Limulus antilipopolysaccharide factor protects rabbits from meningococcal endotoxin shock

Host Defense Proteins and Peptides with Lipopolysaccharide-Binding Activity from Marine Invertebrates and Their Therapeutic Potential in Gram-Negative Sepsis

Sepsis is a life-threatening complication of an infectious process that results from the excessive and uncontrolled activation of the host's pro-inflammatory immune response to a pathogen. Lipopolysaccharide (LPS), also known as endotoxin, which is a major component of Gram-negative bacteria's outer membrane, plays a key role in the development of Gram-negative sepsis and septic shock in humans. To date, no specific and effective drug against sepsis has been developed. This review summarizes data on LPS-binding proteins from marine invertebrates (ILBPs) that inhibit LPS toxic effects and are of interest as potential drugs for sepsis treatment. The structure, physicochemical properties, antimicrobial, and LPS-binding/neutralizing activity of these proteins and their synthetic analogs are considered in detail. Problems that arise during clinical trials of potential anti-endotoxic drugs are discussed.

Cloning and characterization of tyrosine decarboxylase (TDC) from Litopenaeus vannamei, and its roles in biogenic amines synthesis, immune regulation, and resistance to Vibrio alginolyticus by RNA interference

The biogenic amines, tyramine and octopamine, in the octopaminergic synthesis pathway play critical roles in regulating physiological and immunological homeostasis in Litopenaeus vannamei. Tyrosine decarboxylase (TDC) is an enzyme catalyzing the first decarboxylation step in the biosynthesis of tyramine and octopamine. The full-length gene sequence of TDC cloned from the brain of L. vannamei (LvTDC) was predicted to encode a 779-amino acid protein with a pyridoxal-dependent decarboxylase-conserved domain in close phylogenetic relationship with arthropod TDCs. LvTDC gene expression was found to be abundant in nervous thoracic ganglia. RNA interference was used to assess the immune and physiological function of LvTDC. The LvTDC knockdown shrimp revealed significant decreases in the total haemocyte count, hyaline cells, antimicrobial peptides, respiratory bursts, gene expression, respiratory bursts of haemocytes per unit of haemolymph, and phagocytic activity and clearance efficiency toward Vibrio alginolyticus. Furthermore, LvTDC knockdown was accompanied by decreases in octopamine deficiency. In the V. alginolyticus challenge test, the survival rate of LvTDC knockdown shrimp was lower than the shrimp injected with DEPC-water or GAPDH-dsRNA. In conclusion, the cloned LvTDC was responsible for octopaminergic synthesis, which then regulated physiological and immune responses in L. vannamei.

Yeast recombinant Factor C from horseshoe crab binds endotoxin and causes bacteriostasis

Carcinoscorpius rotundicauda Factor C cDNA has been cloned and expressed in Pichia pastoris to produce a recombinant full-length Factor C (rFC) which is both immunoreactive and functional. The presence of a functional endotoxin-binding domain on rFC was ascertained by LPS-binding assays. One involved the relative binding affinity of rFC to electroblotted lipid A moiety of LPS. The second assay showed that rFC competed against native Factor C contained in C. rotundicauda amebocyte lysate (CAL) to bind LPS. Purification of rFC enhanced its binding affinity to LPS. By agglutination, rFC caused bacteriostasis of Gram-negative bacteria within 2 h. In an in vivo system, rFC also decreased the mortality of actinomycin D-sensitized/LPS-challenged mice. The rFCEE, bearing the 5' terminal LPS binding domain displayed a lowered affinity for LPS. This is in contrast to the rFCSN subclone that is devoid of the 5' end of Factor C, and which does not bind LPS. The presence of a fully-functional endotoxin binding domain in rFC probably requires a full-length protein for co-operative interaction of its downstream sequences. Thus, rFC has potential in the detection and removal of contaminating LPS from biological specimens and fluids for injection, since it is capable of binding both free and bound lipid A.

Invited review: Neisseria meningitidis lipopolysaccharides in human pathology

Neisseria meningitidis causes meningitis, fulminant septicemia or mild meningococcemia attacking mainly children and young adults. Lipopolysaccharides (LPS) consist of a symmetrical hexa-acyl lipid A and a short oligosaccharide chain and are classified in 11 immunotypes. Lipid A is the primary toxic component of N. meningitidis . LPS levels in plasma and cerebrospinal fluid as determined by Limulus amebocyte lysate (LAL) assay are quantitatively closely associated with inflammatory mediators, clinical symptoms, and outcome. Patients with persistent septic shock, multiple organ failure, and severe coagulopathy reveal extraordinarily high levels of LPS in plasma. The cytokine production is compartmentalized to either the circulation or to the subarachnoid space. Mortality related to shock increases from 0% to > 80% with a 10-fold increase of plasma LPS from 10 to 100 endotoxin units/ml. Hemorrhagic skin lesions and thrombosis are caused by up-regulation of tissue factor which induces coagulation, and by inhibition of fibrinolysis by plasminogen activator inhibitor 1 (PAI-1). Effective antibiotic treatment results in a rapid decline of plasma LPS (half-life 1—3 h) and cytokines, and reduced generation of thrombin, and PAI-1. Early antibiotic treatment is mandatory. Three intervention trials to block lipid A have not significantly reduced the mortality of meningococcal septicemia.

Invited review: Mechanisms of endotoxin neutralization by synthetic cationic compounds

A basic challenge in the treatment of septic patients in critical care units is the release of bacterial pathogenicity factors such as lipopolysaccharide (LPS, endotoxin) from the cell envelope of Gram-negative bacteria due to killing by antibiotics. LPS aggregates may interact with serum and membrane proteins such as LBP (lipopolysaccharide-binding protein) and CD14 leading to the observed strong reaction of the immune system. Thus, an effective treatment of patients infected by Gram-negative bacteria must comprise beside bacterial killing the neutralization of endotoxins. Here, data are summarized for synthetic compounds indicating the stepwise development to very effective LPS-neutralizing agents. These data include synthetic peptides, based on the endotoxin-binding domains of natural binding proteins such as lactoferrin, Limulus anti-LPS factor, NK-lysin, and cathelicidins or based on LPS sequestering polyamines. Many of these compounds could be shown to act not only in vitro, but also in vivo (e.g . in animal models of sepsis), and might be useful in future clinical trials and in sepsis therapy.

TALF peptide-immunoglobulin G conjugates that bind lipopolysaccharide

Several peptides mimicking the amino acid sequence of Tachypleus anti-LPS factor (TALF) bind LPS with high affinity and some neutralize LPS in vitro and in vivo (Kloczewiak M., Black K.M., Loiselle P., Cavaillon J-M., Wainwright N., Warren H.S. Synthetic peptides that mimic the binding site of horseshoe crab anti-lipopolysaccharide factor. J Infect Dis 1994; 170: 1490-1497). Two such peptides, TALF29-59 and TALF41-53, were covalently coupled to human IgG via a disulfide bond using the heterobifunctional linker, N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP). The resulting peptide-lgG conjugates contained 4-8 moles peptide per mole IgG and were evaluated for the ability to bind and neutralize LPS. Both conjugates bound LPS in a LPS capture Western blot assay. In a fluid-phase radioimmunoassay, half-maximal binding of 5 μg/ml LPS by many different Escherichia coli strains occurred at 50-100 μg/ml for both conjugates. Coagulation of Limulus amoebocyte lysate was only minimally inhibited by 5 μg/ml of each conjugate. Our data suggest that TALF peptide-lgG conjugates bind LPS with high affinity, but only weakly neutralize LPS. These studies provide an initial step towards the development of peptide-lgG preparations that might be useful for the treatment of Gram-negative sepsis by binding and clearing LPS.

Recent advances in researches on the innate immunity of shrimp in China

The annual production of shrimp culture in mainland of China has been over one million tons for several years. The major cultivated penaeidae species are Litopenaeus vannamei, Fenneropenaeus chinensis, Penaeus monodon and Marsupenaeus japonicus. Due to the importance of shrimp aquaculture in China, researchers have paid more attention to the molecular mechanism of shrimp disease occurrence and tried to develop an efficient control strategy for disease. This paper summarizes the research progress related to innate immunity of penaeid shrimp made in the last decade in Mainland China. Several pattern recognition receptors, such as lectin, toll, lipopolysaccharide and β-1,3-glucan binding protein (LGBP) and tetraspanin were identified. The major signal transduction pathways, including Toll pathway, IMD pathway, which might be involved in the immune response of shrimp, were focused on and most of the components in Toll pathway were identified. Also, cellular immune responses such as phagocytosis and apoptosis were regarded playing very important roles in anti-WSSV infection to shrimp. The molecules involved in the maintenance of the immune homeostasis of shrimp and the progress on molecular structure and pathogenic mechanism of WSSV were summarized. Therefore, the brief outline about the immune system of shrimp is drawn based on the recent data which will help us to understand the immune responses of shrimp to different pathogens.

Structure-function relationships of tachyplesins and their analogues

Haemocytes of the horseshoe crab (Limulus) contain a new family of arthropodous peptide antibiotics, termed the tachyplesin family. These cationic peptides are composed of 17-18 amino acid residues with a C-terminal arginine alpha-amide. Tachyplesin I takes on a fairly rigid conformation constrained by two disulphide bridges and adopts a conformation consisting of an antiparallel beta-sheet connected by a beta-turn. Isopeptides of tachyplesin I with amino acid replacements, tachyplesins II and III, and polyphemusins I and II have also been found in the haemocytes of the South-East Asian species and Limulus polyphemus. These peptides are present in abundance in the small granules of the haemocytes and inhibit strongly the growth of not only Gram-negative and Gram-positive bacteria but also fungi such as Candida albicans. Tachyplesin exists in the prepro form consisting of 77 residues; this precursor is probably processed by intracellular proteases and an amidation enzyme before incorporation into the small granules of the haemocytes. We examined the mode of action of tachyplesin I on biomembranes, comparing it with that of gramicidin S. Tachyplesin caused an efflux of K+ from Staphylococcus aureus and Escherichia coli cells similar to that caused by gramicidin S. Another antimicrobial substance, anti-LPS factor, has been isolated from haemocytes.

Shrimp (Penaeus monodon) anti-lipopolysaccharide factor reduces the lethality of Pseudomonas aeruginosa sepsis in mice

We investigated the efficacy of amino acids 55-76 of the synthetic shrimp anti-lipopolysaccharide factor peptide (SALF(55-76) cyclic peptide), the C-terminal part of the shrimp anti-lipopolysaccharide factor. This study was conducted to elucidate the effects of the antiseptic action of this peptide. The SALF(55-76) cyclic peptide was tested against bacterial clinical isolates and showed broad-spectrum antimicrobial activity. Transmission electron microscopic (TEM) examination of SALF(55-76) cyclic peptide-treated Pseudomonas aeruginosa showed that severe swelling preceded cell death and breakage of the outer membrane; the intracellular inclusion was found to have effluxed extracellularly. When mice were treated with the SALF(55-76) cyclic peptide before bacterial challenge with P. aeruginosa, the peptide highly protected mice against death by sepsis. The P. aeruginosa recovered from SALF(55-76) cyclic peptide-treated mice after 4 h exhibited reduced bacterial growth similar to that recovered from vancomycin-treated mice. In addition, the syntheses of inflammatory cytokines, such as interleukin (IL)-2, IL-4, IL-10, IL-12, IL-13, interferon-gamma, and tumor necrosis factor [TNF]-alpha, were significantly upregulated 4 h after SALF(55-76) cyclic peptide treatment except for IL-4 in the liver. The expressions of Toll-like receptor 4 (Tlr4), Irf3, myd88, and Tram, were considerably elevated, but only Tlr4 existed in the spleen 4 h after SALF(55-76) cyclic peptide treatment. The prophylactic administration of SALF(55-76) cyclic peptide was begun the TNF-alpha response in comparison to untreated mice by an ELISA analysis. Due to its multifunctional properties, the SALF(55-76) cyclic peptide may become an important prophylaxis against and therapy for bacterial infectious diseases, as well as for septic shock.

Response of the blood clotting system of the American horseshoe crab, Limulus polyphemus, to a novel form of lipopolysaccharide from a green alga

Lipopolysaccharide (LPS, endotoxin) is a component of Gram-negative bacteria and is the principal indicator to the innate immune systems of higher animals of a Gram-negative bacterial invasion. LPS activates the blood clotting system of the American horseshoe crab, Limulus polyphemus. By stimulating blood cell degranulation, LPS triggers the release of the proteins of the clotting system from the cells, and by activating a protease cascade that converts coagulogen, a soluble zymogen, to coagulin, the structural protein of the clot, LPS triggers the production of the fibrillar coagulin blood clot. Although originally thought to be restricted to the Gram-negative bacteria and the cyanobacteria, LPS, or a very similar molecule, has recently been described from a eukaryotic green alga, Chlorella. Here we show that, like LPS from Gram-negative bacteria, the algal molecule stimulates exocytosis of the Limulus blood cell and the clotting of coagulin. The coagulin clot efficiently entraps the cells of Chlorella in a network of fibrils. Invasion and erosion of the carapace by green algae is an important cause of mortality of Limulus, and it is suggested that the cellular response to aLPS may contribute to defense against this pathogen.

Molecular cloning and expression profile of putative antilipopolysaccharide factor in Chinese shrimp(Fenneropenaeus chinensis)

A new antimicrobial protein gene of the anti-lipopolysaccharide factor family (tentatively named as ALFFc) has been cloned from hemocytes of the Chinese shrimp Fenneropenaeus chinensis by rapid amplification of 3' and 5' complementary DNA ends with polymerase chain reaction. The full-length complementary DNA of ALFFc consists of 600 bp with a 369-bp open reading frame, encoding 123 amino acids. The deduced peptide contains a putative signal peptide of 25 amino acids and mature peptide of 98 amino acids. The molecular mass of the deduced mature peptide is 13799.16 Da. It is highly cationic, with a theoretical pI of 10.3. The deduced amino acid sequence of ALFFc showed 56% homology with sequences of Tachypleus tridentatus and L. polyhemus. The tissue expression profile of this gene was studied by Northern blot, and ALFFc transcripts were mainly detected in hemocytes, gill, and intestine. RNA in situ hybridization showed that ALFFc was constitutively expressed in hemocytes. Capillary electrophoresis reverse transcriptase PCR was used to quantify the variation of messenger RNA transcription level during the artificial infection process with Vibrio anguillarum. Significant enhancement of ALFFc transcription appeared during the first 24 hours in response to Vibrio infection. These results provide useful information for understanding the function of ALFFc in shrimp.

Cyclic antimicrobial peptides based on Limulus anti-lipopolysaccharide factor for neutralization of lipopolysaccharide

Bacterial endotoxin (lipopolysaccharide, LPS) is responsible for the septic shock syndrome. As potential therapeutic agents cyclic cationic antimicrobial peptides of different length, based on the Limulus anti-lipopolysaccharide factor (LALF), were synthesized, and their interaction with LPS was characterized physico-chemically and related to results in biological assays. All peptides inhibited the LPS-induced cytokine production in human mononuclear cells and the Limulus amebocyte lysate in a concentration-dependent way, with the peptide comprising the complete LPS-binding loop of the LALF (cLALF22) being the most effective. The peptides were neither cytotoxic nor hemolytic, except a slight effect of cLALF22. The peptides were able to displace Ca(2+) cations from a LPS monolayer, with cLALF22 being again most effective in accordance with results from isothermal titration calorimetry, in which saturation of binding was observed at an equimolar [cLALF22]:[LPS] ratio, and at a ratio 2-2.5 for the other peptides. For cLALF22, zeta (xi) potential experiments exhibited a complete compensation of the negative charges of LPS, whereas for the other peptides a residual negative potential of -20 to -40mV was found. X-ray diffraction experiments showed that the mixed unilamellar/cubic inverted aggregate structure of the lipid A part of LPS was converted into a multilamellar one. The gel to liquid crystalline phase transition of the acyl chains of LPS was changed upon cLALF22 binding, leading to a clear fluidization, which was not observed or only to a lesser degree for the other peptides. The affinity of the peptides for LPS led to a reduced binding of lipopolysaccharide-binding protein (LBP) to target membranes and hence to an inhibition of cytokine induction in human mononuclear cells.

Biophysical characterization of the interaction of Limulus polyphemus endotoxin neutralizing protein with lipopolysaccharide

Endotoxin-neutralizing protein (ENP) of the horseshoe crab is one of the most potent neutralizers of endotoxins [bacterial lipopolysaccharide (LPS)]. Here, we report on the interaction of LPS with recombinant ENP using a variety of physical and biological techniques. In biological assays (Limulus amebocyte lysate and tumour necrosis factor-alpha induction in human mononuclear cells), ENP causes a strong reduction of the immunostimulatory ability of LPS in a dose-dependent manner. Concomitantly, the accessible negative surface charges of LPS and lipid A (zeta potential) are neutralized and even converted into positive values. The gel to liquid crystalline phase transitions of LPS and lipid A shift to higher temperatures indicative of a rigidification of the acyl chains, however, the only slight enhancement of the transition enthalpy indicates that the hydrophobic moiety is not strongly disturbed. The aggregate structure of lipid A is converted from a cubic into a multilamellar phase upon ENP binding, whereas the secondary structure of ENP does not change due to the interaction with LPS. ENP contains a hydrophobic binding site to which the dye 1-anilino-8-sulfonic acid binds at a K(d) of 19 micro m, which is displaced by LPS. Because lipopolysaccharide-binding protein (LBP) is not able to bind to LPS when ENP and LPS are preincubated, tight binding of ENP to LPS can be deduced with a K(d) in the low nonomolar range. Importantly, ENP is able to incorporate by itself into target phospholipid liposomes, and is also able to mediate the intercalation of LPS into the liposomes thus acting as a transport protein in a manner similar to LBP. Thus, LPS-ENP complexes might enter target membranes of immunocompetent cells, but are not able to activate due to the ability of ENP to change LPS aggregates from an active into an inactive form.

Role of functional plasminogen-activator-inhibitor-1 4G/5G promoter polymorphism in susceptibility, severity, and outcome of meningococcal disease in Caucasian children*

OBJECTIVE

Meningococcal sepsis invariably is associated with coagulopathy. We have previously reported an association between mortality rate in meningococcal disease and the functional 4G/5G promoter polymorphism of the plasminogen-activator-inhibitor (PAI)-1 gene in a small patient cohort. In a much larger cohort, we aimed to confirm these results and further investigate the role of the 4G/5G polymorphism in determining susceptibility, outcome, and complications of disease.DESIGN Susceptibility was investigated in two separate studies, a case-control study and a family-based transmission study, each test using a separate patient cohort. Severity was investigated using clinical diagnosis, the presence of vascular complications, Pediatric Risk of Mortality (PRISM)-predicted morality, and actual mortality.

SETTING

University hospital and laboratories.

SUBJECTS

Subjects were 510 UK pediatric patients, 210 parents of patients, and 155 UK Caucasian controls.

INTERVENTIONS

DNA extraction and 4G/5G PAI-1 genotyping was carried out using published techniques.

MEASUREMENTS AND MAIN RESULTS

Predicted mortality distribution differed significantly between genotypes (p =.05) with a significantly higher median PRISM in the 4G/4G (41.1%) than the 4G/5G (23.4%) and 5G/5G (19.0%) genotyped patients combined (p =.02). Actual mortality rate was significantly associated with both genotype (chi-square = 14.8, p =.001) and allele frequencies (chi-square = 14.0, p <.0001), with more deaths in the 4G/4G (28.4%) than the 4G/5G and 5G/5G genotyped patients combined (14.9%; chi-square = 7.9; p =.005; risk ratio, 1.9; 95% confidence interval, 1.2-3.0). Logistic regression indicated a 40% and 91% reduction in the odds of dying if a patient was either 4G/5G or 5G/5G, respectively, in comparison to a 4G homozygous patient. When analyzed by clinical diagnosis, the association with death was found only in the sepsis group (chi-square = 18.7, p <.0001; risk ratio, 2.7; 95% confidence interval, 1.6-4.6). In survivors of disease, a significantly higher proportion of 4G/4G patients suffered from vascular complications (chi-square = 6.7, p =.03; risk ratio, 2.4; 95% confidence interval, 1.1-5.0). The 4G/5G polymorphism was not associated or linked with susceptibility (case-control result, p =.6; family-based transmission study results, p =.2).

CONCLUSIONS

This study confirms that Caucasian pediatric patients carrying the functional PAI-1 4G/4G genotype are at an increased risk of developing vascular complications and dying from meningococcal disease.

Mechanisms of bacterial lipopolysaccharide-induced endothelial apoptosis

Gram-negative bacterial sepsis remains a common, life-threatening event. The prognosis for patients who develop sepsis-related complications, including the development of acute respiratory distress syndrome (ARDS), remains poor. A common finding among patients and experimental animals with sepsis and ARDS is endothelial injury and/or dysfunction. A component of the outer membrane of gram-negative bacteria, lipopolysaccharide (LPS) or endotoxin, has been implicated in the pathogenesis of much of the endothelial cell injury and/or dysfunction associated with these disease states. LPS is a highly proinflammatory molecule that elicits a wide array of endothelial responses, including the upregulation of cytokines, adhesion molecules, and tissue factor. In addition to activation, LPS induces endothelial cell death that is apoptotic in nature. This review summarizes the evidence for LPS-induced vascular endothelial injury and examines the molecular signaling pathways that activate and inhibit LPS-induced endothelial apoptosis. Furthermore, the role of apoptotic signaling molecules in mediating LPS-induced activation of endothelial cells will be considered.

Novel therapies for sepsis: antiendotoxin therapies

Severe sepsis and septic shock is a common problem encountered in the critical care unit with an estimated incidence in the US of 750,000 cases/year and a mortality rate of 30-50%. Sepsis involves a complex interaction between bacterial factors and the host immune system producing a systemic inflammatory state that may progress to multiple organ failure and death. Endotoxin (a lipopolysaccharide) released from Gram-negative bacteria has been implicated as a potent, prototypical stimulus of the immune response to bacterial infection. Current antiendotoxin strategies utilise various approaches ranging from the prevention of binding to endotoxin receptors with antibodies (monoclonal or polyclonal) against endotoxin or endotoxin receptor/carrier molecules (antiCD14 or antilipopolysaccharide-binding protein antibodies), enhancing clearance or neutralisation (haemoperfusion, lipoproteins, lipopolysaccharide-neutralising proteins) or impairing cellular signalling (lipid A analogues, tyrosine kinase inhibitors). In the future, innovative therapies involving Toll-like receptors and their downstream signalling elements will be developed. This review discusses current knowledge regarding endotoxin signalling, antiendotoxin therapies currently under development, and future areas for research.

Cloning of anti-lPS factor cDNA from Tachypleus tridentatus, expression in Bombyx mori larvae and its biological activity in vitro

In this article we report the cloning and expression of a cDNA encoding Tachypleus anti-lipopolysaccharide (LPS) factor, which is of interest for use as a potential inhibitor of the common core subunit of Gram-negative bacterial endotoxins. First, two degenerate primers were designed based on the sequence homology of anti-LPS factors purified from different species of horseshoe crab. The total RNA was extracted from amebocytes of Tachypleus tridentatus. The cDNA was then obtained by using the RT-PCR methods. Second, the cDNA of Tachypleus anti-LPS factor (TALF) was expressed in Bombyx mori larvae using baculovirus expression system, which showed a yield of up to 600 mg/L. Last, we determined the biological activity of the recombinant proteins by LPS neutralization assay and bacteriostatic assay in vitro.

Platelet-mediated activation of endothelial cells: implications for the pathogenesis of transplant rejection

BACKGROUND

Platelets exert their normal functions at sites of endothelial disruption by plugging discontinuities in blood vessels and secreting products that promote thrombosis, inflammation, and the healing of wounds. Whether platelets might induce these changes in xenograft blood vessels, leading to development of acute vascular rejection, has been uncertain.

METHODS

To examine the role of human platelets in modulation of xenograft endothelium, pig endothelial cells were treated with human platelets.

RESULTS

Treatment of quiescent porcine endothelial cells with human platelets modulated the endothelial cells. Whereas resting human platelets caused little change in normal porcine endothelial cells, platelets activated with small amounts of thrombin induced striking changes in the endothelial cells, including the induction of tissue factor activity, the expression of E-selectin, and the secretion of endothelin-1. These changes were induced, at least in part, by interleukin-1 (IL-1) associated with the platelet surface and were modified by the secretion of transforming growth factor-beta (TGF-beta).

CONCLUSION

These findings may explain how the activation of platelets at an early point in the rejection of vascularized organ xenografts or in chronic diseases might contribute to thrombotic, ischemic, and inflammatory changes characteristic of an organ xenograft undergoing rejection.

Synthetic endotoxin-binding peptides block endotoxin-triggered TNF-alpha production by macrophages in vitro and in vivo and prevent endotoxin-mediated toxic shock

Lipid A, the conserved portion of endotoxin, is the major mediator of septic shock; therefore, endotoxin-neutralizing molecules could have important clinical applications. Here we show that peptides derived from Limulus anti-LPS factor (LALF), bactericidal/permeability increasing protein (BPI) and endotoxin-binding protein, bind to lipid A and block the recombinant LALF/lipid A interaction in vitro. Because their neutralizing capacity in vitro as well as in vivo has been limited, we created hybrid peptides comprising two endotoxin-binding domains. The hybrid molecule LL-10-H-14, containing endotoxin-binding domains from LALF and endotoxin-binding protein, turned out to be the most active peptide within the series of peptides tested here to inhibit the CD14/lipid A interaction and is able in vitro to block the endotoxin-induced TNF-alpha release of murine macrophages up to 90%. Furthermore, LL-10-H-14 not only reduced peak serum levels of TNF-alpha of mice when preinjected but also reduced TNF-alpha levels when given 15 min after the endotoxin challenge. As compared with other peptides, only LL-10-H-14 is able to strongly decrease endotoxin-stimulated TNF-alpha release by human macrophage cell lines as well as by PBMC. Furthermore, the hybrid peptide is protective against endotoxin-provoked lethal shock. As such, LL-10-H-14 could have prophylactic and/or therapeutic properties in humans for the management of septic shock.

Update on meningococcal disease with emphasis on pathogenesis and clinical management

The only natural reservoir of Neisseria meningitidis is the human nasopharyngeal mucosa. Depending on age, climate, country, socioeconomic status, and other factors, approximately 10% of the human population harbors meningococci in the nose. However, invasive disease is relatively rare, as it occurs only when the following conditions are fulfilled: (i) contact with a virulent strain, (ii) colonization by that strain, (iii) penetration of the bacterium through the mucosa, and (iv) survival and eventually outgrowth of the meningococcus in the bloodstream. When the meningococcus has reached the bloodstream and specific antibodies are absent, as is the case for young children or after introduction of a new strain in a population, the ultimate outgrowth depends on the efficacy of the innate immune response. Massive outgrowth leads within 12 h to fulminant meningococcal sepsis (FMS), characterized by high intravascular concentrations of endotoxin that set free high concentrations of proinflammatory mediators. These mediators belonging to the complement system, the contact system, the fibrinolytic system, and the cytokine system induce shock and diffuse intravascular coagulation. FMS can be fatal within 24 h, often before signs of meningitis have developed. In spite of the increasing possibilities for treatment in intensive care units, the mortality rate of FMS is still 30%. When the outgrowth of meningococci in the bloodstream is impeded, seeding of bacteria in the subarachnoidal compartment may lead to overt meningitis within 24 to 36 h. With appropriate antibiotics and good clinical surveillance, the mortality rate of this form of invasive disease is 1 to 2%. The overall mortality rate of meningococcal disease can only be reduced when patients without meningitis, i.e., those who may develop FMS, are recognized early. This means that the fundamental nature of the disease as a meningococcus septicemia deserves more attention.

Update on meningococcal disease with emphasis on pathogenesis and clinical management

The only natural reservoir of Neisseria meningitidis is the human nasopharyngeal mucosa. Depending on age, climate, country, socioeconomic status, and other factors, approximately 10% of the human population harbors meningococci in the nose. However, invasive disease is relatively rare, as it occurs only when the following conditions are fulfilled: (i) contact with a virulent strain, (ii) colonization by that strain, (iii) penetration of the bacterium through the mucosa, and (iv) survival and eventually outgrowth of the meningococcus in the bloodstream. When the meningococcus has reached the bloodstream and specific antibodies are absent, as is the case for young children or after introduction of a new strain in a population, the ultimate outgrowth depends on the efficacy of the innate immune response. Massive outgrowth leads within 12 h to fulminant meningococcal sepsis (FMS), characterized by high intravascular concentrations of endotoxin that set free high concentrations of proinflammatory mediators. These mediators belonging to the complement system, the contact system, the fibrinolytic system, and the cytokine system induce shock and diffuse intravascular coagulation. FMS can be fatal within 24 h, often before signs of meningitis have developed. In spite of the increasing possibilities for treatment in intensive care units, the mortality rate of FMS is still 30%. When the outgrowth of meningococci in the bloodstream is impeded, seeding of bacteria in the subarachnoidal compartment may lead to overt meningitis within 24 to 36 h. With appropriate antibiotics and good clinical surveillance, the mortality rate of this form of invasive disease is 1 to 2%. The overall mortality rate of meningococcal disease can only be reduced when patients without meningitis, i.e., those who may develop FMS, are recognized early. This means that the fundamental nature of the disease as a meningococcus septicemia deserves more attention.

Gram-negative bacterial sepsis and the sepsis syndrome

Gram-negative sepsis syndrome is an increasingly common complication in medical and surgical patients. The molecular and cellular mechanisms underlying this dreaded complication are yielding to investigation. These studies have led to a multiplicity of targets for novel therapies. Despite highly promising results in many animal studies, clinical studies have been disappointing.

Antiendotoxin strategies

Endotoxin is a potent stimulator of the inflammatory response and is believed to initiate the pathology in Gram-negative sepsis. Agents are being developed that bind and neutralize or block the effects of endotoxin, with the goal of improving outcome in the treatment of sepsis. Strategies discussed in this article include anti-LPS antibodies, LPS binding proteins and lipoproteins, polymyxin B conjugates, lipid A analogues, and extracorporeal techniques for endotoxin removal.

Potent immunoregulatory effects of Salmonella typhi flagella on antigenic stimulation of human peripheral blood mononuclear cells

A key function of monocytes/macrophages (Mphi) is to present antigens to T cells. However, upon interaction with bacteria, Mphi lose their ability to effectively present soluble antigens. This functional loss was associated with alterations in the expression of adhesion molecules and CD14 and a reduction in the uptake of soluble antigen. Recently, we have demonstrated that Salmonella typhi flagella (STF) markedly decrease CD14 expression and are potent inducers of proinflammatory cytokine production by human peripheral blood mononuclear cells (hPBMC). In order to determine whether S. typhi and soluble STF also alter the ability of Mphi to activate T cells to proliferate to antigens and mitogens, hPBMC were cultured in the presence of tetanus toxoid (TT) or phytohemagglutinin (PHA) and either killed whole-cell S. typhi or purified STF protein. Both whole-cell S. typhi and STF suppressed proliferation to PHA and TT. This decreased proliferation was not a result of increased Mphi production of nitric oxide, prostaglandin E2, or oxygen radicals or the release of interleukin-1beta, tumor necrosis factor alpha, interleukin-6, or interleukin-10 following exposure to STF. However, the ability to take up soluble antigen, as determined by fluorescein isothiocyanate-labeled dextran uptake, was reduced in cells cultured with STF. Moreover, there was a dramatic reduction in the expression of CD54 on Mphi after exposure to STF. These results indicate that whole-cell S. typhi and STF have the ability to alter in vitro proliferation to soluble antigens and mitogens by affecting Mphi function.

Endotoxin-neutralizing protein protects against endotoxin-induced endothelial barrier dysfunction

Bacterial lipopolysaccharide induces tyrosine phosphorylation of paxillin, actin reorganization, and opening of the transendothelial paracellular pathway through which macromoles flux. In this study, lipid A was shown to be the bioactive portion of the lipopolysaccharide molecule responsible for changes in endothelial barrier function. We then studied whether endotoxin-neutralizing protein, a recombinant peptide that is derived from Limulus antilipopolysaccharide factor and targets lipid A, could block the effects of lipopolysaccharide on protein tyrosine phosphorylation, actin organization, and movement of 14C-bovine serum albumin across bovine pulmonary artery endothelial cell monolayers. In the presence of serum, a 6-h exposure to lipopolysaccharide (10 ng/ml) increased transendothelial 14C-albumin flux compared to the simultaneous media control. Coadministration of endotoxin-neutralizing protein (> or =10 ng/ml) with lipopolysaccharide (10 ng/ml) protected against lipopolysaccharide-induced barrier dysfunction. This protection was dose dependent, conferring total protection at endotoxin-neutralizing protein/lipopolysaccharide ratios of > or =10:1. Similarly, endotoxin-neutralizing protein was capable of blocking the lipopolysaccharide-induced endothelial cell responses that are prerequisite to barrier dysfunction, including tyrosine phosphorylation of paxillin and actin depolymerization. Finally, endotoxin-neutralizing protein cross-protected against lipopolysaccharide derived from diverse gram-negative bacteria. Thus, endotoxin-neutralizing protein offers a novel therapeutic intervention for the vascular endothelial dysfunction of gram-negative sepsis and its attendant endotoxemia.

A comparison of bactericidal/permeability-increasing protein variant versus recombinant endotoxin-neutralizing protein for the treatment of Escherichia coli sepsis in rats

OBJECTIVE

To compare a recombinant bactericidal/permeability-increasing protein variant and a recombinant endotoxin-neutralizing protein.

DESIGN

Randomized, blinded, controlled study, using a rat model of sepsis.

SETTING

Animal research facility.

SUBJECTS

Male Wistar rats.

INTERVENTIONS

An inoculum of 1.5 x 10(7) to 1.8 x 10(8) Escherichia coli O18ac K1, implanted in the peritoneum, produced bacteremia in 95% of animals after 1 hr. One hour after E. coli challenge, animals received recombinant bactericidal/permeability-increasing protein variant, recombinant endotoxin-neutralizing protein, or saline intravenously, followed by ceftriaxone and gentamicin intramuscularly.

MEASUREMENTS AND MAIN RESULTS

Twenty-four (85.7%) of 28 animals receiving recombinant endotoxin-neutralizing protein (p < .001 vs. control) survived 7 days compared with nine (33.3%) of 27 recombinant bactericidal/permeability-increasing protein variant-treated (p < .001 vs. control) and two (6.5%) of 31 control animals.

CONCLUSIONS

Both recombinant endotoxin-neutralizing protein and recombinant bactericidal/permeability-increasing protein variant improved survival. Recombinant endotoxin-neutralizing protein was superior to recombinant bactericidal/permeability-increasing protein variant in its protective effect at the doses tested. Our results suggest that both proteins may be useful in the treatment of human Gram-negative sepsis.

High affinity endotoxin-binding and neutralizing peptides based on the crystal structure of recombinant Limulus anti-lipopolysaccharide factor

Lipid A, the conserved portion of endotoxin or lipopolysaccharide, is the major mediator of septic shock, and therefore endotoxin-neutralizing molecules could have important clinical applications. The crystal structure of recombinant Limulus anti-lipopolysaccharide factor (rLALF) (Hoess, A., Watson, S., Siber, G. R., and Liddington, R. (1993) EMBO J. 12, 3351-3356), has been used to design synthetic peptides comprising different parts of the exposed amphipathic loop in the proposed endotoxin-binding domain of rLALF. We investigated the minimal requirements of rLALF for endotoxin and lipid A binding with linear 10-mer peptides. Only one linear peptide, corresponding to amino acids 36-45 of rLALF, was able to bind lipid A and endotoxin above background levels. Cyclic peptides, however, bind lipid A and endotoxin with high affinity, presumably by mimicking the three dimensional characteristics of the exposed hairpin loop. The cyclic peptide including amino acids 36-47, LALF-14, has a lipid A binding activity comparable to the high affinity endotoxin-binding peptide polymyxin B. LALF-14 has an improved serum half-life compared with its linear counterpart, and it is not toxic for cultured human monocytes or red blood cells. In mice, it blocks tumor necrosis factor-alpha induction after endotoxin challenge. The characterization of the minimal endotoxin-binding domain of rLALF and, importantly, its structure provided a basis for designing small molecules that could have prophylactic and/or therapeutic properties in humans for the management of septic shock.

Comparison of early and late treatment with a recombinant endotoxin neutralizing protein in a rat model of Escherichia coli sepsis

OBJECTIVE

To test the efficacy of a recombinant endotoxin neutralizing protein as compared with saline in rats with Escherichia coli sepsis.

DESIGN

Prospective, controlled animal trial.

SETTING

Hospital animal research laboratory.

SUBJECTS

Male Wistar rats challenged with intraperitoneal E. coli, O18ac K1, and treated 1 hr later with ceftriaxone and gentamicin.

INTERVENTIONS

Recombinant endotoxin neutralizing protein, 50 mg/kg, was administered to rats 1, 2, or 3 hrs after E. coli challenge; saline was administered to control animals.

MEASUREMENTS AND MAIN RESULTS

Quantitative bacteremia, 1 hr after challenge and before antibiotic administration, was not significantly different between treatment groups (range geometric mean 451 to 621 colony-forming units [cfu]/mL). The endotoxin concentration, measured immediately before recombinant endotoxin neutralizing protein administration, was significantly higher in animals sampled and treated at 2 hrs (geometric mean 260 EU/mL; 95% confidence interval 140 to 480 EU/mL), or 3 hrs (geometric mean 697 EU/mL; 95% confidence interval 307 to 1585 EU/mL) after E. coli challenge, compared with animals sampled and treated at 1 hr (geometric mean 17 EU/mL; 95% confidence interval 7 to 69 EU/ mL). Survival rate was significantly greater in rats treated with recombinant endotoxin neutralizing protein at 1 hr (23/27; p < .001) or 2 hrs (8/30; p < .01) after E. coli challenge than in controls (1/32).

CONCLUSION

Administration of recombinant endotoxin neutralizing protein delayed up to 2 hrs after challenge with E. coli improves survival in antibiotic-treated rats with Gram-negative sepsis.

High-dose recombinant endotoxin neutralizing protein improves survival in rabbits, with Escherichia coli sepsis

OBJECTIVE

To assess the benefit of a recombinant endotoxin neutralizing protein from Limulus polyphemus in treating Gram-negative bacterial sepsis in rabbits.

DESIGN

Prospective, blinded, controlled, laboratory trial.

SETTING

Animal research laboratory.

SUBJECTS

New Zealand White rabbits.

INTERVENTIONS

We established a rabbit model of Escherichia coli peritonitis and bacteremia, with high mortality rate, despite treatment with gentamicin and ceftriaxone. Twenty-five pairs of male New Zealand White rabbits were challenged intraperitoneally with E. coli O18ac K1 in 5% porcine mucin (mean 7 x 10(1) colony-forming units). All animals were treated with intravenous gentamicin (2.5 mg/kg) and ceftriaxone (100 mg/kg), and with either intravenous endotoxin neutralizing protein (50 mg/kg) or saline 1 hr after E. coli challenge.

MEASUREMENTS AND MAIN RESULTS

All animals were bacteremic 1 hr after challenge (mean 3.6 x 10(5) colony-forming units/mL). Animals in both groups developed tachycardia, hypotension, and acidosis (NS). Geometric mean serum endotoxin and tumor necrosis factor (TNF) concentrations were significantly ( p < .001) higher 1 hr after challenge compared with baseline prechallenge concentrations in both groups. From 1 to 2 hrs after challenge, endotoxin concentrations increased 2.5-fold in control animals (95% confidence interval = 13.1 to 32.9 endotoxin units/mL, p = .024), whereas endotoxin concentrations increased only 1.2-fold in endotoxin neutralizing protein-treated animals (95% confidence interval = 20.4 to 23.6 endotoxin units/mL, NS). TNF concentrations increased significantly (p < .001) in both groups from 1 to 2 hrs after challenge. Eighteen (72%) of 25 endotoxin neutralizing protein-treated animals vs. 11 (44%) of 25 controls survived 24 hrs (p = .032).

CONCLUSIONS

Treatment with endotoxin neutralizing protein had the following effects: a) the increase in serum endotoxin was blunted, but not TNF concentrations measured 1 hr after antibiotic treatment; and b) survival in rabbits with E. Coli sepsis was improved.

Preexposure of mouse peritoneal macrophages to lipopolysaccharide and other stimuli enhances the nitric oxide response to secondary stimuli

The aim of this study was to compare the regulation of the production of tumor necrosis factor-alpha (TNF-alpha) and secondary nitric oxide (NO) in macrophages submitted to a sequence of two stimulations. Pre-exposure for 18 h of mouse thioglycollate-elicited peritoneal macrophages to low doses (1-10 ng/ml) of lipopolysaccharide (LPS), in the presence or absence of serum, induces on one hand a desensitization (endotoxin tolerance) for secondary TNF-alpha responses to LPS and, on the other hand, a 4 fold increase (priming) of secondary NO responses. Preexposure to components from Gram-positive bacteria (lipoteichoic acid, peptidoglycan) and to a synthetic lipid structurally related to lipid A (compound M4), induced similar effects. In contrast to the desensitization for TNF-alpha secretion, the priming for NO production was not mimicked by sodium nitroprusside, a generator of NO. The results suggest that concomitant but distinct activation pathways induced by LPS and other agents can be dissociated by serum-independent modulation processes elicited by pre-exposure of the cells to LPS itself, or to other stimuli.

Direct activation of murine peritoneal macrophages for nitric oxide production and tumor cell killing by interferon-gamma

Interferon-gamma (IFN-gamma) is known to prime macrophages for tumor cell lysis and nitric oxide (NO) production as measured by enhanced sensitivity to lipopolysaccharide (LPS). In the present study, the ability of IFN-gamma to directly activate peritoneal macrophages from C57BL/6 and Balb/c mice for tumor cytotoxicity and NO production was evaluated. Macrophage-mediated tumor cell killing was measured by an 18 h 51Cr release assay using P815 mastocytoma cells as targets. Concurrent NO production was measured as nitrite in the supernatants of macrophage cultures. Incubation of macrophages with IFN-gamma resulted in activation of macrophages for tumor cell lysis. IFN-gamma alone also activated macrophages for NO production under identical conditions. Addition of LPS along with IFN-gamma resulted in synergism in the activation of macrophages for both cytolysis and NO production. LPS contamination of the IFN-gamma preparation was absent as evidenced by the following criteria: (1) the IFN-gamma preparation as well as the reagents used were shown to be free of LPS contamination based on LAL endotoxin tests (sensitivity 25 pg/ml), (2) the ability of IFN-gamma to activated macrophages was not abrogated by prior treatment of the cytokine with polymyxin B, whereas the effect of LPS was inhibited (70-100%) under similar conditions, (3) pretreatment of the IFN-gamma preparation with a specific endotoxin neutralizing protein did not abrogate the ability of IFN-gamma to induce macrophage activation, and (4) heat treatment of solutions containing IFN-gamma alone or IFN-gamma+LPS abolished only the effect of IFN-gamma, not that of LPS.(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant endotoxin neutralizing protein improves survival from Escherichia coli sepsis in rats

OBJECTIVE

A recombinant endotoxin neutralizing protein was evaluated for its ability to ameliorate the effects of Escherichia coli sepsis in rats.

DESIGN

Prospective, controlled animal trial.

SETTING

Hospital animal research laboratory.

SUBJECTS

Wistar rats, treated with gentamicin 1 hr after challenge with intraperitoneal E. coli O18ac.

INTERVENTIONS

The animals received a recombinant endotoxin neutralizing protein, in doses of 5, 25, or 50 mg/kg, either 30 or 60 mins after challenge; controls received saline.

MEASUREMENTS AND MAIN RESULTS

Geometric mean serum endotoxin concentrations in endotoxin neutralizing protein-treated animals did not differ from control animals. Tumor necrosis factor concentrations in animals treated with endotoxin neutralizing protein 30 mins after challenge were significantly lower than controls. Animals treated with 25 or 50 mg/kg of endotoxin neutralizing protein 30 mins after E. coli challenge had significant improvements in survival compared with controls. Animals treated with 50 mg/kg of endotoxin neutralizing protein 60 mins after E. coli challenge had significant improvements in survival compared with controls.

CONCLUSION

Endotoxin neutralizing protein significantly reduces mortality from Gram-negative sepsis in an antibiotic-treatment model of E. coli peritonitis and bacteremia in rats, mediated by a neutralization of the biological effects of endotoxin.

Bactericidal/permeability-increasing protein protects vascular endothelial cells from lipopolysaccharide-induced activation and injury

Bactericidal/permeability-increasing protein (BPI), a human neutrophil granule protein, has been shown to bind lipopolysaccharide (LPS) and neutralize LPS-mediated cytokine production in adherent monocytes and the whole-blood system. In this study we investigated the ability of recombinant human BPI (rBPI) to inhibit LPS-induced vascular endothelial cell (EC) injury and activation. rBPI inhibited significantly both rough and smooth LPS-mediated injury for cultured bovine brain microvessel ECs, as measured by lactic dehydrogenase release, and blocked the LPS-induced interleukin-6 (IL-6) release from human umbilical vein ECs in a dose-dependent manner. BPI was able to inhibit LPS-mediated EC injury or activation whether it was added before or at the same time with LPS, but delaying the time of addition of rBPI resulted only in a partial inhibition. BPI also inhibited LPS-induced tumor necrosis factor alpha, IL-1 beta, and IL-6 release from human whole blood. This inhibition of tumor necrosis factor alpha, IL-1 beta, and IL-6 release from whole blood was maximal when BPI was premixed with LPS before addition to blood and was partial when BPI was added simultaneously with LPS, but no inhibition was observed when the addition of rBPI was delayed for 5 min. These findings suggest that rBPI is a potent inhibitor of LPS-mediated responses in ECs and whole blood and underscore the potential use of BPI in treatment or prevention of endotoxic shock. In contrast, the anti-lipid A monoclonal antibodies HA-1A and E5 were ineffective in inhibiting LPS-mediated EC injury and activation as well as LPS-induced cytokine release in whole blood.

Crystal structure of an endotoxin-neutralizing protein from the horseshoe crab, Limulus anti-LPS factor, at 1.5 A resolution

Lipopolysaccharide (LPS), or endotoxin, is the major mediator of septic shock, a serious complication of Gram-negative bacterial infections in humans. Molecules that bind LPS and neutralize its biological effects or enhance its clearance could have important clinical applications. Limulus anti-LPS factor (LALF) binds LPS tightly, and, in animal models, reduces mortality when administered before or after LPS challenge or bacterial infection. Here we present the high resolution structure of a recombinant LALF. It has a single domain consisting of three alpha-helices packed against a four-stranded beta-sheet. The wedge-shaped molecule has a striking charge distribution and amphipathicity that suggest how it can insert into membranes. The binding site for LPS probably involves an extended amphipathic loop, and we propose that two mammalian LPS-binding proteins will have a similar loop. The amphipathic loop structure may be used in the design of molecules with therapeutic properties against septic shock.

Microbial cell-wall contaminants in peptides: a potential source of physiological artifacts

Microbial cell-wall products (MCWP) such as endotoxins are easily introduced into peptides produced under standard laboratory conditions. Because these products stimulate the induction of cytokines and other mediators, which, in turn, trigger a broad range of physiological responses. MCWP in peptide preparations are potential sources of artifacts. This brief tutorial outlines the physical/chemical nature of MCWP, some of their sources, their physiological effects, and a simple method to control for them in some peptide preparations.

Lipopolysaccharide-binding proteins of Limulus amebocyte lysate

Limulus amebocyte lysate, obtained from horseshoe crab (Limulus polyphemus) blood cells, contains a coagulation system which is activated by bacterial lipopolysaccharide (LPS). A chromatographic fraction of Limulus lysate, containing the endotoxin-sensitive factor(s) which initiates the coagulation cascade, was studied. We utilized a photoreactive, cleavable, radiolabeled derivative of Salmonella minnesota LPS, LPS-(p-azidosalicylamido)-1,3'-dithiopropionamide (LPS-ASD), to identify LPS-binding proteins. The lysate fraction was incubated with LPS-ASD, and LPS-binding proteins were identified by autoradiography of sodium dodecyl sulfate-polyacrylamide gels. An 82-kDa protein, a major protein component of this fraction from Limulus lysate, was identified as a LPS-binding protein in a majority of lysates. Incubation of whole Limulus lysate with antiserum to this protein resulted in enhanced sensitivity of the lysate to LPS, suggesting that this 82-kDa protein is a negative regulator of coagulation. A minor 50-kDa protein component of lysate also was identified as a LPS-binding protein and is a candidate for the LPS-sensitive coagulation protein in L. polyphemus.

Molecular mechanism of hemolymph clotting system in Limulus

Limulus (horseshoe crab) hemolymph is known to be very sensitive to bacterial endotoxin (LPS), which causes a rapid coagulation response. Hemolymph contains a single type of hemocyte that undergoes aggregation, adhesion, and degranulation in response to LPS. The granule contents are released into the hemolymph, where they form an insoluble gel. We have characterized four components involved in this coagulation response that comprise a cascade of three serine protease zymogens (factor C, factor B, and proclotting enzyme) and one clottable protein (coagulogen). Of these components, factor C sensitive to LPS is a protein composed of five complement-related domains ("Sushi" or SCR), an EGF-like domain, and a C-type lectinlike domain as well as a putative amino-terminal LPS-binding domain. This domain structure is very similar to that of selectin family of cell adhesion molecules, suggesting that it might also function as a cell adhesion molecule after the release into the hemolymph. Factor B and the proclotting enzyme share a common Cys-rich motif ("cliplike" domain) in the amino-terminal portions. This domain is also found in a putative serine protease zymogen ("easter") in Drosophila, which is essential for normal embryonic development. All four of the components of the cascade and an antibacterial protein (anti-LPS factor) are localized to a specific type of the hemocyte granule. Another antibacterial peptide (tachyplesins I and II) is localized in a distinct granule population. The contents of both granule populations are released into the hemolymph in response to LPS, where they cooperate in immobilization and killing of Gram-negative bacteria.

Binding and neutralization of endotoxin by Limulus antilipopolysaccharide factor

In order to examine the ability of Limulus antilipopolysaccharide factor (LALF) to bind lipopolysaccharide (LPS), we purified LALF to homogeneity from Limulus amoebocyte lysate and coupled it covalently to agarose beads. LALF-coupled beads captured more tritiated LPS from rough and smooth strains of gram-negative bacteria than did control human serum albumin-coupled beads. Unlabeled homologous and heterologous LPS competed for the binding of 3H-LPS to LALF-coupled beads. LALF bound LPS in a dose-dependent manner as assessed by the precipitation of LPS-LALF complexes with 50% saturated ammonium sulfate. We also studied the ability of LALF to neutralize LPS. LPS preincubated with LALF was less mitogenic for murine splenocytes, was less pyrogenic in the rabbit fever assay, was less lethal in mice which had been sensitized to LPS with actinomycin D, and induced less fever, neutropenia, and pulmonary hypertension when infused into sheep. Our findings extend prior studies which suggested that LALF binds to and neutralizes LPS from multiple strains of gram-negative bacteria.