumonia and other infections. Although it is recognized as an increasing threat to immunocompromised patients, the mechanism of host defense against A. baumannii infection remains poorly understood. In this study, we examined the potential role of macrophages in host defense against A. baumannii infection using in vitro macrophage culture and the mouse model of intranasal (i.n.) infection. Large numbers of A. baumannii were taken up by alveolar macrophages in vivo as early as 4 h after i.n. inoculation. By 24 h, the infection induced significant recruitment and activation (enhanced expression of CD80, CD86 and MHC-II) of macrophages into bronchoalveolar spaces. In vitro cell culture studies showed that A. baumannii were phagocytosed by J774A.1 (J774) macrophage-like cells within 10 minutes of co-incubation, and this uptake was microfilament- and microtubule-dependent. Moreover, the viability of phagocytosed bacteria dropped significantly between 24 and 48 h after co-incubation. Infection of J774 cells by A. baumannii resulted in the production of large amounts of proinflammatory cytokines and chemokines, and moderate amounts of nitric oxide (NO). Prior treatment of J774 cells with NO inhibitors significantly suppressed their bactericidal efficacy (P<0.05). Most importantly, in vivo depletion of alveolar macrophages significantly enhanced the susceptibility of mice to i.n. A. baumannii challenge (P<0.01). These results indicate that macrophages may play an important role in early host defense against A. baumannii infection through the efficient phagocytosis and killing of A. baumannii to limit initial pathogen replication and the secretion of proinflammatory cytokines and chemokines for the rapid recruitment of other innate immune cells such as neutrophils

Structures of minor ether lipids isolated from the aceticlastic methanogen, Methanothrix concilii GP6.

Structures were determined for two phospholipids and three glycolipids purified from chloroform-methanol extracts of Methanothrix concilii GP6. Together they accounted for 14% of the total lipid and were based on a C20,20-diether core structure consisting of either 2,3-di-O-phytanyl-sn-glycerol or its 3'-hydroxy analog, namely, 2-O-[3,7,11,15-tetramethylhexadecyl]-3-O-[3'- hydroxy-3',7',11',15'-tetramethylhexadecyl]-sn-glycerol. These two core lipids formed phosphodiester bonds to ethanolamine and glycosidic bonds to beta-D-galactopyranose. A third glycolipid consisted of the triglycosyl head group beta-D-galactopyranosyl-(1----6)-[beta-D-glucopyranosyl-(1----3)]-beta-D - galactopyranose in glycosidic linkage to the 3'-hydroxydiether core lipid

Intranasal Immunization with an Archaeal Lipid Mucosal Vaccine Adjuvant and Delivery Formulation Protects against a Respiratory Pathogen Challenge

Archaeal lipid mucosal vaccine adjuvant and delivery (AMVAD) is a safe mucosal adjuvant that elicits long lasting and memory boostable mucosal and systemic immune responses to model antigens such as ovalbumin. In this study, we evaluated the potential of the AMVAD system for eliciting protective immunity against mucosal bacterial infections, using a mouse model of intranasal Francisella tularensis LVS (LVS) challenge. Intranasal immunization of mice with cell free extract of LVS (LVSCE) adjuvanted with the AMVAD system (LVSCE/AMVAD) induced F. tularensis-specific antibody responses in sera and bronchoalveolar lavage fluids, as well as antigen-specific splenocyte proliferation and IL-17 production. More importantly, the AMVAD vaccine partially protected the mice against a lethal intranasal challenge with LVS. Compared to LVSCE immunized and naïve mice, the LVSCE/AMVAD immunized mice showed substantial to significant reduction in pathogen burdens in the lungs and spleens, reduced serum and pulmonary levels of proinflammatory cytokines/chemokines, and longer mean time to death as well as significantly higher survival rates (p<0.05). These results suggest that the AMVAD system is a promising mucosal adjuvant and vaccine delivery technology, and should be explored further for its applications in combating mucosal infectious diseases

Acinetobacter baumannii Infection Inhibits Airway Eosinophilia and Lung Pathology in a Mouse Model of Allergic Asthma

Allergic asthma is a dysregulation of the immune system which leads to the development of Th2 responses to innocuous antigens (allergens). Some infections and microbial components can re-direct the immune response toward the Th1 response, or induce regulatory T cells to suppress the Th2 response, thereby inhibiting the development of allergic asthma. Since Acinetobacter baumannii infection can modulate lung cellular and cytokine responses, we studied the effect of A. baumannii in modulating airway eosinophilia in a mouse model of allergic asthma. Ovalbumin (OVA)-sensitized mice were treated with live A. baumannii or phosphate buffered saline (PBS), then intranasally challenged with OVA. Compared to PBS, A. baumannii treatment significantly reduced pulmonary Th2 cytokine and chemokine responses to OVA challenge. More importantly, the airway inflammation in A. baumannii-treated mice was strongly suppressed, as seen by the significant reduction of the proportion and the total number of eosinophils in the bronchoalveolar lavage fluid. In addition, A. baumannii-treated mice diminished lung mucus overproduction and pathology. However, A. baumannii treatment did not significantly alter systemic immune responses to OVA. Serum OVA-specific IgE, IgG1 and IgG2a levels were comparable between A. baumannii- and PBS-treated mice, and tracheobronchial lymph node cells from both treatment groups produced similar levels of Th1 and Th2 cytokines in response to in vitro OVA stimulation. Moreover, it appears that TLR-4 and IFN-γ were not directly involved in the A. baumannii-induced suppression of airway eosinophilia. Our results suggest that A. baumannii inhibits allergic airway inflammation by direct suppression of local pulmonary Th2 cytokine responses to the allergen

Archaeosome immunostimulatory vaccine delivery system

Archaeosomes are liposomes made from the polar ether lipids of Archaea. These lipids are unique and distinct in structure from the ester lipids found in Eukarya and Bacteria. The regularly branched and usually fully saturated isopranoid chains of archaeal polar lipids are attached via ether bonds to the sn-2,3 carbons of the glycerol backbone(s). The polar head groups are usually the same as those encountered in the ester lipids from the other two domains, except that phosphatidylcholine is rarely present. These lipid structures provide formulary advantages, and contribute to the excellent physico-chemical stability of the archaeosomes and their efficacy as self-adjuvanting vaccine delivery vesicles. The uptake of archaeosomes by phagocytic cells is several folds greater than that of liposomes made from ester lipids. In addition, archaeosomes enhance the recruitment and activation of professional antigen presenting cells in vivo, and deliver the antigen to both MHC class I and II pathways for antigen presentation, without eliciting overt inflammatory responses. In murine models, systemic administration of archaeosomes containing encapsulated antigen(s) elicits strong and sustained antigen-specific antibody responses which are comparable, in some formulations, to those obtained with Freunds adjuvant. Additionally, archaeosomes promote robust antigen-specific cell-mediated immunity, including CD8+ CTL responses. The immune responses induced by archaeosomes are sustained over long periods and exhibit strong memory responses. More importantly, immunization of mice with archaeosome-based vaccines induces robust protective immunity against intracellular pathogens, and prophylactic and therapeutic efficacies against the development of experimental cancers. Extensive murine model studies suggest that archaeosomes are safe.Peer reviewed: YesNRC publication: Ye

Studies on Cellulose Hydrolysis by Acetivibrio cellulolyticus

Acetivibrio cellulolyticus extracellular cellulase extensively hydrolyzed crystalline celluloses such as Avicel (FMC Corp., Food and Pharmaceutical Products Div., Philadelphia, Pa.) but only if it was desalted and supplemented with Ca(2+). The Ca(2+) effect was one of increased enzyme stability in the presence of the ion. Although preincubation of the cellulase complex at 40°C for 5 h without added Ca(2+) had a negligible effect on endoglucanase activity or on the subseqent hydrolysis of amorphous cellulose, the capacity of the enzyme to hydrolyze crystalline cellulose was almost completely lost. Adsorption studies showed that 90% of the Avicel-solubilizing component of the total enzyme preparation bound to 2% Avicel at 40°C. Under these conditions, only 15% of the endoglucanase and 25% of the protein present in the enzyme preparation adsorbed to the substrate. The protein profile of the bound enzyme, as analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was complex and distinctly different from the profile observed for total cellulase preparations. The specific activity of A. cellulolyticus cellulase with respect to Avicel hydrolysis was compared with that of commercially available Trichoderma reesei cellulase