Plaque antibody selection: rapid immunological analysis of a large number of recombinant phage clones positive to sera raised against Plasmodium falciparum antigens

Neural correlates of inhibitory control are associated with stimulant-like effects of alcohol

Poor inhibitory control and heightened feelings of stimulation after alcohol are two well-established risk factors for alcohol use disorder (AUD). Although these risk factors have traditionally been viewed as orthogonal, recent evidence suggests that the two are related and may share common neurobiological mechanisms. Here we examined the degree to which neural activity during inhibition was associated with subjective reports of stimulation following alcohol. To assess neural changes during inhibition, moderate alcohol drinkers performed a stop signal task during fMRI without drug. To assess subjective responses to alcohol they ingested alcohol (0.8 g/kg) or placebo beverages under double-blind conditions and provided subjective reports of stimulation and sedation. Feelings of stimulation following alcohol were inversely associated with activity in the supplementary motor area, insula, and middle frontal gyrus during inhibition (successful stop trials compared to go trials). Feelings of sedation did not correlate with brain activation. These results extend previous findings suggesting that poor inhibitory control is associated with more positive subjective responses to alcohol. These interrelated risk factors may contribute to susceptibility to future excessive alcohol use, and ultimately lead to neurobiological targets to prevent or treat AUD.

Cloning and characterization of a cDNA fragment encoding a Schistosoma mansoni actin-binding protein (Smfilamin)

To identify vaccine candidates for Schistosoma mansoni, the IgG fraction of rabbit antiserum raised against immature female worms affinity purified over a NP-40 extract of 3-h schistosomula was used to immunoscreen a cercarial lambdagt11 cDNA library. One clone with a 1.5-kb cDNA insert revealed an encoded peptide of 479 amino acids, which bears homology to human actin-binding protein (ABP-280=filamin). Northern blot analysis revealed a transcript of about 8.6 kb, indicating that the complete gene was not cloned. Overlapping clones, which encode a composite sequence of 983 amino acids (45% identity with filamin), were subsequently isolated from the cDNA library. The 1.5-kb insert was cloned into pGEX, overexpressed, and the 479 amino acid peptide purified. Western blot analysis using polyclonal antisera specific to the peptide identified a 280-kDa molecule in adult worm extracts. RT-PCR demonstrated that Smfilaimin is expressed in various stages. Immunofluorescence studies with specific antisera revealed a tegument-associated fluorescence in adult worms. IgG specific to the Smfilamin fragment showed 36.6% killing of schistosomules in an in vitro killing assay.

A cement protein of the tick Rhipicephalus appendiculatus, located in the secretory e cell granules of the type III salivary gland acini, induces strong antibody responses in cattle

Protein components of the cement cone of ixodid ticks are candidates for inclusion in vaccines against tick infestation, since they are essential for tick attachment and feeding. We describe here the cloning of a cDNA encoding a 36 kDa protein, designated Rhipicephalus Immuno-dominant Molecule 36 (RIM36), present in salivary glands and the cement cone material secreted by Rhipicephalus appendiculatus. The 334-amino-acid sequence of RIM36 has a high content of glycine, serine and proline. The protein contains a predicted N-terminal signal peptide and two classes of glycine-rich amino acid repeats, a GL[G/Y/S/F/L] tripeptide and a GSPLSGF septapeptide. Comparison of genomic and cDNA sequences reveals a 597 bp intron within the 3' end of the RIM36 gene. Immuno-electron microscopy demonstrates that RIM36 is predominantly located in the e cell granules of the type III salivary gland acini. An Escherichia coli recombinant form of the proline-rich C-terminal domain of RIM36 reacts with antisera from Bos indicus cattle, either experimentally infested with R. appendiculatus, or exposed to ticks in the field. The 36 kDa protein is strongly recognised on Western blots of salivary gland lysates and soluble extracts of purified R. appendiculatus cement cones by polyclonal antibodies generated against recombinant RIM36, and by antisera from cattle experimentally infested with ticks. The data indicate that this tick cement component is a target of strong antibody responses in cattle exposed to feeding ticks.

Plasmodium vivax merozoite surface proteins-3beta and-3gamma share structural similarities with P. vivax merozoite surface protein-3alpha and define a new gene family

The genes encoding two merozoite surface proteins of Plasmodium vivax that are related to PvMSP3 [1] are reported. One of these genes was identified within P. vivax lambdagt11 clone 5.4, which was selected by immunoscreening with a Saimiri monkey antiserum. The insert DNA of this clone was used as a probe to isolate the complete gene from a P. vivax lambdaDASH genomic (g) DNA library. Antibodies to recombinant 5.4 and subsequent fusion proteins produce a pattern of circumferential surface fluorescence by indirect immunofluorescence assays (IFA) on segmented schizonts and free intact merozoites, and recognize a 125 kDa protein via western immunoblots. The gene, however, encodes a protein with a calculated size of 75677 Da, and 3' and 5' RACE analyses were employed to confirm the size of the gene and its coding region. The second related P. vivax gene was isolated by hybridization of a fragment of an orthologous P. knowlesi gene. The encoded proteins of all three related P. vivax genes have putative signal peptides, large central domains that contain >20% alanine residues bound by charged regions, are predicted to form alpha-helices with heptad repeat coiled-coil structures, and do not have a hydrophobic region that could anchor them to the surface of the merozoite. Although the overall identity in amino acid alignment among the three encoded proteins is low (<40%), the shared predicted structural features and motifs indicate that they are members of an intra-species family, which we are designating as the PvMSP-3 family with the reported members being Pvmsp-3alpha, Pvmsp-3beta, and Pvmsp-3gamma. We further demonstrate that this family also includes related proteins from P. knowlesi and P. falciparum.

Molecular cloning and demonstration of an aminopeptidase activity in a filarial nematode glycoprotein

ES-62 is an abundant phosphorylcholine-containing secreted glycoprotein of the filarial nematode Acanthocheilonema viteae. Using an antiserum directed against the parasite molecule, 3 cDNAs of size, approximately 1.5-1.6 kbp were isolated from an A. viteae expression library. Sequence analysis in combination with N-terminal amino acid sequencing of purified ES-62 revealed that each clone contained a full-length cDNA for ES-62 corresponding to 474 amino acid residues but differed in their 5' and 3' untranslated regions. Characterisation of the 5' end of ES-62 mRNA using 5' rapid amplification of cDNA ends showed that it coded for a signal sequence. Several tryptic peptides were independently sequenced using quadruple-time-of-flight mass spectrometry and used to confirm the cDNA sequence. The mature protein was found to contain three potential N-linked glycosylation sites. Comparison of the derived amino acid sequence of ES-62 with the SwissProt database identified a sequence (between amino acid residues approximately 250 and 350 of mature ES-62) with significant similarity to several bacterial/fungal aminopeptidases. Incubation of ES-62 with leucine-7-amino-4-methylcoumarin as substrate confirmed that ES-62 possessed aminopeptidase activity.

Novel target antigens of the variant-specific immune response to Plasmodium falciparum identified by differential screening of an expression library

A primary infection by the Plasmodium falciparum Palo Alto O and R antigenic variants induces a variant-specific immunity in the Saimiri sciureus monkey. We have shown that these variants express distinct PfEMP1 antigens and differ in their levels of expression of additional antigens, including two conserved erythrocyte membrane-associated proteins, HRP1 and PfEMP3. To identify the antigens eliciting a variant-specific response, we conducted a differential screening of a lambdagt11 library with variant-specific sera. We report here the analysis of the 46 anti-R-specific clones. Two specific targets of the anti-R response were identified: (i) PfEMP3, suggesting that immunogenicity of this antigen is modulated by its relative abundance in different variants, and (ii) Asn-rich motifs. Most anti-R-specific clones, derived from so-far-undescribed genes, were detected by a cross-reaction on poly(Asn) stretches, as indicated by elimination of the signal after absorption on Asn-rich sequences. Reverse transcription-PCR (RT-PCR) showed that expression of the gene defined by clone 13 was R specific. Pepscan analysis of clone 13 identified three Asn-rich polypeptides and one unique peptide reacting specifically with antibodies eluted from the R-infected erythrocyte surface. Antisera raised to the unique peptide reacted with an R-specific protein. Attempts to demonstrate that clone 13 was derived from a var gene by using PCRs combining clone 13 and var-derived primers were unsuccessful. The var genes expressed by O and R parasites were identified not by this strategy but by RT-PCR with var-specific primers. This work has provided novel insights into immunity to antigenic variants and has identified a novel gene switched on during antigenic variation.

Tropomyosin implicated in host protective responses to microfilariae in onchocerciasis

A cDNA from adult female Onchocerca volvulus encoding the C-terminal portion of a tropomyosin isoform (termed MOv-14) has been shown previously to confer protective immunity in rodent models of onchocerciasis. The full-length sequence (designated Ov-tmy-1) obtained by PCR amplification, codes for a protein of 33 kDa and shares 91% identity with tropomyosins from other nematodes, falling to 57% identity with human alpha-tropomyosin. Ov-TMY-1 migrates with an apparent molecular mass of 42 kDa on SDS/PAGE and is present in all life-cycle stages, as determined by immunoblotting. Immunogold electron microscopy identified antigenic sites within muscle blocks and the cuticle of microfilariae and infective larvae. Anti-MOv14 antibodies were abundant in mice exhibiting serum-transferable protection against microfilariae conferred by vaccination with a PBS-soluble parasite extract. In contrast, little or no MOv14-specific antibody was present in mice inoculated with live microfilariae, in which resistance is mediated by antibody-independent mechanisms. In human infections, there was an inverse correlation between anti-tropomyosin IgG levels and densities of microfilariae in the skin. Seropositivity varied with the relative endemicity of infection. An immunodominant B cell epitope within Ov-TMY-1 (AQLLAEEADRKYD) was mapped to the N terminus of the MOv14 protein by using sera from protectively vaccinated mice. Intriguingly, the sequence coincides with an IgE-binding epitope within shrimp tropomyosin, believed to be responsible for hypersensitivity in individuals exhibiting allergy to shellfish. IgG and IgE antibodies reacting with the O. volvulus epitope were detected in human infections. It is concluded that antibody responses to tropomyosin may be important in limiting microfilarial densities in a proportion of individuals with onchocerciasis and have the potential to mediate hypersensitivity reactions to dead microfilariae, raising the possibility of a link with the immunopathology of infection.

Cloning and characterization of a gene encoding a novel immunodominant antigen of Trypanosoma cruzi

A Trypanosoma cruzi genomic expression library was screened with a pool of sera obtained from chronic chagasic patients. The recombinant antigen (Tc40) isolated from this library reacted with a large number of serum samples of chronic chagasic patients, suggesting that the presence of anti-Tc40 antibodies may be specifically associated to Chagas' disease. The full-length sequence of the Tc40 gene was determined after isolation of genomic and cDNA clones. The Tc40 cDNA includes a large open reading frame (2745 bp-long) that encodes a polypeptide of 100 kDa without any homology with previously described T. cruzi sequences. In contrast with other T. cruzi antigens whose immunodominant B-cell epitopes are composed by amino acid repetitive motifs, Tc40 does not show any amino acid repetition. Antibodies against the Tc40 recombinant protein reacted with three native polypeptides of 100, 41 and 38 kDa which are tightly associated with membranes or cytoskeleton and expressed in all developmental stages of the parasite life cycle. A transcript of 3.9-kb was detected in Northern blot analysis which is large enough to encode a 100 kDa polypeptide. Tc40 genes were mapped on a chromosomal band of 1.1 Mbp and in a few copies per haploid genome in the G strain.

Cloning and expression of DiT33 from Dirofilaria immitis: a specific and early marker of heartworm infection

Dirofilaria immitis is an important filarial parasite of dogs and cats, and a useful model for human filariasis. Current diagnostic tests for heartworm infection in animals rely on the presence of fecund female worms (usually found 6.5 months post-infection or later) and therefore fail to detect pre-patent infections. Putative pepsin inhibitors from 2 filarial parasites of humans namely Onchocerca volvulus (Ov33, Oc3.6, OvD5B) and Brugia malayi (Bm33), have been shown to be useful in diagnosis of onchocerciasis and lymphatic filariasis, respectively. Previous studies have suggested that a homologue exists in D. immitis (DiT33), which may have potential in diagnosis of heartworm infection. In this study, the isolation and characterization of a cDNA clone encoding DiT33 is described. This cDNA contains 12 bases of the nematode-specific 22 nucleotide spliced leader sequence and encodes a 26.4 kDa-protein with a high level of similarity (87-89%) to other filarial members of the family. DiT33 was over-expressed in E. coli as a fusion with the maltose-binding protein and serological analysis was performed using a panel of clinically defined dog sera. The findings of this study indicate that DiT33 is a promising antigen for the early detection of D. immitis and may be a valuable tool in the control and management of heartworm infection.

Molecular cloning and characterization of the major allergen Myr p II from the venom of the jumper ant Myrmecia pilosula: Myr p I and Myr p II share a common protein leader sequence

A major allergen Myr p II of the Australian jumper ant Myrmecia pilosula has been cloned, immunocharacterized and nucleotide sequenced. An open reading frame of 225 bases was identified and found to encode a deduced amino acid sequence of 75 residues which contained a typical hydrophobic peptide leader sequence. Expressed fusion proteins of Myr p II in both phage and plasmid vectors bind high levels of ant venom-specific IgE and the expressed clones are recognised by 35% of ant venom-allergic individuals. IgE antibodies that recognise the expressed clone have been shown to recognise IgE-binding bands in blots of native venom after separation by SDS-PAGE. The amino acid sequence of Myr p II shares close structural homology with the other major jumper ant allergen Myr p I, differing by only three amino acids in the first 47 residues of both sequences. However, N-terminal analysis of IgE-binding bands derived from Tricine-SDS-PAGE gel blots indicates that both Myr p I and Myr p II undergo extensive post-translational proteolytic processing to unique peptides of 45 and 27 residues, respectively.

OvB20, an Onchocerca volvulus-cloned antigen selected by differential immunoscreening with vaccination serum in a cattle model of onchocerciasis

A cDNA of Onchocerca volvulus has been isolated by differential immunoscreening of an adult worm expression library using sera raised in cattle against the related species, O. lienalis. It was selected because of its recognition by antibodies from cattle immunized with irradiated third-stage (L3) larvae and not by antibodies from animals infected with non-irradiated larvae. The original 311-bp clone was used to isolate a 1478-bp cDNA. Designated OvB20, this codes for 460 amino acid residues, hybridizes with a approximately 1.6 kBp transcript and appears to be transcribed from a filarial-specific, single copy gene. It is expressed in developing stages from embryo to L4 larva, but not in the adult. The product of OvB20 appears to undergo co- or post-translational processing: in vitro transcription and translation give rise to a polypeptide consistent with the deduced amino acid sequence (approximately 52 kDa), whilst products of 52 and 65 kDa are detected in larvae by immunoblotting and following in vitro translations to which exogenous microsomes have been added. A 42-kDa protein was also detected in all in vitro translations. No homologous genes were found in the computer databases, although there are regions of weak sequence similarity with C-reactive proteins. The functional role of OvB20 may warrant further attention, as it has recently been shown that the recombinant protein confers host protection against a related rodent filaria following active immunization (Taylor, M.J., Abdel-Wahab, N., Wu, Y., Jenkins, R.E. and Bianco, A.E. (1995) Onchocerca volvulus larval antigen, OvB20 induces partial protection in a rodent model of onchocerciasis. Infect. Immun. 63, 4417-4422).

Serum and colostrum antibody responses induced by jet-injection of sheep with DNA encoding a Cryptosporidium parvum antigen

In an effort to generate high titer colostrum for immunotherapy of cryptosporidiosis, a study was conducted to test the efficacy of immunizing sheep with recombinant plasmid DNA (pCMV-CP15/60) encoding epitopes of 15 and 60 kDa surface antigens of Cryptosporidium parvum sporozoites. The plasmid DNA was used to immunize preparturient ewes at three dose levels by jet-injection into either hind limb muscle (IM) or mammary tissue (IMAM). Regardless of route of injection, a dose-dependent anti-CP15/60 immunoglobulin response was observed in sera and colostrum from sheep immunized with pCMV-CP15/60 plasmid DNA. High titer antibody responses were observed in one of three animals per group receiving an IM injection of 100 or 1000 micrograms pCMV-CP15/60. IMAM immunization with 100 or 1000 micrograms pCMV-CP15/60 plasmid DNA elicited higher titer colostrum responses and more consistent serum responses compared to IM injections. A negligible serum and colostrum anti-CP15/60 response was observed in ewes injected IM with 10 micrograms pCMV-CP15/60 or 1000 micrograms control plasmid DNA. Immunoblotting of native C. parvum sporozoite/oocyst protein with hyperimmune serum and colostrum corroborated the increased titers against CP15/60 antigen. Serum and colostrum antibodies from pCMV-CP15/60-immunized sheep were eluted from native CP15 protein and bound a surface antigen of C. parvum sporozoites as indicated by indirect immunofluorescence staining.

Extensive diversity in repeat unit sequences of the cDNA encoding the polyprotein antigen/allergen from the bovine lungworm Dictyocaulus viviparus

The complete sequence of the cDNA encoding the nematode polyprotein allergen/antigen (NPA) of the bovine lungworm Dictyocaulus viviparus was obtained by immunoscreening of cDNA expression libraries and by 5' RACE (rapid amplification of cDNA ends). The encoded polypeptide is similar in sequence to the ABA-1 allergen of Ascaris, the gp15/400 'ladder' protein of Brugia malayi, Brugia pahangi and Wuchereria bancrofti, and a 15-kDa antigen of Dirofilaria immitis. As with these, the predicted amino-acid sequence comprises a head-to-tail array of similar polypeptides with regularly spaced consensus proteinase cleavage sites. The D. viviparus protein was designated DvA-1 (D. viviparus antigen-1) and the gene dva-1. The deduced amino-acid sequence of DvA-1 showed features not observed before in other NPAs: (i) a hydrophobic leader peptide is present, (ii) none of the 12 units in the array are identical and the sequences diverge to a degree hitherto unseen in the NPAs of other nematode parasites, (iii) the predicted proteinase cleavage sites are also diverse in sequence and, in two instances, no consensus cleavage site was identifiable at the expected position, (iv) a short repeat unit is present, which is the only one containing a consensus N-glycosylation site and (v) a C-terminal extension peptide is encoded which shows no similarity to that from A. suum ABA-1. Comparison of independent cDNAs revealed slight variations in the sequence of the gene within the parasite population. Antisera to recombinant DvA-1 polypeptide identified 14-15-kDa antigens in both parasite somatic and excretory-secretory material. DvA-1 is the only NPA for which the complete coding sequence is available and the new principles which it illustrates may lie unsuspected in the NPA-encoding genes of all nematode parasites.

Protection of immunocompromised mice against lethal infection with Pseudomonas aeruginosa by active or passive immunization with recombinant P. aeruginosa outer membrane protein F and outer membrane protein I fusion proteins

Recombinant outer membrane proteins (Oprs) of Pseudomonas aeruginosa were expressed in Escherichia coli as glutathione S-transferase (GST)-linked fusion proteins. GST-linked Oprs F and I (GST-OprF190-350 [GST linked to OprF spanning amino acids 190 to 350] and GST-OprI21-83, respectively) and recombinant hybrid Oprs (GST-OprF190-342-OprI21-83 and GST-OprI21-83-OprF190-350) were isolated and tested for their efficacy as vaccines in immunodeficient mice. GST-OprF-OprI protected the mice against a 975-fold 50% lethal dose of P. aeruginosa. Expression of GST-unfused OprF-OprI failed in E. coli, although this hybrid protein has been expressed without a fusion part in Saccharomyces cerevisiae and used for immunizing rabbits. The immune rabbit sera protected severe combined deficient (SCID) mice against a 1,000-fold 50% lethal dose of P. aeruginosa. Evidence is provided to show that the most C-terminal part of OprF (i.e., amino acids 332 to 350) carries an important protective epitope. Opr-based hybrid proteins may have implications for a clinical vaccine against P. aeruginosa.

Separation of jumper ant (Myrmecia pilosula) venom allergens: a novel group of highly basic proteins

The sting of the jumper ant (Myrmecia pilosula) causes severe allergic reactions, including anaphylaxis in sensitized individuals. Two of the major allergens, Myr p I and Myr p II, have been cloned, immunocharacterized and nucleotide-sequenced and they encode 112 and 75 residue polypeptides, respectively. Both allergens are highly basic proteins having isoelectric point values greater than 10. However, electrophoretic analysis has generated conflicting results as to the actual sizes of the allergens in the native venom. Electrophoretic, immunological and N-terminal analyses suggested that these allergens undergo extensive post-translational processing to final forms of 45 and 27 residues, respectively. The results highlight the difficulties in the study of small, basic proteins and polypeptides by electrophoretic techniques.

Trypanosoma cruzi exoantigen is a member of a 160 kDa gene family

During the chronic stage of Chagas disease a 160 kDa antigen appears in the blood of patients and remains detectable many years after the onset of the disease. This antigen is secreted by the trypomastigote form of the parasite while it is undetectable in the epimastigote form. We report here that the chronic 160 kDa exoantigen is encoded by a gene family (CEA 160 family). We describe the cloning and partial nucleotide sequence of a gene (CEA 160-1) belonging to the CEA160 family. Comparison of the gene sequence with other sequences present in the databases revealed homologies with several Trypanosoma cruzi surface antigens. Highest amino acid identity (59%) was with members of a family containing epitopes that mimic nervous tissues (Van Voorhis et al. 1993). Another related group (18-22% amino acid identity) comprises proteins of 85 or 160 kDa sharing an amino acid motif that is conserved among bacterial neuraminidases (Fouts et al. 1991; Pollevick et al. 1991; Kahn et al. 1991; Takle & Cross, 1991; Franco et al. 1993). The amino acid identities with the different antigens were not homogeneously distributed. Regions of higher identity (40-60%) were grouped in the central region of each protein.

Expression and analysis of the diagnostic value of an Echinococcus granulosus antigen gene clone

A pool of 9 sera from Echinococcus granulosus infected patients (PSP) was used to screen an E. granulosus cDNA library constructed in the expression vector lambda gt11. Ten reactive phage clones were isolated and 8 were confirmed in spot-lysis arrays probed with PSP. The insert of 1 of these clones (lambda AgEg4) previously characterized as an E. granulosus cytosolic malate dehydrogenase encoding gene was subcloned into the plasmid vector pGEX-1 and expressed as a fusion with glutathione S-transferase. The fusion peptide (Ag4-GST) was produced in Escherichia coli and its antigenicity was confirmed in colony immunoassay and in immunoblot using nondenaturing conditions. The lack of antigenicity of Ag4-GST in immunoblot using denaturing conditions suggests that the recognized epitopes are conformational. Ag4-GST was purified by affinity chromatography and tested in ELISA and immunodots to access its sensitivity and specificity in the diagnosis of human cystic hydatid disease. An overall sensitivity of 53.6% was obtained. Cross-reactions were observed with some sera from patients infected with Schistosoma mansoni and Wuchereria bancrofti. Ag4-GST was not recognized by any of the sera from Taenia solium infected patients tested. These preliminary results suggest that Ag4-GST could be useful as an accessory antigen to discriminate some cross-reactions with sera from cysticercosis patients, especially in regions like southern Brazil, where schistosomiasis and filariasis are not prevalent.

Cloning and characterization of a gene for the stage-specific 82-kDa surface antigen of metacyclic trypomastigotes of Trypanosoma cruzi

We have cloned and sequenced a cDNA clone coding for a metacyclic trypomastigote-specific surface glycoprotein with a molecular mass of 82 kDa (MTS-gp82). By immunoblotting and immunoprecipitation, antibodies against the recombinant protein recognized an 82-kDa protein of metacyclic trypomastigotes, without any detectable reaction towards amastigotes, epimastigotes or tissue culture-derived trypomastigotes. The insert of the MTS-gp82 cDNA clone strongly hybridized with a single 2.2-kb metacyclic trypomastigote mRNA, suggesting that the steady-state levels of mRNAs for MTS-gp82 are developmentally regulated. MTS-gp82 is encoded by a multigene family whose members are distributed in several chromosomes. Sequence analysis revealed 40-56% identity at amino acid level between MTS-gp82 and members of Trypanosoma cruzi gp85/sialidase family (TSA-1, Tt34c1, SA85-1.1). MTS-gp82 showed several amino acid motifs that are characteristic of gp85/sialidase family, such as the Asp box (SxDxGxTW), the subterminal (VTVxNVFLYNR) motif and the putative GPI-anchor sequence. On the basis of its structural features, the MTS-gp82 gene could be included in the T. cruzi gp85/sialidase family, but constituting a distinct group which is preferentially expressed in metacyclic trypomastigotes.

A species-specific antigen of Trypanosoma (Duttonella) vivax detectable in the course of infection is encoded by a differentially expressed tandemly reiterated gene

A monoclonal antibody that is used as a Trypanosoma vivax species-specific diagnostic reagent on antigen-trapping enzyme-linked immunosorbent assay recognized an 8-kDa peptide on western blots. The 8-kDa species-specific antigen was isolated and employed in raising rabbit polyclonal antibodies, which were used in the immunoscreening of a T. vivax cDNA library in lambda gt11.2. A clone containing a 0.8-kb insert was isolated. The cloned gene is tandemly repeated, with a monomeric unit length of 900 bp, in the genomes of all T. vivax isolates from diverse geographic locations in Africa and South America. The gene is differentially expressed, since both the transcript and antigen are present in bloodstream-stage parasites, but not in the epimastigotes of T. vivax. Although the gene is found in all T. vivax isolates so far tested, it either exists in low copy number or in a divergent form in one isolate from Kilifi at the Kenya Coast. Sequence translation revealed a remarkable degree of bias in codon usage with preference for G and C (82%) in the wobble position. Using the deduced amino acid sequence to search the databases for any structurally related peptides, revealed no significant identity with any known proteins. The function of the species-specific antigen of T. vivax is thus unknown. Nevertheless the identification and characterization of proteins released into the circulation of protozoan parasite-infected animals is important and should allow the determination of what role such molecules may play in the modulation of disease pathology.

Molecular cloning of Brugia malayi antigens for diagnosis of lymphatic filariasis

Immunological crossreactivity among nematodes has hampered development of specific serodiagnostic assays for lymphatic filariasis. In the present study, we report the molecular cloning and characterization of two filaria-specific recombinant clones (BmM5 and BmM14) with immunodiagnostic potential. BmM5 is a 505-bp cDNA which codes for a protein of 130 residues that ends with an endoplasmic reticulum targeting sequence. BmM14 is closely related to a recently reported clone (SXP-1), and it has 62% homology (deduced amino acid sequence) with a previously described Onchocerca volvulus clone, lambda RAL-2. Glutathione S-transferase fusion proteins of BmM5 and BmM14 were tested in various ELISA formats. The best results were obtained by measuring IgG4 antibodies to the fusion proteins. ELISA studies showed that approximately 90% of 111 sera from Indian and Egyptian patients with brugian and bancroftian filariasis were reactive with both antigens. Nonendemic sera as well as sera from patients with schistosomiasis or intestinal helminths were uniformly nonreactive. Assays based on BmM5 and BmM14 may be useful for large scale screening as an alternative to microfilaria or filarial antigen detection as a means of obtaining a rough index of filariasis endemicity in previously unstudied areas.

Molecular cloning of a house dust mite allergen with common antibody binding specificities with multiple components in mite extracts

Plaque radio-immuno assay has been used to isolate an IgE-binding clone from a lambda gt11 library of Dermatophagoides pteronyssinus cDNA. The clone HD6 contained DNA encoding a 215 residue protein which contained a predicted 17 amino acid residue leader sequence, no cysteines and a single N-glycosylation site. The 198 residue mature protein would have a predicted MW of 22,177 D. No homologues were found in searches of the data banks. Sera from 14/38 allergic children reacted strongly with the polypeptide produced by the clone (37%). Skin tests showed reactivity in 16/30 (53%) allergic patients and 0/10 of controls. Affinity purification of rabbit antibodies with the clone showed that antibodies to the polypeptide had specificities to multiple products in mite extracts corresponding to components of Mr 29, 27 and 24 K by Western blotting. Absorption studies of IgE in allergic serum indicated further entities at 13 and 11.5 kD. It is proposed to name this allergen Der p VII.

Characterization of a cDNA clone encoding the carboxy-terminal domain of a 90-kilodalton surface antigen of Trypanosoma cruzi metacyclic trypomastigotes

We have cloned and sequenced a cDNA for a metacyclic trypomastigote-specific glycoprotein with a molecular mass of 90 kDa, termed MTS-gp90. By immunoblotting, antibodies to the MTS-gp90 recombinant protein reacted exclusively with a 90-kDa antigen of metacyclic trypomastigotes. The insert of the MTS-gp90 cDNA clone strongly hybridized with a single 3.0-kb mRNA of metacyclic forms, whereas the hybridization signal with epimastigote mRNA was weak and those with RNAs from other developmental stages were negative, indicating that transcription of the MTS-gp90 gene is developmentally regulated. A series of experiments showed that the MTS-gp90 gene is present in multiple copies in the Trypanosoma cruzi genome, arranged in a nontandem manner, and that there are at least 40 copies of the gene per haploid genome. Sequence analysis of recombinant MTS-gp90 revealed 40 to 60% identity at the amino acid level with members of a family of mammalian stage-specific, 85-kDa surface antigens of T. cruzi. However, there are considerable differences in the amino acid compositions outside the homology region.

Immunoaffinity analysis of cross-reacting allergens by protein blotting

IgE antibodies from sera having reactivity against ryegrass pollen protein allergens, wheat endosperm protein allergens and also several other cereal protein allergens were adsorbed with either ryegrass pollen or the wheat/globulin fraction immobilised on solid phases and subsequently eluted with low pH buffer. The eluted antibodies were reacted with sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) blots of the different allergens. Antibodies adsorbed and subsequently eluted from the two allergen sources recognised different spectra of proteins in the ryegrass pollen and cereal allergen sources and indicated the degree of immunological cross-reactivity. Intra-species cross-reactivity of IgE antibodies was demonstrated employing similar methods to those used for the pollen and cereal allergens by using a recombinant allergen from the venom of the ant Myrmecia pilosula as the immunoadsorbent protein on the solid phase.

Cloning and characterisation of cDNA clones encoding two Babesia bovis proteins with homologous amino- and carboxy-terminal domains

A dextran sulphate protein (DSP) fraction derived from Babesia bovis has previously been shown to induce a protective immune response in cattle. A B. bovis cDNA library was screened with both the complete anti-DSP serum and a subfraction of the anti-DSP serum affinity purified on a native B. bovis protein of approx. 80 kDa. cDNA clones encoding two different B. bovis proteins were identified. The product of one gene, Bv80, has a single divergent copy of a sequence of 149 amino acids (approx. 30% amino acid identity) in both the amino- and carboxy-terminal domains. These domains are separated by an array of short variant repeat sequences rich in proline and glutamic acid. The product of the other gene, BvVAl (homologous to the previously described 225-kDa B. bovis protein)[19], is predicted to have a single divergent copy of a sequence of 170-171 amino acids (approx. 35% amino acid identity) in both the amino- and carboxy-terminal domains. These domains are also separated by an array of repeats. The 73-amino acid repeat unit of this array is composed of a number of variant derivatives of shorter repeat units. Detailed analysis of genomic clones flanking two alleles of the gene encoding BvVAl/225 kDa identified further members of a multi-gene family. This region of the genome of B. bovis has been subject to a large number of amplification processes.

Cloning and characterization of a Plasmodium falciparum gene encoding a novel high-molecular weight host membrane-associated protein, PfEMP3

The rat monoclonal antibody, mAb 12C11, reacts with numerous proteins from mature asexual stages of Plasmodium falciparum. The largest is 315 kDa and is designated PfEMP3. A lambda gt11 expression library, generated from genomic DNA of Malayan Camp strain parasites, was screened with mAb 12C11. One positive clone, lambda 12.1.3, contained a 1.4-kb fragment in frame with the beta-galactosidase gene of lambda gt11. The deduced 455-amino acid sequence is a novel, highly charged sequence encoding two 15-amino acid repeats at the N-terminus followed by 27 repeats of 13 amino acids. The last 59 C-terminal residues are non-repetitive. Two in-frame stop codons at the 3' end of the DNA suggests that this DNA fragment encodes the C-terminus of the protein. Southern blotting with the cloned fragment identified two copies of this fragment per haploid genome in knob-positive, parasitized erythrocytes (K+PE). Both DNA fragments are absent from K - PE. Northern blotting of trophozoite-stage PE total RNA revealed mRNAs of 10, 4.4 and 2 kb in K+PE, but no hybridization with K - PE. Immune sera were elicited against the lambda 12.1.3 beta-galactosidase fusion protein and peptides generated from the predicted lambda 12.1.3 amino acid sequence. These sera and mAb 12C11 reacted specifically with PfEMP3 in Western blots of mature K+PE but not with K - PE. Rat and mouse sera against the recombinant protein produced an immunofluorescence pattern in fixed mature K+PE almost identical to the pattern produced by a monoclonal antibody against the knob-associated protein, Histidine Rich Protein 1. The same antibodies were immunofluorescence negative with fixed K - PE. Mouse antibodies against the recombinant protein reacted on immunoelectron microscopy with the erythrocyte membrane of K+PE, labeling knobs as well as the membrane between knobs. In contrast, a mAb against Histidine Rich Protein 1 reacted only under the electron dense material of knobs. We conclude that the lambda 12.1.3 clone encodes the C-terminal portion of the 315 kD PfEMP3 antigen and that PfEMP3 may be involved in knob formation or other perturbations of the erythrocyte membrane.

Molecular cloning and characterization of a major allergen (Myr p I) from the venom of the Australian jumper ant, Myrmecia pilosula

Five IgE-binding components were identified in the venom of the Australian jumper ant, Myrmecia pilosula using SDS polyacrylamide gel electrophoresis and Western blotting. A cDNA clone which encodes the entire amino acid sequence of one of the major IgE-binding venom allergens has been nucleotide sequenced. The IgE-binding determinants of this allergen are located in its C-terminal domain. Database searches, however, did not reveal any homology with any other known nucleotide or protein sequence. The sequenced allergenic polypeptide has, according to the convention recommended by the International Union of Immunological Societies (IUIS), been named Myr p I.

Cloning and sequencing of a cDNA fragment from Plasmodium chabaudi chabaudi that contains repetitive sequences coding for a potentially lysine-rich aspartic acid-rich protein

Screening of a cDNA library (prepared in lambda gt11) of the blood stages of Plasmodium chabaudi chabaudi (AS) with immune serum has revealed an antigen the elicits a strong antibody response in infected mice. The clone (clone 6) expressing that antigen contains a 0.7 kb insert and produces a beta-galactosidase fusion protein of about 150 kDa. In Western blot analysis performed on parasite extracts, monoclonal antibodies and polyclonal sera prepared against the fusion protein revealed that the fusion protein contains part of a malarial protein of 93 kDa. Northern hybridization with clone 6 insert as probe detected a plasmodial RNA of about 3.2 kb, which could well code for a protein of this size. The insert hybridized to a single EcoRI fragment and a single HindIII fragment in genomic Southern blotting, suggesting that the gene is present in one copy in the P. chabaudi genome. The DNA sequence of clone 6 insert predicts a hydrophilic, acidic polypeptide consisting of seven repeats of 23-34 amino acids rich in lysine (24%) and aspartic acid (17.5%).

Cloning and characterisation of members of a family of Babesia bigemina antigen genes containing repeated sequences

Bovine polyclonal antisera to Babesia bigemina antigens separated by phenyl-Sepharose chromatography were used to screen a B. bigemina lambda gt11 cDNA expression library. Eleven B. bigemina-specific cDNA clones were studied in detail. DNA sequencing of 2 representative clones identified open reading frames encoding polypeptides representing the carboxy-termini of 2 different proteins. Both polypeptides contained a related central motif of tandem repeats flanked by a highly conserved carboxy-terminal region, but the sequences preceding the repeats were not related. Hybridisation and restriction enzyme analysis of the cDNA clones indicated that they were derived from a family of at least nine related, but not identical genes. Four different members of the gene family have been isolated from a B. bigemina lambda EMBL3 genomic library. The genes are not closely linked and they occur on the largest and smallest B. bigemina chromosomes resolved by pulsed field gel electrophoresis (PFGE). Antibodies raised against the native antigens and purified on recombinant fusion proteins bound to multiple proteins (50-70 kDa) in the original B. bigemina antigenic fractions.

Metacyclic form-specific variable surface glycoprotein-encoding genes of Trypanosoma (Nannomonas) congolense

A complementary DNA expression library in phage lambda gt11 was synthesized using mRNA from in vitro-produced metacyclic forms of a clone of Trypanosoma (Nannomonas) congolense. The unamplified library was screened with antiserum from a goat immune to infection with metacyclic (m)-forms of T. congolense ILRAD Nannomonas antigen repertoire 2(ILNaR2). Of the 100 antiserum-reactive phage clones identified, 22 were analyzed further: 21 of the clones contained overlapping portions of a single transcript, while one other contained a different transcript. Northern blot analyses indicated that the sequences contained in the clones were transcribed only by m-forms of ILNaR2. Immunological and sequence analyses indicated that the two different cloned sequences encode m-form-specific variable surface glycoproteins.

Isolation and characterization of recombinant antigens from Leishmania aethiopica that react with human antibodies

A genomic expression library of Leishmania aethiopica was constructed in lambda gt11 and screened with patient sera and sera from healthy people living in an area of endemicity. Forty-five recombinant clones were isolated and partly characterized. Clone-specific antibodies were prepared and used with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western immunoblot analysis to estimate the molecular masses of the parasite-derived antigens containing the reactive epitope(s). Antigens with apparent molecular masses of 90, 85, 63, 50, 41, 25 and 24 kDa as well as several antigens with lower molecular masses were detected. The clone-specific antibodies from patients with diffuse cutaneous leishmaniasis reacted with high-molecular-weight antigens (30,000 less than Mr less than 90,000), whereas antibodies from patients with localized cutaneous leishmaniasis recognized low-molecular-weight antigens (Mr less than 25,000). Nine different purified recombinant antigens were obtained from lysogens in Escherichia coli Y1089 by immunoaffinity chromatography on anti-beta-galactosidase columns and were subsequently tested with patient sera. It is suggested that some of these recombinant antigens might be used for immunodiagnostic purposes.

Cloning of a 21.7-kDa vaccine-dominant antigen gene of Schistosoma mansoni reveals an EF hand-like motif

Several cDNA clones encoding a 21.7-kDa antigen (Sm21.7) were detected from a Schistosoma mansoni sporocyst cDNA expression library using irradiated cercaria-vaccinated rabbit serum. The antigen was designated 'vaccine dominant' because parasite-derived Sm21.7 was recognised preferentially by mouse vaccine sera compared with mouse infection sera. The cDNA and corresponding gDNA sequences showed 64% identity at the nucleotide level and 47% identity at the amino acid level with the sequence of a previously described S. mansoni tegumental antigen, sma22.6. Whereas sma22.6 mRNA occurs almost exclusively in the adult worm, Sm21.7 mRNA was equally abundant in the sporocyst, schistosomular and adult stages. Both Sm21.7 and sma22.6 sequences reveal a motif strongly homologous to the EF hand calcium binding domain but lacking the invariant glycine in the calcium binding loop. The disruptive nature of the glutamine which in Sm21.7 replaces the glycine explains why the motif is non-functional, as shown by the inability of Sm21.7 to bind calcium.

Antibody recognition and isoelectrofocusing of antigens of the malaria parasite Plasmodium yoelii

Inbred BALB/c mice were either immunized with Triton X-100-extracted antigens of blood-stage Plasmodium yoelii or infected with P. yoelii and cured in three successive schedules. Whereas the immunized BALB/c became only partially protected from subsequent challenge infection with blood-stage P. yoelii, the convalescent mice acquired total immunity. When total P. yoelii antigen extract was resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transferred to nitrocellulose, and immunoblotted with anti-P. yoelii serum, five major protein bands of 150, 84, 40, 19, and 16 kDa were recognized by the sera of fully protected convalescent mice but not by the sera of partially protected mice. The utility of comparing reactivities of sera from fully protected and partially protected malaria hosts and the possibility that antigens uniquely recognized by the convalescent mouse sera may contribute to immunity against P. yoelii infection are discussed. Although previously reported to be an effective adjuvant for immunization against P. yoelii infection in (BALB/c x C57BL)F1 hybrid mice, saponin did not promote protection any better than did Freund adjuvant in BALB/c mice immunized with detergent-extracted P. yoelii antigen. Most of the P. yoelii proteins (14 to 250 kDa) found in Triton X-100 extracts of P. yoelii-parasitized erythrocytes isoelectrofocused as a single peak in the pH region 4.4 to 4.6, suggesting a rationale for previous findings that the most anti-P. yoelii protective and T-helper activities are induced by antigens isoelectrically focused in a fraction of similar pH.

cDNA clones of Onchocerca volvulus low molecular weight antigens provide immunologically specific diagnostic probes

We report here a panel of cDNA clones from Onchocerca volvulus which were isolated on the basis of being uniquely recognised by onchocerciasis sera and not by sera from patients infected with the major lymphatic filarial nematode parasite Wuchereria bancrofti. Over 90% of O. volvulus recombinants from a primary screen were found to cross-react with lymphatic filariasis sera and were discarded. The subset of specific clones, selected with pooled sera, was then screened with panels of individual patient sera. Individual onchocerciasis cases showed a highly heterogeneous pattern of recognition of recombinant peptides, but several clones were identified which could be combined in a cocktail of antigenic epitopes to successfully detect all infected cases in the study. All these clones encode low molecular weight proteins of the parasite, confirming earlier reports that antigens of this size class show greater species specificity. Several clones encode proteins of 20-23 kDa, the same molecular weight range as the major surface protein of adult worms. The two most commonly recognised clones, Ov22/31M and Ov20/36M were subcloned into the vector pNGS 8 which produces fusion proteins attached to a polyasparagine leader. The fusion peptides of both Ov22/31M and Ov20/36M were soluble and easily purified by gel filtration. Purified fusion protein was used in ELISA to assess reactivity of infected patients giving 90% sensitivity with 100% specificity.

Trypanosoma cruzi: cloning and expression of an antigen recognized by acute and chronic human chagasic sera

Here we describe the characterization of a Trypanosoma cruzi DNA sequence (clone A13) that codes for a polypeptide recognized by IgM and IgG antibodies from sera of acute and congenital chagasic patients. Antibodies to A13 antigen are also detected in the sera of chronic patients with different clinical forms of Chagas' disease, but not in sera of patients with leishmaniasis or other parasitic diseases. The antigenic determinants encoded by clone A13 are found in amastigotes and trypomastigotes of several T. cruzi strains, but not in the noninfective epimastigotes. The DNA sequence of the recombinant clone reveals one open reading frame encoding 251 amino acids without tandemly repeated sequences. Our data suggest that the A13 antigen may be useful for the development of serodiagnostic procedures.

Identification of the gene for a Plasmodium yoelii rhoptry protein. Multiple copies in the parasite genome

Serum from mice hyperimmune to Plasmodium yoelii was used to screen a P. yoelii genomic DNA library. Antibodies selected from hyperimmune serum by lambda gt11 clone J7 or raised against a specific fusion protein or peptide produced a punctate pattern of immunofluorescence on fixed smears of parasitised erythrocytes and immunoprecipitated a 235-kDa protein apparently identical to a rhoptry protein previously implicated in red cell invasion. The cloned DNA hybridised to at least seven RsaI fragments of P. yoelii genomic DNA and to three DraI fragments of similar but not identical sequence. These results suggest that the gene encoding the 235-kDa rhoptry protein may be represented more than once in the P. yoelii genome.

Identification and characterisation of a Leishmania donovani antigen belonging to the 70-kDa heat-shock protein family

A Leishmania donovani promastigote cDNA library was screened with serum obtained from a patient infected with visceral leishmaniasis. Sequence analysis of a clone obtained from this library revealed that the 600-bp insert corresponded to the carboxy-terminal region of an antigen related to the 70-kDa heat-shock protein family. The full-length sequence of the corresponding gene (1959 nucleotides) was determined after isolation of genomic clones. Genes encoding the antigen are present on a single chromosome as a series of approximately twelve 3.7-kb direct tandem repeats. The antigen can be identified as a 70-kDa heat-shock cognate protein by virtue of its molecular mass, sequence and constitutive expression during heat shock. It is expressed at all stages of the parasite life-cycle. Antibodies against the lambda gt11 fusion protein were detected in more than 50% of serum samples obtained from patients with visceral leishmaniasis, but were not detected in sera from patients with cutaneous leishmaniasis or Chagas' disease.

Identification of lambda gt11 clones encoding the major antigenic determinants expressed by Theileria parva sporozoites

An antiserum, C16, was raised in cattle against freeze-thawed extracts of sporozoites of Theileria parva (Muguga). This antiserum, which neutralizes sporozoite infectivity in vitro, identified theileria-specific antigens having approximate molecular masses of 105, 90, 85, 69, 67, 52, 47, and 43 kilodaltons (kDa) on Western blots (immunoblots) of infected tick salivary gland extracts. The antiserum was used to screen an expression library of T. parva (Muguga) genomic DNA fragments. Three recombinant bacteriophage clones carrying different theileria DNA inserts were studied. The expressed gene product from each clone was used to affinity purify antibodies from C16 antiserum for use in probing Western blots of uninfected and infected tick salivary gland extracts. The population of antibodies selected by each clone specifically recognized a subset of the antigens identified by C16 antiserum. The antigens fell into three distinct groups as defined by their reactivity with each set of selected antibodies. One group included antigens of 105, 90, 85, and 35 kDa, a second group included antigens of 69, 67, 52, 47, and 43 kDa, and the third group included an apparently distinct pair of antigens of 47 and 43 kDa. Thus, antibodies that reacted with determinants encoded by the three recombinant phage clones recognized all of the major antigens seen on Western blots probed with whole C16 antiserum. These results suggest that there may be only three immunodominant antigens expressed in T. parva (Muguga) sporozoites. Additionally, monoclonal antibodies have been raised which neutralize sporozoite infectivity in vitro. These antibodies react with epitopes of the antigens with Mrs of 69,000, 67,000, 52,000, 47,000, and 43,000 which are encoded in clone pgT-42 and have been used to localize these epitopes on the sporozoite surface.

Regions of an Eimeria tenella antigen contain sequences which are conserved in circumsporozoite proteins from Plasmodium spp. and which are related to the thrombospondin gene family

Coccidiosis, caused by Eimeria spp., is a major disease of economic importance to the poultry industry. The cloning and characterisation of genes coding for antigens of those species infecting chickens is an initial step in the identification of protective antigens suitable for the development of a genetically engineered vaccine. This report describes the molecular characterisation of an antigen of E. tenella produced by the recombinant lambda amp3 bacteriophage EtHL6. Three native polypeptides corresponding to the EtHL6 antigen, with sizes between 110 and 94 kDa, have been identified on both sporozoites and second generation merozoites of E. tenella by mouse antisera raised against the EtHL6 fusion protein. The DNA insert is a 722-bp EcoRI fragment encoding a polypeptide comprising three tandem blocks of amino acids which are highly homologous to each other. Each region, A, B and C, contains a strongly hydrophilic domain and two pairs of cysteine residues. Computer analysis has identified similarities with a group of proteins which include the circumsporozoite antigen and thrombospondin-related anonymous protein (TRAP) of malaria parasites, human thrombospondin, mouse properdin and the terminal components of the complement pathway.

Isolation and characterization of a gene associated with a virulent strain of Babesia microti

Babesia microti genomic DNA was purified from parasitized murine erythrocytes, digested with mung bean nuclease and used to construct an expression library in lambda gt11. Polyspecific antisera from mice infected with virulent B. microti organisms (ATCC30221) were used to screen the genomic library for genes encoding major immunogens. High titer antisera selected a recombinant phage, Bm13, containing 3.3 kb of B. microti DNA. Hybridization analysis confirmed the parasite origin of the clone; affinity-purified antibody revealed a native molecular weight of 54,000 for the B. microti protein encoded by the recombinant. Only genomic DNA isolated from the virulent strain of B. microti contained sequences which hybridized to Bm13. Genomic DNA prepared from the Peabody attenuated strain of B. microti or from Babesia bovis DNA did not contain any complementary sequences. These data suggest a possible role for the gene in the virulence of the organism.

Parasite antigens expressed in Escherichia coli. A refined approach for epidemiological analysis

A simple method is described to generate carrier-free recombinant antigens following their expression in Escherichia coli. A plasmid, called pMSgt11, has been constructed such that the cleavage site for the protease factor Xa separates the recombinant antigen from an enzymatically active beta-galactosidase. Thus, rapid purification of the active beta-galactosidase recombinant protein, followed by digestion with factor Xa, releases the antigen of interest. The pMSgt11 plasmid is compatible with the phage expression vector, lambda gt11 and the feasibility of applying this system has been demonstrated using malarial recombinant antigens. Inserts from lambda gt11 recombinant Plasmodium falciparum clones have been recloned into the EcoRI site of pMSgt11 and the expressed soluble fusion proteins have been purified from crude extracts using a one step affinity chromatography. After protease digestion, the fusion protein cleavage products were analysed by immunoblot with a panel of different human immune sera. We were able to successfully demonstrate specific antibody titers to the parasite-derived carrier-free antigen, without interference from anti-Escherichia coli-specific antibodies. The general application of this approach to epidemiological analysis is discussed.

Expression in Escherichia coli of a dominant immunogen of Trypanosoma cruzi recognized by human chagasic sera

A genomic clone expressing a Trypanosoma cruzi antigen in Escherichia coli was identified using human chagasic sera. Chagasic antibodies affinity purified on extracts of this clone recognized a high-molecular-weight protein expressed in all developmental stages of the parasite life cycle, as well as in various T. cruzi strains. The antigen is associated with the cytoskeleton of the parasite and localizes along the attachment region between the flagellum and the cell body. Antibodies to the recombinant antigen were detected in the sera of 115 chagasic patients from different endemic regions, but not in sera of patients with leishmaniasis, T. rangeli infection, or other parasitic diseases. Our data suggest that the presence of antibodies to this antigen may be specifically associated with Chagas' disease.

A heat shock-like protein from the human malaria parasite Plasmodium falciparum induces autoantibodies

The humoral immune response to a 72-kDa heat shock-like protein of Plasmodium falciparum has been analyzed using mouse monoclonal antibodies (mAb) and human immune sera. Three regions of the molecule containing B cell epitopes were identified by screening a sublibrary encoding the COOH-terminal half of the antigen with the mAb. One B cell epitope mapped to a region poorly conserved between the parasite 72-kDa polypeptide and mammalian heat-shock proteins (Hsp 70). Another mAb, G10C9, reacted with an amino acid region that has a high degree of homology with mouse (87.5%) and human (81.2%) Hsp 70. Both mouse and human cells were recognized by this mAb when analyzed by indirect immunofluorescence and by two-dimensional immunoblots. Sera from humans infected with malaria also recognized the human Hsp 70. Thus, our results indicate that autoantibodies directed against host Hsp 70 can be induced by the homologous parasite protein.

Plasmodium falciparum: an intervening sequence in the GBP 130/96 tR gene

The 96 tR antigen is a heat stable protein produced during the late stages of the intraerythrocytic development of the malaria parasite Plasmodium falciparum and is released into the culture supernatant or the sera of infected patients at the time of schizont rupture. This antigen, identified as a putative protective antigen, was shown to be identical to the glycophorin-binding protein GBP 130 (Perkins 1988, Bonnefoy et al. 1988). We report here that the gene contains a small undescribed intervening sequence located immediately after the sequence coding for the signal sequence. This shows that in P. falciparum, all the genes described so far coding for proteins exported outside the parasitophorous vacuole share a common organization.

The gene coding for the 190,000-dalton iron-regulated protein of Yersinia species is present only in the highly pathogenic strains

A genomic library containing DNA fragments of 0.5 to 2 kilobase pairs in length from Yersinia enterocolitica serovar O:8 was constructed in a bacteriophage lambda gt11 expression vector. Mouse antibodies specific for the iron-regulated high-molecular-weight proteins (HMWPs) were used to screen the library. Two positive clones of 1 and 0.5 kilobase pairs, designated A13 and D7, respectively, were detected and isolated. They coded for beta-galactosidase fusion proteins of 151,000 and 138,000 daltons (Da). Antibodies affinity purified on the two recombinant lambda gt11 vectors specifically recognized the smaller HMWP (190,000 Da) and not the larger (240,000 Da). The two cloned DNA fragments were used to construct recombinant amplification plasmid pUC13 and to obtain large amounts of purified A13 and D7 inserts. Southern hybridizations performed with the inserts used as probes revealed that: (i) the two cloned DNA fragments overlap; (ii) only one gene hybridizes with the A13 and D7 inserts; (iii) the gene coding for the HMWP is conserved among all highly pathogenic Yersinia species studied; (iv) this gene is missing in the low-virulence and nonvirulent strains; and (v) transcription of the HMWP gene is induced by iron starvation.

Molecular cloning, genomic structure and localization in a blood stage antigen of Plasmodium falciparum characterized by a serine stretch

Two short DNA segments were isolated by screening of a lambda gt11 library from Plasmodium falciparum schizont cDNA with an antiserum against the 140 kDa protein, which confers protective immunity to monkeys. The segments were used to identify a genomic fragment which carries the entire coding sequence for a protein of 113 kDa characterized by a stretch of serine residues (SERP I). We present the complete nucleotide and deduced amino acid sequence as well as the structure of the SERP I gene. The gene consists of four exons interrupted by three short introns located at the amino-terminal half. Exon 1 and the first part of exon 2 code for hydrophobic amino acids of a putative signal sequence. Exon 2 contains two repetitive segments, the first encoding six glycine rich octapeptides and a second region coding for 37 consecutive serine residues. Southern blot analysis demonstrated the conservation of the SERP I gene in four different parasite strains. SERP I could be localized in the parasitophorous vacuole and in the surrounding membranes. We discuss the relationship of this protein to the recently described P126 polypeptide and the possible role of this antigen as a vaccine candidate.