Modulating fast skeletal muscle contraction protects skeletal muscle in animal models of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a lethal muscle disease caused by absence of the protein dystrophin, which acts as a structural link between the basal lamina and contractile machinery to stabilize muscle membranes from mechanical stress. In DMD, mechanical stress leads to exaggerated membrane injury and fiber breakdown, with fast fibers being the most susceptible to damage. A major contributor to this injury is muscle contraction, controlled by the motor protein myosin. However, the relationship between how muscle contraction and fast muscle fiber damage contribute to the pathophysiology of DMD has not been well characterized. We explored the role of fast skeletal muscle contraction in DMD with a novel, selective, orally active inhibitor of fast skeletal muscle myosin, EDG-5506. Surprisingly, even modest decreases of contraction (<15%) were sufficient to protect skeletal muscles in dystrophic mdx mice from stress injury. Longer-term treatment also decreased muscle fibrosis in key disease-implicated tissues. Importantly, therapeutic levels of myosin inhibition with EDG-5506 did not detrimentally affect strength or coordination. Finally, in dystrophic dogs, EDG-5506 reversibly reduced circulating muscle injury biomarkers and increased habitual activity. This unexpected biology may represent an important alternative treatment strategy for Duchenne and related myopathies.

Unconstrained muscle-tendon workloops indicate resonance tuning as a mechanism for elastic limb behavior during terrestrial locomotion

In terrestrial locomotion, there is a missing link between observed spring-like limb mechanics and the physiological systems driving their emergence. Previous modeling and experimental studies of bouncing gait (e.g., walking, running, hopping) identified muscle-tendon interactions that cycle large amounts of energy in series tendon as a source of elastic limb behavior. The neural, biomechanical, and environmental origins of these tuned mechanics, however, have remained elusive. To examine the dynamic interplay between these factors, we developed an experimental platform comprised of a feedback-controlled servo-motor coupled to a biological muscle-tendon. Our novel motor controller mimicked in vivo inertial/gravitational loading experienced by muscles during terrestrial locomotion, and rhythmic patterns of muscle activation were applied via stimulation of intact nerve. This approach was based on classical workloop studies, but avoided predetermined patterns of muscle strain and activation-constraints not imposed during real-world locomotion. Our unconstrained approach to position control allowed observation of emergent muscle-tendon mechanics resulting from dynamic interaction of neural control, active muscle, and system material/inertial properties. This study demonstrated that, despite the complex nonlinear nature of musculotendon systems, cyclic muscle contractions at the passive natural frequency of the underlying biomechanical system yielded maximal forces and fractions of mechanical work recovered from previously stored elastic energy in series-compliant tissues. By matching movement frequency to the natural frequency of the passive biomechanical system (i.e., resonance tuning), muscle-tendon interactions resulting in spring-like behavior emerged naturally, without closed-loop neural control. This conceptual framework may explain the basis for elastic limb behavior during terrestrial locomotion.

Timing matters: tuning the mechanics of a muscle-tendon unit by adjusting stimulation phase during cyclic contractions

A growing body of research on the mechanics and energetics of terrestrial locomotion has demonstrated that elastic elements acting in series with contracting muscle are critical components of sustained, stable and efficient gait. Far fewer studies have examined how the nervous system modulates muscle-tendon interaction dynamics to optimize 'tuning' or meet varying locomotor demands. To explore the fundamental neuromechanical rules that govern the interactions between series elastic elements (SEEs) and contractile elements (CEs) within a compliant muscle-tendon unit (MTU), we used a novel work loop approach that included implanted sonomicrometry crystals along muscle fascicles. This enabled us to decouple CE and SEE length trajectories when cyclic strain patterns were applied to an isolated plantaris MTU from the bullfrog (Lithobates catesbeianus). Using this approach, we demonstrate that the onset timing of muscle stimulation (i.e. stimulation phase) that involves a symmetrical MTU stretch-shorten cycle during active force production results in net zero mechanical power output, and maximal decoupling of CE and MTU length trajectories. We found it difficult to 'tune' the muscle-tendon system for strut-like isometric force production by adjusting stimulation phase only, as the zero power output condition involved significant positive and negative mechanical work by the CE. A simple neural mechanism - adjusting muscle stimulation phase - could shift an MTU from performing net zero to net positive (energy producing) or net negative (energy absorbing) mechanical work under conditions of changing locomotor demand. Finally, we show that modifications to the classical work loop paradigm better represent in vivo muscle-tendon function during locomotion.

More is not always better: modeling the effects of elastic exoskeleton compliance on underlying ankle muscle-tendon dynamics

Development of robotic exoskeletons to assist/enhance human locomotor performance involves lengthy prototyping, testing, and analysis. This process is further convoluted by variability in limb/body morphology and preferred gait patterns between individuals. In an attempt to expedite this process, and establish a physiological basis for actuator prescription, we developed a simple, predictive model of human neuromechanical adaptation to a passive elastic exoskeleton applied at the ankle joint during a functional task. We modeled the human triceps surae-Achilles tendon muscle tendon unit (MTU) as a single Hill-type muscle, or contractile element (CE), and series tendon, or series elastic element (SEE). This modeled system was placed under gravitational load and underwent cyclic stimulation at a regular frequency (i.e. hopping) with and without exoskeleton (Exo) assistance. We explored the effect that both Exo stiffness (kExo) and muscle activation (Astim) had on combined MTU and Exo (MTU + Exo), MTU, and CE/SEE mechanics and energetics. Model accuracy was verified via qualitative and quantitative comparisons between modeled and prior experimental outcomes. We demonstrated that reduced Astim can be traded for increased kExo to maintain consistent MTU + Exo mechanics (i.e. average positive power (P⁺mech) output) from an unassisted condition (i.e. kExo = 0 kN · m⁻¹). For these regions of parameter space, our model predicted a reduction in MTU force, SEE energy cycling, and metabolic rate (Pmet), as well as constant CE P⁺mech output compared to unassisted conditions. This agreed with previous experimental observations, demonstrating our model's predictive ability. Model predictions also provided insight into mechanisms of metabolic cost minimization, and/or enhanced mechanical performance, and we concluded that both of these outcomes cannot be achieved simultaneously, and that one must come at the detriment of the other in a spring-assisted compliant MTU.

Elastic ankle exoskeletons reduce soleus muscle force but not work in human hopping

Inspired by elastic energy storage and return in tendons of human leg muscle-tendon units (MTU), exoskeletons often place a spring in parallel with an MTU to assist the MTU. However, this might perturb the normally efficient MTU mechanics and actually increase active muscle mechanical work. This study tested the effects of elastic parallel assistance on MTU mechanics. Participants hopped with and without spring-loaded ankle exoskeletons that assisted plantar flexion. An inverse dynamics analysis, combined with in vivo ultrasound imaging of soleus fascicles and surface electromyography, was used to determine muscle-tendon mechanics and activations. Whole body net metabolic power was obtained from indirect calorimetry. When hopping with spring-loaded exoskeletons, soleus activation was reduced (30–70%) and so was the magnitude of soleus force (peak force reduced by 30%) and the average rate of soleus force generation (by 50%). Although forces were lower, average positive fascicle power remained unchanged, owing to increased fascicle excursion (+4–5 mm). Net metabolic power was reduced with exoskeleton assistance (19%). These findings highlighted that parallel assistance to a muscle with appreciable series elasticity may have some negative consequences, and that the metabolic cost associated with generating force may be more pronounced than the cost of doing work for these muscles.

Combined diazepam and HDAC inhibitor treatment protects against seizures and neuronal damage caused by soman exposure

The occurrence of status epilepticus (SE) is considered the main cause of brain lesions and morphological alterations, such as hippocampal neuron loss, that result in chronic epilepsy. Previous work demonstrated the convulsive and widespread neuropathological effects of soman, an organophosphorus compound that causes SE and severe recurrent seizures as a result of exposure. Seizures begin rapidly after exposure, can continue for hours, and contribute to prolonged physical incapacitation of the victim. This study attempts to identify anticonvulsive and neuroprotective drugs against soman exposure. Male Sprague-Dawley rats were exposed to 1.0 LD(50) soman. EEGraphical and neuropathological (Fluoro-Jade B staining) effects were analyzed at 72 h post-exposure to soman and subsequent treatments with diazepam (DZP) alone or in combination with histone deacetylase inhibitors, suberoylanilide hydroxamic acid (SAHA) or valproic acid (VPA). The extent of brain damage was dependent on the length of SE and not on the number of recurrent seizures. DZP treatment alone decreased SE time and damage in hippocampus, amygdala, thalamus and cortex, but not in piriform nuclei. The combination of DZP and VPA 100 mg/kg showed more anticonvulsive effects, decreased SE time, and afforded more neuroprotection in the hippocampus, mainly the ventral portion. The combination DZP and SAHA 25 mg/kg was more neuroprotective, but not more anticonvulsant than DZP alone. The DZP combination with VPA HDAC inhibitor proved to be a good treatment for SE and neuronal damage caused by soman exposure.

Influence of parallel spring-loaded exoskeleton on ankle muscle-tendon dynamics during simulated human hopping

Robotic assistance for rehabilitation and enhancement of human locomotion has become a major goal of biomedical engineers in recent years. While significant progress to this end has been made in the fields of neural interfacing and control systems, little has been done to examine the effects of mechanical assistance on the biomechanics of underlying muscle-tendon systems. Here, we model the effects of mechanical assistance via a passive spring acting in parallel with the triceps surae-Achilles tendon complex during cyclic hopping in humans. We examine system dynamics over a range of biological muscle activation and exoskeleton spring stiffness. We find that, in most cases, uniform cyclic mechanical power production of the coupled system is achieved. Furthermore, unassisted power production can be reproduced throughout parameter space by trading off decreases in muscle activation with increases in ankle exoskeleton spring stiffness. In addition, we show that as mechanical assistance increases the biological muscle-tendon unit becomes less 'tuned' resulting in higher mechanical power output from active components of muscle despite large reductions in required force output.

Analysis of pathogen-host cell interactions in purpura fulminans: expression of capsule, type IV pili, and PorA by Neisseria meningitidis in vivo

The pattern of meningococcal surface structure expression in different microenvironments following bloodstream invasion in vivo is not known. We used immunohistochemistry to determine the expression of capsule, type IV pili, and PorA by meningococci residing in the skin lesions of children with purpura fulminans. All the skin biopsy samples showed evidence of thrombosis and, frequently, a perivascular inflammatory cell infiltrate consisting of neutrophils (elastase positive) and monocytes/macrophages (CD68 positive). Modified Gram staining revealed 20 to over 100 gram-negative diplococci in each 4-microm-thick section, usually grouped into microcolonies. Immunoperoxidase staining demonstrated that the invading meningococci expressed PorA, capsule, and type IV pilin. Expression of these antigens was not restricted to any particular environment and was found in association with meningococci located in leukocytes, small blood vessels, and the dermal interstitium. Confocal laser scanning microscopy demonstrated coexpression of pilin and capsule by numerous microcolonies. However, there was some discordance in capsule and pilin expression within the microcolonies, suggesting phase variation. The strategy employed in this study will be helpful in investigating invasive bacterial diseases where antigenic and phase variation has a significant impact on virulence and on vaccine design.

Diagnostic assays for leprosy based on T-cell epitopes

To date, only a limited number of antigens have been described as specific for Mycobacterium leprae, and in many cases, homologues have subsequently been shown to exist in mycobacteria such as M. avium and M. intracellulare. A Leprosy Synthetic Peptide Skin Test Initiative was established by the Steering Committee on the Immunology of Mycobacteria of the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases, to investigate the potential of synthetic peptides that encode T-cell epitopes as diagnostic tools, which could be used to develop a skin-test reagent specific for leprosy. Such M. leprae-specific peptides should have unique amino acid sequences, or significant sequence-dissimilarity from those in other mycobacteria. Synthetic peptides, 15 amino acids long, were synthesised from 33 genes or open reading frames within the M. leprae genome. Tuberculoid leprosy patients from four leprosy-endemic countries, Brazil, Ethiopia, Nepal and Pakistan, were tested as subjects known to have been infected with M. leprae, and to make good T-cell responses to antigens of M. leprae; UK blood donors were used as non-exposed or non-infected subjects. Peptides inducing potentially specific responses in leprosy patients and not in UK controls, and those inducing cross-reaction responses, present in both leprosy patients and non-exposed, non-infected controls, were identified. A difference from the equivalent M. tuberculosis sequence of five or more amino acid residues did not, by itself, identify peptides that were M. leprae-specific, suggesting that many of these peptides may have homologues in environmental mycobacteria. To date, this approach has identified a number of peptides with greater than 90% specificity and 19-47% sensitivity, which are undergoing further specificity-testing. Such peptides would have great potential as T-cell reagents with which to monitor exposure to M. leprae within communities, formulated either as skin-test reagents, or as antigens for tests in vitro.

A postgenomic approach to identification of Mycobacterium leprae-specific peptides as T-cell reagents

To identify Mycobacterium leprae-specific human T-cell epitopes, which could be used to distinguish exposure to M. leprae from exposure to Mycobacterium tuberculosis or to environmental mycobacteria or from immune responses following Mycobacterium bovis BCG vaccination, 15-mer synthetic peptides were synthesized based on data from the M. leprae genome, each peptide containing three or more predicted HLA-DR binding motifs. Eighty-one peptides from 33 genes were tested for their ability to induce T-cell responses, using peripheral blood mononuclear cells (PBMC) from tuberculoid leprosy patients (n = 59) and healthy leprosy contacts (n = 53) from Brazil, Ethiopia, Nepal, and Pakistan and 20 United Kingdom blood bank donors. Gamma interferon (IFN-gamma) secretion proved more sensitive for detection of PBMC responses to peptides than did lymphocyte proliferation. Many of the peptides giving the strongest responses in leprosy donors compared to subjects from the United Kingdom, where leprosy is not endemic, have identical, or almost identical, sequences in M. leprae and M. tuberculosis and would not be suitable as diagnostic tools. Most of the peptides recognized by United Kingdom donors showed promiscuous recognition by subjects expressing differing HLA-DR types. The majority of the novel T-cell epitopes identified came from proteins not previously recognized as immune targets, many of which are cytosolic enzymes. Fifteen of the tested peptides had > or =5 of 15 amino acid mismatches between the equivalent M. leprae and M. tuberculosis sequences; of these, eight gave specificities of > or =90% (percentage of United Kingdom donors who were nonresponders for IFN-gamma secretion), with sensitivities (percentage of responders) ranging from 19 to 47% for tuberculoid leprosy patients and 21 to 64% for healthy leprosy contacts. A pool of such peptides, formulated as a skin test reagent, could be used to monitor exposure to leprosy or as an aid to early diagnosis.

The lipopolysaccharide structures of Salmonella enterica serovar Typhimurium and Neisseria gonorrhoeae determine the attachment of human mannose-binding lectin to intact organisms

Mannose-binding lectin (MBL) is an important component of the innate immune system. It binds to the arrays of sugars commonly presented by microorganisms and activates the complement system independently of antibody. Despite detailed knowledge of the stereochemical basis of MBL binding, relatively little is known about how bacterial surface structures influence binding of the lectin. Using flow cytometry, we have measured the binding of MBL to a range of mutants of Salmonella enterica serovar Typhimurium and Neisseria gonorrhoeae which differ in the structure of expressed lipopolysaccharide (LPS). For both organisms, the possession of core LPS structures led to avid binding of MBL, which was abrogated by the addition of O antigen (Salmonella serovar Typhimurium) or sialic acid (N. gonorrhoeae). Truncation of the LPS within the core led to lower levels of MBL binding. It was not possible to predict the magnitude of MBL binding from the identity of the LPS terminal sugar alone, indicating that the three-dimensional disposition of LPS molecules is probably also of importance in determining MBL attachment. These results further support the hypothesis that LPS structure is a major determinant of MBL binding.

Comparison of Mycobacterium tuberculosis genomes reveals frequent deletions in a 20 kb variable region in clinical isolates

The Mycobacterium tuberculosis complex is associated with a remarkably low level of structural gene polymorphism. As part of a search for alternative forms of genetic variation that may act as a source of biological diversity in M. tuberculosis, we have identified a region of the genome that is highly variable amongst a panel of unrelated clinical isolates. Fifteen of 24 isolates examined contained one or more copies of the M. tuberculosis-specific IS6110 insertion element within this 20 kb variable region. In nine of the isolates, including the laboratory-passaged strain H37Rv, genomic deletions were identified, resulting in loss of between two and 13 genes. In each case, deletions were associated with the presence of a copy of the IS6110 element. Absence of flanking tri- or tetra-nucleotide repeats identified homologous recombination between adjacent IS6110 elements as the most likely mechanism of the deletion events. IS6110 insertion into hot-spots within the genome of M. tuberculosis provides a mechanism for generation of genetic diversity involving a high frequency of insertions and deletions.

Gonococcal resistance to beta-lactams and tetracycline involves mutation in loop 3 of the porin encoded at the penB locus

penB is a chromosomal mutation that confers resistance to beta-lactams and tetracyclines and reduced susceptibility to quinolones in Neisseria gonorrhoeae. It is linked to the porin gene (por) and requires the increased expression of an efflux pump due to mtr. Transformation of a susceptible gonococcus (strain H1) with chromosomal DNA from strain FA140 (penA mtr penB; porin serovar IB1) and conjugal transfer of a beta-lactamase-expressing plasmid was used to produce isogenic strains for determination of equilibrium periplasmic penicillin concentrations by the method of Zimmermann and Rosselet (W. Zimmermann and A. Rosselet, Antimicrob. Agents Chemother. 12:368-372, 1977). In transformants with the Mtr and PenB phenotypes, equilibrium concentrations of penicillin were reduced. DNA sequence analysis of por from isogenic penB and penB+ transformants revealed 14 sequence differences; nine of these differences resulted in amino acid changes. Three amino acid changes were found in the putative gonococcal equivalent of the pore-constricting loop 3 of Escherichia coli OmpF. Two of these changes (Gly-101-Ala-102-->Asp-Asp) result in an increased negative charge at this position in por loop 3. PCR products comprising the complete por gene from strain FA140 were transformed into strain H1-2 (penA mtr; porin serovar IB-3), with the resulting transformants having the antibiotic susceptibility phenotype associated with penB. penB-like mutations were found in loop 3 of clinical isolates of gonococci with chromosomally mediated resistance to penicillin. We conclude that penB is a mutation in loop 3 of por that reduces porin permeability to hydrophilic antibiotics and plays an important role in the development of chromosomally mediated resistance to penicillin and tetracycline in gonococci.

Involvement of the gonococcal MtrE protein in the resistance of Neisseria gonorrhoeae to toxic hydrophobic agents

Low-level resistance of Neisseria gonorrhoeae to toxic hydrophobic agents (HAs), including some antibiotics, is chromosomally mediated via the multiple transferable resistance (mtr) efflux system. The gene encoding the 48:3 kDa outer-membrane protein MtrE, which is associated with the mtr phenotype, was identified and is homologous to export-associated outer-membrane proteins, including the OprM (formerly OprK) lipoprotein of Pseudomonas aeruginosa. Insertional inactivation of the mtrE gene in N. gonorrhoeae strain FA19 resulted in the loss o the outer-membrane protein, with concomitant hypersusceptibility of the mutant strain to a range of HAs. The properties of this mutant confirmed the role of MtrE in multidrug resistance mediated by an active efflux mechanism. Secondary structure predictions for MtrE indicated a largely hydrophilic protein with a single alpha-helical transmembrane region. A transposon-like element, similar to that found downstream of the region containing the promoters for mtrR and mtrC in Neisseria meningitidis, was identified 63 bp downstream of the mtrE gene.

Induction of human endothelial tissue factor expression by Neisseria meningitidis: the influence of bacterial killing and adherence to the endothelium

Tissue factor (TF), a small membrane bound high affinity receptor for factor VII, has an important procoagulant role in the haemostatic dysfunction associated with severe sepsis. Using an in vitro model of human endothelial TF expression, defined strains of Neisseria meningitidis were found to upregulate endothelial cell procoagulant activity (PCA) in a dose dependent manner. This TF response was detected with as little as 10(4) cfu/ml and reached similar levels to those seen with high concentrations of purified endotoxin (> 1 ng/ml). Treatment of N. meningitidis with either adult donor immune serum, penicillin or gentamicin failed to enhance this PCA. Limulus amoebocyte lysate assay of lipopolysaccharide in bacterial culture filtrates together with polymyxin B inhibition experiments suggest that endotoxin is largely responsible for endothelial TF induction by N. meningitidis. Incubation of endothelial cells with N. meningitidis B1940 and B1940 siaD- (an eight-fold more adherent unencapsulated isogenic strain), revealed a significantly greater TF response to B1940 siaD- (P < 0.01). In conclusion, bacterial adhesion to the vessel wall and therefore local levels of endotoxin may be important determinants of the endothelial procoagulant response to N. meningitidis and the consequent coagulopathy commonly associated with the disease.

Rapid detection of multidrug-resistant tuberculosis

Transmission of multidrug-resistant strains of Mycobacterium tuberculosis (MDR-TB) presents a serious problem for infection control in hospitals, particularly in the context of co-infection with the human immunodeficiency virus (HIV). We report on the use of molecular genetic tools to allow rapid assessment of samples from patients potentially infected with MDR-TB. Sputum and bronchoalveolar lavage samples were obtained from two HIV-positive patients with suspected tuberculosis, who had previous contact with a known MDR-TB index case. Polymerase chain reaction (PCR) was used directly on clinical samples to amplify genetic loci associated with rifampicin resistance (rpoB), and strain-specific polymorphisms (the direct repeat (DR) region). Drug resistance was determined using a commercially available kit for detection of point mutations in the rpoB gene (Inno-Lipa RifTB; Innogenetics, Belgium), and confirmed by nucleotide sequencing. Strain variation was determined using the spoligotyping method, based on the presence or absence of variable linker sequences within the DR region. In one patient, infection with a MDR strain identical to that of a known index case was demonstrated. A second patient, although positive for M. tuberculosis, was found to be infected with a rifampicin-sensitive strain. Results were obtained within 48 h, allowing appropriate treatment to be initiated and infection control measures to be implemented. PCR-based tests for strain-typing and for identification of rifampicin resistance provide important tools for identifying patients with MDR-TB and for rapid monitoring of potential nosocomial spread of MDR-TB. Prompt confirmation or exclusion of possible transmission allows early clinical intervention to prevent future outbreaks of multidrug-resistant M. tuberculosis.

Genes associated with meningococcal capsule complex are also found in Neisseria gonorrhoeae

A homolog of the meningococcal cps locus region E has been identified in Neisseria gonorrhoeae immediately upstream of the gonococcal region D locus. Region E has no detectable function in capsule biosynthesis in Neisseria meningitidis or in lipopolysaccharide biosynthesis in either organism. The open reading frame is homologous to proteins of unknown function in Escherichia coli and Haemophilus influenzae. Further analysis of the N. meningitidis cps cluster has identified a second copy of region D encoding three additional open reading frames, including homologs of DNA methyltransferases. The organization of the region D and E genes in N. gonorrhoeae and N. meningitidis in relation to the cps genes provides some insight into the evolutionary origin of encapsulation in N. meningitidis.

An abundant, trans-spliced mRNA from Toxocara canis infective larvae encodes a 26-kDa protein with homology to phosphatidylethanolamine-binding proteins

A full-length mRNA encoding a secreted 26-kDa antigen of infective larvae of the ascarid nematode parasite Toxocara canis has been identified. This was characterized as a 1,082-base pair clone highly abundant (0.8-1.9%) in cDNA prepared from infective stage larvae but absent from cDNA from adult male worms. Sequence analysis revealed an open reading frame corresponding to a hydrophilic 263-amino acid residue polypeptide with a 20-residue N-terminal signal peptide, indicating that it is secreted. The 5' end of the cDNA was isolated by polymerase chain reaction using a primer containing the nematode-spliced leader sequence, SL1, showing that the mRNA is trans-spliced. The molecular mass of the putative protein with the signal peptide removed is 26.01 kDa, and antibody to the recombinant protein expressed in bacterial vectors reacts with a similarly sized protein in T. canis excretory/secretory (TES) products. An identical sequence was obtained from a genomic clone isolated by expression screening with mouse antibody to TES. The 72 amino acid residues adjacent to the signal peptide form two homologous 36-residue motifs containing 6 cysteine residues; this motif is found also in the T. canis-secreted glycoprotein TES-120 and in genes of Caenorhabditis elegans. Sequence data base searches revealed significant similarity to 7 other sequences in a newly recognized gene family of phosphatidylethanolamine-binding proteins that includes yeast, Drosophila, rat, bovine, simian, and human genes and a representative from the filarial nematode Onchocerca volvulus. Assays with the T. canis recombinant 26-kDa protein expressed as a fusion with maltose-binding protein have confirmed phosphatidylethanolamine-binding specificity for this novel product.

Molecular mechanisms and implications for infection of lipopolysaccharide variation in Neisseria

The lipopolysaccharides of the pathogenic Neisseria species are subject to structural variation owing to a combination of intrinsic changes in lipopolysaccharide (LPS) biosynthesis and external modification of the LPS molecule with sialic acid. This variation appears to control bacterial behaviour by altering their ability to interact with human cells and to evade host immune defences. This interconversion of LPS phenotypes, which is also observed during the natural infection, is probably due to environmental regulation of LPS biosynthesis superimposed on spontaneous changes in the DNA of distinct LPS loci. LPS variation may be a common strategy of mucosal pathogens to colonize and persist within the human host.

Gonococcal rfaF mutants express Rd2 chemotype LPS and do not enter epithelial host cells

We have investigated the function of the Isi-1 gene of Neisseria gonorrhoeae previously implicated in lipopolysaccharide (LPS)-inner-core biosynthesis (Petricoin et al., 1991). Disruption of the gene in gonococcal strain MS11 resulted in the production of LPS that migrated faster than that from an isogenic galE mutant, typical for a mutation that influences the inner-core region. Complementation of a panel of Salmonella typhimurium mutants with defined defects in rfa loci demonstrated conclusively that the Isi-1 gene of MS11 is functionally homologous to the rfaF gene, which encodes heptosyltransferase II in both E. coli and S. typhimurium. Comparison of deduced amino acid sequences of the gonococcal and the Salmonella RfaF demonstrated 70% similarity, including 47% identical amino acid residues. Immunochemical analysis of the LPS using monoclonal antibodies directed against chemically defined inner-core glycoconjugates revealed that the gonococcal and Salmonella Rd2-chemotypes were antigenically similar, further extending the genetic and functional homology. Infection experiments in vitro demonstrated that the Isi-1 mutant could not invade human Chang epithelial cells despite expression of a genetically defined invasion-promoting gonococcal opacity protein. These data imply that the LPS phenotype is a critical factor for gonococcal invasiveness.

The identification of cryptic rhamnose biosynthesis genes in Neisseria gonorrhoeae and their relationship to lipopolysaccharide biosynthesis

Neisseria gonorrhoeae synthesizes a rough lipopolysaccharide that does not contain any of the repetitive units characteristic of the smooth lipopolysaccharide of members of the family Enterobacteriaceae. Three gonococcal homologs of Salmonella serovar typhimurium genes involved in the synthesis of the rhamnose component of the repetitive subunits have been isolated. Gonococcal homologs for rfbB, rfbA, and rfbD were found downstream of the galE gene in a region of the chromosome which shows overall homology with the meningococcal capsule gene complex region D. Sequence alignment demonstrated that the gonococcal gene products have 69, 65, and 54% amino acid identity with the Salmonella proteins RfbB, RfbA, and RfbD. The gonococcal RfbB and RfbA amino acid sequences share even more identical residues (73 and 65%, respectively) with the amino acid sequences derived from Escherichia coli genes o355 and o292, respectively. These genes are clustered with the genes involved in the biosynthesis of enterobacterial common antigen, and o355 is listed in the GenBank and Swiss Protein data banks as rffE (encoding UDP-GlcNAc-2-epimerase). However, complementation studies demonstrated that o355 does not encode the enzyme UDP-GlcNAc-2-epimerase. Gonococcal strains constructed with null mutations in the rfbBAD genes were unchanged in lipopolysaccharide phenotype and in the synthesis of gonococcal carbohydrate-containing C antigen. We were unable to detect any changes in gonococcal phenotype with respect to lipopolysaccharide sialylation, monoclonal-antibody binding, serum sensitivity, or interaction with eukaryotic cells in vitro. We conclude that the absence of a homolog for rfbC precludes the existence of a functional dTDP-rhamnose biosynthesis pathway in the gonococcal strains examined and that these genes are only maintained in N. gonorrhoeae either because of the presence of the galE gene or because of another as yet unrecognized function.

Contribution of genes from the capsule gene complex (cps) to lipooligosaccharide biosynthesis and serum resistance in Neisseria meningitidis

Within the capsule gene complex (cps) of Neisseria meningitidis B a 5.5 kb DNA fragment encodes proteins with strong homologies to enzymes of the lipopolysaccharide biosynthetic pathway of Salmonella typhimurium and Escherichia coli, GalE, RfbB, RfbC and RfbD. A meningococcal galE mutant expressed a truncated lipooligosaccharide (LOS), which terminated at the glucose residue between inner and outer core, and a second galE gene present outside the cps cluster was found to be transcriptionally and functionally inactive and, thus, unable to complement this defect. Because of the defect in the outer core, the LOS of the galE-defective meningococcal mutant was not sialylated. In contrast, carbohydrate analysis of the LOS of an rfb-defective meningococcal mutant revealed no difference from the LOS of the wild-type strain, suggesting that the rfb genes are inactive. This was supported by Northern blot analysis, which showed that expression of the rfb gene products was transcriptionally regulated. The inability of the meningococcal galE mutant, which cannot sialylate the LOS, allowed us to investigate the significance of LOS sialylation in relation to the presence of the polysialic acid capsule. Sialylated LOS, but not the polysialic acid capsule, is necessary to confer complete serum resistance on the meningococcus by inhibition of the alternative complement pathway.

Diagnosis of human toxocariasis by antigen capture enzyme linked immunosorbent assay

AIMS

To evaluate an antigen capture enzyme linked immunosorbent assay (ELISA) which detects a carbohydrate epitope on the excretory-secretory (ES) antigens of Toxocara canis in clinical practice.

METHODS

Serum specimens from healthy adults, patients with acute visceral larva migrans, ocular and inactive toxocariasis, and with other helminth infections were examined by two site antigen capture ELISA.

RESULTS

Over half of the patients (19/28) with acute toxocariasis had a positive result in contrast to a small proportion of those with inactive disease (1/10) or ocular infection (2/7). False positive reactions, however, were found in 25% of the patients with serologically confirmed schistosomiasis and filariasis.

CONCLUSIONS

This assay is useful in confirming the diagnosis of acute visceral larva migrans but could not be used alone in diagnosis because of false positive reactions in patients with other helminth infections.

The role of galE in the biosynthesis and function of gonococcal lipopolysaccharide

Lipopolysaccharide is an essential component of the outer membrane of Gram-negative bacteria and an important virulence factor of many pathogens, such as Neisseria gonorrhoeae. We have cloned the gonococcal galE gene which was found to be located in the gonococcal homologue of the meningococcal capsule gene complex region D. Sequence alignment indicated extensive homology with the Escherichia coli and Salmonella GalE proteins. Mutants with insertions in the galE gene were used as a tool to characterize the structure and function of gonococcal lipopolysaccharide. They displayed deep rough phenotypes, and chemical analysis confirmed the loss of galactose from the mutant lipopolysaccharide. Functional analysis indicated that the terminal oligosaccharides contain galactose and that these are lost in galE mutants. The importance of these oligosaccharides in gonococcal biology is clear from the fact that they contain the epitopes that are the targets for killing by normal human serum, and the acceptor site for sialic acid, which acts to protect the gonococcus from this killing. Furthermore, infection experiments in vitro indicate that the galE mutants exhibit unaltered intergonococcal adhesion as well as adhesion to, and invasion of, epithelial cells.

Genetic variation in pathogenic bacteria

In contrast to textbook ideas of pure cultures and defined strains, genetic variation is a fact of life in the microbial world. It not only allows pathogens to establish themselves in their chosen host, but also allows them to resist that host's subsequent attempts to evict them. Here we review some of the mechanisms that bring about this variation, and some of the functional consequences that result from it.

Developmentally regulated expression and secretion of a polymorphic antigen by Onchocerca infective-stage larvae

In order to analyse the developmental biology of Onchocerca spp. with a view to identifying molecules with specialised functions, we have devised a novel method for labelling proteins synthesised by larvae during growth in the vectors. Pulse labelling of Onchocerca lienalis by micro-injections of [35S]methionine into blackflies have revealed a major acidic protein of 23 kDa which is developmentally expressed almost exclusively by infective, third-stage larvae. The protein appears to be antigenically conserved between O. lienalis and Onchocerca volvulus, but exhibits size polymorphisms both among species and among individual organisms. It continues to be elaborated after terminal differentiation of the parasite in flies, but not by post-infective larvae entering the phase of development in the vertebrate host. A shift in temperature from 26 degrees C to 37 degrees C triggers secretion of the 23-kDa molecule as a discrete event 24-72 h after transmission. The labelling technique has been successfully employed with filarial species that develop in mosquitoes, and in principle should be widely applicable to the study of endoparasite gene expression within arthropods.

Toxocara canis: proteolytic enzymes secreted by the infective larvae in vitro

Second-stage larvae of the dog nematode Toxocara canis are infective to man and cause the syndromes of visceral larva migrans and ocular toxocariasis. Larvae cultured in vitro secrete proteases which degrade components of a model of extracellular matrix and basement membranes. These enzymes have been characterized using a variety of techniques. Multiple enzyme activities were demonstrated by substrate gel electrophoresis, associated with proteins of molecular weights of 120 and 32 kDa. The enzyme activity was inhibited both in substrate gels and in a radiogelatin microplate assay by phenylmethylsulfonyl fluoride. Optimal activity occurred at pH 9, with minor activities apparent at pH 5 and 7; the relationship between these proteolytic activities is currently under investigation.

Detection of circulating parasite antigen and specific antibody in Toxocara canis infections

Serological surveys, measuring humoral antibody responses, have indicated significant levels of human infection with the zoonotic nematode Toxocara canis, and raised concern about the resultant risk of ocular and neurological damage. Such measurements do not distinguish with certainty current infection from past exposure. Thus, we have developed a test for circulating Toxocara antigen released by parasites in the host. This monoclonal antibody-based two-site 'sandwich' assay discriminates between T. canis and the related feline ascarid T. cati, and has been used, in tandem with the standard ELISA, to examine experimental and human infections. In experimental animals, antigen is transiently detectable, disappearing when immunocomplexed with host antibody. Antigen was also found in sera from UK patients diagnosed with visceral or ocular toxocariasis, and in four asymptomatic Papua New Guinean children. In the latter population, individuals positive for parasite antigens were not necessarily positive for antibody, implying that some infected cases may be negative in the current diagnostic ELISA. The antibody test was also adapted to measure host antibody directed to single monoclonal antibody-defined epitopes, revealing evidence of differential temporal regulation of distinct antibody specificities.

A sensitive microplate assay for the detection of proteolytic enzymes using radiolabeled gelatin

A sensitive, microplate assay is described for the detection of a wide range of proteolytic enzymes, using radio-iodine-labeled gelatin as substrate. The technique uses the Bolton-Hunter reagent to label the substrate, which is then coated onto the wells of polyvinyl chloride microtiter plates. By measuring the radioactivity released the assay is able to detect elastase, trypsin, and collagenase in concentrations of 1 ng/ml or less, while the microtiter format permits multiple sample handling and minimizes sample volumes required for analysis.

Age-relationships of Toxocara canis seropositivity and geohelminth infection prevalence in two communities in St. Lucia, West Indies

Sera were examined from an age-stratified sample of two Caribbean communities using the Toxocara-ELISA with larval ES antigen. Seropositivity was markedly age dependent, attaining maximal values (40 and 60%) in 5-15 year olds and declining in adults. The rate of acquisition of infection with Toxocara canis and the age-prevalence profile are similar to those of Ascaris lumbricoides and Trichuris trichiura. It is suggested that toxocariasis is likely to be prevalent in tropical areas with endemic geohelminthiasis.

Secretory acetylcholinesterases from Brugia malayi adult and microfilarial parasites

Brugia malayi, a lymphatic filarial parasite, secretes acetylcholinesterase during in vitro cultivation. A significant amount of enzyme activity was detected both in culture media and somatic extracts of adult and microfilarial stages of the parasite. The microfilarial stage produces three times more enzyme than adult parasites as a proportion of total protein. The enzyme has true acetylcholinesterase (AChE) activity as hydrolysis of acetylthiocholine is three times faster than butyrylthiocholine and is inhibited by eserine, a specific inhibitor of AChE. Secretory enzyme from adult female parasite excretory-secretory material (ES) was enriched 23 fold using copper chelating and concanavalin A (Con A) affinity chromatography. The Con A eluate showed a major protein band of 100 kDa and a minor 200 kDa component. The ES enzyme is antigenic and cross reacts with antibodies raised in mice against AChE from electric eel by enzyme-linked immunosorbent assay and immunoprecipitation. Immunoprecipitation of 125I-labelled microfilarial ES and adult ES with anti-electric eel AChE antibodies revealed three proteins of 30, 40 and 200 kDa in microfilariae and two proteins of 100 and 200 kDa in adult female ES. It appears that filarial secretory AChE exists in multiple molecular forms.

Shared carbohydrate epitopes on distinct surface and secreted antigens of the parasitic nematode Toxocara canis

The nematode parasite Toxocara canis is found in all dog populations and poses a poorly defined health hazard to humans. We have studied excretory-secretory antigen (ES) and surface antigens of the infective larval stage which is tissue-invasive in mammalian hosts. Antigens were probed with a panel of eight monoclonal antibodies raised in mice to whole ES. Six of eight antibodies reacted with periodate-sensitive carbohydrate epitopes on ES molecules, and the remaining two (Tcn-3 and Tcn-6) recognized either peptide or periodate-resistant sugar determinants. By immunoprecipitation and immunoblotting, the anti-carbohydrate monoclonals each reacted with several distinct ES molecules, known from previously published work to possess contrasting biochemical properties. Tcn-3 and -6 were directed predominantly against 32,000 and 120,000 m.w. molecules, respectively. Iodinated surface antigens of similar m.w. were precipitated by each antibody after detergent solubilization, but only two clones (Tcn-2 and -8) were able to bind exposed sites on the epicuticle of intact Toxocara larvae. Significantly, these antibodies do not bind to newly hatched larvae, and their target antigens are poorly expressed until the second day of in vitro cultivation. The specificities of the monoclonals were further studied by cold antibody inhibition of radiolabeled monoclonal binding, and by a matrix of two-site binding assays. These data show that Tcn-2, -4, -5, and -8 recognize a related group of repetitive carbohydrate epitopes, whereas Tcn-1, -6, and -7 bind discrete determinants on the same molecules. These studies are being continued to define further the structure of antigenic Toxocara carbohydrates and to compare the diagnostic utility of carbohydrate and peptide antigens.

Shared carbohydrate epitopes on distinct surface and secreted antigens of the parasitic nematode Toxocara canis

The nematode parasite Toxocara canis is found in all dog populations and poses a poorly defined health hazard to humans. We have studied excretory-secretory antigen (ES) and surface antigens of the infective larval stage which is tissue-invasive in mammalian hosts. Antigens were probed with a panel of eight monoclonal antibodies raised in mice to whole ES. Six of eight antibodies reacted with periodate-sensitive carbohydrate epitopes on ES molecules, and the remaining two (Tcn-3 and Tcn-6) recognized either peptide or periodate-resistant sugar determinants. By immunoprecipitation and immunoblotting, the anti-carbohydrate monoclonals each reacted with several distinct ES molecules, known from previously published work to possess contrasting biochemical properties. Tcn-3 and -6 were directed predominantly against 32,000 and 120,000 m.w. molecules, respectively. Iodinated surface antigens of similar m.w. were precipitated by each antibody after detergent solubilization, but only two clones (Tcn-2 and -8) were able to bind exposed sites on the epicuticle of intact Toxocara larvae. Significantly, these antibodies do not bind to newly hatched larvae, and their target antigens are poorly expressed until the second day of in vitro cultivation. The specificities of the monoclonals were further studied by cold antibody inhibition of radiolabeled monoclonal binding, and by a matrix of two-site binding assays. These data show that Tcn-2, -4, -5, and -8 recognize a related group of repetitive carbohydrate epitopes, whereas Tcn-1, -6, and -7 bind discrete determinants on the same molecules. These studies are being continued to define further the structure of antigenic Toxocara carbohydrates and to compare the diagnostic utility of carbohydrate and peptide antigens.