Novel antimalarial antibodies highlight the importance of the antibody Fc region in mediating protection

Parasite drug resistance and difficulties in developing effective vaccines have precipitated the search for alternative therapies for malaria. The success of passive immunization suggests that immunoglobulin (Ig)-based therapies are effective. To further explore the mechanism(s) by which antibody mediates its protective effect, we generated human chimeric IgG1 and IgA1 and a single-chain diabody specific for the C-terminal 19-kDa region of Plasmodium yoelii merozoite surface protein 1 (MSP119), a major target of protective immune responses. These novel human reagents triggered in vitro phagocytosis of merozoites but, unlike their parental mouse IgG2b, failed to protect against parasite challenge in vivo. Therefore, the Fc region appears critical for mediating protection in vivo, at least for this MSP119 epitope. Such antibodies may serve as prototype therapeutic agents, and as useful tools in the development of in vitro neutralization assays with Plasmodium parasites.

Crystal structure of a Fab complex formed with PfMSP1-19, the C-terminal fragment of merozoite surface protein 1 from Plasmodium falciparum: a malaria vaccine candidate

Merozoite surface protein 1 (MSP1) is the major protein component on the surface of the merozoite, the erythrocyte-invasive form of the malaria parasite Plasmodium. Present in all species of Plasmodium, it undergoes two distinct proteolytic maturation steps during the course of merozoite development that are essential for invasion of the erythrocyte. Antibodies specific for the C-terminal maturation product, MSP1-19, can inhibit erythrocyte invasion and parasite growth. This polypeptide is therefore considered to be one of the more promising malaria vaccine candidates. We describe here the crystal structure of recombinant MSP1-19 from P.falciparum (PfMSP1-19), the most virulent species of the parasite in humans, as a complex with the Fab fragment of the monoclonal antibody G17.12. This antibody recognises a discontinuous epitope comprising 13 residues on the first epidermal growth factor (EGF)-like domain of PfMSP1-19. Although G17.12 was raised against the recombinant antigen expressed in an insect cell/baculovirus system, it binds uniformly to the surface of merozoites from the late schizont stage, showing that the cognate epitope is exposed on the naturally occurring MSP1 polypeptide complex. Although the epitope includes residues that have been mapped to regions recognised by invasion-inhibiting antibodies studied by other workers, G17.12 does not inhibit erythrocyte invasion or MSP1 processing.

MSP-1 malaria pseudopeptide analogs: biological and immunological significance and three-dimensional structure

Merozoite Surface Protein-1 (MSP-1) has been considered as a malaria vaccine candidate. It is processed during the Plasmodium falciparum invasion process of red blood cells (RBCs). A conserved MSP-1 C-terminal peptide was identified as a high-activity erythrocyte-binding peptide (HAEBP) termed 1585. Since conserved HAEBPs are neither antigenic nor immunogenic we decided to assess the significance of a single peptide bond replacement in 1585. Thus, two pseudopeptides were obtained by introducing a Y[CH2-NH] reduced amide isoster into the 1585 critical binding motif. The pseudopeptides bound to different HLA-DR alleles, suggesting that backbone modifications affect MHC-II binding patterns. Pseudopeptide-antibodies inhibit in vitro parasite RBC invasion by recognizing MSP-1. Each pseudopeptide-induced antibody shows distinct recognition patterns. 1H-NMR studies demonstrated that isoster bonds modulate the pseudopeptides' structure and thus their immunological properties, therefore representing a possible subunit malaria vaccine component.

Schistosoma mansoni proteases Sm31 (cathepsin B) and Sm32 (legumain) are expressed in the cecum and protonephridia of cercariae

Adult Schistosoma mansoni parasites live in the bloodstream of their vertebrate hosts where they consume red blood cells. Hemoglobin, released from the ingested red blood cells, is degraded by a variety of parasite proteases, including Sm31 (cathepsin B) and Sm32 (schistosome legumain). In this study the localization pattern of the Sm31 and Sm32 enzymes in cercariae (the infectious life cycle stage) was examined. Antibodies generated against recombinant Sm31 and Sm32 recognize their respective proteins in Western blots of soluble parasite extracts. Highest levels are seen in adult female extracts, whereas the level of both proteins is below detection in cercarial extracts. However, in fixed, whole cercariae, both proteins are seen in the cecum and protonephridia. In the cecum, the staining pattern has a granular appearance, suggesting that the proteins are packaged in vesicles. In the protonephridial system, Sm31 and Sm32 are detected in all 8 flame cells in the cercarial body and in both flame cells in the cercarial tail. The distribution of the 2 proteins differs in the flame cells. Examination of immunostained cercariae using laser scanning confocal microscopy shows that whereas Sm31 is located in the tubule cell, Sm32 is found in both the tubule cell and its adjoining cap cell. These findings suggest that the proteins are involved in the proposed excretory and osmoregulatory roles of flame cells.

Trypanosoma evansi: demonstration of a transferrin receptor derived from expression site-associated genes 6 and 7

In Trypanosoma brucei, uptake of host transferrin is mediated by a heterodimeric, glycosylphosphatidylinositol-anchored receptor derived from the 2 expression site-associated genes 6 and 7 (ESAG6 and ESAG7). By using specific antibodies, it is shown here that T. evansi, a trypanosome species transmitted mechanically by biting flies, also expresses a transferrin receptor composed of ESAG6 and ESAG7. The cellular uptake of transferrin in T. evansi is completely inhibited with anti-T. brucei (ESAG6/7 heterodimer) antibodies. The demonstration of a functional ESAG6/7 transferrin receptor in T. evansi supports further its close relationship to T. brucei.

Commitment to the production of male and female gametocytes in the human malaria parasite Plasmodium falciparum

Commitment to the production of female and male gametocytes was studied in the NF54 line of the human malaria parasite Plasmodium falciparum. The development of sibling parasites derived from individual schizonts was followed, and 2 antisera against the female gametocyte-specific protein Pfg377 and the male gametocyte-specific protein alpha-tubulin II were used to determine the sex of sibling gametocytes. The experiment showed that individual cohorts of sibling gametocytes were stained in a mutually exclusive fashion by only one or the other antiserum, indicating that individual schizonts committed to yield sexual parasite progeny produce gametocytes of the same sex. This work suggests that in P. falciparum commitment to sexual differentiation occurs prior to schizont maturation, at the same moment when the sex of the resulting gametocytes is determined.

Anomalous colloidal stability of protein coated polystyrene latex beads studied by small angle light scattering

Results of small angle laser light scattering experiments carried out on polystyrene latex beads coated with lysate of Plasmodium falciparum (Pf) antigen (Ag) and human seropositive sera (10:1 ratio) are reported for various NaCl concentrations (0-300 mM). The protein coated beads showed time-dependent coagulation. The normalised intensity of scattered light I(s)(t)/I(0) showed I(s)(t)/I(0)=1+(Gammat)(delta) behaviour with the coagulation rate, Gamma and exponent, delta showing anomalous dependence on NaCl concentration. The coagulation rate exhibited strong increase up to NaCl concentration of 50 mM, above this and up to 300 mM the coagulation rate was found to remain independent of NaCl concentration yielding non-DLVO behaviour. The same was true for delta which increased from 1.04+/-0.06 to 6.94+/-0.07 as NaCl concentration was raised from 0 to 50 mM. Above 50 mM it remained constant with delta=6.94+/-0.07. Results are discussed through Smoluchowski aggregation kinetics and theoretical construction of interparticle interaction potentials relevant to our problem.

In vivo expression and distribution of dense granule protein 7 (GRA7) in the exoenteric (tachyzoite, bradyzoite) and enteric (coccidian) forms of Toxoplasma gondii

The in vivo expression and distribution of the dense granule protein GRA7 was examined in both the exoenteric (tachyzoite and bradyzoite) and enteric (coccidian) forms of Toxoplasma gondii by immunocytochemistry. There was strong staining of GRA7 in granules within all the infectious stages (tachyzoite, bradyzoite, merozoite and sporozoite). During tachyzoite development, GRA7 was secreted and was associated with the parasitophorous vacuole. In contrast, although there was staining of granules within the bradyzoites of more mature cysts, there appeared to be little staining of the tissue cyst wall or host cell. The apparent stage-specific variation in secretion of GRA7 between tachyzoites and bradyzoites was confirmed by double labelling using stage-specific markers (SAG1 and BAG1). In the enteric forms in the cat gut there was strong labelling of the PV containing early asexual and sexual stages and staining of a few granules in the apical cytoplasm of the merozoite. The positive enteric staining pattern differentiates GRA7 from the other GRA proteins (GRA1-6) which were absent in the merozoites and enteric stages. The staining pattern of GRA7 with strong staining during tachyzoite and enteric development and reduced staining in the tissue cysts is similar to that seen for NTPases. The function of GRA7 is unknown but it is unique among the dense granule proteins in being expressed in all the infectious forms of T. gondii which would point to a basic role in the vacuolar adaptations required for active parasite development.

Preparation of recombinant human monoclonal antibody Fab fragments specific for Entamoeba histolytica

Genes coding for human antibody Fab fragments specific for Entamoeba histolytica were cloned and expressed in Escherichia coli. Lymphocytes were separated from the peripheral blood of a patient with an amebic liver abscess. Poly(A)+ RNA was isolated from the lymphocytes, and then genes coding for the light chain and Fd region of the heavy chain were amplified by a reverse transcriptase PCR. The amplified DNA fragments were ligated with a plasmid vector and were introduced into Escherichia coli. Three thousand colonies were screened for the production of antibodies to E. histolytica HM-1:IMSS by an indirect fluorescence-antibody (IFA) test. Lysates from five Escherichia coli clones were positive. Analysis of the DNA sequences of the five clones showed that three of the five heavy-chain sequences and four of the five light-chain sequences differed from each other. When the reactivities of the Escherichia coli lysates to nine reference strains of E. histolytica were examined by the IFA test, three Fab fragments with different DNA sequences were found to react with all nine strains and another Fab fragment was found to react with seven strains. None of the four human monoclonal antibody Fab fragments reacted with Entamoeba dispar reference strains or with other enteric protozoan parasites. These results indicate that the bacterial expression system reported here is effective for the production of human monoclonal antibodies specific for E. histolytica. The recombinant human monoclonal antibody Fab fragments may be applicable for distinguishing E. histolytica from E. dispar and for use in the serodiagnosis of amebiasis.

Anti-immunoglobulin antisera used in an ELISA to detect antibodies in barramundi Lates calcarifer to Cryptocaryon irritans

Immunoglobulins (Ig) in serum from barramundi vaccinated with bovine serum albumin (BSA) were purified by ammonium sulphate precipitation and affinity chromatography using BSA as the ligand. The BSA-binding activity of eluted putative Ig fractions was assessed by enzyme-linked immunosorbent assay (ELISA) before being pooled and characterised by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Double affinity purification did not improve the purity of the Ig preparation compared to single affinity purification. Barramundi Ig were injected into sheep to produce anti-Ig antisera which were assessed in an indirect ELISA as the secondary antibody to detect serum Ig in barramundi vaccinated with Cryptocaryon irritans theronts. Affinity-purified Ig induced a more specific reagent for use as secondary antibody in ELISA than did normal whole-barramundi sera. The heavy (H) chain of barramundi Ig had an apparent molecular weight of 70 kDa while that of the light (L) chain was 27 kDa in SDS-PAGE studies. Under non-reducing conditions 2 putative populations of Ig were identified, at 768 and 210 kDa. The N-terminal sequence of the barramundi Ig H chain showed 78% homology with channel catfish Ictalurus punctatus Ig H chain sequence.

Detection of nitrosylated epitopes in Trypanosoma brucei gambiense by polyclonal and monoclonal anti-conjugated-NO-cysteine antibodies

Activated macrophages with the Calmette/Guérin bacillus (BCG) have a cytotoxic/cytostatic effect on the extracellular parasite, Trypanosoma brucei gambiense. This effect was inhibited when the NO-synthase inhibitor NG-monomethyl-L-arginine (NMMA; 0.5 mM) was added to the culture media. Using an immunocytochemical method with rabbit polyclonal or mouse monoclonal antibodies directed against conjugated nitroso-epitopes (anti-conjugated-NO-cysteine), nitrosylated antigens were visualized in fixed trypanosomes. These results suggest that NO was synthesized by the activated macrophages and that it reacted with some parasitic proteins containing cysteine. The release of NO bound to parasitic proteins may cause the killing of trypanosomes. The immunoreactivity was positive when the trypanosomes were obtained from the supernatant of the BCG-activated macrophages that contains BSA (4 mg/mL). In contrast, the parasites cocultured with non-activated macrophages remained completely viable, and, the immunoreactivity was completely negative.

Immune response against Leishmania antigens in dogs naturally and experimentally infected with Leishmania infantum

Cell-mediated and humoral immune response in naturally and experimentally infected dogs was studied using crude and pure antigens. Both types of infections induced severe signs of visceral disease, but the symptoms observed in natural infections were more pronounced than in experimental infections. In addition, asymptomatic infections were not observed in experimentally infected animals. Disease evolution in laboratory infections was rapid and an increase in antibody titer to crude parasite antigen was correlated with the appearance and aggravation of clinical symptoms. Peripheral blood lymphocyte proliferation to crude antigen and pure gp63 was observed early following experimental infection, but was abolished once the infected dogs began to exhibit clinical signs. A similar pattern was observed in naturally infected dogs. Serum from all patent dogs showed high antibody titers to rK39 in enzyme-linked immunosorbent assays (ELISA), and reacted by western blotting with several antigens, 12 to 120 KDa, including gp63 and gp70. In the case of asymptomatic dogs. antibody titers to crude antigen were low and only a few antigens were identified by western blotting. None of the pure proteins examined, gp63, gp70, and rK39 were recognized by western blotting or ELISA. However, asymptomatic dogs exhibited specific lymphocyte proliferation to both crude antigen and the potential vaccine candidate gp63.

Plasmodium falciparum: stage-related expression of topoisomerase I

The expression and activity of topoisomerase I (PfTopoI) has been examined during the intraerythrocytic stages of the Plasmodium falciparum life cycle. The promoter is inactive during the early ring stage and becomes active only during the later trophozoite and schizont stages. The PfTOP1 transcript starts to accumulate in the trophozoite stage parasite, decreasing again in the schizont stage. Using both stage-specific Western analysis and immunofluorescent assays we show that PfTopoI is present at low levels in rings and accumulates to approximately equal levels in the trophozoite and schizont stages. Experiments to determine the activity of PfTopoI, using a topoisomerase I relaxation assay, show that there is a low level of PfTopoI activity in both ring and trophozoite stages, but activity increases dramatically in the schizont stage. The PfTopoI activity can be inhibited by treatment with specific antiserum and by the type I topoisomerase-specific inhibitor camptothecin.

Bacterial expression of a neutralizing mouse monoclonal antibody Fab fragment to a 150-kilodalton surface antigen of Entamoeba histolytica

A mouse monoclonal antibody (MAb) (EH3015, IgG1 with a K light chain) prepared by hybridoma technology recognizes a 150-kD surface antigen of Entamoeba histolytica and inhibits adherence and cytotoxicity of the ameba to mammalian cells. The genes encoding the light chain and the Fd region of the heavy chain of the MAb were cloned and expressed in Escherichia coli. The plasmid used was designed for the expression of Fab with a hexa-histidine tag in the periplasmic space. Recombinant Fab fragments were purified and analyzed by an indirect immunofluorescence antibody test and Western immunoblot. The specificity of the recombinant Fab fragment was comparable with the parent whole IgG. In addition, the Fab fragments significantly inhibited the adherence of E. histolytica to erythrocytes. These results suggest that the production of a neutralizing MAb in Escherichia coli is practical and efficient with this expression system.

Use of a leishmanin skin test in the detection of canine Leishmania-specific cellular immunity

The leishmanin skin test was used to detect Leishmania-specific cellular immunity in asymptomatic dogs from an endemic region of visceral leishmaniosis. The test was safe since no clinical signs of intolerance to leishmanin were detected during 1 month, in 14 dogs after inoculations of 3 x 10(8) promastigotes/ml. In another group of four dogs no cross reactivity was found after inoculations of a PPD which demonstrated the specificity of the test. In the same group of animals, repeatability was assessed by repeated inoculations of leishmanin at 1-5-month intervals and the threshold of sensitivity was the concentration of 3 x 10(6) promastigotes/ml. Secondly, we applied the test in a dog population that live in an endemic region of visceral leishmaniosis and found a significant increase in Leishmania-infected dogs after the application of this test in the field.

Pathways for potentiation of immunogenicity during adjuvant-assisted immunizations with Plasmodium falciparum major merozoite surface protein 1

Vaccine adjuvants exert critical and unique influences on the quality of immune responses induced during active immunizations. We investigated the mechanisms of action of immunological adjuvants in terms of their requirements for cytokine-mediated pathways for adjuvanticity. Antibody responses potentiated by several adjuvants to a Plasmodium falciparum MSP1-19 (C-terminal 19-kDa processing fragment of MSP1) vaccine were studied in gamma interferon (IFN-gamma) or interleukin (IL-4) knockout mice. The levels of anti-MSP1-19 antibodies and the induction of Th1- and Th2-type antibodies were analyzed. Results revealed a spectrum of requirements for cytokine-mediated pathways in the potentiation of immunogenicity, and such requirements were influenced by interactions among individual components of the adjuvant formulations. One adjuvant strictly depended on IFN-gamma to induce appreciable levels of anti-MSP1-19 antibodies, while some formulations required IFN-gamma only for the induction of Th1-type antibodies. Other formulations induced exclusively Th2-type antibodies and were not affected by IFN-gamma knockout. There were three patterns of requirements for IL-4 by various adjuvants in the induction of Th2-type anti-MSP1-19 antibodies. Moreover, the induction of Th1-type anti-MSP1-19 antibodies by adjuvants showed two distinct patterns of regulation by IL-4. The utilization of an IL-4 regulated pathway(s) for the induction of Th2-type antibodies by the same adjuvant differed between mouse strains, suggesting that animal species variability in responses to vaccine adjuvants may be due, at least in part, to differences in the utilization of immune system pathways by an adjuvant among animal hosts.

Neosporosis in a dog in Italy

Clinical neosporosis was diagnosed in a 2-month-old Pit Bull Terrier from Italy. Neospora caninum tachyzoites were found in semitendinosus muscle with myositis. The diagnosis was confirmed by immunohistochemical staining with anti-N. caninum specific antibodies. This is the first report of systemic neosporosis in dogs from Italy.

The third member of the Tetrahymena CCT subunit gene family, TpCCT alpha, encodes a component of the hetero-oligomeric chaperonin complex

The sequence of a third member of the Tetrahymena pyriformis chaperonin CCT ('chaperonin containing TCP1') subunit gene family is presented. This gene, designated TpCCT alpha, is the orthologue of the mouse chaperonin gene TCP1/CCT alpha. To characterize the CCT complex in this ciliate, we have produced polyclonal antibodies against synthetic peptides based on C-terminal sequences deduced from the primary sequences of the TpCCT alpha, TpCCT gamma and TpCCT eta subunits. We have also used polyclonal antibodies produced against recombinant yeast CCT alpha and CCT beta subunits. Using these antibodies, we show that Tetrahymena cells contain a hetero-oligomeric CCT chaperonin comprising at least seven distinct subunits. Three of these were assigned to specific TpCCT genes, whereas a fourth was recognized by the polyclonal antibody against yeast CCT beta, suggesting that this gene is also present in the ciliate. The CCT complex also contains other unidentified proteins that were recognized by the polyclonal antibody UM-1, raised against the putative ATP binding domain of the chaperonin proteins. TpCCT alpha gene expression was shown in exponentially growing cells and cells regenerating their cilia for different periods to have a similar pattern to the previously identified genes TpCCT gamma and TpCCT eta, and also to tubulin genes.

Recognition of phage-expressed peptides containing Asx-Pro sequences by monoclonal antibodies produced against Plasmodium falciparum circumsporozoite protein

The immunodominant region of the Plasmodium falciparum circumsporozoite protein is comprised mainly of a series of tetrapeptide repeats that can, depending on the starting cadence chosen, be described as (NANP)n, (ANPN)n, (NPNA)n or (PNAN)n in one-letter amino acid code. Data from several studies suggest that the NPNA cadence alone is structurally correct, in that each NPNA tetrapeptide effectively forms a structural unit initiated by an Asx-Pro turn. To explore this idea further and to assess the immunological relevance of peptide conformation as it relates to the cadence of these tetrapeptide repeats, we used ELISA to compare the abilities of monoclonal antibodies (MAbs) produced against P. falciparum sporozoites to recognize repeat-related heptapeptides expressed on the surface of filamentous bacteriophage. Having included representatives of both NANP and NPNA cadences and other peptides in which the number and location of Asx-Pro sequences varied, we provide evidence that Asx-Pro sequences play an important role in peptide conformation and antibody recognition, that peptide conformation is influenced by the cadence of the tetrapeptide repeats and that peptide conformation is important to the abilities of these MAbs to recognize their epitopes.

Characterisation of the binding sites of monoclonal antibodies reacting with the Plasmodium falciparum rhoptry protein RhopH3

Twenty one mouse monoclonal antibodies reacting or cross-reacting with the Plasmodium falciparum RhopH3 protein reacted with Ag44, a recombinant antigen expressing the 134 C-terminal RhopH3 residues. Using overlapping peptides scanning this region, two major binding sites were identified. The first one, recognised by eight anti-RhopH3 and seven cross-reacting mAbs, was mapped to the sequence Thr Asp Asn Thr Tyr or Thr Asp Asn Thr Tyr Lys (aa 823-828), depending on the support used for synthesis. Binding specificity and affinity were investigated for a subset of four mAbs reacting with this epitope, including one growth inhibitory mAb. Systematic replacements showed that the various mAbs had similar requirements. The inhibitory mAb presented a higher affinity for this sequence and bound to the adjacent sequence, Tyr Lys Glu Met Glu Leu (aa 827-832). A 2nd binding site, located around residue 850, was recognised by two anti-RhopH3 mAbs, which reacted exclusively with the 110 kDa RhopH3 polypeptide, unlike the other mAbs, which reacted with the 110 and 105 kDa RhopH3 antigens. This suggested that the 105 kDa RhopH3 polypeptide derives from the 110 kDa by C-terminal processing. Experimental evidence substantiating this conclusion was provided by the observation that antisera raised to peptides located upstream of the putative cleavage site reacted with both the 110 kDa and 105 kDa polypeptides, whereas antisera raised to the 45 C-terminal amino acids of RhopH3 reacted exclusively with the larger, 110 kDa product. The biological significance of this processing is discussed.

Improved detection of human antibodies to a Plasmodium antigen using a peptide modified with Aib residues

A 17-mer sequence was selected as a model to study the influence of modifications of terminal ends both on the conformational of a peptide and on its antigenicity towards naturally developing antibodies. This sequence corresponded to a tandemly repeated motif, found in a long repetitive region, with high helical propensity, of a Plasmodium falciparum liver-stage antigen (LSA-1), immunogenic in man. Our model peptide was synthesized with ionizable or non-ionizable ends, or modified in both extremities by introduction of the helix-promoting residue alpha-aminoisobutyric acid (Aib). Helical contribution, absent in the 17 amino-acid sequence possessing ionizable ends, was detectable when non-ionizable ends were introduced, and dramatically increased in the Aib-modified analogue. The presence of ionizable ends totally abolished reactivity towards human sera, otherwise detectable with the peptide possessing non-ionizable ends. While modification by Aib residues was neither detrimental nor beneficial to antigenicity in solution, it clearly resulted in an improved sensitivity of the specific antibody detection when used as solid-phase antigen in ELISA.

Cholesterol sulphate-reactive autoantibodies are specifically increased in chronic chagasic human patients

An antibody reactive with cholesterol sulphate (CS) was characterized in human sera by ELISA, erythrocyte and liposome absorption. This antibody was found evenly distributed between the IgA and IgM classes, and whilst this was present at low titres in the serum of 16% of healthy individuals studied, it was significantly elevated in 78% of Trypanosoma cruzi-infected subjects. No association was found between antibody levels and the degree of myocardial damage. No significant difference in immunoreactivity was found between healthy and chagasic subjects using dehydro-epiandrosterone sulphate and pregnenolone sulphate and cholesterol, ergosterol, lanosterol, stigmastanol, beta-stigmasterol, pregnenolone, prednisolone and dehydroepiandrosterone as antigens, suggesting that in chagasic sera the whole sterol molecule is important for optimal antibody binding. CS-reactive antibodies were easily purified by absorption either with CS-bearing liposomes or with dextran sulphate gel and further elution with 1.5 M NaCl. The optimal pH of CS-antibody interaction was 4.0 with 85% binding at pH 7.0. Polylysine strongly decreased the binding of these antibodies to the corresponding antigen. Furthermore, these antibodies were strongly absorbed by rabbit and guinea pig erythrocyte but not by rat or human erythrocyte. In contrast with anti-sulphatide antibodies, no significant increase in CS-reactive antibodies was found in dilated cardiomyopathies. Whilst CS itself was not detected in T. cruzi lipid extracts, there is an unidentified sulphated sterol, which migrates close to standard CS and which strongly binds chagasic but not control sera. This latter sterol might be acting in chagasic patients as a powerful antigen, triggering specific autoantibody production.

Monoclonal rat antibodies directed against Toxoplasma gondii suitable for studying tachyzoite-bradyzoite interconversion in vivo

We previously reported the in vitro analysis of stage differentiation of Toxoplasma gondii in murine bone marrow-derived macrophages. The purpose of this study was to generate monoclonal rat antibodies that might be suitable for investigating tachyzoite-bradyzoite interconversion in vivo with the murine model. Immunization of Fischer rats with cysts of T. gondii NTE resulted in the generation of seven monoclonal antibodies of the immunoglobulin G2a, G2b, or M isotype, which were further characterized by the immunoblot technique, immunofluorescence assay, immunohistology, and immunoelectron microscopy. Immunoblots demonstrated specific reactivity of five monoclonal antibodies with proteins with molecular masses of 40, 52, 55, 60, 64, 65, and 115 kDa. One antibody (CC2) appeared to recognize a differently expressed antigen depending on the parasite stage, reacting with a 40-kDa molecule in tachyzoites and a 115-kDa antigen in bradyzoites and oocysts. Several other monoclonal antibodies were shown to be stage specific and to react in immunofluorescence assays or in immunoblots with either tachyzoites or bradyzoites. Kinetics of stage conversion in vitro could be monitored by immunofluorescence with two of these monoclonal antibodies. Preliminary immunohistological investigations of tissue sections from infected mice demonstrated the possible usefulness of these monoclonal antibodies for future in vivo studies on stage differentiation of T. gondii in the murine system.

Evidence for anti-Plasmodium falciparum antibodies that cross-react with human T-lymphotropic virus type I proteins in a population in Irian Jaya, Indonesia

This study was performed to demonstrate the presence of anti-Plasmodium falciparum antibodies in a population living in Irian Jaya, Indonesia that cross-react with human T-lymphotropic virus type I (HTLV-I) proteins. Serum samples from 63 volunteers living in Oksibil, a secluded highland valley in Irian Jaya, were tested for anti-P. falciparum antibodies by an immunofluorescence assay and for anti-HTLV-I antibodies by an enzyme immunoassay (EIA). All samples were positive for anti-P. falciparum antibodies at titers of > or = 1:256. Twenty-four samples were reactive by EIA for HTLV-I, and of these, 23 were tested by western blotting (immunoblotting). Five of the 23 samples were classified as western blot positive and 18 were classified as western blot indeterminate. In competitive blocking assays with malaria proteins, western blot immunoreactivity to all HTLV-I Gag proteins was either reduced or eliminated. Significant reductions in the HTLV-I EIA optical density values of the Oksibil sera occurred when the sera were competitively blocked with the malaria antigens. The optical density values of HTLV-I-positive control sera showed no significant change. Competitive blocking with HTLV-I antigens produced reductions in the optical density values of both the Oksibil sera and the HTLV-I-positive control sera. These data suggest that in this population, anti-P. falciparum antibodies are cross-reactive with HTLV-I proteins in the western blot and EIA tests.