Protective meningococcal capsular polysaccharide epitopes and the role of O acetylation

Previous studies with group C meningococcal polysaccharide-tetanus toxoid (GCMP-TT) conjugates had suggested that the GCMP O-acetyl group masked the protective epitope for group C meningococci through steric hindrance or altered conformations. For this report, we confirmed this phenomenon and performed comparative studies with group Y meningococcal polysaccharide (GYMP)-TT to determine whether it might extend to other serogroups. The de-O-acetylated (dOA) polysaccharides (PSs) resulted in higher serum bactericidal activities (SBA) towards the O-acetylated (OA) meningococcal strains from the respective serogroups. High-resolution H-nuclear magnetic resonance spectroscopy at 500 MHz and competitive inhibition serum bactericidal assays were used to characterize the nature of the protective epitope. In head-to-head comparisons with OA PSs as SBA inhibitors, the dOA PSs provided 10 to 1,000 times better inhibition for GCMP in human and mouse antisera and 6 to 13 times better inhibition for GYMP in mouse antisera, using OA strains in all assays. In addition, the SBA for OA strains was highly correlated with dOA PS-specific immunoglobulin G (r=0.72 to 0.98) for both GCMP and GYMP. The results suggest that there may be a generalized role for the O-acetyl group to provide an epitope of misdirected immunogenicity for meningococcal PS capsules, enabling escape from immune surveillance. In addition to greater chemical consistency, the dOA forms of GCMP and GYMP conjugate vaccines endow greater immunologic competence to the PSs, rendering them capable of eliciting higher levels of functional antibodies toward the protective epitopes.

Secondary acylation of Klebsiella pneumoniae lipopolysaccharide contributes to sensitivity to antibacterial peptides

Klebsiella pneumoniae is an important cause of nosocomial Gram-negative sepsis. Lipopolysaccharide (LPS) is considered to be a major virulence determinant of this encapsulated bacterium and most mutations to the lipid A anchor of LPS are conditionally lethal to the bacterium. We studied the role of LPS acylation in K. pneumoniae disease pathogenesis by using a mutation of lpxM (msbB/waaN), which encodes the enzyme responsible for late secondary acylation of immature lipid A molecules. A K. pneumoniae B5055 (K2:O1) lpxM mutant was found to be attenuated for growth in the lungs in a mouse pneumonia model leading to reduced lethality of the bacterium. B5055DeltalpxM exhibited similar sensitivity to phagocytosis or complement-mediated lysis than B5055, unlike the non-encapsulated mutant B5055nm. In vitro, B5055DeltalpxM showed increased permeability of the outer membrane and an increased susceptibility to certain antibacterial peptides suggesting that in vivo attenuation may be due in part to sensitivity to antibacterial peptides present in the lungs of BALB/c mice. These data support the view that lipopolysaccharide acylation plays a important role in providing Gram-negative bacteria some resistance to structural and innate defenses and especially the antibacterial properties of detergents (e.g. bile) and cationic defensins.

Immunomodulatory effects of fosfomycin in an endotoxin model in human blood

OBJECTIVES

Although a wide range of therapeutic strategies have been developed to improve the outcome of severe sepsis, a convincing reduction in mortality is lacking. Recently, increasing attention has been paid to immunomodulatory effects of antimicrobials. This study set out to explore the immunomodulatory effects of fosfomycin, a broad-spectrum antibiotic frequently used in septic patients, at the protein and molecular levels in vitro.

METHODS

Whole blood from 11 healthy volunteers was incubated with 50 pg/mL endotoxin and 100 microg/mL fosfomycin or physiological sodium chloride for 4 h. Real-time RT-PCR was performed for various pro- and anti-inflammatory cytokines. Concentrations of tumour necrosis factor (TNF)-alpha and interleukin (IL)-6 in the supernatant were measured using a commercially available ELISA.

RESULTS

Incubation of human leucocytes with endotoxin increased messenger RNA (mRNA) levels of cytokines several thousand fold compared with baseline. The addition of fosfomycin significantly inhibited mRNA levels of pro-inflammatory cytokines such as IL-1-alpha, IL-6 and TNF-alpha after 2 h (P < 0.01), while no significant reduction was observed for the anti-inflammatory cytokines IL-4, IL-10 and IL-13 (P = 0.26). At the protein level, the concentrations of IL-6 and TNF-alpha increased approximately 3000- and 600-fold after 4 h of incubation with lipopolysaccharide as compared with baseline, respectively. Addition of fosfomycin significantly reduced cytokine levels by 56% and 73% for IL-6 and TNF-alpha, respectively.

CONCLUSIONS

Fosfomycin extensively decreased mRNA levels and release of pro-inflammatory cytokines in human blood. The broad antimicrobial coverage of fosfomycin and its immunosuppressive effects could be clinically useful in patients with sepsis.

Haemophilus influenzae surface fibrils contribute to serum resistance by interacting with vitronectin

Vitronectin inhibits the membrane attack complex of the complement system and is found both in plasma and the extracellular matrix. In this study, we have identified the outer membrane protein Haemophilus surface fibrils (Hsf) as the major vitronectin-binding protein in encapsulated H. influenzae type b. A H. influenzae mutant devoid of Hsf showed a significantly decreased binding to both soluble and immobilized vitronectin as compared with the wild-type counterpart. Moreover, Escherichia coli-expressing Hsf at the surface strongly adhered to immobilized vitronectin. Importantly, the H. influenzae Hsf mutant had a markedly reduced survival as compared with the wild-type bacterium when incubated with normal human serum. A series of truncated Hsf fragments were recombinantly manufactured in E. coli. The vitronectin binding regions were located within two separate binding domains. In conclusion, Hsf interacts with vitronectin and thereby inhibits the complement-mediated bactericidal activity, and thus is a major H. influenzae virulence factor.

The meningococcal vaccine candidate GNA1870 binds the complement regulatory protein factor H and enhances serum resistance

Neisseria meningitidis binds factor H (fH), a key regulator of the alternative complement pathway. A approximately 29 kD fH-binding protein expressed in the meningococcal outer membrane was identified by mass spectrometry as GNA1870, a lipoprotein currently under evaluation as a broad-spectrum meningococcal vaccine candidate. GNA1870 was confirmed as the fH ligand on intact bacteria by 1) abrogation of fH binding upon deleting GNA1870, and 2) blocking fH binding by anti-GNA1870 mAbs. fH bound to whole bacteria and purified rGNA1870 representing each of the three variant GNA1870 families. We showed that the amount of fH binding correlated with the level of bacterial GNA1870 expression. High levels of variant 1 GNA1870 expression (either by allelic replacement of gna1870 or by plasmid-driven high-level expression) in strains that otherwise were low-level GNA1870 expressers (and bound low amounts of fH by flow cytometry) restored high levels of fH binding. Diminished fH binding to the GNA1870 deletion mutants was accompanied by enhanced C3 binding and increased killing of the mutants. Conversely, high levels of GNA1870 expression and fH binding enhanced serum resistance. Our findings support the hypothesis that inhibiting the binding of a complement down-regulator protein to the neisserial surface by specific Ab may enhance intrinsic bactericidal activity of the Ab, resulting in two distinct mechanisms of Ab-mediated vaccine efficacy. These data provide further support for inclusion of this molecule in a meningococcal vaccine. To reflect the critical function of this molecule, we suggest calling it fH-binding protein.

The peptidoglycan-degrading property of lysozyme is not required for bactericidal activity in vivo

Lysozyme is an abundant, cationic antimicrobial protein that plays an important role in pulmonary host defense. Increased concentration of lysozyme in the airspaces of transgenic mice enhanced bacterial killing whereas lysozyme deficiency resulted in increased bacterial burden and morbidity. Lysozyme degrades peptidoglycan in the bacterial cell wall leading to rapid killing of Gram-positive organisms; however, this mechanism cannot account for the protective effect of lysozyme against Gram-negative bacteria. The current study was therefore designed to test the hypothesis that the catalytic activity (muramidase activity) of lysozyme is not required for bacterial killing in vivo. Substitution of serine for aspartic acid at position 53 (D53S) in mouse lysozyme M completely ablated muramidase activity. Muramidase-deficient recombinant lysozyme (LysM(D53S)) killed both Gram-positive and Gram-negative bacteria in vitro. Targeted expression of LysM(D53S) in the respiratory epithelium of wild-type (LysM(+/+)/LysM(D53S)) or lysozyme M(null) mice (LysM(-/-)/LysM(D53S)) resulted in significantly elevated lysozyme protein in the airspaces without any increase in muramidase activity. Intratracheal challenge of transgenic mice with Gram-positive or Gram-negative bacteria resulted in a significant increase in bacterial burden in LysM(-/-) mice that was completely reversed by targeted expression of LysM(D53S). These results indicate that the muramidase activity of lysozyme is not required for bacterial killing in vitro or in vivo.

Macrophages Acquire Neutrophil Granules for Antimicrobial Activity against Intracellular Pathogens

A key target of many intracellular pathogens is the macrophage. Although macrophages can generate antimicrobial activity, neutrophils have been shown to have a key role in host defense, presumably by their preformed granules containing antimicrobial agents. Yet the mechanism by which neutrophils can mediate antimicrobial activity against intracellular pathogens such as Mycobacterium tuberculosis has been a long-standing enigma. We demonstrate that apoptotic neutrophils and purified granules inhibit the growth of extracellular mycobacteria. Phagocytosis of apoptotic neutrophils by macrophages results in decreased viability of intracellular M. tuberculosis. Concomitant with uptake of apoptotic neutrophils, granule contents traffic to early endosomes, and colocalize with mycobacteria. Uptake of purified granules alone decreased growth of intracellular mycobacteria. Therefore, the transfer of antimicrobial peptides from neutrophils to macrophages provides a cooperative defense strategy between innate immune cells against intracellular pathogens and may complement other pathways that involve delivery of antimicrobial peptides to macrophages.

Immunoglobulin G subclass response to a meningococcal quadrivalent polysaccharide-diphtheria toxoid conjugate vaccine

Changes in the immunoglobulin G1 (IgG1)/IgG2 ratio following vaccination can indicate the activation of cellular control mechanisms typical of a T-cell-dependent response. We examined IgG subclass ratios in 17 healthy adults (26 to 55 years of age) before and 4 to 6 weeks following immunization with a quadrivalent meningococcal-polysaccharide diphtheria toxoid conjugate vaccine against serogroups A, C, Y, and W135. Serologic responses were determined by serum bactericidal antibody assay and serogroup-specific IgG, IgG1, and IgG2 enzyme-linked immunosorbent assay. Prevaccination serogroup A-specific IgG1/IgG2 ratios were <1 for all subjects and differed by subject for C, Y, and W-135. Postvaccination, significant increases in IgG, IgG1, and IgG2, were observed for all serogroups. Serogroup-specific IgG1/IgG2 ratios increased for group A (14/17 subjects, 88%), decreased in more than half of subjects for groups C (9/17, 53%) and W135 (12/17, 71%) and decreased for serogroup Y (16/17, 94%). IgG1/IgG2 ratios differed between individual vaccinees and were similar to the responses of adults who received pneumococcal conjugate vaccines or a monovalent C conjugate vaccine. Further studies on IgG subclasses following meningococcal polysaccharide and conjugate vaccination are needed.

Functional significance of factor H binding to Neisseria meningitidis

Neisseria meningitidis is an important cause of septicemia and meningitis. To cause disease, the bacterium must successfully survive in the bloodstream where it has to avoid being killed by host innate immune mechanisms, particularly the complement system. A number of pathogenic microbes bind factor H (fH), the negative regulator of the alternative pathway of complement activation, to promote their survival in vivo. In this study, we show that N. meningitidis binds fH to its surface. Binding to serogroups A, B, and C N. meningitidis strains was detected by FACS and Far Western blot analysis, and occurred in the absence of other serum factors such as C3b. Unlike Neisseria gonorrhoeae, binding of fH to N. meningitidis was independent of sialic acid on the bacterium, either as a component of its LPS or its capsule. Characterization of the major fH binding partner demonstrated that it is a 33-kDa protein; examination of insertion mutants showed that porins A and B, outer membrane porins expressed by N. meningitidis, do not contribute significantly to fH binding. We examined the physiological consequences of fH bound to the bacterial surface. We found that fH retains its activity as a cofactor of factor I when bound to the bacterium and contributes to the ability of N. meningitidis to avoid complement-mediated killing in the presence of human serum. Therefore, the recruitment of fH provides another mechanism by which this important human pathogen evades host innate immunity.

Production of protective antibodies againstPorphyromonas gingivalisstrains by immunization with recombinant gingipain domains

We studied the effect of antibodies against Porphyromonas gingivalis gingipain domains, preparing them against three recombinant fragments of RgpA (catalytic domain, r-Rgp CAT; hemagglutinin domains, r-Rgp 44 and r-Rgps 15-27) and one fragment of Kgp (catalytic domain, r-Kgp CAT). Enhancement of opsonization and killing by human polymorphonuclear leukocytes were measured in the noninvasive FDC 381 and invasive W50 strains of P. gingivalis. Anti-r-Rgp 44 was the most effective in both strains of P. gingivalis. The present findings lead us to recommend RgpA 44 as a candidate immunogen for vaccines against P. gingivalis.

[Investigation of serum resistance for Pseudomonas aeruginosa and Acinetobacter baumannii strains]

Serum resistance is one of the major virulence factors of Gram negative bacteria. The aim of this study was to investigate the serum resistance of Pseudomonas aeruginosa and Acinetobacter baumannii strains isolated from various clinical samples (19 tracheal aspirates, 14 urine, 7 sputum, 7 wound and one peritoneal fluid specimens). Forty-eight P. aeuginosa and 48 A. baumannii strains were tested for human serum bactericidal effect by using Benge's method. Thirty-five (72.9%), 9 (18.7%), and 4 (8.3%) of P. aeruginosa strains were found to be resistant, intermediate sensitive and sensitive to serum, respectively. These rates were detected as 81.2% (39/48), 14.5% (7/48), and 4.1% (2/48) for A. baumannii strains, respectively. It can be concluded that, high serum resistance rates of P. aeruginosa and A. baumannii isolates might have an important role in the pathogenesis of infections of these bacteria.

Logarithmic phase Escherichia coli K1 efficiently avoids serum killing by promoting C4bp-mediated C3b and C4b degradation

Meningitis caused by Escherichia coli K1 is a serious illness in neonates with neurological sequelae in up to 50% of survivors. A high degree of bacteremia is required for E. coli K1 to cross the blood-brain barrier, which suggests that the bacterium must evade the host defence mechanisms and survive in the bloodstream. We previously showed that outer membrane protein A (OmpA) of E. coli binds C4b-binding protein (C4bp), an inhibitor of complement activation via the classical pathway. Nevertheless, the exact mechanism by which E. coli K1 survives in serum remains elusive. Here, we demonstrate that log phase (LP) OmpA+ E. coli K1 avoids serum bactericidal activity more effectively than postexponential phase bacteria. OmpA- E. coli cannot survive in serum grown to either phase. The increased serum resistance of LP OmpA+ E. coli is the result of increased binding of C4bp, with a concomitant decrease in the deposition of C3b and the downstream complement proteins responsible for the formation of the membrane attack complex. C4bp bound to E. coli K1 acts as a cofactor to factor I in the cleavage of both C3b and C4b, which shuts down the ensuing complement cascade. Accordingly, a peptide corresponding to the complement control protein domain 3 of C4bp sequence, was able to compete with C4bp binding to OmpA and cause increased deposition of C3b. Thus, binding of C4bp appears to be responsible for survival of E. coli K1 in human serum.

Comparisons of innate immune activity of all known living crocodylian species

Serum samples from all twenty-three known living members of the Crocodylia were tested for antibacterial activity against eight bacterial species. These data were used to generate an immune profile for each crocodylian species. Statistical analyses revealed that the three living lineages of crocodylians, Alligatoroidea, Crocodyloidea, and Gavialoidea, were distinguishable by their immunological activities. For instance, species within the Alligatoroidea and Crocodyloidea exhibited remarkable immune activity similarities to others in their own lineages. Comparisons of the members of the different lineages, however, revealed substantial differences in immune profiles. Furthermore, species that are in the same genus were shown to exhibit more immune similarities to each other than to members of other genera within the same family. Finally, our immunological analyses reveal that Tomistoma schlegelii aligns more closely with the Gavialoidea than the Crocodyloidea.

Bactericidal activity of normal bovine serum (NBS) directed against some Enterobacteriaceae with sialic acid-containing lipopolysaccharides (LPS) as a component of cell wall

The sensitivity of bacteria to the bactericidal activity of serum depends on the structure and organization of the bacterial outer membrane. Sialic acid has been found in the O-specific region of bacterial lipopolysaccharide (LPS) and it plays an essential role in protecting Gram-negative bacteria against the bactericidal activity of human and animal serum. The susceptibility of Gram-negative bacilli with sialic acid-containing LPS to the bactericidal action of normal bovine serum (NBS) was determined. The examined strains (Escherichia coli O104 (PCM 270), E. coli O24 (PCM 195), E. coli O56 (PCM 2372), Citrobacter braakii O37 (PCM 2346) and Salmonella enterica ssp. enterica serovar Toucra O48 (PCM 2359) showed variable sensitivity to the bactericidal effect of the serum. The role of the mechanisms of complement activation in the killing process was also determined.

Human C4b-binding protein selectively interacts with Neisseria gonorrhoeae and results in species-specific infection

Neisseria gonorrhoeae is the causative agent of gonorrhea, a disease that is restricted to humans. Complement forms a key arm of the innate immune system that combats gonococcal infections. N. gonorrhoeae uses its outer membrane porin (Por) molecules to bind the classical pathway of complement down-regulatory protein C4b-binding protein (C4bp) to evade killing by human complement. Strains of N. gonorrhoeae that resisted killing by human serum complement were killed by serum from rodent, lagomorph, and primate species, which cannot be readily infected experimentally with this organism and whose C4bp molecules did not bind to N. gonorrhoeae. In contrast, we found that Yersinia pestis, an organism that can infect virtually all mammals, bound species-specific C4bp and uniformly resisted serum complement-mediated killing by these species. Serum resistance of gonococci was restored in these sera by human C4bp. An exception was serotype Por1B-bearing gonococcal strains that previously had been used successfully in a chimpanzee model of gonorrhea that simulates human disease. Por1B gonococci bound chimpanzee C4bp and resisted killing by chimpanzee serum, providing insight into the host restriction of gonorrhea and addressing why Por1B strains, but not Por1A strains, have been successful in experimental chimpanzee infection. Our findings may lead to the development of better animal models for gonorrhea and may also have implications in the choice of complement sources to evaluate neisserial vaccine candidates.

Constitutive innate immunity is a component of the pace-of-life syndrome in tropical birds

We studied the relationship between one component of immune function and basal metabolic rate (BMR), an indicator of the 'pace-of-life syndrome', among 12 tropical bird species and among individuals of the tropical house wren (Troglodytes aedon), to gain insights into functional connections between life history and physiology. To assess constitutive innate immunity we introduced a new technique in the field of ecological and evolutionary immunology that quantifies the bactericidal activity of whole blood. This in vitro assay utilises a single blood sample to provide a functional, integrated measure of constitutive innate immunity. We found that the bactericidal activity of whole blood varied considerably among species and among individuals within a species. This variation was not correlated with body mass or whole-organism BMR. However, among species, bacteria killing activity was negatively correlated with mass-adjusted BMR, suggesting that species with a slower pace-of-life have evolved a more robust constitutive innate immune capability. Among individuals of a single species, the house wren, bacteria killing activity was positively correlated with mass-adjusted BMR, pointing to physiological differences in individual quality on which natural selection potentially could act.

Binding of the complement inhibitor C4bp to serogroup B Neisseria meningitidis

Neisseria meningitidis (meningococcus) is an important cause of meningitis and sepsis. Currently, there is no effective vaccine against serogroup B meningococcal infection. Host defense against neisseriae requires the complement system (C) as indicated by the fact that individuals deficient in properdin or late C components (C6-9) have an increased susceptibility to recurrent neisserial infections. Because the classical pathway (CP) is required to initiate efficient complement activation on neisseriae, meningococci should be able to evade it to cause disease. To test this hypothesis, we studied the interactions of meningococci with the major CP inhibitor C4b-binding protein (C4bp). We tested C4bp binding to wild-type group B meningococcus strain (H44/76) and to 11 isogenic mutants thereof that differed in capsule expression, lipo-oligosaccharide sialylation, and/or expression of either porin (Por) A or PorB3. All strains expressing PorA bound radiolabeled C4bp, whereas the strains lacking PorA bound significantly less C4bp. Increased binding was observed under hypotonic conditions. Deleting PorB3 did not influence C4bp binding, but the presence of polysialic acid capsule reduced C4bp binding by 50%. Bound C4bp remained functionally active in that it promoted the inactivation of C4b by factor I. PorA-expressing strains were also more resistant to C lysis than PorA-negative strains in a serum bactericidal assay. Binding of C4bp thus helps Neisseria meningitidis to escape CP complement activation.

Myeloperoxidase plays critical roles in killing Klebsiella pneumoniae and inactivating neutrophil elastase: effects on host defense

Activated neutrophils use myeloperoxidase (MPO) to generate an array of potent toxic oxidants. In the current studies we used genetically altered mice deficient in MPO to investigate the role of the enzyme in host defense against the Gram-negative bacterium Klebsiella pneumoniae, an important human pathogen. For comparison, we used mice deficient in the antimicrobial molecule, neutrophil elastase (NE). When challenged i.p., mice deficient in either MPO or NE were markedly more susceptible to bacterial infection and death. In vitro studies suggested that MPO impairs the morphology of bacteria in a distinctive way. Of importance, our in vitro studies found that MPO mediated oxidative inactivation of NE, an enzyme that has been widely implicated in the pathogenesis of various tissue-destructive diseases. This pathway of oxidative inactivation may be physiologically relevant, because activated neutrophils isolated from MPO-deficient mice exhibited increased elastase activity. Our observations provide strong evidence that MPO, like NE, is a key player in the killing of K. pneumoniae bacteria. They also suggest that MPO may modulate NE to protect the host from the tissue-degrading activity of this proteinase.

Naturally-acquired immunity to Neisseria meningitidis group A

Group A meningococcal disease is epidemic in Sudan, less common in Uganda, a country bordering the "meningitis belt," and rare in North America. The basis of naturally-acquired group A immunity is unknown but in North America protection has been attributed to a high prevalence of serum anticapsular antibodies elicited by cross-reacting bacteria. We measured group A anticapsular antibody concentrations and bactericidal titers in sera from 236 adults (47 from the Sudan obtained at the height of a group A epidemic, 57 from Uganda, and 132 from North America). Anticapsular antibody concentrations were higher in Sudanese sera than in North American or Ugandan sera (geometric mean of 31.5 versus 5.4 and 5.3 microg/ml, respectively, P < 0.0001). Bactericidal titers of > or =1:4 (presumed to be a protective titer when measured with human complement) were detected in 66% of Sudanese sera as compared with 27 and 23%, respectively, of North American and Ugandan sera (P < 0.0001). Bactericidal activity was inhibited by group A polysaccharide in 58% of the Sudanese bactericidal sera as compared to 17 and 6% of North America and Ugandan bactericidal sera (P < 0.0005). Approximately 50% of non-bactericidal Sudanese sera had high IgA anticapsular antibody concentrations, which were rare in bactericidal Sudanese sera. Thus, serum anticapsular antibodies and bactericidal activity are prevalent in Sudanese exposed to a group A epidemic. Cross-reacting group A anticapsular antibodies are prevalent in North American and Ugandan sera, but bactericidal activity is infrequent and when present is largely directed at non-capsular antigens.

Bacterial lipoprotein induces resistance to Gram-negative sepsis in TLR4-deficient mice via enhanced bacterial clearance

TLRs are highly conserved pathogen recognition receptors. As a result, TLR4-deficient C3H/HeJ mice are highly susceptible to Gram-negative sepsis. We have previously demonstrated that tolerance induced by bacterial lipoprotein (BLP) protects wild-type mice against polymicrobial sepsis-induced lethality. In this study, we assessed whether pretreatment of C3H/HeJ mice with BLP could induce resistance to a subsequent Gram-negative Salmonella typhimurium infection. Pretreatment with BLP resulted in a significant survival benefit in TLR4-deficient C3H/HeJ mice (p < 0.0002 vs control C3H/HeJ) after challenge with live S. typhimurium (0.25 x 10(6) CFU/mouse). This survival benefit was associated with enhanced bacterial clearance from the circulation and in the visceral organs (p < 0.05 vs control C3H/HeJ). Furthermore, pretreatment with BLP resulted in significant increases in complement receptor type 3 (CR3) and FcgammaIII/IIR expression on polymorphonuclear neutrophils (PMNs) and macrophages (p < 0.05 vs control C3H/HeJ). There was impaired bacterial recognition and phagocytosis in TLR4-deficient mice compared with wild-type mice. However, a significant augmented uptake, ingestion, and intracellular killing of S. typhimurium by PMNs and peritoneal macrophages was evident in BLP-pretreated C3H/HeJ mice (p < 0.05 vs control C3H/HeJ). An up-regulation of inducible NO synthase and increased production of intracellular NO were observed in peritoneal macrophages from BLP-pretreated C3H/HeJ mice (p < 0.05 vs control C3H/HeJ). Depletion of PMNs did not diminish the beneficial effects of BLP with regard to both animal survival and bacterial clearance. These results indicate that BLP, a TLR2 ligand, protects highly susceptible TLR4-deficient mice from Gram-negative sepsis via enhanced bacterial clearance.

Effects of zinc supplementation as adjunct therapy on the systemic immune responses in shigellosis

BACKGROUND

Zinc is lost during diarrheal diseases, and zinc deficiency induces intestinal morphology-altering inflammatory responses that zinc supplementation can correct.

OBJECTIVE

We assessed the in vivo effect of zinc supplementation on systemic and mucosal responses in mildly to moderately malnourished (defined as <-1 but >-2 and <-2 but >-3 weight-for-height z scores, respectively, based on the National Center for Health Statistics growth reference) children with shigellosis.

DESIGN

A double-blind placebo-controlled trial was conducted in Shigella flexneri-infected children aged 12-59 mo. Daily for 14 d, elemental zinc (20 mg) and multivitamins (vitamins A and D, thiamine, riboflavin, and nicotinamide) plus calcium were given at twice the US recommended dietary allowance to the zinc group (n=28), and multivitamins plus calcium were given to the control group (n=28). All subjects received standard antibiotic therapy.

RESULTS

There was no significant interaction between zinc supplementation and time, but zinc supplementation showed a significant effect on serum zinc concentrations. With a >or=4-fold increase in serum shigellacidal antibody titers from baseline used as the cutoff, the proportion of children with shigellacidal antibody response was greater in the zinc group than in the control group (P<0.03). There was a significant (P=0.02) treatment x time interaction for the proportions of circulating CD20+ and CD20+CD38+ cells, which were higher on day 7 in the zinc group than in the control group (P<0.007). No effect was seen on histopathologic features or the expression of innate and inflammatory mediators in the rectum.

CONCLUSION

Adjunct therapy with zinc during acute shigellosis significantly improved seroconversion to shigellacidal antibody response and increased the proportions of circulating B lymphocytes and plasma cells.

[Determination of the bactericidal activity of blood serum by recombinant luminescence strains of Escherichia coli]

It has been experimentally proven as possible to use recombinant strains of Escherichia coli carrying the genes of luminescence of natural fluorescent bacteria in evaluating the bactericidal activity of blood serum (BABS). The shaping fluorescence inhibition was shown to be in proportion to the developing bactericidal effect in respect to the luminescent strains of Escherichia coli, which depended on a used concentration of blood serum and time of contact. The list of E. coli recombinant strains, which fit in most of all with the evaluation of BABS, was drawn. The values of the bactericidal activity of blood serum determined by the routine bacteriological and nephelometric methods were demonstrated to coincide with those determined by the worked-out bio-luminescent method.

Vγ9Vδ2 T cells use a combination of mechanisms to limit the spread of the pathogenic bacteria Brucella

Human Vgamma9Vdelta2 T cells play a crucial role in early immune response to intracellular pathogens. In brucellosis infection, this population of cells is drastically increased in the peripheral blood of patients during the acute phase of infection. In vitro, Vgamma9Vdelta2 T cells exhibit strong cytolytic activity against Brucella-infected cells and are able to impair intracellular growth of Brucella suis in autologous macrophages. In this study, we have investigated the relative importance of contact-dependent mechanisms versus soluble factors in the intracellular growth and viability of B. suis. We show that Vgamma9Vdelta2 T cells use contact-dependent mechanisms, such as the release of lytic granules and Fas-mediated signals, to decrease intracellular B. suis through lysis of infected macrophages, but these mechanisms have little impact on Brucella survival. Moreover, we demonstrate that soluble factors secreted by Vgamma9Vdelta2 T cells can directly affect B. suis survival through their potent bactericidal effects. From these results, we conclude that Vgamma9Vdelta2 T cells are able to use a combination of mechanisms that reduce the total numbers of B. suis and thus, may benefit the host by limiting the spread of this intracellular pathogen.

Neutrophils and keratinocytes in innate immunity--cooperative actions to provide antimicrobial defense at the right time and place

The human neutrophil is a professional phagocyte of fundamental importance for defense against microorganisms, as witnessed by the life-threatening infections occurring in patients with neutropenia or with defects that result in decreased microbicidal activity of the neutrophil. Likewise, the skin and mucosal surfaces provide important barriers against infections. Traditionally, these major defense systems, the epithelial cells and the neutrophils, have been viewed as limited in their armory: The epithelial cells provide defense by constituting a physical barrier, and the neutrophils provide instant delivery of preformed antimicrobial substances or on-the-spot assembly of the multicomponent reduced nicotinamide adenine dinucleotide phosphate oxidase from stored components for the generation of reactive oxygen metabolites. Recent research has shown that epithelial cells are highly dynamic and able to generate antimicrobial peptides in response not only to microbial infection itself but more importantly, to the growth factors that are called into play when the physical barrier is broken, and the risk of microbial infection is imminent. Likewise, the neutrophil changes its profile of actively transcribed genes when it diapedeses into wounded skin. This results in generation of signaling molecules, some of which support the growth and antimicrobial potential of keratinocytes and epithelial cells. This paper will highlight some recent advances in this field.

Immunoglobulin M-enriched intravenous immunoglobulin inhibits classical pathway complement activation, but not bactericidal activity of human serum

Acute or even hyperacute humoral graft rejection, mediated by classical pathway complement activation, occurs in allo- and xenotransplantation due to preformed anti-graft antibodies. Intravenous immunoglobulin (IVIg) preparations can prevent complement-mediated tissue injury and delay hyperacute xenograft rejection. It is known that IgM-enriched IVIg (IVIgM) has a higher capacity to block complement than IVIgG. Different IVIgs were therefore tested for specificity of complement inhibition and effect on anti-bacterial activity of human serum. IVIgM-I (Pentaglobin), 12% IgM), IVIgM-II (IgM-fraction of IVIgM-I, 60% IgM), and three different IVIgG (all >95% IgG) were used. The known complement inhibitor dextran sulfate was used as control. Hemolytic assays were performed to analyze pathway-specificity of complement inhibition. Effects of IVIg on complement deposition on pig cells and Escherichia coli were assessed by flow cytometry and cytotoxicity as well as bactericidal assays. Complement inhibition by IVIgM was specific for the classical pathway, with IC50 values of 0.8 mg/ml for IVIgM-II and 1.7 mg/ml for IVIgM-I in the CH50 assay. Only minimal inhibition of the lectin pathway was seen with IVIgM-II (IC50 15.5 mg/ml); no alternative pathway inhibition was observed. IVIgG did not inhibit complement in any hemolytic assay. Classical pathway complement inhibition by IVIgM was confirmed in an in vitro xenotransplantation model with PK15 cells. In contrast, IVIgM did not inhibit (mainly alternative pathway mediated) killing of E. coli by human serum. In conclusion, IgM-enriched IVIg is a specific inhibitor of the classical complement pathway, leaving the alternative pathway intact, which is an important natural anti-bacterial defense, especially for immunosuppressed patients.