Non-covalent interactions result in aggregation of surface antigens of the parasitic nematode Trichinella spiralis

Changes in the surface ofDipetalonema viteae(Filarioidea) during its development as shown by comparative peptide mapping

The cuticle of parasitic nematodes, the main contact site with the host, plays an important role in host-parasite interaction and thus also in immunological control. We compared different surface-iodinated life-stages of the filarial wormDipetalonema viteae(microfilariae, infective 3rd-stage larvae (L3), adult males and females) with respect to changes in their surface composition. Autoradiographs of peptide maps show that all stages present an identical set of peptide spots reflecting common surface protein(s). Spots specific for larvae L3show that the composition of the iodinated surface differs in microfilariae and adults i.e. it changes during development. Adults show a spot typical for males or females. Identical spots are found in L3. This suggests that a surface component is also sex specific.

The occurrence of antibodies to hidden and exposed determinants of surface antigens of Trichinella spiralis

Mice were infected per os with Trichinella spiralis and their lymphocytes were removed and fused with mouse myeloma cell line P3 × 63Ag8653P3 for the selection of monoclonal antibodies to biochemically defined, stage-specific surface antigens of 3 parasite developmental stages: muscle larvae, adults and newborn larvae. Two separate antibodies against a defined single surface antigen of each stage were isolated. In each separate case the pair of monoclonal antibodies precipitated the same component from detergent-solubilized surface antigen preparations, but only one was able to bind to the surface of the living worm. The other must therefore be directed against an antigenic epitope which is obscured in the intact worm surface. The latter type of antibody is unlikely to be involved in the initial phase of parasite rejection and hence is another example of a non-protective host antibody response. The stimulus for its synthesis may be release of surface antigen, which does occur in vitro. One surface antigen of the newborn larvae is only detected by antibody in the first 6 h after birth; thereafter its presence is obscured as other antigens appear. The major surface antigen of the infective larvae contains carbohydrate determinants which are not available at the parasite surface. In addition, it displays great molecular heterogeneity but all variants appear to be derived from a common polypeptide structure.

Trichuris muris: antigen recognition and transfer of immunity in mice by IgA monoclonal antibodies

Mesenteric node lymphocytes from mice that had been infected with the nematode Trichuris muris, and then boosted with adult worm excretory-secretory antigens were fused with myeloma cells to produce a panel of 9 monoclonal antibodies (MoAbs). Five of the MoAbs were of the IgA isotype. The antigen recognition profiles of these MoAbs were studied using SDS-PAGE and immunoblotting; three major profile patterns were identified. Five MoAbs recognized a major band in the MW range 43-48 kD; all recognized a range of antigens. Three MoAbs were used to localize antigens in the bodies of adult worms. Granules within the anterior stichocytes were recognized strongly, as was material within the eggs and pseudocoelom. Two MoAbs stained the cuticle. Although the phosphorylcholine (PC) determinant was widely distributed within worm tissues none of the MoAbs tested recognized PC. Passive transfer of immunity was achieved using two of the IgA monoclonals; no immunity was transferred by the IgM and IgG MoAbs used. The limited recognition profiles of these IgA MoAbs, and the ability to stain stichocyte granules, suggest that their protective activity results from an interaction with ES antigens.

Extraction and identification of a 31,000 mol.wt glycoprotein antigen of Ostertagia circumcincta by sera from resistant sheep

Under similar extraction conditions, Triton X-100 sonicates gave higher yields of protein from third stage larvae and adult O. circumcincta than seven other detergents tested. Using sera from sheep which had been experimentally defined by both immunological and parasitological parameters as being either resistant or susceptible to O. circumcincta, a molecule from Triton X-100 extracts of third stage O. circumcincta larvae was identified which reacted preferentially with sera from resistant sheep. This molecule has a molecular weight of 31,000 and preliminary characterization studies revealed it to be a glycoprotein which was not found in later larval stages or adult worms. Antibodies to this 31,000 mol.wt antigen were present in sera of sheep as early as 3 weeks after experimental infection with O. circumcincta.

Protection against Trichinella spiralis induced by purified stage-specific surface antigens of infective larvae

The stage-specific surface antigens of the infective larvae of Trichinella spiralis, isolated using an affinity column of monoclonal antibody (Mab) NIM-M1, consisted of four components with molecular weights of 72, 65, 52, and 47 kDa, respectively. These four components may have unique as well as shared structural features and appear to be products of the stichosome. When injected i.p. as an emulsion in complete Freund's adjuvant, the purified antigens induced protection against infection of BALB/c mice with T. spiralis, as assessed by reductions in both the muscle larvae load and the number of adult intestinal worms.

Solubilization of epicuticular antigen from Dirofilaria immitis third-stage larvae

The solubilization of epicuticle from third-stage (L3) Dirofilaria immitis larval cuticles was investigated. Cuticles collected after L3 had molted were incubated in 1.5% sodium dodecyl sulfate (SDS) at 37 degrees C with vigorous shaking. Solubilization of epicuticular layers was accomplished as demonstrated by electron microscopy. Diminished binding of an epicuticular specific monoclonal antibody (DIM-229) was seen when SDS-treated cuticles were compared to untreated cuticles in an indirect fluorescence antibody assay. Cuticles which were extracted further by boiling in 1.5% dithiothreitol (DTT) produced less protein than cuticles solubilized in SDS. Both extracts reacted with DIM-229 in an indirect enzyme-linked immunosorbent assay, indicating retention of antigenic reactivity of the solubilized epitope. SDS-polyacrylamide gel electrophoresis of SDS-derived antigens revealed, after silver staining, proteins from 12 to 77 kDa and only 1 band at 15 kDa for SDS-treated cuticles boiled in DTT. Western blot analyses of the extracts with DIM-229 were inconclusive.

Purification, characterization, and immunochemical studies of beta-N-acetyl-D-hexosaminidase from the parasitic nematode Trichinella spiralis

The exoglycosidase, beta-N-acetyl-D-hexosaminidase was purified 600-fold from the muscle-stage larvae (L1) of Trichinella spiralis. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the purified enzyme-active fraction contained 4 polypeptides with apparent molecular weights of 100,000, 68,000, 58,000 and 54,000. The beta-N-acetyl-D-hexosaminidase corresponds to the Mr 100,000 polypeptide as demonstrated by SDS-PAGE analysis of the enzyme-stained region isolated from a non-denaturing polyacrylamide gel. In addition, rabbit antiserum to a homogeneous preparation of the Mr 100,000 polypeptide (isolated by electroelution from an SDS-PAGE gel) specifically immunoprecipitated beta-N-acetyl-D-hexosaminidase activity from an extract of L1. Isoelectrofocusing (pH 3-10) resolved 4 isoenzymes of T. spiralis beta-N-acetyl-D-hexosaminidase with isoelectric points (pI) of 5.35, 5.49, 5.63 and 5.79. The T. spiralis beta-N-acetyl-D-hexosaminidase is a glycoprotein based on its binding to lentil-lectin Sepharose affinity column and its specific binding of concanavalin A on Western blots. The IgG fraction of T. spiralis-infected mouse serum specifically immunoprecipitated T. spiralis beta-N-acetyl-D-hexosaminidase. The removal of carbohydrate from T. spiralis beta-N-acetyl-D-hexosaminidase significantly reduced its antigenicity. Immunocytochemical analysis of L1 tissue sections with polyclonal rabbit antisera to the homogeneous beta-N-acetyl-D-hexosaminidase enzyme indicated localization on cell membranes and the epicuticle.

The biochemical and immunochemical characterisation of the 30 kilodalton surface antigen of Brugia pahangi

The major surface antigen (30 kDa) of Brugia pahangi has been characterised by a number of biochemical and immunochemical means. The 30 kDa polypeptide is a glycoprotein which can be extracted from the worm surface by homogenization in the absence of detergents. The 30 kDa polypeptide can be metabolically labelled with [35S]methionine in adult male and female parasites. In addition small amounts of the 35S-labelled 30 kDa antigen can be detected in the medium of worms cultured in vitro. 125I labelling of the excretory-secretory (ES) products of adult male and female parasites followed by immunoprecipitation and peptide mapping has confirmed the relationship between the surface located 30 kDa polypeptide and that released in vitro.

Biophysical properties of the surface lipid of parasitic nematodes

The biophysical properties of the surface lipid layer (the epicuticle) of living parasitic nematodes (Trichinella spiralis and Toxocara canis) were examined using fluorescent lipid analogues. A variety of such probes were screened, and only 5-N-(octadecanoyl)-aminofluorescein was found to insert into the outer lipid layer. Fluorescence quenching experiments showed that this probe was confined to the surface, and the rate of its lateral diffusion was then measured by Fluorescence Recovery After Photobleaching. This showed that the probe was not free to diffuse within the plane of the epicuticle. This structure is, therefore, extraordinary in its selectivity to lipid probes, and in the restricted lateral mobility of inserted lipid components.

Isolation of an antigenic fraction for diagnosis of onchocerciasis

A surface enriched fraction was prepared from adults of Onchocerca volvulus by brief extraction of entire worms with detergent. This was then gel filtered to yield a low molecular weight fraction which functioned specifically in ELISA analysis. An identical result was also obtained when the related cattle parasite, O. gibsoni, was similarly fractionated and tested. The low molecular weight fraction contained at least four antigenic components when examined by coprecipitation and immunoblotting studies. One ml of packed worms yielded sufficient low molecular weight antigen to examine about 2,000 human sera by the ELISA procedure, and the test was sensitive at human serum dilutions down to 1/400. A preliminary study with individual sera from Onchocerciasis endemic and non-endemic areas of Southern Mexico yielded 0/24 false positives, 3/24 false negatives and a significant ELISA value in 21/24 sera from proven cases of Onchocerciasis.

Regional specialization of the surface of a parasitic nematode

A monoclonal antibody (NIM-M7) has been prepared which reacts with a major surface antigen of adult males and females of Trichinella spiralis. This specificity is only demonstrable when the antigen is liberated by detergent solubilization of surface-labelled worms. When reacted with living adults, on the other hand, NIM-M7 reacts well with only the eversible cloaca, or copulatory bell, of the male, binding weakly, if at all, to other surface areas of male or female worms. A similar staining pattern is also given by Concanavalin A. The differential staining given by NIM-M7 must indicate a molecular difference between the organization of the same surface antigen on the cuticular surface of the copulatory bell and other areas of the worm surface. This example of regional specialization demonstrates that the nematode cuticle is not necessarily chemically uniform.

A comparison of the surface and secretions of Trichinella pseudospiralis and T. spiralis

Intact, viable adults, infective and newborn larvae of Trichinella pseudospiralis were surface labelled with 125I by the chloramine T method and labelled proteins were compared with those obtained from equivalent stages of T. spiralis. Electron-microscope autoradiography determined that labelled proteins were restricted to the cuticle for all stages of both isolates. Comparative polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate (SDS-PAGE), using thin gradient gel slabs, of proteins obtained from each stage, demonstrated that the profile of surface-labelled proteins of T. pseudospiralis were restricted in number, stage specific, and similar to equivalent proteins of T. spiralis both in size and in their organization into aggregates. The stage-specific profiles of surface-labelled proteins derived from newborn larvae were indistinguishable, but differences were noted between adults and infective larvae of the two isolates. These differences in protein structure were confirmed by two dimensional mapping of tryptic peptides. Stage-specific profiles were also obtained when [35S]methionine biosynthetically labelled secretions of the 3 stages of T. pseudospiralis were compared by SDS-PAGE. Comparison of the profiles obtained with secretions for respective stages of T. spiralis again failed to distinguish newborn larvae, but adults and infective larvae of T. spiralis and T. pseudospiralis displayed a mixture of common and species-specific proteins. These findings are discussed in relation to the different pathology associated with infection with two isolates.

Immunoglobulin class specific responses to biochemically defined antigens of Trichinella spiralis

A comparison of the humoral response to resistant (NIH) and susceptible (C3H) strains of mice, which reject adult worms at different rates during a primary infection, was made following infection with Trichinella spiralis. The serum concentration of immunoglobulins of the heavy chain classes IgM, IgG1, IgG2, IgG3 and IgA were determined by single radial immunodiffusion. Antibodies of the same immunoglobulin isotypes to biochemically defined, stage specific surface and secreted components of three stages of parasite development were also determined using an isotype specific immuno-coprecipitation assay. Independent variation of the responses of each immunoglobulin isotype was observed. The specific anti-parasite response did not reflect total serum immunoglobulin levels in all immunoglobulin classes, and this is discussed in relation to basic mechanisms of immunoglobulin class switching. Finally a close correlation was observed in resistant (NIH) mice between the production of IgA antibody to surface components of adult worms and accelerated expulsion of this stage of the worm from the gastrointestinal tract. The possible relevance of this IgA response is further indicated by the failure of susceptible mice to synthesise IgA antibodies to the same surface antigens.

Surface components of Onchocerca volvulus

A technique employing Sephadex G25 gel filtration has been developed for the rapid isolation and purification of live microfilariae of Onchocerca volvulus from subcutaneous nodules and skin samples. Microfilariae, adult worms and L3 larvae have been surface radiolabelled using the Iodogen technique. Two proteins have been characterised on the surface of uterine microfilariae: these have apparent molecular weights of 14,800 and 15,000. A MW 15,000 protein was the only molecule labelled on the surface of skin microfilariae. Ten proteins were labelled on adult male worms: these have molecular weights of 15,000, 17,500, 20,000, 22,000, 24,000, 29,000, 32,000, 37,000, 42,000, and 50,000. Some, if not all, of these proteins were also identified on female worms. Seven proteins were labelled on the surface of L3 larvae: these have molecular weights of 17,500, 48,000, 50,000, 52,000, 54,000, 57,000, and 105,000. Three of the adult surface proteins were precipitated by selected human infection serum: these are the MW 17,500, 32,000 and 42,000 molecules. The microfilarial surface proteins were not precipitated by human infection serum. The antiserum used in these experiments was shown by Western blot analysis to contain high levels of antibody with specificity for microfilarial and adult antigens. Indirect immunofluorescent assays showed these sera to contain antibody which bound to the surface of adult worms and eggs but not microfilariae. The possibility that skin microfilariae absorb host serum albumin was investigated: Western blot analysis and surface immunofluorescence assays using a specific anti-human albumin serum gave negative results. Fluorescent lectin binding studies revealed the presence of stage-specific carbohydrate moieties exposed on the surface of adult worms and eggs. Microfilariae do not have surface carbohydrate determinants.

Changes in cell surface proteins and glycoproteins during the encystation of Entamoeba invadens

Changes in cell surface components of axenically grown trophozoites of Entamoeba invadens which occur during encystation were followed. Protein patterns of trophozoites, immature and mature cyst forms, were analyzed by sodium dodecyl sulphate gel electrophoresis. Total protein profiles of trophozoites and cyst forms stained by Coomassie blue gave similar patterns. In contrast, a number of different bands were observed in gels stained with the carbohydrate-specific Schiff's reagent as well as when nitrocellulose blottings were treated with 125I-radiolabelled wheat germ or soybean agglutinins. The most notable differences were bands at 250 and 95-105 kDa present in the cyst forms and absent in the trophozoites, and two bands at 70 and 75 kDa present in the latter and missing in the cysts. Labelling of trophozoites and cyst cell surfaces by iodination with lactoperoxidase revealed a number of protein bands which were exposed on the trophozoite surface and missing in the cysts. Moreover, gel electrophoresis patterns of non-reduced or reduced samples also differed considerably, indicating that a number of proteins are linked by disulphide bonds. This study shows that specific glycoproteins are produced during cyst formation.

Stage-specific antigens of Trichinella spiralis

Infective larvae, adults and newborn larvae of Trichinella spiralis were surface labelled with radioactive iodine, and the surface material was solubilized in the mild detergent sodium deoxycholate. The radio-isotope labelled products were stage-specific glycoproteins that were few in number (2-4 components) and antigenic in infected mice and rats. Antibodies synthesized in infected animals against these biochemically defined surface antigens may or may not interact with the surface of the living worm. The latter type of antibody is unlikely to be involved in the initial phase of parasite rejection and is therefore another example of a non-protective host antibody response. The stimulus for its synthesis must be the observed release of surface antigen. A monoclonal antibody to a surface glycoprotein of newborn larvae protected against infection, and also promoted eosinophil killing in vitro. This observation emphasizes the importance of surface antigens in protection against infection, suggests a role for granulocytes in vivo, and provides encouragement for the possible use of nematode surface antigens in protection. An example of regional specialization of the nematode cuticle was given by a monoclonal antibody reactive with only the surface of the male intromittent organ and not the female or remainder of the male. The same stages were labelled in vitro with radioactive methionine, and the secreted proteins were also found to be stage-specific. Some, but not all, were antigenic in infected mice. The total concanavalin A-binding somatic glycoproteins of each stage exhibited considerable individuality, and hence stage specificity, when resolved by two-dimensional gel electrophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection against Trichinella spiralis induced by a monoclonal antibody that promotes killing of newborn larvae by granulocytes

Mouse monoclonal antibodies directed against biochemically defined surface antigens of Trichinella spiralis were selected and tested for their ability to destroy parasites in vivo and in vitro. One of these (NIM-M5; IgG1), which recognised a surface component of approximately 64 K molecular weight in newborn larvae (NBL), bound to a surface component of this stage (as shown by fluorescence), and mediated the adherence of rodent eosinophil leucocytes to the surface of living NBL. Following cell adherence mediated by this monoclonal antibody, the worms were killed. This effect was enhanced by fresh normal serum suggesting a role for complement in this phenomenon. A monoclonal antibody directed against a surface component of infective larvae (NIM-M1; IgM) did not promote adherence of cells nor killing of NBL in vitro. The effect of NIM-M5 on the development of NBL to the intramuscular stage was examined. Treatment of NBL with the NIM-M5 monoclonal antibody prior to their injection into mice, together with passive transfer of NIM-M5 for 3 days, significantly reduced (36-51%) the proportion of larvae recovered by digestion 28 days later. Thus a single monoclonal antibody to NBL was able to mediate eosinophil-dependent destruction of worms in vitro and reduce infectivity in vivo. These observations suggest that antibodies capable of mediating eosinophil-induced destruction of nematodes in vitro may also be important in protection against infection.

Differences in the surface radioiodinated proteins of skin and uterine microfilariae of Onchocerca gibsoni

Surface labeling studies using two populations of Onchocerca gibsoni microfilariae revealed important differences in major radioiodinated proteins. Small numbers of microfilariae harvested from the skin of cattle or the uteri of adult worms from skin nodules were purified, radioiodinated, solubilized and the proteins analysed by two dimensional gel electrophoresis and autoradiography. As reported previously, uterine microfilariae showed a complex profile of radioiodinated proteins, none of which appeared to be bovine albumin or immunoglobulin. In contrast, application of the same techniques to skin microfilariae demonstrated only one major labeled protein complex of approximate Mr 67 000. This protein complex was immunoprecipitated with an antiserum to bovine serum albumin. Surprisingly, fluorescence techniques failed to show bovine serum albumin on the surface of living microfilariae. Although the evidence is circumstantial at present, acquisition of host albumin (perhaps oriented in a particular way) may be a means whereby skin microfilariae evade immune effector mechanisms and, when living, generally fail to elicit inflammatory reactions in the skin of the host.

Characterization of surface and excretory-secretory antigens of Toxocara canis infective larvae

The surface antigens of Toxocara canis infective larvae have been identified by radio-iodination and compared with the excretory-secretory (ES) products released by the larvae in vitro. Common antigens, of molecular weight 32 000 and 120 000 are found on the larval surface, in the ES material and in culture supernatant following surface iodination of living T. canis larvae. The 120 000 antigens consist of three closely migrating bands in each of these preparations. However, one prominent ES component, of molecular weight 400 000, is not found on the larval surface. Additional molecules of 55 000 and 70 000 are present in the ES material, but while these may be discerned in surface preparations there appears to be more heterogeneity of surface molecules in this size range. Both sets of molecules are antigens to infected patients and experimental animals. A comparison of characterized human sera show that a radio-immunoprecipitation assay correlates with the established ELISA test (r = 0.89), and that all labelled molecules are antigenic to the infected host.

Stage specific secreted and somatic antigens of Trichinella spiralis

Infective larvae, adult males and newborn larvae of Trichinella spiralis were cultured with [35S]methionine in vitro. Total secreted and total somatic (sodium deoxycholate-soluble) proteins were analyzed by electrophoresis in the presence of sodium dodecyl sulphate (SDS-PAGE). Secreted proteins were relatively few in number and were different for each stage, whereas somatic proteins gave an unresolved smear in all cases. Immune precipitation with serum from infected mice revealed only one major antigen in secretions of all stages. In a similar investigation of the solubilised somatic antigens, the complexity of antigens ranged from none in infective larvae, through few in the adult, to many in the newborn larvae. The total concanavalin A-binding glycoproteins of each stage exhibited considerable individuality, and hence stage specificity, when resolved by two dimensional gel analysis. These results extend our knowledge of stage specific components of T. spiralis, and allow a rational approach towards the construction of diagnostic procedures.