Using C. elegans to identify the protease targets of serpins in vivo

Most serpins inhibit serine and/or cysteine proteases, and their inhibitory activities are usually defined in vitro. However, the physiological protease targets of most serpins are unknown despite many years of research. This may be due to the rapid degradation of the inactive serpin:protease complexes and/or the conditions under which the serpin inhibits the protease. The model organism Caenorhabditis elegans is an ideal system for identifying protease targets due to powerful forward and reverse genetics, as well as the ease of creating transgenic animals. Using combinatorial approaches of genetics and biochemistry in C. elegans, the true in vivo protease targets of the endogenous serpins can be elucidated.

Necrotic cell death: harnessing the Dark side of the Force in mammary gland involution

In response to major cellular insults, a massive increase in lysosomal membrane permeability (LMP) leads to necrosis. Data now reveal that this potent lysosomal-mediated necrotic cell-death machinery can also be harnessed for complex physiological processes, such as post-lactation mammary gland involution.

Automated high-content live animal drug screening using C. elegans expressing the aggregation prone serpin α1-antitrypsin Z

The development of preclinical models amenable to live animal bioactive compound screening is an attractive approach to discovering effective pharmacological therapies for disorders caused by misfolded and aggregation-prone proteins. In general, however, live animal drug screening is labor and resource intensive, and has been hampered by the lack of robust assay designs and high throughput work-flows. Based on their small size, tissue transparency and ease of cultivation, the use of C. elegans should obviate many of the technical impediments associated with live animal drug screening. Moreover, their genetic tractability and accomplished record for providing insights into the molecular and cellular basis of human disease, should make C. elegans an ideal model system for in vivo drug discovery campaigns. The goal of this study was to determine whether C. elegans could be adapted to high-throughput and high-content drug screening strategies analogous to those developed for cell-based systems. Using transgenic animals expressing fluorescently-tagged proteins, we first developed a high-quality, high-throughput work-flow utilizing an automated fluorescence microscopy platform with integrated image acquisition and data analysis modules to qualitatively assess different biological processes including, growth, tissue development, cell viability and autophagy. We next adapted this technology to conduct a small molecule screen and identified compounds that altered the intracellular accumulation of the human aggregation prone mutant that causes liver disease in α1-antitrypsin deficiency. This study provides powerful validation for advancement in preclinical drug discovery campaigns by screening live C. elegans modeling α1-antitrypsin deficiency and other complex disease phenotypes on high-content imaging platforms.

Serpins flex their muscle: II. Structural insights into target peptidase recognition, polymerization, and transport functions

Inhibitory serpins are metastable proteins that undergo a substantial conformational rearrangement to covalently trap target peptidases. The serpin reactive center loop contributes a majority of the interactions that serpins make during the initial binding to target peptidases. However, structural studies on serpin-peptidase complexes reveal a broader set of contacts on the scaffold of inhibitory serpins that have substantial influence on guiding peptidase recognition. Structural and biophysical studies also reveal how aberrant serpin folding can lead to the formation of domain-swapped serpin multimers rather than the monomeric metastable state. Serpin domain swapping may therefore underlie the polymerization events characteristic of the serpinopathies. Finally, recent structural studies reveal how the serpin fold has been adapted for non-inhibitory functions such as hormone binding.

Serpins flex their muscle: I. Putting the clamps on proteolysis in diverse biological systems

Serpins compose the largest superfamily of peptidase inhibitors and are well known as regulators of hemostasis and thrombolysis. Studies using model organisms, from plants to vertebrates, now show that serpins and their unique inhibitory mechanism and conformational flexibility are exploited to control proteolysis in molecular pathways associated with cell survival, development, and host defense. In addition, an increasing number of non-inhibitory serpins are emerging as important elements within a diversity of biological systems by serving as chaperones, hormone transporters, or anti-angiogenic factors.

Modeling molecular and cellular aspects of human disease using the nematode Caenorhabditis elegans

As an experimental system, Caenorhabditis elegans offers a unique opportunity to interrogate in vivo the genetic and molecular functions of human disease-related genes. For example, C. elegans has provided crucial insights into fundamental biologic processes, such as cell death and cell fate determinations, as well as pathologic processes such as neurodegeneration and microbial susceptibility. The C. elegans model has several distinct advantages, including a completely sequenced genome that shares extensive homology with that of mammals, ease of cultivation and storage, a relatively short lifespan and techniques for generating null and transgenic animals. However, the ability to conduct unbiased forward and reverse genetic screens in C. elegans remains one of the most powerful experimental paradigms for discovering the biochemical pathways underlying human disease phenotypes. The identification of these pathways leads to a better understanding of the molecular interactions that perturb cellular physiology, and forms the foundation for designing mechanism-based therapies. To this end, the ability to process large numbers of isogenic animals through automated work stations suggests that C. elegans, manifesting different aspects of human disease phenotypes, will become the platform of choice for in vivo drug discovery and target validation using high-throughput/content screening technologies.

Prostasin expression is regulated by airway surface liquid volume and is increased in cystic fibrosis

Airway surface liquid (ASL) absorption is initiated by Na+ entry via epithelial Na+ channels (ENaC), which establishes an osmotic gradient that drives fluid from the luminal to serosal airway surface. We and others have recently reported that a protease/anti-protease balance regulates ENaC in human airway epithelial cells (HAEC) and provides a mechanism for autoregulation of ASL volume. In cystic fibrosis (CF), this balance is disturbed, leading to constitutive proteolytic activation of ENaC and the pathological Na+ hyperabsorption characteristic of this airway disease. Prostasin is a glycosylphosphatidylinositol-anchored serine protease that activates ENaC and is expressed on the surface epithelium lining the airway. In this report we present evidence that prostasin expression is regulated by the ASL volume, allowing for increased proteolytic activation of ENaC when the ASL volume is high. Prostasin activity is further regulated by the cognate serpin protease nexin-1 (PN-1), which is expressed in HAEC and inhibits Na+ absorption by forming an inactive complex with prostasin and preventing the proteolytic processing of prostasin. Whereas these mechanisms regulate prostasin expression in response to ASL volume in non-CF epithelia, HAEC cultured from CF patients express >50% more prostasin on the epithelial surface. These findings suggest that a proteolytic cascade involving prostasin, an upstream prostasin-activating protease, and PN-1 regulate Na+ absorption in the airway and that abnormal prostasin expression contributes to excessive proteolytic activation of ENaC in CF patients.

An intracellular serpin regulates necrosis by inhibiting the induction and sequelae of lysosomal injury

Extracellular serpins such as antithrombin and alpha1-antitrypsin are the quintessential regulators of proteolytic pathways. In contrast, the biological functions of the intracellular serpins remain obscure. We now report that the C. elegans intracellular serpin, SRP-6, exhibits a prosurvival function by blocking necrosis. Minutes after hypotonic shock, srp-6 null animals underwent a catastrophic series of events culminating in lysosomal disruption, cytoplasmic proteolysis, and death. This newly defined hypo-osmotic stress lethal (Osl) phenotype was dependent upon calpains and lysosomal cysteine peptidases, two in vitro targets of SRP-6. By protecting against both the induction of and the lethal effects from lysosomal injury, SRP-6 also blocked death induced by heat shock, oxidative stress, hypoxia, and cation channel hyperactivity. These findings suggest that multiple noxious stimuli converge upon a peptidase-driven, core stress response pathway that, in the absence of serpin regulation, triggers a lysosomal-dependent necrotic cell death routine.

SERPINB11 Is a New Noninhibitory Intracellular Serpin

SERPINB11, the last of 13 human clade B serpins to be described, gave rise to seven different isoforms. One cDNA contained a premature termination codon, two contained splice variants, and four contained full-length open reading frames punctuated by eight single nucleotide polymorphisms (SNPs). The SNPs encoded amino acid variants located within the serpin scaffold but not the reactive site loop (RSL). Although the mouse orthologue, Serpinb11, could inhibit trypsin-like peptidases, SERPINB11 showed no inhibitory activity. To determine whether the human RSL targeted a different class of peptidases or the serpin scaffold was unable to support inhibitory activity, we synthesized chimeric human and mouse proteins, in which the RSLs had been swapped. The human RSL served as a trypsin inhibitor when supported by mouse scaffold sequences. Conversely, the mouse RSL on the human scaffold showed no inhibitory activity. These findings suggested that variant residues in the SERPINB11 scaffold impaired serpin function. SDS-PAGE analysis supported this notion as RSL-cleaved SERPINB11 was unable to undergo the stressed-to-relaxed transition typical of inhibitory type serpins. Mutagenesis studies supported this hypothesis, since the reversion of amino acid sequences in helices D and I to those conserved in other clade B serpins partially restored the ability of SERPINB11 to form covalent complexes with trypsin. Taken together, these findings suggested that SERPINB11 SNPs encoded amino acids in the scaffold that impaired RSL mobility, and HapMap data showed that the majority of genomes in different human populations harbored these noninhibitory SERPINB11 alleles. Like several other serpin superfamily members, SERPINB11 has lost inhibitory activity and may have evolved a noninhibitory function.

The Caenorhabditis elegans muscle specific serpin, SRP-3, neutralizes chymotrypsin-like serine peptidases

Members of the intracellular serpin family may help regulate apoptosis, tumor progression, and metastasis. However, their in vivo functions in the context of a whole organism have not been easily defined. To better understand the biology of these serpins, we initiated a comparative genomics study using Caenorhabditis elegans as a model organism. Previous in silico analysis suggested that the C. elegans genome harbors nine serpin-like sequences bearing significant similarities to the human clade B intracellular serpins. However, only five genes appear to encode full-length serpins with intact reactive site loops. To determine if this was the case, we have cloned and expressed a putative inhibitory-type C. elegans serpin, srp-3. Analysis of SRP-3 inhibitory activity indicated that SRP-3 was a potent inhibitor of the serine peptidases, chymotrypsin and cathepsin G. Spatial and temporal expression studies using GFP and LacZ promoter fusions indicated that SRP-3 was expressed primarily in the anterior body wall muscles, suggesting that it may play a role in muscle cell homeostasis. Combined with previous studies showing that SRP-2 is an inhibitor of the serine peptidase, granzyme B, and lysosomal cysteine peptidases, these data suggested that C. elegans expressed at least two inhibitory-type serpins with nonoverlapping expression and inhibitory profiles. Moreover, the profiles of these clade L serpins in C. elegans share significant similarities with the profiles of clade B intracellular serpin members in higher vertebrates. This degree of conservation suggests that C. elegans should prove to be a valuable resource in the study of metazoan intracellular serpin function.

Selective conservation of the RSL-encoding, proteinase inhibitory-type, clade L serpins in Caenorhabditis species

Serpins are a highly conserved superfamily of serine and papain-like cysteine proteinase inhibitors that are divided phylogenetically into clades. Serpins also can be divided anatomically into those that reside predominately outside or inside cells. While the activities of the extracellular serpins are well understood, the biological functions, as well as the overall distribution of the intracellular (serpinIC) serpins is less well defined. Conceivably, the biological function of the serpinsIC might be revealed by analysis of species with genomes of lower complexity. To this end, we sought to define the clade L serpin repertoire of Caenorhabditis elegans and other nematode species. Analysis of the C. elegans genome revealed the presence of 9 serpin genes. Five genes encoded for full-length serpins with functional reactive site loops (RSL). By definition, these genes were designated proteinase inhibitory-type, RSL-encoding serpins. Four of the C. elegans genes encoded for proteins without an RSL or transcripts with premature termination codons. The high percentage of non-RSL encoding to RSL-encoding serpin genes suggested that the former served a unique biological function rather than residing in the genome as simple pseudogenes. If this hypothesis was correct, we expected these non-RSL encoding genes to be conserved precisely in other Caenorhabditis species. However, in contrast to the RSL-encoding serpins that were well conserved and segregated into 3 sub-clades, we failed to detect non-RSL encoding serpin orthologues in the genomes of Caenorhabditis briggsae and Caenorhabditis remanei. These data suggested that unlike their RSL-encoding paralogues, the relatively high percentage of non-RSL encoding serpins in C. elegans was a vestige of recent duplication events and these latter genes were unlikely to serve essential functions in Caenorhabditis species.

The amplified mouse squamous cell carcinoma antigen gene locus contains a serpin (Serpinb3b) that inhibits both papain-like cysteine and trypsin-like serine proteinases

The clade B serpins occupy a unique niche among a larger superfamily by predominantly regulating intracellular proteolysis. In humans, there are 13 family members that map to serpin gene clusters at either 6p25 or 18q21. While most of these serpins display a unique inhibitory profile and appear to be well conserved in mammals, the clade B loci of several species show evidence of relatively recent genomic amplification events. However, it is not clear whether these serpin gene amplification events yield paralogs with functional redundancy or, through selective pressure, inhibitors with more diverse biochemical activities. A recent comparative genomic analysis of the mouse clade B cluster at 1D found nearly complete conservation of gene number, order, and orientation relative to those of 18q21 in humans. The only exception was the squamous cell carcinoma antigen (SCCA) locus. The human SCCA locus contains two genes, SERPINB3 (SCCA1) and SERPINB4 (SCCA2), whereas the mouse locus contains four serpins and three pseudogenes. At least two of these genes encoded functional, dual cross-class proteinase inhibitors. Mouse Serpinb3a was shown previously to inhibit both chymotrypsin-like serine and papain-like cysteine proteinases. We now report that mouse Serpinb3b extends the inhibitory repertoire of the mouse SCCA locus to include a second cross-class inhibitor with activity against both papain-like cysteine and trypsin-like serine proteinases. These findings confirmed that the genomic expansion of the clade B serpins in the mouse was associated with a functional diversification of inhibitory activity.

Identification and activity of a lower eukaryotic serine proteinase inhibitor (serpin) from Cyanea capillata: analysis of a jellyfish serpin, jellypin

Delineating the phylogenetic relationships among members of a protein family can provide a high degree of insight into the evolution of domain structure and function relationships. To identify an early metazoan member of the high molecular weight serine proteinase inhibitor (serpin) superfamily, we initiated a cDNA library screen of the cnidarian, Cyanea capillata. We identified one serpin cDNA encoding for a full-length serpin, jellypin. Phylogenetic analysis using the deduced amino acid sequence showed that jellypin was most similar to the platyhelminthe Echinococcus multiocularis serpin and the clade P serpins, suggesting that this serpin evolved approximately 1000 million years ago (MYA). Modeling of jellypin showed that it contained all the functional elements of an inhibitory serpin. In vitro biochemical analysis confirmed that jellypin was an inhibitor of the S1 clan SA family of serine proteinases. Analysis of the interactions between the human serine proteinases, chymotrypsin, cathepsin G, and elastase, showed that jellypin inhibited these enzymes in the classical serpin manner, forming a SDS stable enzyme/inhibitor complex. These data suggest that the coevolution of serpin structure and inhibitory function date back to at least early metazoan evolution, approximately 1000 MYA.

Serpin production using rapid in vitro transcription/translation systems

In vitro transcription/translation systems are becoming more useful to produce proteins and determine the protein function. Expression of proteins in vitro provides a rapid and controllable system to express proteins. The ability to control the system by addition of other compounds has allowed for the production of proteins that had been difficult to produce by conventional expression systems. More recently, the development of continuous in vitro systems has allowed the production of larger quantities of proteins for downstream purification techniques. Also, the use of different cell lysates allows for specific post-translational modifications of the synthesized proteins. The ability to label the translated proteins can aid structural analysis and allow tracking of specific proteins.

Human clade B serpins (ov-serpins) belong to a cohort of evolutionarily dispersed intracellular proteinase inhibitor clades that protect cells from promiscuous proteolysis

Serpins are unique among the various types of active site proteinase inhibitors because they covalently trap their targets by undergoing an irreversible conformational rearrangement. Members of the serpin superfamily are present in the three major domains of life (Bacteria, Archaea and Eukarya) as well as several eukaryotic viruses. The human genome encodes for at least 35 members that segregate evolutionarily into nine (A-I) distinct clades. Most of the human serpins are secreted and circulate in the bloodstream where they reside at critical checkpoints intersecting self-perpetuating proteolytic cascades such as those of the clotting, thrombolytic and complement systems. Unlike these circulating serpins, the clade B serpins (ov-serpins) lack signal peptides and reside primarily within cells. Most of the human clade B serpins inhibit serine and/or papain-like cysteine proteinases and protect cells from exogenous and endogenous proteinase-mediated injury. Moreover, as sequencing projects expand to the genomes of other species, it has become apparent that intracellular serpins belonging to distinct phylogenic clades are also present in the three major domains of life. As some of these serpins also guard cells against the deleterious effects of promiscuous proteolytic activity, we propose that this cytoprotective function, along with similarities in structure are common features of a cohort of intracellular serpin clades from a wide variety of species.

SRP-2 is a cross-class inhibitor that participates in postembryonic development of the nematode Caenorhabditis elegans: initial characterization of the clade L serpins

High molecular weight serpins are members of a large superfamily of structurally conserved proteins that inactivate target proteinases by a suicide substrate-like mechanism. In vertebrates, different clades of serpins distribute predominantly to either the intracellular or extracellular space. Although much is known about the function, structure, and inhibitory mechanism of circulating serpins such as alpha(1)-antitrypsin (SERPINA1) and antithrombin III (SERPINC1), relatively little is known about the function of the vertebrate intracellular (clade B) serpins. To gain a better understanding of the biology of the intracellular serpins, we initiated a comparative genomics study using Caenorhabditis elegans as a model system. A screen of the C. elegans genomic and cDNA databases revealed nine serpin genes, tandemly arrayed on chromosome V. Although the C. elegans serpins represent a unique clade (L), they share significant functional homology with members of the clade B group of intracellular serpins, since they lack typical N-terminal signal peptides and reside intracellularly. To determine whether nematode serpins function as proteinase inhibitors, one family member, srp-2, was chosen for further characterization. Biochemical analysis of recombinant SRP-2 protein revealed SRP-2 to be a dual cross-class inhibitor of the apoptosis-related serine proteinase, granzyme B, and the lysosomal cysteine proteinases, cathepsins K, L, S, and V. Analysis of temporal and spatial expression indicated that SRP-2 was present during early embryonic development and highly expressed in the intestine and hypoderm of larval and adult worms. Transgenic animals engineered to overexpress SRP-2 were slow growing and/or arrested at the first, second, or third larval stages. These data suggest that perturbations of serpin-proteinase balance are critical for correct postembryonic development in C. elegans.

OspA immunization decreases transmission of Borrelia burgdorferi spirochetes from infected Peromyscus leucopus mice to larval Ixodes scapularis ticks

Recombinant outer surface protein A (OspA) vaccination of wild animal reservoirs has potential application for reducing Borrelia burgdorferi transmission in nature and subsequent risk of human infection. As a major reservoir host, the white-footed mouse (Peromyscus leucopus) is a candidate for a vaccination program designed to reduce infection prevalence in vector ticks. In this study we characterized the effect of various levels of immunization with recombinant OspA-glutathione transferase fusion protein on transmission dynamics from infected P. leucopus to larval ticks. Control mice were vaccinated with glutathione transferase alone. All mice were experimentally infected with B. burgdorferi before vaccination. The immune responses of the immunized mice were assessed by enzyme-linked immunosorbent assay for antibodies to OspA. Transmission of B. burgdorferi from infected mice was determined by xenodiagnosis with uninfected larval ticks. Spirochetes in ticks were counted by direct immunofluorescence assay. The concentration of antibody to OspA increased with each OspA vaccination but most markedly after the first and second vaccinations. In comparison with control mice, there was reduced transmission by OspA-vaccinated mice to uninfected ticks. One, two, or three doses of OspA reduced infection prevalence in xenodiagnostic ticks by 48%, 92%, or 99% and the numbers of spirochetes per tick by 84%, 98%, or 99%, respectively. This study suggests that vaccination of P. leucopus with OspA could reduce transmission to the tick vector in nature despite prior infection of the reservoir host.

The serpin SQN-5 is a dual mechanistic-class inhibitor of serine and cysteine proteinases

SQN-5 is a mouse serpin that is highly similar to the human serpins SCCA1 (SERPINB3) and SCCA2 (SERPINB4). Previous studies characterizing the biochemical activity of SQN-5 showed that this serpin, like SCCA2, inhibited the chymotrypsin-like enzymes mast cell chymase and cathepsin G. Using an expanded panel of papain-like cysteine proteinases, we now show that SQN-5, like SCCA1, inhibited cathepsins K, L, S, and V but not cathepsin B or H. These interactions were characterized by stoichiometries of inhibition that were nearly 1:1 and second-order rate constants of >10(4) M(-1) s(-1). Reactive site loop (RSL) cleavage analysis showed that SQN-5 employed different reactive centers to neutralize the serine and cysteine proteinases. To our knowledge, this is the first serpin that serves as a dual inhibitor of both chymotrypsin-like serine and the papain-like cysteine proteinases by employing an RSL-dependent inhibitory mechanism. The ability of serpins to inhibit both serine and/or papain-like cysteine proteinases may not be a recent event in mammalian evolution. Phylogenetic studies suggested that the SCCA and SQN genes evolved from a common ancestor approximately 250-280 million years ago. When the fact that mammals and birds diverged approximately 310 million years ago is considered, an ancestral SCCA/SQN-like serpin with dual inhibitory activity may be present in many mammalian genomes.

SERPINB12 is a novel member of the human ov-serpin family that is widely expressed and inhibits trypsin-like serine proteinases

Members of the human serpin family regulate a diverse array of serine and cysteine proteinases associated with essential biological processes such as fibrinolysis, coagulation, inflammation, cell mobility, cellular differentiation, and apoptosis. Most serpins are secreted and attain physiologic concentrations in the blood and extracellular fluids. However, a subset of the serpin superfamily, the ov-serpins, also resides intracellularly. Using high throughput genomic sequence, we identified a novel member of the human ov-serpin gene family, SERPINB12. The gene mapped to the ov-serpin cluster at 18q21 and resided between SERPINB5 (maspin) and SERPINB13 (headpin). The presence of SERPINB12 in silico was confirmed by cDNA cloning. Expression studies showed that SERPINB12 was expressed in many tissues, including brain, bone marrow, lymph node, heart, lung, liver, pancreas, testis, ovary, and intestines. Based on the presence of Arg and Ser at the reactive center of the RSL, SERPINB12 appeared to be an inhibitor of trypsin-like serine proteinases. This hypothesis was confirmed because recombinant SERPINB12 inhibited human trypsin and plasmin but not thrombin, coagulation factor Xa, or urokinase-type plasminogen activator. The second-order rate constants for the inhibitory reactions were 2.5 +/- 1.6 x 10(5) and 1.6 +/- 0.2 x 10(4) M(-1) S(-1), respectively. These data show that SERPINB12 encodes for a new functional member of the human ov-serpin family.

Recombinant Semliki Forest virus vector exhibits potential for avian virus vaccine development

The Semliki Forest virus (SFV) expression system was evaluated as a basis for avian vaccine development. Initial studies indicated that 1-day-old specific pathogen-free (SPF) chicks were susceptible to infection with an infectious strain of SFV, producing SFV-specific antibodies but no clinical disease. One-day-old SPF chicks immunised intramuscularly with recombinant replication-defective SFV (rSFV) particles expressing the Escherichia coli (E. coli) lacZ reporter gene developed high titres of beta-gal- specific antibodies at 4 weeks p.i. after two inoculations. In contrast, significantly lower antibody levels were elicited in chicks immunised with a recombinant SFV-based DNA construct or a conventional CMV promoter-based DNA plasmid. rSFV particles encoding the protective VP2 protein or the VP2/VP4/VP3 polyprotein of infectious bursal disease virus (IBDV) were produced and the expressed antigens were characterised in cell culture. Proteins of the correct size were generated and found to react against a range of IBDV-specific monoclonal antibodies. Immunisation of 1-day-old SPF chicks with rSFV particles encoding the IBDV proteins resulted in specific antibodies being elicited in all birds, neutralising antibodies being induced in some but not all birds.

Development of specific monoclonal antibodies and a sensitive discriminatory immunoassay for the circulating tumor markers SCCA1 and SCCA2

The squamous cell carcinoma antigen (SCCA) serves as a serologic marker for advanced squamous cell carcinomas (SCC) of the uterine cervix, lung, esophagus, head and neck and vulva. Elevations in serum levels of SCCA following treatment for SCC correlate with tumor relapse or metastasis. Recent molecular studies show that SCCA is transcribed by two nearly identical genes (SCCA1 and SCCA2) that encode for members of the high molecular weight serine proteinase inhibitor (serpin) family. Despite a high degree of similarity in their amino acid sequences, SCCA1 and SCCA2 have distinct biochemical properties: SCCA1 is an inhibitor of papain like cysteine proteinases, such as cathepsins (cat) L, S and K, whereas SCCA2 inhibits chymotrypsin-like serine proteinases, catG and mast cell chymase. In this paper, we report the generation and characterization of anti-SCCA1 and anti-SCCA2 specific monoclonal antibodies (MAbs). Using these MAbs, we developed an enzyme-linked immunoassay (ELISA) that discriminated between SCCA1 and SCCA2 without any cross-reaction. This assay measured both the native and complexed forms of SCCA1 and SCCA2. The sensitivity of detection of SCCA1 and SCCA2 assays were 0.17 ngml(-1) and 0.19 ngml(-1), respectively. Mean inter- and intra-assay coefficients of variation were 12.1% and 9.9% for SCCA1 assay and 12% and 8.8% for SCCA2 assay, respectively. Recovery and parallellism studies indicated that SCCA1 and SCCA2 were detected in the plasma and amniotic fluids without any major interference by the biologic fluid components. This assay provides a simple and accurate procedure for the quantitation of total SCCA1 and SCCA2.

Growth-inhibiting antibody responses of humans vaccinated with recombinant outer surface protein A or infected with Borrelia burgdorferi or both

Serial serum samples from a 2-year human trial of outer surface protein (Osp) A vaccine were analyzed by Borrelia burgdorferi growth-inhibition assay (GIA) and anti-OspA ELISA to assess the antibody responses of vaccine recipients and subjects with Lyme disease. Although 74% of OspA recipients had a reciprocal GIA titer >/=64 after 3 vaccinations, none of the placebo recipients, even those with Lyme disease, had a GIA titer this high. The correlation between GIA and ELISA titers after 3 doses of vaccine was.84; however, more vaccine recipients had an elevated ELISA titer paired with low GIA titer than had a low ELISA titer with a high GIA titer. OspA-vaccine recipients who acquired Lyme disease had significantly lower serum GIA and ELISA titers after 3 immunizations than did age- and sex-matched OspA recipients without Lyme disease. Thus, vaccinated subjects had antibodies to native antigen on viable cells, and antibody assays with this specificity may predict protection of vaccinees against infection.

Safety and immunogenicity of recombinant Bacille Calmette-Guérin (rBCG) expressing Borrelia burgdorferi outer surface protein A (OspA) lipoprotein in adult volunteers: a candidate Lyme disease vaccine

This phase I clinical trial was designed to determine the feasibility of using rBCG as a live bacterial vaccine vector for the outer surface protein A (OspA) of Borrelia burgdorferi and as model for other vaccines based on a rBCG vector. To construct the vaccine, a signal peptide derived from a mycobacterial lipoprotein was used to direct the export, and membrane-associated surface expression, of OspA in a standard strain of BCG (Connaught). The rBCG OspA vaccine was safe and immunogenic in several animal species, and protective in a mouse model of Lyme borreliosis. An intradermal injection (0.1 ml) of rBCG OspA was administered to 24 healthy adult volunteers sequentially at one of four dose levels, ranging from 2.0 x 10(4) CFU to 2 x 10(7) CFU, using a dose-escalation design. All volunteers were initially PPD-skin test and OspA antibody negative, and they were monitored for 2 years after immunization. Three volunteers had mild flu-like reactions 1-2 days after vaccination. Local ulceration and drainage at the site of injection, which occurred in 50% and 83% of volunteers in the two highest dose groups, persisted for 1-70 days before the ulcers healed. Most of the drainage samples yielded rBCG colonies that contained the OspA plasmid. Thirteen of 24 vaccinees, principally in the two highest dose groups, converted their PPD skin tests from negative to positive. None of the 24 volunteers developed OspA antibody. In conclusion, the current rBCG vaccine construct, the first such construct tested in humans, had a safety profile comparable to that of licensed BCG, but it did not elicit primary humoral responses to the vectored antigen.