Extracellular accumulation of potently microbicidal bactericidal/permeability-increasing protein and p15s in an evolving sterile rabbit peritoneal inflammatory exudate

Bactericidal permeability-increasing protein/LPS-binding protein (BPI/LBP) enhances resistance of golden pompano Trachinotus ovatus against bacterial infection

Antimicrobial peptides are crucial components of innate immunity against microbial invasions. As a kind of antimicrobial peptides, bactericidal permeability-increasing protein (BPI)/lipopolysaccharide-binding protein (LBP) play vital roles in defending the host against gram-negative bacteria. In the current study, a novel BPI/LBP from Trachinotus ovatus (TroBPI/LBP) was characterized. The full length of TroBPI/LBP cDNA sequence is 1434 bp, which contained 477 amino acids. Multiple amino acid alignments of TroBPI/LBP shows 34.07%-84.49% identity with other fish BPI/LBP. Similar to other BPI/LBP, TroBPI/LBP also possesses an N-terminal signal peptide, a BPI/LBP/CETP N-terminal domain, and a BPI/LBP/CETP C-terminal domain. In vitro, the recombinant protein of TroBPI/LBP showed effective bacterial depression activity and binding activity to gram-negative bacteria. In vivo, TroBPI/LBP was constitutively expressed in tested tissues, and the highest expression level was in liver. Following Vibrio alginolyticus stimulation, the mRNA expression of TroBPI/LBP was significantly upregulated in immune-related tissues, and peaked at 12 h post-infection, which confirmed that TroBPI/LBP was highly sensitive to V. alginolyticus stimuli. Furthermore, functional analyses showed that the overexpression of TroBPI/LBP could enhance the ability of fish to against V. alginolyticus infection, and the knockdown of TroBPI/LBP significantly diminished bacterial clearance capacity post-infection. Therefore, these results suggest that TroBPI/LBP may play an important role in host defense against bacterial infection.

Antimicrobial peptides and proteins in human biological fluids

Antimicrobial peptides and proteins (AMPs) are endogenous compounds that have a direct antimicrobial effect on bacteria (e. g., by disrupting bacterial membranes), as well as on fungi and viruses. AMPs are the main component of the innate immunity of living organisms and are produced by both epithelial cells (skin cells, cells of respiratory tract, intestine, urinary and genital tracts) and cells of the immune system and are secreted into secretory fluids. AMPs can also act as chemoattractants for immunocompetent cells (neutrophils, monocytes, T lymphocytes, dendritic cells) in the inflammation site and affect the antigen presenting cells by modulating adaptive T cell immune responses. The representatives of the main 15 AMP classes, that we describe in this review, are the most studied group of the large pool of these compounds. We discuss their localization, expression, and concentration in various biofluids of humans under normal and pathological conditions.

Differential Enhancement of Neutrophil Phagocytosis by Anti-Bactericidal/Permeability-Increasing Protein Antibodies

Bactericidal/permeability-increasing protein (BPI) plays a major role in innate immunity through the ability of the N-terminal domain (NTD) to bind LPS, mediate cytotoxicity, and block LPS-induced inflammation. The C-terminal domain mediates phagocytosis of bacteria bound to the NTD. These two domains are linked by a surface-exposed loop at amino acids 231-249 for human BPI, known as the "hinge region." Autoantibodies to human BPI are prevalent in many chronic lung diseases; their presence is strongly correlated with Pseudomonas aeruginosa and with worse lung function in patients with cystic fibrosis and bronchiectasis. Although prior literature has reported BPI neutralization effect with autoantibodies targeting either NTD or C-terminal domain, the functionality of BPI Ab to the hinge region has never been investigated. Here, we report that Ab responses to the BPI hinge region mediate a remarkably selective potentiation of BPI-dependent phagocytosis of P. aeruginosa with both human and murine neutrophils in vitro and in vivo. These findings indicate that autoantibodies to the BPI hinge region might enhance bacterial clearance.

Killing three birds with one BPI: Bactericidal, opsonic, and anti-inflammatory functions

Bactericidal/permeability-increasing protein (BPI) is an anti-microbial protein predominantly expressed in azurophilic granules of neutrophils. BPI has been shown to mediate cytocidal and opsonic activity against Gram-negative bacteria, while also blunting inflammatory activity of lipopolysaccharide (LPS). Despite awareness of these functions in vitro, the magnitude of the contribution of BPI to innate immunity remains unclear, and the nature of the functional role of BPI in vivo has been submitted to limited investigation. Understanding this role takes on particular interest with the recognition that autoimmunity to BPI is tightly linked to a specific infectious trigger like Pseudomonas aeruginosa in chronic lung infection. This has led to the notion that anti-BPI autoantibodies compromise the activity of BPI in innate immunity against P. aeruginosa, which is primarily mediated by neutrophils. In this review, we explore the three main mechanisms in bactericidal, opsonic, and anti-inflammatory of BPI. We address the etiology and the effects of BPI autoreactivity on BPI function. We explore BPI polymorphism and its link to multiple diseases. We summarize BPI therapeutic potential in both animal models and human studies, as well as offer therapeutic approaches to designing a sustainable and promising BPI molecule.

Bactericidal/Permeability-Increasing Protein Preeminently Mediates Clearance of Pseudomonas aeruginosa In Vivo via CD18-Dependent Phagocytosis

Chronic Pseudomonas aeruginosa infection mysteriously occurs in the airways of patients with cystic fibrosis (CF), bronchiectasis (BE), and chronic obstructive pulmonary disease (COPD) in the absence of neutrophil dysfunction or neutropenia and is strongly associated with autoimmunity to bactericidal permeability-increasing protein (BPI). Here, we define a critical role for BPI in in vivo immunity against P. aeruginosa. Wild type and BPI-deficient (Bpi-/-) mice were infected with P. aeruginosa, and bacterial clearance, cell infiltrates, cytokine production, and in vivo phagocytosis were quantified. Bpi-/- mice exhibited a decreased ability to clear P. aeruginosa in vivo in concert with increased neutrophil counts and cytokine release. Bpi-/- neutrophils displayed decreased phagocytosis that was corrected by exogenous BPI in vitro. Exogenous BPI also enhanced clearance of P. aeruginosa in Bpi-/- mice in vivo by increasing P. aeruginosa uptake by neutrophils in a CD18-dependent manner. These data indicate that BPI plays an essential role in innate immunity against P. aeruginosa through its opsonic activity and suggest that perturbations in BPI levels or function may contribute to chronic lung infection with P. aeruginosa.

The phospholipid-repair system LplT/Aas in Gram-negative bacteria protects the bacterial membrane envelope from host phospholipase A2 attack

Secretory phospholipases A2 (sPLA2s) are potent components of mammalian innate-immunity antibacterial mechanisms. sPLA2 enzymes attack bacteria by hydrolyzing bacterial membrane phospholipids, causing membrane disorganization and cell lysis. However, most Gram-negative bacteria are naturally resistant to sPLA2 Here we report a novel resistance mechanism to mammalian sPLA2 in Escherichia coli, mediated by a phospholipid repair system consisting of the lysophospholipid transporter LplT and the acyltransferase Aas in the cytoplasmic membrane. Mutation of the lplT or aas gene abolished bacterial lysophospholipid acylation activity and drastically increased bacterial susceptibility to the combined actions of inflammatory fluid components and sPLA2, resulting in bulk phospholipid degradation and loss of colony-forming ability. sPLA2-mediated hydrolysis of the three major bacterial phospholipids exhibited distinctive kinetics and deacylation of cardiolipin to its monoacyl-derivative closely paralleled bacterial death. Characterization of the membrane envelope in lplT- or aas-knockout mutant bacteria revealed reduced membrane packing and disruption of lipid asymmetry with more phosphatidylethanolamine present in the outer leaflet of the outer membrane. Moreover, modest accumulation of lysophospholipids in these mutant bacteria destabilized the inner membrane and rendered outer membrane-depleted spheroplasts much more sensitive to sPLA2 These findings indicated that LplT/Aas inactivation perturbs both the outer and inner membranes by bypassing bacterial membrane maintenance mechanisms to trigger specific interfacial activation of sPLA2 We conclude that the LplT/Aas system is important for maintaining the integrity of the membrane envelope in Gram-negative bacteria. Our insights may help inform new therapeutic strategies to enhance host sPLA2 antimicrobial activity.

Of Men Not Mice: Bactericidal/Permeability-Increasing Protein Expressed in Human Macrophages Acts as a Phagocytic Receptor and Modulates Entry and Replication of Gram-Negative Bacteria

Macrophages as immune cells prevent the spreading of pathogens by means of active phagocytosis and killing. We report here the presence of an antimicrobial protein, bactericidal/permeability-increasing protein (BPI) in human macrophages, which actively participates in engulfment and killing of Gram-negative pathogens. Our studies revealed increased expression of BPI in human macrophages during bacterial infection and upon stimulation with various pathogen-associated molecular patterns, viz., LPS and flagellin. Furthermore, during the course of an infection, BPI interacted with Gram-negative bacteria, resulting in enhanced phagocytosis and subsequent control of the bacterial replication. However, it was observed that bacteria which can maintain an active replicating niche (Salmonella Typhimurium) avoid the interaction with BPI during later stages of infection. On the other hand, Salmonella mutants, which cannot maintain a replicating niche, as well as Shigella flexneri, which quit the endosomal vesicle, showed interaction with BPI. These results propose an active role of BPI in Gram-negative bacterial clearance by human macrophages.

Regulation of interactions of endotoxin with host cells

Potent Toll-like receptor 4 (TLR4)-dependent cell activation by endotoxin requires lipopolysaccharide-binding protein (LBP) and CD14-dependent delivery of endotoxin to cells containing MD-2 and TLR4. We have used metabolically labeled [14C] meningococcal lipooligosaccharide (LOS), purified recombinant endotoxin-binding proteins, and cultured endothelial cells to better define protein: endotoxin intermediates key in cell activation in the absence of functional membrane (m) CD14. Protein:endotoxin complexes or aggregates ( agg) were purified by gel sieving and characterized by immunocapture and bio-assays. Cell activation closely correlated with LBP, albumin and soluble (s) CD14-dependent conversion of endotoxin agg (Mr≥ 20 × 106) to monomeric (M ~55 × 103) endotoxin:sCD14 complexes. Ordered interaction of LBP (+ albumin) and sCD14 withrLOS agg was required for the efficient formation of a bioactive endotoxin:sCD14 complex and potent cell activation. Increasing the ratio of LBP/sCD14 or addition of bactericidal/permeability-increasing protein (BPI) reduced accumulation of endotoxin:sCD14 complexes and instead yielded aggregates of endotoxin (Mr~1—20 × 106) containing LBP or BPI that were taken up by cells in a CD14- and TLR4-independent manner without inducing pro-inflammatory responses. These findings strongly suggest that host machinery linked to TLR4-dependent cellular activation or TLR4-independent cellular clearance of endotoxin selectively recognizes different protein:endotoxin complexes. At the outset of infection, the low concentrations of LBP present and absence of extracellular BPI favor formation of pro-inflammatory endotoxin:CD14 complexes. The mobilization of LBP and BPI that is triggered by inflammation directs endotoxin for clearance and hence resolution of endotoxin-triggered inflammation.

A Teleost Bactericidal Permeability-Increasing Protein Kills Gram-Negative Bacteria, Modulates Innate Immune Response, and Enhances Resistance against Bacterial and Viral Infection

Bactericidal/permeability-increasing protein (BPI) is an important factor of innate immunity that in mammals is known to take part in the clearance of invading Gram-negative bacteria. In teleost, the function of BPI is unknown. In the present work, we studied the function of tongue sole (Cynoglossus semilaevis) BPI, CsBPI. We found that CsBPI was produced extracellularly by peripheral blood leukocytes (PBL). Recombinant CsBPI (rCsBPI) was able to bind to a number of Gram-negative bacteria but not Gram-positive bacteria. Binding to bacteria led to bacterial death through membrane permeabilization and structural destruction, and the bound bacteria were more readily taken up by PBL. In vivo, rCsBPI augmented the expression of a wide arrange of genes involved in antibacterial and antiviral immunity. Furthermore, rCsBPI enhanced the resistance of tongue sole against bacterial as well as viral infection. These results indicate for the first time that a teleost BPI possesses immunoregulatory effect and plays a significant role in antibacterial and antiviral defense.

Bactericidal/permeability-increasing protein in host defense and its efficacy in the treatment of bacterial sepsis

The 55-kD bactericidal/permeability-increasing protein (BPI) is a neutrophil-derived polypeptide belonging to a family of lipid and endotoxin binding proteins. BPI is composed of two functionally distinct structural domains: a potently antibacterial and antiendotoxin ∼ 20-kD aminoterminal half, and an opsonic carboxy-terminal portion. In multiple animal models, a recombinant amino-terminal fragment of BPI (rBPI21) is nontoxic and protects against gram-negative bacteria and endotoxin. In humans, rBPI21 is also nontoxic and nonimmunogenic and has undergone phase II/III clinical trials with apparent therapeutic benefit.

Lactoferrin: an alternative view of its role in human biological fluids

Lactoferrin is a major component of biologically important mucosal fluids and of the specific granules of neutrophils. Understanding its biological function is essential for understanding neutrophil- and mucosal-mediated immunity. In this review, we reevaluate the in vivo functions of human lactoferrin (hLF) emphasizing in vivo studies and in vitro studies performed in biologically relevant fluids. We discuss the evidence in the literature that supports (or does not support) proposed roles for hLF in mucosal immunity and in neutrophil function. We argue that the current literature supports a microbiostatic role, but not a microbicidal role, for hLF in vivo. The literature also supports a role for hLF in inhibiting colonization and infection of epithelial surfaces by microorganisms and in protecting tissues from neutrophil-mediated damage. Using this information, we briefly discuss hLF in the context of the complex biological fluids in which it is found.

Campylobacter capsule and lipooligosaccharide confer resistance to serum and cationic antimicrobials

The innate immune system plays a critical role in host defense against mucosal bacteria. Campylobacter jejuni is a major cause of human gastroenteritis that usually resolves spontaneously within several days, suggesting that innate mechanisms are important to control the infection. However, the specific means by which this occurs is not well understood. While diarrheal isolates of C. jejuni usually are susceptible to human serum, we found that a systemic strain of C. jejuni, isolated from the cerebrospinal fluid of an infant with meningitis, is relatively more resistant to human serum, the Bactericidal/Permeability-Increasing Protein (BPI), an endogenous cationic antimicrobial protein, and the cationic peptide antibiotic polymyxin B. To test the hypothesis that the surface properties of this strain contributed to its ability to withstand these innate host defenses, we constructed isogenic mutants in capsule (kpsM) and lipooligosaccharide (waaF) and complemented these mutants by insertion of the complementation construct in trans into hipO, a chromosomal locus. We found that capsule expression was essential for serum resistance, whereas lipooligosaccharide played no substantial role. In contrast, the lipooligosaccharide mutant showed increased sensitivity to polymyxin B, α-defensins, cathelicidins, and BPI. These findings suggest that the polysaccharides of C. jejuni strains contribute differently to resistance against host innate immunity; whereby capsule is more important for resisting human complement and lipooligosaccharide is more important for protection against killing mediated by cationic antimicrobial peptides and proteins.

Neutrophil antimicrobial proteins enhance Shigella flexneri adhesion and invasion

Shigella flexneri is an enteric pathogen that causes massive inflammation and destruction of the human intestinal epithelium. Neutrophils are the first cells of the innate immune system recruited to the site of infection. These cells can attack microbes by phagocytosis, Neutrophil Extracellular Trap (NET) formation and degranulation. Here, we investigated how neutrophil degranulation affects virulence and show that exposure of Shigella to granular proteins enhances infection of epithelial cells. During this process, cationic granular proteins bind to the Shigella surface causing increased adhesion which ultimately leads to hyperinvasion. This effect is mediated by changes in the surface charge, since a lipopolysaccharide (LPS) mutant with a negative surface shows enhanced hyperinvasion compared with wild-type Shigella. We propose that Shigella evolved to use host defence molecules to enhance its virulence and subvert the innate immune system.

Edema toxin impairs anthracidal phospholipase A2 expression by alveolar macrophages

Bacillus anthracis, the etiological agent of anthrax, is a spore-forming Gram-positive bacterium. Infection with this pathogen results in multisystem dysfunction and death. The pathogenicity of B. anthracis is due to the production of virulence factors, including edema toxin (ET). Recently, we established the protective role of type-IIA secreted phospholipase A2 (sPLA2-IIA) against B. anthracis. A component of innate immunity produced by alveolar macrophages (AMs), sPLA2-IIA is found in human and animal bronchoalveolar lavages at sufficient levels to kill B. anthracis. However, pulmonary anthrax is almost always fatal, suggesting the potential impairment of sPLA2-IIA synthesis and/or action by B. anthracis factors. We investigated the effect of purified ET and ET-deficient B. anthracis strains on sPLA2-IIA expression in primary guinea pig AMs. We report that ET inhibits sPLA2-IIA expression in AMs at the transcriptional level via a cAMP/protein kinase A–dependent process. Moreover, we show that live B. anthracis strains expressing functional ET inhibit sPLA2-IIA expression, whereas ET-deficient strains induced this expression. This stimulatory effect, mediated partly by the cell wall peptidoglycan, can be counterbalanced by ET. We conclude that B. anthracis down-regulates sPLA2-IIA expression in AMs through a process involving ET. Our study, therefore, describes a new molecular mechanism implemented by B. anthracis to escape innate host defense. These pioneering data will provide new molecular targets for future intervention against this deathly pathogen.

All mammals are susceptible to infection by Bacillus anthracis, the etiological agent of anthrax. Infection can occur either accidentally or as a potential consequence of a terrorism threat. Pulmonary infection is the most life-threatening form of the disease, causing a near 100% mortality. Despite appropriate therapy, all forms of infection may progress to fatal systemic anthrax, characterized by sepsis and respiratory failure. Thus, it is important to understand the mechanisms of host defense against B. anthracis. We have previously shown that alveolar macrophages produce an enzyme involved in innate defense that can kill B. anthracis: the enzyme is known as secreted phospholipase A2-IIA (sPLA2-IIA). The alveolar macrophage is one of the first cell types to come in contact with B. anthracis. In this study, we show that live B. anthracis spores stimulate the synthesis of sPLA2-IIA, this stimulation being counterbalanced by the inhibitory effect of the edema toxin produced by germinated spores and bacilli. Our study suggests that inhibition of sPLA2-IIA synthesis by edema toxin is a mechanism by which B. anthracis can escape innate host defense. These pioneering data provide new molecular targets for future intervention against this deadly pathogen.

Expression of bactericidal/permeability-increasing protein requires C/EBP epsilon

Bactericidal/permeability-increasing protein (BPI) is a 55-kd cationic protein found mainly in neutrophil primary granules. BPI shows cytotoxicity against Gram-negative bacteria. In this study, we studied the role of a myeloid-specific transcription factor, CCAAT/enhancer binding protein epsilon (C/EBP epsilon), in the regulation of BPI gene expression. A patient with neutrophil-specific granule deficiency with a homozygous inactivating mutation in the CEBP epsilon gene showed severely impaired expression of both BPI messenger RNA (mRNA) and BPI protein. Both U937 and NB4 cells treated with 10-7 M all-trans retinoic acid (ATRA) for 6 days displayed increased levels of BPI protein and accompanying up-regulated C/EBP epsilon expression. Chromatin-immunoprecipitation analysis and electrophoretic mobility shift assays revealed binding of the C/EBP epsilon protein to the C/EBP-binding site in the BPI gene promoter. U937 cells stably transfected with a zinc-inducible C/EBP epsilon expression vector showed a 30-fold increase in BPI mRNA levels compared with cells transfected with control empty vector after culturing for 48 hours with 100 microM ZnSO4. BPI mRNA expression was severely reduced in the bone marrow of C/EBP epsilon-deficient mice compared with wild-type mice. Expression of BPI in human cord blood cells was increased by incubation with 10-7 MATRA for 48 hours. These results demonstrate the requirement for C/EBP epsilon in mediating BPI gene expression in myeloid cells in vitro and in vivo.

A Novel Role for the Bactericidal/Permeability Increasing Protein in Interactions of Gram-Negative Bacterial Outer Membrane Blebs with Dendritic Cells

The bactericidal/permeability-increasing protein (BPI) is thought to play an important role in killing and clearance of Gram-negative bacteria and the neutralization of endotoxin. A possible role for BPI in clearance of cell-free endotoxin has also been suggested based on studies with purified endotoxin aggregates and blood monocytes. Because the interaction of BPI with cell-free endotoxin, during infection, occurs mainly in tissue and most likely in the form of shed bacterial outer membrane vesicles ("blebs"), we examined the effect of BPI on interactions of metabolically labeled ([(14)C]-acetate) blebs purified from Neisseria meningitidis serogroup B with either human monocyte-derived macrophages or monocyte-derived dendritic cells (MDDC). BPI produced a dose-dependent increase (up to 3-fold) in delivery of (14)C-labeled blebs to MDDC, but not to monocyte-derived macrophages in the presence or absence of serum. Both, fluorescently labeled blebs and BPI were internalized by MDDC under these conditions. The closely related LPS-binding protein, in contrast to BPI, did not increase association of the blebs with MDDC. BPI-enhanced delivery of the blebs to MDDC did not increase cell activation but permitted CD14-dependent signaling by the blebs as measured by changes in MDDC morphology, surface expression of CD80, CD83, CD86, and MHC class II and secretion of IL-8, RANTES, and IP-10. These findings suggest a novel role of BPI in the interaction of bacterial outer membrane vesicles with dendritic cells that may help link innate immune recognition of endotoxin to Ag delivery and presentation.

The bactericidal/permeability-increasing protein (BPI) in infection and inflammatory disease

Gram-negative bacteria (GNB) and their endotoxin present a constant environmental challenge. Endotoxins can potently signal mobilization of host defenses against invading GNB but also potentially induce severe pathophysiology, necessitating controlled initiation and resolution of endotoxin-induced inflammation to maintain host integrity. The bactericidal/permeability-increasing protein (BPI) is a pluripotent protein expressed, in humans, mainly neutrophils. BPI exhibits strong antimicrobial activity against GNB and potent endotoxin-neutralizing activity. BPI mobilized with neutrophils in response to invading GNB can promote intracellular and extracellular bacterial killing, endotoxin neutralization and clearance, and delivery of GNB outer membrane antigens to dendritic cells. Tissue expression by dermal fibroblasts and epithelia could further amplify local levels of BPI and local interaction with GNB and endotoxin, helping to constrain local tissue infection and inflammation and prevent systemic infection and systemic inflammation. This review article focuses on the structural and functional properties of BPI with respect to its contribution to host defense during GNB infections and endotoxin-induced inflammation and the genesis of autoantibodies against BPI that can blunt BPI activity and potentially contribute to chronic inflammatory disease.

Basis for the failure of Francisella tularensis lipopolysaccharide to prime human polymorphonuclear leukocytes

Francisella tularensis is the intracellular gram-negative coccobacillus that causes tularemia, and its virulence and infectiousness make it a potential agent of bioterrorism. Previous studies using mononuclear leukocytes have shown that the lipopolysaccharide (LPS) of F. tularensis is neither a typical proinflammatory endotoxin nor an endotoxin antagonist. This inertness suggests that F. tularensis LPS does not bind host LPS-sensing molecules such as LPS-binding protein (LBP). Using priming of the polymorphonuclear leukocyte (PMN) oxidase as a measure of endotoxicity, we found that F. tularensis live vaccine strain LPS did not behave like either a classic endotoxin or an endotoxin antagonist in human PMNs, even when the concentration of LBP was limiting. Furthermore, F. tularensis LPS did not compete with a radiolabeled lipooligosaccharide from Neisseria meningitidis for binding to LBP or to the closely related PMN granule protein, bactericidal/permeability-increasing protein. Our results suggest that the inertness of F. tularensis LPS and the resistance of F. tularensis to oxygen-independent PMN killing may result from the inability of F. tularensis LPS to be recognized by these important LPS-sensing molecules of the innate immune system.

Synergy between extracellular group IIA phospholipase A2 and phagocyte NADPH oxidase in digestion of phospholipids of Staphylococcus aureus ingested by human neutrophils

Acute inflammatory responses to invading bacteria such as Staphylococcus aureus include mobilization of polymorphonuclear leukocytes (PMN) and extracellular group IIA phospholipase A2 (gIIA-PLA2). Although accumulating coincidentally, the in vitro anti-staphylococcal activities of PMN and gIIA-PLA2 have thus far been studied separately. We now show that degradation of S. aureus phospholipids during and after phagocytosis by human PMN requires the presence of extracellular gIIA-PLA2. The concentration of extracellular gIIA-PLA2 required to produce bacterial digestion was reduced 10-fold by PMN. The effects of added gIIA-PLA2 were greater when present before phagocytosis but even apparent when added after S. aureus were ingested by PMN. Related group V and X PLA2, which are present within PMN granules, do not contribute to bacterial phospholipid degradation during and after phagocytosis even when added at concentrations 30-fold higher than that needed for action of the gIIA-PLA2. The action of added gIIA-PLA2 required catalytically active gIIA-PLA2 and, in PMN, a functional NADPH oxidase but not myeloperoxidase. These findings reveal a novel collaboration between cellular oxygen-dependent and extracellular oxygen-independent host defense systems that may be important in the ultimate resolution of S. aureus infections.

In Vivo Protective Role of Human Group IIA Phospholipase A2against Experimental Anthrax

Anthrax is an acute disease caused by Bacillus anthracis. Some animal species are relatively resistant to anthrax infection. This trait has been correlated to the extent of the local inflammatory reaction, suggesting innate immunity to be the first line of defense against B. anthracis infection in nonimmunized hosts. Group IIA secreted phospholipase A2 (sPLA2-IIA) is produced in particular by macrophages and possesses potent antibacterial activity especially against Gram-positive bacteria. We have previously shown in vitro that sPLA2-IIA kills both germinated B. anthracis spores and encapsulated bacilli. Here we show that sPLA2-IIA plays in vivo a protective role against experimental anthrax. Transgenic mice expressing human sPLA2-IIA are resistant to B. anthracis infection. In addition, in vivo administration of recombinant human sPLA2-IIA protects mice against B. anthracis infection. The protective effect was observed both with a highly virulent encapsulated nontoxinogenic strain and a wild-type encapsulated toxinogenic strain, showing that toxemia did not hinder the sPLA2-IIA-afforded protection. sPLA2-IIA, a natural component of the immune system, may thus be considered a novel therapeutic agent to be used in adjunct with current therapy for treating anthrax. Its anthracidal activity would be effective even against strains resistant to multiple antibiotics.

[Secreted phospholipases A2 (sPLA2): friends or foes? Are they actors in antibacterial and anti-HIV resistance?]

In this paper the authors update on the deletereous or beneficial roles of human and animal secretory phospholipases A2 (sPLA2). Although human sPLA2-IIA (inflammatory) was initially thought as a foe because its pathogenic implication in sepsis, multiorganic failure or other related syndromes, recent data indicates its role in in the antiinfectious host resistance. Thus, sPLA2-IIA exhibits potent bactericidal activities against gram-negative and gram-positive (in this case, together with other endogenous inflammatory factors) bacteria. Surprisingly, human sPLA-IIA does not show in vitro anti-human immunodeficiency virus (HIV) activity, whilst several sPLA2-IA isolated from bee and serpent venons do it: this is the case for crotoxin, a sPLA2-IA isolated from the venon of Crotalus durissus terrificus (sPLA2-Cdt). The mechanism for the in vitro anti-HIV activity of sPLA2-Cdt (inhibition of Gag p24) appears to be related to the ability of the drug to desestabilize ancorage (heparans) and fusion (cholesterol) receptors on HIV target cells.

Autoantibodies against the bactericidal/permeability-increasing protein from inflammatory bowel disease patients can impair the antibiotic activity of bactericidal/permeability-increasing protein

Bactericidal/permeability-increasing protein (BPI) is an antineutrophil cytoplasmic autoantibody (ANCA) target antigen in inflammatory bowel disease (IBD). The aim of this study was to characterize binding regions of BPI-autoantibodies and to analyze their ability to block the antibiotic effect of BPI. Sera of 24 ulcerative colitis and Crohn's disease patients were examined in indirect immuno-fluorescence, ANCA enzyme-linked immunosorbent assay (ELISA), and by epitope mapping with 13mer peptides and Western blot for presence of BPI-autoantibodies. IgG preparations were used to determine inhibition of BPI's antimicrobial function by BPI-autoantibodies in a bacterial growth inhibition assay. BPI-autoantibodies were detected by ELISA in 18/24 patients. Epitope mapping and western blotting revealed an additional 3 patients with BPI-autoantibodies. IgG preparations of all patients with Crohn's disease and 9 of 12 ulcerative colitis patients could inhibit the antibiotic function of BPI in vitro as compared with healthy control subjects. Inhibiting BPI-autoantibodies correlated with extraintestinal manifestations, peripheral blood leukocyte counts, and anemia. BPI-autoantibodies recognizing the N-terminal portion were associated with greater mucosal damage and intestinal extent of disease. BPI is a frequent target antigen of autoantibodies in ulcerative colitis and Crohn's disease. Inhibition of the antibiotic function mediated by the N-terminal region of BPI by these autoantibodies may contribute to a proinflammatory environment in IBD patients.

High bactericidal efficiency of type iia phospholipase A2 against Bacillus anthracis and inhibition of its secretion by the lethal toxin

There is a considerable body of evidence supporting the role of secretory type II-A phospholipase A(2) (sPLA(2)-IIA) as an effector of the innate immune response. This enzyme also exhibits bactericidal activity especially toward Gram-positive bacteria. In this study we examined the ability of sPLA(2)-IIA to kill Bacillus anthracis, the etiological agent of anthrax. Our results show that both germinated B. anthracis spores and encapsulated bacilli were sensitive to the bactericidal activity of recombinant sPLA(2)-IIA in vitro. In contrast, nongerminated spores were resistant. This bactericidal effect was correlated to the ability of sPLA(2)-IIA to hydrolyze bacterial membrane phospholipids. Guinea pig alveolar macrophages, the major source of sPLA(2)-IIA in an experimental model of acute lung injury, released enough sPLA(2)-IIA to kill extracellular B. anthracis. The production of sPLA(2)-IIA was significantly inhibited by B. anthracis lethal toxin. Human bronchoalveolar lavage fluids from acute respiratory distress syndrome patients are known to contain sPLA(2)-IIA; bactericidal activity against B. anthracis was detected in a high percentage of these samples. This anthracidal activity was correlated to the levels of sPLA(2)-IIA and was abolished by an sPLA(2)-IIA inhibitor. These results suggest that sPLA(2)-IIA may play a role in innate host defense against B. anthracis infection and that lethal toxin may help the bacteria to escape from the bactericidal action of sPLA(2)-IIA by inhibiting the production of this enzyme.

Antimicrobial proteins and peptides: anti-infective molecules of mammalian leukocytes

Phagocytic leukocytes are a central cellular element of innate-immune defense in mammals. Over the past few decades, substantial progress has been made in defining the means by which phagocytes kill and dispose of microbes. In addition to the generation of toxic oxygen radicals and nitric oxide, leukocytes deploy a broad array of antimicrobial proteins and peptides (APP). The majority of APP includes cationic, granule-associated (poly)peptides with affinity for components of the negatively charged microbial cell wall. Over the past few years, the range of cells expressing APP and the potential roles of these agents have further expanded. Recent advances include the discovery of two novel families of mammalian APP (peptidoglycan recognition proteins and neutrophil gelatinase-associated lipocalin), that the oxygen-dependent and oxygen-independent systems are inextricably linked, that APP can be deployed in the context of novel subcellular organelles, and APP and the Toll-like receptor system interact. From a clinical perspective, congeners of several of the APP have been developed as potential therapeutic agents and have entered clinical trials with some evidence of benefit.

Identification of a novel Fc gamma RIIIa alpha-associated molecule that contains significant homology to porcine cathelin

The following studies are the first to demonstrate the association of porcine FcgammaRIIIaalpha with a molecule that contains significant homology to the cathelin family of antimicrobial proteins. We performed immunoprecipitation of the porcine FcgammaRIIIaalpha multisubunit complex from Brij 96 lysates of polymorphonuclear leukocytes using the G7 mAb, which binds to FcgammaRIIIaalpha on the surface of porcine NK cells and phagocytes. Previous results indicate that the transmembrane alpha subunit of the FcgammaRIIIa complex is associated with the gamma subunit on the surface of porcine polymorphonuclear leukocytes and with several other unique proteins that surface iodinate and migrate at approximately 15, 20, and 25 kDa when analyzed by reducing SDS-PAGE. Through characterization of the porcine FcgammaRIIIa complex, we identified the 15-kDa molecule as a unique FcgammaR-associated protein that has not been described in other systems. We now report an association between FcgammaRIIIaalpha and a 15-kDa molecule that shares homology to cathelin, a protein of undetermined function initially identified in porcine leukocytes. A domain with a high degree of homology to cathelin is found in the proregions of a family of antibiotic proteins referred to as cathelicidins. The results of our studies indicate the presence of a novel FcgammaRIIIa complex in the porcine system, and may provide new insights into the function of this antimicrobial protein homologue in relation to the variety of responses mediated through FcgammaRs.

BPI-ANCA of pediatric cystic fibrosis patients can impair BPI-mediated killing of E. coli DH5alpha in vitro

Gram-negative bacterial lung infections and chronic bacterial colonization are major threats for pediatric cystic fibrosis (CF) patients. Besides impeded mucociliary clearance, other mechanisms that contribute to increased susceptibility to infections are presumed. The bactericidal/permeability-increasing protein (BPI), which is delivered by neutrophil granulocytes and mucosal epithelial cells, is one of the most potent innate antibiotics against Gram-negative bacteria and endotoxin. Antineutrophil cytoplasmic autoantibodies against BPI (BPI-ANCA) have been found in up to 90% of CF patients, and titers correlated inversely with lung function parameters. As major pulmonary damage is mediated by Gram-negative bacteria and their products, the question was raised as to whether BPI-ANCA can inhibit the antibiotic function of BPI in these patients. Sera of 23 pediatric CF patients were analyzed for the presence of BPI-ANCA by indirect immunofluorescence, ELISA, epitope mapping, and Western blotting. Patients' IgG were tested in a bacterial growth inhibition assay with recombinant BPI (rBPI) and an amino-terminal fragment of BPI (rBPI(21)) that retains antibiotic activity for inhibition of the antibiotic function of BPI against E. coli DH5alpha in vitro. BPI was recognized by 21 of 23 patients' sera in our detection assays. Thirteen of 23 patients' BPI-ANCA (56%) could inhibit the antibiotic function in vitro. Moreover, epitope mapping over the whole BPI sequence revealed that more patients' BPI-ANCA recognize the amino-terminal part of BPI than can be detected by ELISA. Thus, in pediatric CF patients, BPI-ANCA may contribute to diminished bacterial clearance by inhibiting the antibiotic function of BPI.

Bactericidal properties of group IIa secreted phospholipase A2 against Pseudomonas aeruginosa clinical isolates

It has been shown that human group IIa secreted phospholipase A(2) (sPLA(2)), found at high levels in inflammatory fluids, displays direct bactericidal properties against Gram-positive bacteria, while activity against Gram-negative bacteria requires the complement system or additional co-factors produced by neutrophils. Pseudomonas aeruginosa, an increasingly prevalent opportunistic human pathogen, is the most common Gram-negative rod found in cystic fibrosis lung infections, where it is associated with an inflammatory environment. Because murine intestinal group II sPLA(2) produced by Paneth cells has been shown to be directly bactericidal against Gram-negative bacteria, IIa sPLA(2) activity against P. aeruginosa clinical isolates was evaluated and provides the first evidence that the enzyme can be fully bactericidal in a concentration- and time-dependent manner against Gram-negative rods. Furthermore, it was demonstrated that these bactericidal properties were unaffected by high protein and salt concentrations, as observed in cystic fibrosis secretions, and that bacterial killing paralleled phospholipid hydrolysis. Finally, no cytotoxicity was observed when IIa sPLA(2) was incubated with human pulmonary cells, highlighting its potential use to synergize bactericidal antibiotics by promoting sublethal alterations of the bacterial cell wall.

Protection from endotoxemia by adenoviral-mediated gene transfer of human bactericidal/permeability-increasing protein

Sepsis represents a growing concern in high-risk patients and there has been a lack of effective preventives and therapies. Bacterial/permeability increasing protein (BPI) is a human neutrophil granule-associated defense molecule specific for Gram-negative bacteria and their products. To develop a BPI-transgene-based prophylactic or therapeutic modality, we have developed a recombinant, replication-deficient adenoviral vector expressing full-length human BPI protein (AdhBPI). The expression of BPI is under control of a murine cytomegalovirus (CMV) promoter. Using in vitro and in vivo systems, AdhBPI-mediated gene transfer led to extracellular secretion of BPI protein, which effectively neutralized endotoxin (lipopolysaccharide [LPS]) and markedly reduced the production of proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and macrophage inflammatory protein 2 (MIP-2) by freshly isolated murine alveolar macrophages. By using a mouse model of nonlethal sepsis elicited with LPS, we demonstrated that in vivo gene transfer of BPI was able to markedly inhibit the effect of a large dose of LPS on cytokine responses when injected intraperitoneally. Furthermore, such in vivo BPI gene transfer also improved the survival of mice suffering from lethal septic shock elicited by intraperitoneal injection of d-galactosamine and LPS. Thus, our results suggest that human BPI gene transfer vector has the potential to be used as a therapeutic agent for septic conditions.

BPI-ANCA in transporter associated with antigen presentation (TAP) deficiency: possible role in susceptibility to Gram-negative bacterial infections

Although HLA class I expression is diminished in patients with defects in the transporter associated with antigen presentation (TAP), recurrent Gram-negative bacterial lung infections are found from childhood onwards. As MHC class II-mediated responses are normal, other mechanisms that contribute to susceptibility to infections are presumed. The bactericidal/permeability-increasing protein (BPI) is a potent neutrophil antibiotic that neutralizes endotoxin efficiently. As antineutrophil cytoplasmic autoantibodies (ANCA) against BPI were found in the majority of cystic fibrosis patients and correlate with disease severity we examined the prevalence of BPI-ANCA and their contribution to susceptibility to bacterial infections in six TAP-deficient patients. Although only two patients showed ANCA in indirect immunofluorescence, BPI-ANCA occurred in five of six patients in ELISA. Purified IgG from BPI-ANCA-positive sera (five of six) inhibited the antimicrobial function of BPI in vitro. Epitope mapping revealed binding sites not only on the C-terminal but also on the antibiotic N-terminal portion of BPI, indicating that short linear BPI peptide fragments may be long-lived enough to become immunogens. In conclusion, BPI-ANCA are associated strongly with TAP deficiency. Inhibition of the antimicrobial BPI function by BPI-ANCA demonstrates a possible mechanism of how autoantibodies may contribute to increased susceptibility for pulmonary Gram-negative bacterial infections by diminished bacterial clearance.

Receptors, mediators, and mechanisms involved in bacterial sepsis and septic shock

Bacterial sepsis and septic shock result from the overproduction of inflammatory mediators as a consequence of the interaction of the immune system with bacteria and bacterial wall constituents in the body. Bacterial cell wall constituents such as lipopolysaccharide, peptidoglycans, and lipoteichoic acid are particularly responsible for the deleterious effects of bacteria. These constituents interact in the body with a large number of proteins and receptors, and this interaction determines the eventual inflammatory effect of the compounds. Within the circulation bacterial constituents interact with proteins such as plasma lipoproteins and lipopolysaccharide binding protein. The interaction of the bacterial constituents with receptors on the surface of mononuclear cells is mainly responsible for the induction of proinflammatory mediators by the bacterial constituents. The role of individual receptors such as the toll-like receptors and CD14 in the induction of proinflammatory cytokines and adhesion molecules is discussed in detail. In addition, the roles of a number of other receptors that bind bacterial compounds such as scavenger receptors and their modulating role in inflammation are described. Finally, the therapies for the treatment of bacterial sepsis and septic shock are discussed in relation to the action of the aforementioned receptors and proteins.

Lipid mediator-induced expression of bactericidal/ permeability-increasing protein (BPI) in human mucosal epithelia

Epithelial cells which line mucosal surfaces are the first line of defense against bacterial invasion and infection. Recent studies have also indicated that epithelial cells contribute significantly to the orchestration of ongoing inflammatory processes. Here, we demonstrate that human epithelial cells express bactericidal/permeability-increasing protein (BPI), an antibacterial and endotoxin-neutralizing molecule previously associated with neutrophils. Moreover, we demonstrate that such BPI expression is transcriptionally regulated by analogs of endogenously occurring anti-inflammatory eicosanoids (aspirin-triggered lipoxins, ATLa). Initial studies to verify microarray analysis revealed that epithelial cells of wide origin (oral, pulmonary, and gastrointestinal mucosa) express BPI and each is similarly regulated by aspirin-triggered lipoxins. Studies aimed at localization of BPI revealed that such expression occurs on the cell surface of cultured epithelial cell lines and dominantly localizes to epithelia in human mucosal tissue. Functional studies employing a BPI-neutralizing anti-serum revealed that surface BPI blocks endotoxin-mediated signaling in epithelia and kills Salmonella typhimurium. These studies identify a previously unappreciated "molecular shield" for protection of mucosal surfaces against Gram-negative bacteria and their endotoxin.

The carboxyl-terminal domain of closely related endotoxin-binding proteins determines the target of protein-lipopolysaccharide complexes

The bactericidal/permeability increasing (BPI) and lipopolysaccharide (LPS)-binding (LBP) proteins are closely related two-domain proteins in which LPS binding is mediated by the NH(2)-terminal domain. To further define the role of the COOH-terminal domain of these proteins in delivery of LPS to specific host acceptors, we have compared interactions of LBP, BPI, LBP(N)-BPI(C) (NH(2)-terminal domain of LBP, COOH-terminal domain of BPI), and BPI(N)-LBP(C) with purified (3)H-LPS and, subsequently, with purified leukocytes and soluble (s)CD14. The COOH-terminal domain of LBP promotes delivery of LPS to CD14 on both polymorphonuclear leukocytes and monocytes resulting in cell activation. In the presence of Ca(2+) and Mg(2+), LBP and BPI each promote aggregation of LPS to protein-LPS aggregates of increased size (apparent M(r) > 20 x 10(6) Da), but only LPS associated with LBP and BPI(N)-LBP(C) is disaggregated in the presence of CD14. BPI and LBP(N)-BPI(C) promote apparently CD14-independent LPS association to monocytes without cell activation. These findings demonstrate that the carboxyl-terminal domain of these closely related endotoxin-binding proteins dictates the route and host responses to complexes they form with endotoxin.

Host defense functions of proteolytically processed and parent (unprocessed) cathelicidins of rabbit granulocytes

Members of the cathelicidin family are present in all mammals studied. Generally, these proteins contain a conserved N-terminal domain and a structurally and functionally divergent C-terminal region that expresses antibacterial or other activities when proteolytically released. Rabbit granulocytes produce CAP18, a cathelicidin that conforms to this structural and functional organization, and also 15-kDa protein isoforms (p15s) that share several key structural features with other cathelicidins but apparently do not undergo processing with release of an active peptide. To further define the importance of proteolysis in the antibacterial activities of these proteins, we have purified from granulocytes proCAP18, its C-terminal peptide (CAP18p), and two p15 isoforms to apparent homogeneity. Of these four polypeptides, only CAP18p was independently cytotoxic to encapsulated Escherichia coli (90% inhibitory concentration, approximately 600 nM) but it was approximately 50-fold less potent on a molar basis than the bactericidal/permeability-increasing protein (BPI). However, all four cathelicidin species, notably including proCAP18, exhibited antibacterial synergy with BPI, and the p15s also displayed synergy with CAP18p in the absence of BPI. Subnanomolar concentrations of proCAP18 blocked lipopolysaccharide-induced chemiluminescence of human leukocytes, showing a molar potency more than 100-fold greater than that of CAP18p ( approximately 20 nM) or BPI ( approximately 50 nM). Thus, while independent bactericidal activity of cathelicidins requires processing, other host-defense functions do not and are more potently expressed by the unprocessed protein than by the C-terminal peptide.

Susceptibilities of oral bacteria and yeast to mammalian cathelicidins

The effects of cathelicidins against oral bacteria and clinically important oral yeasts are not known. We tested the susceptibilities of Actinobacillus actinomycetemcomitans, Fusobacterium nucleatum, Porphyromonas gingivalis, Streptococcus sanguis, Candida krusei, Candida tropicalis and Candida albicans to the following cathelicidins: FALL39, SMAP29, and CAP18. SMAP29 and CAP18 were antimicrobial, whereas FALL39 did not exhibit antimicrobial activity. Future studies are needed to determine the potential use of these antimicrobial peptides in prevention and treatment of oral infections.

The antibacterial properties of secreted phospholipases A(2)

There is a considerable body of evidence to support the antibacterial properties of the group IIa phospholipase A(2) as an important physiological function. This enzyme is able to act as an acute phase protein and may be part of the innate defence system of the body, acting in concert with other antibacterial proteins and peptides. The enzyme is most effective against Gram-positive bacteria whereas penetration of the lipopolysaccharide coat of Gram-negative bacteria requires bactericidal/permeability-increasing protein (BPI) as an additional permeabilizing factor. The global cationic nature of this protein (pI>10.5) appears to facilitate penetration of the anionic bacterial cell wall. In addition, the considerable preference of the enzyme for anionic phospholipid interfaces provides specificity toward anionic bacterial membranes as opposed to zwitterionic eucaryotic cell membranes.

Antimicrobial proteins and peptides of blood: templates for novel antimicrobial agents

The innate immune system provides rapid and effective host defense against microbial invasion in a manner that is independent of prior exposure to a given pathogen.1 It has long been appreciated that the blood contains important elements that mediate rapid responses to infection. Thus, anatomic compartments with ample blood supply are less frequently infected and recover more readily once infected, whereas regions with poor perfusion are prone to severe infection and may require surgical débridement. Blood-borne innate immune mediators are either carried in circulating blood cells (ie, leukocytes and platelets) or in plasma after release from blood cells or on secretion by the liver.

Antimicrobial proteins and peptides of blood: templates for novel antimicrobial agents

The innate immune system provides rapid and effective host defense against microbial invasion in a manner that is independent of prior exposure to a given pathogen.1 It has long been appreciated that the blood contains important elements that mediate rapid responses to infection. Thus, anatomic compartments with ample blood supply are less frequently infected and recover more readily once infected, whereas regions with poor perfusion are prone to severe infection and may require surgical débridement. Blood-borne innate immune mediators are either carried in circulating blood cells (ie, leukocytes and platelets) or in plasma after release from blood cells or on secretion by the liver.

Autoantibodies directed against bactericidal/permeability-increasing protein in patients with cystic fibrosis: association with microbial respiratory tract colonization

BACKGROUND

Cystic fibrosis (CF) is associated with the appearance of serum autoantibodies directed against bactericidal/permeability-increasing protein (BPI).

OBJECTIVES

To determine the age-specific seroprevalence rates of anti-BPI-IgG and IgA in a population of patients with CF and to correlate anti-BPI antibody concentrations with microbial respiratory tract colonization and pulmonary function variables at the time of serum sampling and 6 years thereafter.

METHODS

Determination of BPI antibodies of the IgG and IgA isotypes using a commercial enzyme-linked immunosorbent assay in sera of a CF serum bank of 1992; correlation of anti-BPI antibody concentrations with age, clinical score, pulmonary function variables in 1992 and 1998, total serum immunoglobulin isotype concentrations and respiratory tract colonization with Pseudomonas aeruginosa and Aspergillus spp.

RESULTS

Seventy-one patients (age in 1992, 14.1 +/- 7.5 years) were studied. Reactivities for anti-BPI-IgG and IgA were found in 28 (39%) and 26 (37%) patients, respectively. The seroprevalence of anti-BPI-IgA, but not IgG, increased significantly with age. P. aeruginosa colonization was associated with elevated concentrations of anti-BPI-IgG (P = 0.003) and IgA (P = 0.037). There were significant negative correlations between pulmonary function variables (vital capacity, forced expiratory volume in 1 s) in 1992 and 1998, respectively, and concentrations of anti-BPI-IgG or IgA in a multiple regression analysis. Anti-BPI-IgG, but not IgA, remained significantly associated with P. aeruginosa colonization (P = 0.006) and with reduced vital capacity (P = 0.01) in 1998 after correction for total serum isotype concentration.

CONCLUSIONS

Anti-BPI-IgG are strongly associated with concurrent P. aeruginosa colonization and with long term restrictive pulmonary function abnormalities.

Phospholipid synthesis by Staphylococcus aureus during (Sub)Lethal attack by mammalian 14-kilodalton group IIA phospholipase A2

Killing of gram-positive bacteria by mammalian group IIA phospholipases A2 (PLA2) requires the catalytic activity of the enzyme. However, nearly complete degradation of the phospholipids can occur with little effect on bacterial viability, suggesting that PLA2-treated bacteria can biosynthetically replace phospholipids that are lost due to PLA2 action. In the presence of albumin, phospholipid degradation products are quantitatively sequestered extracellularly. In the absence of albumin, the bacteria retain and substantially reutilize the phospholipid breakdown products and survive an otherwise lethal dose of PLA2. PLA2-treated bacteria also continue to incorporate sodium [2-(14)C]acetate into phospholipids, suggesting that the bacteria are attempting to repair the damaged membranes by de novo synthesis of phospholipids. To determine whether PLA2 action also triggers activation of bacterial lipolytic enzymes, the effects of nisin and PLA2 on the degradation of S. aureus lipids were compared. In contrast to nisin treatment, PLA2 treatment does not stimulate endogenous phospholipase activity in S. aureus. These findings show that S. aureus responds to PLA2 attack by continued phospholipid (re)synthesis by both de novo and salvage pathways. The fate of PLA2-treated S. aureus therefore appears to depend on the relative rates of phospholipid degradation and synthesis.

Deacylation of lipopolysaccharide in whole Escherichia coli during destruction by cellular and extracellular components of a rabbit peritoneal inflammatory exudate

Deacylation of purified lipopolysaccharides (LPS) markedly reduces its toxicity toward mammals. However, the biological significance of LPS deacylation during infection of the mammalian host is uncertain, particularly because the ability of acyloxyacyl hydrolase, the leukocyte enzyme that deacylates purified LPS, to attack LPS residing in the bacterial cell envelope has not been established. We recently showed that the cellular and extracellular components of a rabbit sterile inflammatory exudate are capable of extensive and selective removal of secondary acyl chains from purified LPS. We now report that LPS as a constituent of the bacterial envelope is also subject to deacylation in the same inflammatory setting. Using Escherichia coli LCD25, a strain that exclusively incorporates radiolabeled acetate into fatty acids, we quantitated LPS deacylation as the loss of radiolabeled secondary (laurate and myristate) and primary fatty acids (3-hydroxymyristate) from the LPS backbone. Isolated mononuclear cells and neutrophils removed 50% and 20-30%, respectively, of the secondary acyl chains of the LPS of ingested whole bacteria. When bacteria were killed extracellularly during incubation with ascitic fluid, no LPS deacylation occurred. In this setting, the addition of neutrophils had no effect, but addition of mononuclear cells resulted in removal of >40% of the secondary acyl chains by 20 h. Deacylation of LPS was always restricted to the secondary acyl chains. Thus, in an inflammatory exudate, primarily in mononuclear phagocytes, the LPS in whole bacteria undergoes substantial and selective acyloxyacyl hydrolase-like deacylation, both after phagocytosis of intact bacteria and after uptake of LPS shed from extracellularly killed bacteria. This study demonstrates for the first time that the destruction of Gram-negative bacteria by a mammalian host is not restricted to degradation of phospholipids, protein, and RNA, but also includes extensive deacylation of the envelope LPS.

Deacylation of purified lipopolysaccharides by cellular and extracellular components of a sterile rabbit peritoneal inflammatory exudate

The extent to which the mammalian host is capable of enzymatic degradation and detoxification of bacterial lipopolysaccharides (LPS) is still unknown. Partial deacylation of LPS by the enzyme acyloxyacyl hydrolase (AOAH) provides such a mechanism, but its participation in the disposal of LPS under physiological conditions has not been established. In this study, deacylation of isolated radiolabeled LPS by both cellular and extracellular components of a sterile inflammatory peritoneal exudate elicited in rabbits was examined ex vivo. AOAH-like activity, tested under artificial conditions (pH 5.4, 0.1% Triton X-100), was evident in all components of the exudate (mononuclear cells [MNC] > polymorphonuclear leukocytes [PMN] > inflammatory [ascitic] fluid [AF]). Under more physiological conditions, in a defined medium containing purified LPS-binding protein, the LPS-deacylating activity of MNC greatly exceeded that of PMN. In AF, MNC (but not PMN) also produced rapid and extensive CD14-dependent LPS deacylation. Under these conditions, almost all MNC-associated LPS underwent deacylation within 1 h, a rate greatly exceeding that previously found in any cell type. The remaining extracellular LPS was more slowly subject to CD14-independent deacylation in AF. Quantitative analysis showed a comparable release of laurate and myristate but no release of 3-hydroxymyristate, consistent with an AOAH-like activity. These findings suggest a major role for CD14(+) MNC and a secondary role for AF in the deacylation of cell-free LPS at extravascular inflammatory sites.

Cell-wall determinants of the bactericidal action of group IIA phospholipase A2 against Gram-positive bacteria

We have shown previously that a group IIA phospholipase A2 (PLA2) is responsible for the potent bactericidal activity of inflammatory fluids against many Gram-positive bacteria. To exert its antibacterial activity, this PLA2 must first bind and traverse the bacterial cell wall to produce the extensive degradation of membrane phospholipids (PL) required for bacterial killing. In this study, we have examined the properties of the cell-wall that may determine the potency of group IIA PLA2 action. Inhibition of bacterial growth by nutrient deprivation or a bacteriostatic antibiotic reversibly increased bacterial resistance to PLA2-triggered PL degradation and killing. Conversely, pretreatment of Staphylococcus aureus or Enterococcus faecium with subinhibitory doses of beta-lactam antibiotics increased the rate and extent of PL degradation and/or bacterial killing after addition of PLA2. Isogenic wild-type (lyt+) and autolysis-deficient (lyt-) strains of S. aureus were equally sensitive to the phospholipolytic action of PLA2, but killing and lysis was much greater in the lyt+ strain. Thus, changes in cell-wall cross-linking and/or autolytic activity can modulate PLA2 action either by affecting enzyme access to membrane PL or by the coupling of massive PL degradation to autolysin-dependent killing and bacterial lysis or both. Taken together, these findings suggest that the bacterial envelope sites engaged in cell growth may represent preferential sites for the action and cytotoxic consequences of group IIA PLA2 attack against Gram-positive bacteria.

Interleukin-8 controls bacterial transepithelial translocation at the cost of epithelial destruction in experimental shigellosis

In shigellosis, the network of cellular interactions mediated by a balance of pro- and anti-inflammatory cytokines or chemokines is clearly tipped toward acute destructive inflammation of intestinal tissues by the bacterial invader. This work has addressed the role played by interleukin-8 (IL-8) in a rabbit model of intestinal invasion by Shigella flexneri. IL-8, which is largely produced by the epithelial cells themselves, appears to be a major mediator of the recruitment of polymorphonuclear leukocytes (PMNs) to the subepithelial area and transmigration of these cells through the epithelial lining. Neutralization of IL-8 function by monoclonal antibody WS-4 caused a decrease in the amount of PMNs streaming through the lamina propria and the epithelium, thus significantly attenuating the severity of epithelial lesions in areas of bacterial invasion. These findings are in agreement with our previous work (31). In contrast to the PMNs, the bacteria displayed increased transepithelial translocation, as well as overgrowth in the lamina propria and increased passage into the mesenteric blood. By mediating eradication of bacteria at their epithelial entry site, although at the cost of severe epithelial destruction, IL-8 therefore appears to be a key chemokine in the control of bacterial translocation.

Mobilization of potent plasma bactericidal activity during systemic bacterial challenge. Role of group IIA phospholipase A2

Extracellular mobilization of Group IIA 14-kD phospholipase A2 (PLA2) in glycogen-induced rabbit inflammatory peritoneal exudates is responsible for the potent bactericidal activity of the inflammatory fluid toward Staphylococcus aureus (1996. J. Clin. Invest. 97:250-257). Because similar levels of PLA2 are induced in plasma during systemic inflammation, we have tested whether this gives rise to plasma bactericidal activity not present in resting animals. Baboons were injected intravenously (i.v.) with a lethal dose of Escherichia coli and plasma or serum was collected before and at hourly intervals after injection. After infusion of bacteria, PLA2 levels in plasma and serum rose > 100-fold over 24 h to approximately 1 microg PLA2/ml. Serum collected at 24 h possessed potent bactericidal activity toward S. aureus, Streptococcus pyogenes, and encapsulated E. coli not exhibited by serum collected from unchallenged animals. Bactericidal activity toward S. aureus and S. pyogenes was nearly completely blocked by a monoclonal antibody to human Group IIA PLA2 and addition of purified human Group IIA PLA2 to prechallenge serum conferred potent antistaphylococcal and antistreptococcal activity equal to that of the 24 h post-challenge serum. PLA2-dependent bactericidal activity was enhanced approximately 10x by factor(s) present constitutively in serum or plasma. Bactericidal activity toward encapsulated E. coli was accompanied by extensive bacterial phospholipid degradation mediated, at least in part, by the mobilized Group IIA PLA2 but depended on the action of other bactericidal factors in the 24-h serum. These findings further demonstrate the contribution of Group IIA PLA2 to the antibacterial potency of biological fluids and suggest that mobilization of this enzyme during inflammation may play an important role in host defense against invading bacteria.

The role of protegrins and other elastase-activated polypeptides in the bactericidal properties of porcine inflammatory fluids

The mammalian host response to infection includes the production and secretion of antimicrobial peptides from phagocytes and epithelial cells. Protegrins, a group of broadly microbicidal peptides isolated originally from porcine neutrophil lysates, were found to be stored as inactive proforms in porcine neutrophil granules but could be activated extracellularly by neutrophil elastase. We assessed the biological role of protegrins and other elastase-activated polypeptides in the microbicidal activity of neutrophil secretions and inflammatory fluids. When stimulated with phorbol myristate acetate (PMA), neutrophils generated stable microbicidal activity against both Escherichia coli and Listeria monocytogenes under normal-salt conditions and in the presence of 0 to 10% serum. The generation of these antimicrobial substances was dependent on neutrophil elastase, since it was inhibited by 1 mM N-methoxysuccinyl-Ala-Ala-Pro-Val chloromethyl ketone when it was present during activation, but not when this inhibitor was added afterwards. However, elastase-dependent activation of proprotegrins to protegrins in PMA-stimulated neutrophils was not inhibited by the presence of 1 to 2% serum. Porcine neutrophils also released antibacterial activity during phagocytosis of latex beads, and this too was dependent in large part on elastase-activated polypeptides, including protegrins. Moreover, protegrins were found at bactericidal concentrations in cell-free abscess fluid from naturally infected pigs. Taken together, these studies show that protegrins and other elastase-activated polypeptides are important stable antibacterial factors in porcine neutrophil secretions. The potential host defense role of elastase as an activating enzyme for the precursors of microbicidal peptides must be taken into account when therapeutic inhibitors of neutrophil elastase are evaluated for clinical use as anti-inflammatory agents.