Dirofilaria immitis: surface properties of third- and fourth-stage larvae

Onchocerca volvulus bivalent subunit vaccine induces protective immunity in genetically diverse collaborative cross recombinant inbred intercross mice

This study tests the hypothesis that an Onchocerca volvulus vaccine, consisting of two recombinant antigens (Ov-103 and Ov-RAL-2) formulated with the combination-adjuvant Advax-2, can induce protective immunity in genetically diverse Collaborative Cross recombinant inbred intercross mice (CC-RIX). CC-RIX lines were immunized with the O. volvulus vaccine and challenged with third-stage larvae. Equal and significant reductions in parasite survival were observed in 7 of 8 CC-RIX lines. Innate protective immunity was seen in the single CC-RIX line that did not demonstrate protective adaptive immunity. Analysis of a wide array of immune factors showed that each line of mice have a unique set of immune responses to vaccination and challenge suggesting that the vaccine is polyfunctional, inducing different equally-protective sets of immune responses based on the genetic background of the immunized host. Vaccine efficacy in genetically diverse mice suggests that it will also be effective in genetically complex human populations.

The liver proteome in a mouse model for Ascaris suum resistance and susceptibility: evidence for an altered innate immune response

Background

Ascariasis is a neglected tropical disease that affects 800 million people worldwide. Whereas most people only experience light worm burden, some people experience heavy worm burdens even after several rounds of chemotherapy, a phenomenon known as predisposition. Such heavy infections are associated with more severe symptoms and increased chronic morbidity.

Methods

In order to investigate potential mechanisms that may explain the observed predisposition, we infected mice with the porcine ascarid Ascaris suum using an established mouse model with two different mouse strains, where the C57BL/6J strain is more susceptible to infection and therefore a model for heavy infection and the CBA/Ca strain is more resistant and thus a model for light infection. At day 7 post-infection we investigated the liver proteome, using shotgun mass spectrometry, of both infected and control mice of each strain.

Results

We identified intrinsic differences, between the two mouse strains, in both oxidative phosphorylation proteins and proteins involved in retinol metabolism. Additionally, we found differences between the two mouse strains in activation of the complement system, where the CBA/Ca strain has higher protein abundances for lectin pathway proteins and the C57BL/6J strain has higher protein abundances for complement inhibiting proteins. The CBA/Ca strain had a higher abundance of proteins involved in the activation of the complement cascade via the lectin pathway. In contrast, the C57BL/6J strain demonstrated a higher abundance of proteins involved in arresting the complement pathway.

Conclusions

We observed clear differences between the two mouse strains both intrinsically and under infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3655-9) contains supplementary material, which is available to authorized users.

Inactivation of the complement anaphylatoxin C5a by secreted products of parasitic nematodes

Given the importance of the complement anaphylatoxins in cellular recruitment during infection, the ability of secreted products from larval stages of Brugia malayi and Trichinella spiralis to influence C5a-mediated chemotaxis of human peripheral blood granulocytes in vitro was examined. Secreted products from B. malayi microfilariae almost completely abolished chemotaxis. This inhibition was blocked by phenylmethylsulphonyl fluoride, indicating the presence of a serine protease, which was subsequently shown to cleave C5a. In contrast, secreted products from T. spiralis infective larvae showed modest inhibition of C5a-mediated granulocyte chemotaxis, and this was blocked by potato carboxypeptidase inhibitor, an inhibitor of several metallocarboxypeptidases. Adult and larval stages of both parasites were demonstrated to secrete carboxypeptidases which cleaved hippuryl-L-lysine and hippuryl-L-arginine, and the T. spiralis enzyme was partially characterised. The data are discussed with reference to inflammation in parasitic nematode infection.

Loss of complement activation and leukocyte adherence as Nippostrongylus brasiliensis develops within the murine host

Complement activation and C3 deposition on the surface of parasitic helminths may be important for recruitment of leukocytes and for damage to the target organism via cell-mediated mechanisms. Inhibition of complement activation would therefore be advantageous to parasites, minimizing damage and enhancing migration through tissues. The aim of this study was to determine ex vivo if complement activation by, and leukocyte adherence to, the nematode Nippostrongylus brasiliensis change as the parasite matures and migrates through the murine host. Pathways of activation of complement and the mechanism of adherence of leukocytes were also defined using sera from mice genetically deficient in either C1q, factor B, C1q and factor B, C3, or C4. Substantive deposition of C3 and adherence of eosinophil-rich leukocytes were seen with infective-stage (L3) but not with lung-stage (L4) larvae. Adult intestinal worms had low to intermediate levels of both C3 and leukocyte binding. For L3 and adult worms, complement deposition was principally dependent on the alternative pathway. For lung-stage larvae, the small amount of C3 detected was dependent to similar degrees on both the lectin and alternative pathways. The classical pathway was not involved for any of the life stages of the parasite. These results suggest that in primary infections, the infective stage of N. brasiliensis is vulnerable to complement-dependent attack by leukocytes. However, within the first 24 h of infection, N. brasiliensis acquires the ability to largely avoid complement-dependent immune responses.

Development of a recombinant antigen vaccine against infection with the filarial worm Onchocerca volvulus

Efforts to control Onchocerca volvulus, the etiologic agent of river blindness, have been limited to vector control and drug treatment to eliminate microfilariae, with no means available to prevent infection. The goal of this study was to develop a vaccine against this infection using recombinant antigens that are expressed in the early larval stages of the parasite. Five recombinant antigens, Ov7, Ov64, OvB8, Ov9M, and Ov73k, were identified by screening adult and larval cDNA libraries with antibodies from immune humans, chimpanzees, or rabbits. When mice were immunized with the five individual recombinant antigens, statistically significant reductions in parasite survival were induced in mice immunized with Ov7, OvB8, or Ov64, when administered in alum but not when injected in Freund's complete adjuvant (FCA). Live larvae recovered from control and immunized mice were analyzed to determine their developmental stages. A decrease in the percentage of larvae molting from the third stage to the fourth stage was observed with mice immunized with Ov7, Ov64, or OvB8 in alum but not with mice immunized with Ov9 and Ov73k or with mice immunized with any of the five antigens in FCA. Mice immunized with a cocktail of the three protective antigens developed protective immunity equal to that seen with mice immunized with individual antigens. This study has identified, for the first time, three recombinant antigens capable of inducing protective immunity to O. volvulus. Furthermore, since the antigens functioned with alum as the adjuvant, this vaccine could potentially be used clinically to prevent river blindness in humans.

Vaccine research and development for the prevention of filarial nematode infections

The development of vaccines for the prevention of filarial nematode infections is in a state of relative infancy in comparison to vaccines for other parasitic diseases, such as schistosomiasis and malaria. There are many reasons for this slow start. Some of the principal problems are: (1) the lengthy and complex life cycle of these organisms with attendant complex immune responses, (2) the unique characteristics associated with a relatively large number of different pathogens, (3) the lack of suitable model systems for study of medically important infections, (4) the paucity of parasite material for antigen discovery and recombinant library construction, (5) the lack of substantial evidence suggesting the natural occurrence of protective immune responses, and (6) the limited data on mechanisms responsible for protective immunity. As technical hurdles are considered, it is also critical to focus on the characteristics of a vaccine necessary for its eventual utility. In the case of a vaccine for D. immitis a completely successful product will need to approach a 99+% efficacy. This is because of the 99+% efficacy of competitive chemotherapeutic products and the fact that microfilaremia observed on blood examination, resulting from as few as two worms, would present as a vaccine failure. Although very low worm burdens in large dogs could be perceived as success in the context of protection from clinical disease, because of the option of virtually complete chemoprophylactic protection, the typical veterinary practitioner would probably fail to appreciate less than complete vaccine protection. In contrast, a vaccine that produced a reduction in adult worm burdens without complete protection in either lymphatic filariasis or onchocerciasis would be very important. Highly effective chemoprophylactic agents are not widely available for prevention of the human filariases, and dramatically reduced clinical disease provided by less than a completely effective vaccine could occur as the result of fewer adult worms. The importance of developing these vaccines has outweighed the obstacles to this research. There has been a great deal of epidemiological and experimental evidence to suggest a vaccine is feasible and antigen discovery has progressed relatively rapidly within just the past few years. Efforts to generate appropriate larval cDNA libraries are beginning to yield dividends and a variety of fascinating vaccine candidates have been cloned. Additional antigen discovery, research on appropriate modalities for overexpression of genes from these parasites, and the complex tasks associated with vaccinology remain as significant research and development obstacles.(ABSTRACT TRUNCATED AT 400 WORDS)

Rapid changes in the surface of parasitic nematodes during transition from pre- to post-parasitic forms

All mammalian-parasitic stages of a range of nematode species investigated (Brugia pahangi, Acanthocheilonema viteae, Strongyloides ratti, Nippostrongylus brasiliensis, Trichinella spiralis and Ostertagia ostertagi) labelled in a surface-restricted manner with the fluorescent lipid analogues 5-N-(octadecanoyl)aminofluorescein (AF18) or nitrobenzoxadiazole-cholesterol (NBD-chol), but failed to bind other similar probes. In contrast, the surfaces of the 'pre-parasitic' infective stages of these species had affinity for neither AF18 nor NBD-chol. This exclusion of lipid analogues changed rapidly upon exposure of the larvae to tissue culture conditions which mimic the mammalian tissue environment (e.g. RPMI 1640/37 degrees C) such that the above probes could then insert into the surface layer of the larvae. The dauer larva of Caenorhabditis elegans also excluded the probes, but became permissive to labelling upon stimulation to emerge from the dauer state. The time taken for the surface transformation to occur ranged from less than 10 min in the vector-borne parasites to approximately 5 h in those which enter by the oral route, with direct skin-penetrators occupying an intermediate position. In all cases, the alteration proceeded too rapidly for it to have been associated with a moult. Fluorescence Recovery After Photobleaching (FRAP) studies of A. viteae larvae showed that approximately 50% of the AF18 probe was free to diffuse within the plane of the surface immediately after transformation. This is only a transitory state because AF18 was found to be highly restricted in its lateral diffusion on the surface of adult parasites. In the larvae of S. ratti, the change in affinity for AF18 was accompanied by the rapid shedding of an otherwise stable surface coat of polyanionic material, here visualized by labelling with fluorescein-conjugated cationized ferritin. Incubation of larvae in lipid-rich host serum during the induction of transformation inhibited subsequent labelling with AF18. This possibly reflects competition for insertion sites and an in vivo propensity towards the acquisition of host lipid by invading parasites.

Onchocerca volvulus: immunization of chimpanzees with X-irradiated third-stage (L3) larvae

To provide a theoretical basis for the potential development of vaccines against Onchocerca volvulus (Ov) a trial has been conducted to assess the protective efficacy of immunization of chimpanzees with X-irradiated L3 larvae. Approximately 1000 larvae were injected at 0, 1, and 7 months. The immunized animals, and unimmunized controls, were then challenged with 250 live L3. In order to provide possibly protective exposure to the immunologically distinct L4 epicuticle, a radiation dose (45 krad) was chosen which preserved about 50% of the molting ability of unirradiated larvae. Despite the presence of a strong immune response to crude adult worm extracts, and to cloned Ov antigens, at the time of challenge little or no significant protection against patent infection was observed: three of four immunized animals developed patent infection as compared to four of four controls. One immunized animal failed to become patent or to manifest the late antibody response to adult worm antigens seen in both subpatent and patent infections in this model, and may have been protected from infection. The implications of these studies for future attempts to immunize against O. volvulus are discussed.

Changes in the surface composition after transmission of Acanthocheilonema viteae third stage larvae into the jird

This study describes the dynamics and the biochemical nature of changes in the surface of the filarial nematode Acanthocheilonema viteae after its transmission into the vertebrate host. Vector-derived third-stage larvae (mL3) were inoculated into naive Meriones unguiculatus and recovered from the tissues at different times post-infection until their moult to fourth-stage larvae (L4). Surface-specific labelling with fluoresceinated lectins revealed that the larvae are covered by a carbohydrate envelope. Although the mL3 envelope was strongly reduced one day after transmission, new surface carbohydrates appeared until the onset of moulting, some of which could also be identified on the surface of L4. In general, surface carbohydrates were partially shed by moving larvae, suggesting a loose association of these components in the epicuticle. The fate of cuticular lipids and proteins of L3 and L4 was monitored by external 125I-labelling and differential extraction of the components. Thin-layer chromatography of surface-labelled lipids revealed only minor changes 1 day after parasite transmission. Afterwards the number of lipids accessible to label decreased further until moulting was complete. Two-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis of surface-labelled proteins showed a consistent surface exposure of mL3 specific proteins until 1 day post-infection. Thereafter, the composition of surface-labelled proteins changed rapidly, resembling that of the L4 as early as several days before moulting. During this period individual differences in the composition of surface proteins were evident.

Stage-specific expression of a developmentally regulated gene in Dirofilaria immitis

A previously reported cDNA clone encoding 34 kDa antigenic polypeptide of Dirofilaria immitis (lambda cD34) was studied to elucidate the mechanism of stage-specific gene expression. The 34 kDa polypeptide was a larva-specific antigen and the mRNA was detectable in microfilariae but not in adult worms and eggs. The lambda cD34 gene was not sex linked and was contained in the genome of D. immitis at each stage. The stage-specific expression of the developmentally regulated gene in D. immitis may be controlled primarily at the mRNA level.

Perspectives on the in vitro culture of filariae

A primary constraint in the culture of human filariae is in obtaining starting material--either microfilariae (mfs), which infect invertebrates, or third stage larvae (L3s), which are infective to humans. Cryopreservation methods which partially overcome this difficulty have been developed for both mfs and L3s. Complete development of mfs to L3s outside an intact host was obtained recently when mosquito thoraces infected by Brugia malayi (24 h after the bloodmeal) were maintained in vitro. In another recent study in which no host tissues were present, a semidefined culture medium was used to investigate the properties of reduced glutathione (GSH) that stimulate early development of Onchocerca lienalis mfs. An extended cysteinyl backbone and a free sulfhydryl were identified as the key structural elements provided by GSH. Stimulation also required the presence of low and high molecular weight components of serum as well as oxygen. Molting of Onchocerca spp. L3s to the fourth stage at the rate of 50 to 70% has been reported by several researchers. Key factors identified in those successes have been temperature and serum lot. Improved long-term viability occurred with cellular co-culture. Beneficial effects of co-culture were shown to be due both to cellular conditioning of the medium as well as to lowered dissolved oxygen levels as a result of cellular metabolism. With the use of cell-conditioned medium and decreased incubator oxygen levels, long-term viability of Onchocerca larvae in culture exceeded that previously reported. Recently, Brugia malayi adults of both sexes were cultured from L3s using a semidefined medium supplemented with human serum. Many of these sexually matured adults mated and produced viable microfilariae.

Morphological demonstration of essential functional changes after in vitro and in vivo transition of infective Onchocerca volvulus to the post-infective stage

Transmission electron microscopic investigation of the morphogenesis of Onchocerca volvulus through the third moult to the post-infective stage revealed essential alterations in various larval organs. Complete rebuilding of surface structures, the reduction of secretory granules in the glandular oesophagus, the unfolding of the intestine, an increase in the number of nerve fibres in the nerve ring and novel sensory papillae were significant findings. Transition from third- to fourth-stage larvae (L4) started as early as 48 h after transfer to vertebrate conditions in vivo in surrogate hosts and in vitro. After a resting period of about 60 h to enable a reduction in gland size and the loosening of the old cuticle and formation of the new one, the larvae started to cast the infective-stage cuticle. Young L4 exhibited a thin, monolayered cuticle and did not rebuild a glandular oesophagus. The body cavity widened, the intestine unfolded and the increased number of microvilli indicated the resumption of metabolic activity.

Eosinophil-larval-interaction in onchocerciasis: heterogeneity of in vitro adherence of eosinophils to infective third and fourth stage larvae and microfilariae of Onchocerca volvulus

Adherence of eosinophilic granulocytes from patients with onchocerciasis to microfilariae (Mf), third (L3) and fourth (L4) stage larvae of Onchocerca volvulus was studied in vitro. Native and heat-inactivated sera from patients with onchocerciasis (OS), from endemic controls without signs of the disease (ECS), from healthy Caucasians (NS) or foetal calf serum (FCS) served as sources for adherence mediating factors. In FCS-supplemented medium eosinophils did not adhere to any larvae. None of the sera mediated the adherence of eosinophils to L4. Eosinophils adhered to L3 in the presence of OS, ECS and NS, whereas OS exclusively mediated adherence to Mf. Reduced adherence rates of eosinophils to L3 occurred in heat-inactivated or zymosan-activated OS, ECS or CS. Eosinophils bound to the L3 cuticle of moulting stage but not to the newly exposed L4 cuticle. A single adherent layer of effector cells was found around cast L3 cuticle, multiple layers were found around intact L3 leading to subsequent paralysis of the larvae and to an amplification of the toxic effector potential by homotypic intereosinophilic adhesion. Our experiments document heterogeneity of in vitro effector cell adherence to the three larval stages of O. volvulus and indicate that complement-dependent as well as independent mechanisms are operative in eosinophil-larval-interaction. The results emphasize the importance of the invading infective larval stages of O. volvulus as possible targets for vaccine production.

Onchocerca volvulus: biochemical and morphological characteristics of the surface of third- and fourth-stage larvae

The annulated cuticles of third- and fourth-stage larvae of Onchocerca volvulus have the typical structure of other nematodes but the cuticle of fourth-stage larvae was thinner. The surface of the third-stage larva was wrinkled and fuzzy, while that of the fourth-stage was smooth. Intermediate stages in the formation of the new cuticle and epicuticle beneath the old basal layer and of the separation of the cuticles are shown. Monoclonal antibodies specific to the surface of third-stage larvae did not react with the surface of the fourth-stage larvae. Binding of the monoclonal antibodies to the third-stage larvae was abrogated by treatment of the worms with trypsin and proteinase K, but was unaffected by treatment with periodate or the detergents sodium deoxycholate and SDS. The lectins RCA120 and WGA, but not any of the other lectins tested, bound only to the surface of fourth-stage larvae, and not to that of third-stage larvae. The surfaces of third- and fourth-stage larvae were shown to be different and contained stage-specific surface epitopes.

Ultrastructural study of the interaction between eosinophilic granulocytes and third and fourth stage larvae of Onchocerca volvulus

The interaction in vitro between eosinophil effector cells and third and fourth stage larvae of Onchocerca volvulus was studied by electron microscopy. The morphological observations demonstrated different mechanisms of attack of eosinophil cells that are dependent upon the time of incubation. Rapid adherence to the cuticle of the target, flattening, secretion of granule contents, vacuole formation and, finally, complete degranulation of the eosinophils were seen after incubation with third stage larvae and moulting stages. Alterations of the epicuticular and cuticular structures could be found near the attachment site of the cells. The eosinophils, however, showed no interactions with fourth stage larvae of this filarial parasite.

Cuticular proteins of Brugia filarial parasites

Surface-labelling techniques have been used to delineate a number of constituent molecules of the cuticle in adult stage Brugia malayi and Brugia pahangi. These molecules can be separated by virtue of their physical properties, and localised either by sequential solubilisation of intact cuticles or immunoelectron microscopy with relevant antisera. The major structural components of the cuticular matrix consist of a set of collagenous proteins of diverse molecular weight ranging from 36 to 160 kDa, cross-linked by disulphide bonds and confined to the basal and inner cortical layers. Each stage of the parasite has a distinctive set of between 12 to 25 collagenous proteins whose synthesis is regulated temporally with respect to moulting. As in other nematodes, the outer cortex and epicuticle is composed of a cross-linked insoluble proteinaceous structure. Two non-structural and water-soluble proteins are also resolved by Iodogen-mediated labelling; a 15 kDa peptide which shows no evidence of glycosylation, and a major 29 kDa glycoprotein, which carries at least two N-linked oligosaccharide chains and which we have termed Gp29. The former protein can be detected in L3, L4 and adult B. malayi by surface labelling, whereas Gp29 appears to be restricted to L4 and adult worms. The possible significance of cuticular proteins as targets of immunity or causative agents of pathology is discussed.

Surface-associated antigens of second, third and fourth stage larvae of Dirofilaria immitis

The surface-associated molecules of the second (L2), third (L3) and fourth (L4) larval stages of Dirofilaria immitis were characterized employing radiolabeling techniques and SDS-PAGE analysis. Major labeled components of 35 kDa and 6 kDa were present in extracts from IODO-GEN-labeled L2 and L3 parasites. The results of lactoperoxidase-catalyzed reactions also demonstrated that L2 and L3 stages of D. immitis have a similar repertoire of surface-associated antigens. However, in contrast to the results obtained with IODO-GEN, lactoperoxidase reactions labeled components with apparent molecular weights of 66, 48, 25, 16.5 and 12 kDa. The similarities in the molecular weights of the L2 and L3 surface-associated components and the results of immunoprecipitation experiments which demonstrated that antibodies produced against the 35 kDa molecule from D. immitis L3s also recognize the 35 kDa component from L2 parasites suggest that synthesis of the molecules found at the surface of mature infective larvae begins as early as day 6 of development in the mosquito, D. immitis L4s emerged from the molting process with a repertoire of surface-associated antigens distinct from those found on L2s and L3s. IODO-GEN labeling of D. immitis L4s showed major surface-associated molecules with apparent molecular weights of 57, 40, 25, 12 and 10 kDa when analyzed under non-reducing conditions. In addition to molecules of 57, 40, 25, 12 and 10 kDa, extracts of D. immitis L4s labeled with lactoperoxidase contained additional major bands at 45, 43 and 8 kDa. Metabolic labeling experiments demonstrated a shift in the amount and complexity of the excretory/secretory products released by D. immitis during L3 to L4 development.

The surface lipid of parasitic nematodes: organization, and modifications during transition to the mammalian host environment

The biophysical properties of the surface lipid of a range of nematode species and their developmental stages were examined, using fluorescent lipid probes and fluorescence recovery after photobleaching (FRAP). These methods can be applied to living, intact parasites, and the analysis confined to lipid on the outermost surface. In all cases, surface lipid was unusual in its selectivity for the insertion of the lipid probes. In addition, a polar lipid probe was generally not free to diffuse in the plane of the surface, in contrast to a non-polar lipid probe which was free to diffuse. This is evidence that the surface lipid layer is heterogeneous, and possibly comprises lipid domains. The infective larvae of Acanthocheilonema viteae, Nippostrongylus brasiliensis, Trichinella spiralis and Ostertagia ostertagi were found to exhibit a rapid change in lipophilicity upon exposure to conditions simulating entry into a mammalian host environment. Parasitic nematodes, therefore, present their hosts not only with a highly unusual biological surface, but also one which can be rapidly re-organised upon a change of environment.

Anti-idiotypic antibodies function as a surrogate surface epitope of Brugia malayi infective larvae

Anti-idiotypic (AB2) antibodies were generated in rabbits following immunization with a murine IgM monoclonal antibody (AB1) recognizing a surface determinant of Brugia malayi infective stage larvae. AB2 specifically inhibited the binding of AB1 to B. malayi larvae. Furthermore, AB2 had the ability to mimic the original antigen since mice immunized with AB2 possessed serum antibodies (AB3) specific for the B. malayi surface determinant. The presence of anti-surface antibodies (AB3 and AB1) induced either by AB2 immunization or by administration of AB1, did not alter the outcome of an intraperitoneal infection of B. malayi larvae in BABL/c mice when compared to untreated animals. AB3 antibodies like AB1, were IgM, thus indicating an isotype restricted response to the B. malayi epitope. There were no detectable cell mediated responses to the surface determinant in mice immunized with AB2, assessed by lymphocyte blastogenesis or IL3 production in vitro in response to the idiotope as presented by living larvae. The lack of cellular responses and/or the previously demonstrated rapid shedding of the epitope may explain the inability of AB1 or AB2 to protect mice against larval challenge in this study.

Immunologic relevance of the cuticle and epicuticle of larval Dirofilaria immitis and Toxocara canis

Investigations of the immunobiology of tissue stages of larval nematodes reveal several common, immunologically relevant features associated with the cuticle and epicuticle. First, commonality exists between surface and excretory-secretory antigens. Second, larval surfaces are often directly involved in evasion of host immune responses. Third, antigens present on the parasite surface can be involved in immunopathology, either directly through tissue damage or via systemic immunomodulatory events. Finally, in some instances, correlations can be inferred between immune protection and surface antigens. These concepts are illustrated through research on larval Dirofilaria immitis and Toxocara canis.

Seroepidemiological studies on human pulmonary dirofilariasis in Spain

Preliminary data are presented on a serological survey of the human population of an area with a high prevalence of Dirofilaria immitis infection in dogs. Five per cent of the sera were positive for IgG. Simultaneous radiological study revealed a pulmonary nodule in one of the positive patients, and in this case the evolution of IgG and IgM levels was followed over a period of three months. None of the positive sera reacted with Toxocara canis antigens.

Haemonchus contortus: a simple procedure for purifying surface proteins from third- and fourth-stage larvae

Surface proteins were solubilized from exsheathed third (XL3)- and fourth (L4)-stage larvae of Haemonchus contortus by a one-step extraction procedure involving brief heat treatment of the worms in the presence of buffer and 100 mM sodium chloride. Surface proteins also could be preferentially extracted from XL3s, but not from L4s, by heating the worms briefly in 1% sodium dodecyl sulfate. The major proteins extracted by these procedures were similar in molecular weight to those detected by surface-labeling live worms with 125Iodine. Both extraction procedures solubilized a single, major protein with an apparent molecular weight of 68-97 kDa from XL3s. In contrast, extraction of L4s with 100 mM sodium chloride yielded four major proteins with relative molecular weights of 27, 29, 78, and 200 kDa. Antibodies raised in rabbits to surface proteins prepared by the sodium chloride procedure reacted with the surfaces of live worms in indirect immunofluorescence assays. The anti-XL3 surface protein serum was stage specific in immunofluorescence experiments using live worms and in immunoprecipitation experiments using 125Iodine-labeled XL3 and L4 surface proteins. The overall amino acid composition of the surface proteins is hydrophilic. Twenty-six percent of the amino acid residues of the XL3 surface proteins, which consist predominantly of the 68-97 kDa species, are glutamate or glutamine.

Identification and preliminary characterization of cuticular surface proteins of Haemonchus contortus

Cuticular surface antigens of the XL3 and L4 stages of Haemonchus contortus have been studied by surface labeling and immunological techniques. Live worms were labeled with 125I and extracted with sodium dodecyl sulfate (SDS) followed by SDS + 2-mercaptoethanol. The SDS-soluble surface proteins of XL3s and L4s were found to consist of relatively few major species. The pattern of labeled polypeptides was distinctive for each developmental stage. These proteins are refractory to digestion by bacterial collagenase. Several of the proteins are glycosylated. Further extraction of labeled worms with SDS + 2-mercaptoethanol solubilized additional labeled proteins that appeared to be primarily collagens. Rabbit antisera prepared against native XL3 and L4-cuticles reacted strongly with the surfaces of live worms in immunofluorescence assays. In contrast, antisera prepared against SDS-extracted cuticles reacted weakly or not at all with live worms in similar experiments. Rabbit antisera prepared against adult cuticles failed to react with live XL3s or L4s. These studies suggest that the major surface antigens of XL3s and L4s are solubilized by SDS and that there are different antigens present on the cuticular surfaces of XL3s, L4s and adults. Stage-specificity in cuticular surface proteins may contribute to the successful parasitic lifestyle of this nematode.

Antigen shedding from the surface of the infective stage larvae of Dirofilaria immitis

A qualitative and quantitative analysis was made of the release of surface-associated molecules from developing Dirofilaria immitis infective-stage larvae (L3). D. immitis L3s were labelled with 125I using an Iodogen catalysed reaction and either maintained in culture or placed in chambers that were implanted into Lewis rats. The larvae released 10-20% of the labelled material each day during the first 4 days of in vitro and in vivo development. The loss of surface-labelled peptides from developing larvae corresponded with an increase in the amount of trichloroacetic acid-precipitable radioactivity found in the culture medium. SDS-PAGE analysis of the labelled material showed that the same 35 and 6 kDa components found in larval extracts were shed into culture medium by the developing parasites. Metabolic labelling studies and experiments in which larvae were labelled after different times in culture indicated that, once released, the surface-associated molecules were not replaced, and that this net loss of surface peptides resulted in a reduction in the antigenic potential of the cuticular surface. Antibodies from both immunized rabbits and naturally infected dogs immunoprecipitated the 35 kDa component. In contrast, the 6 kDa molecule was not recognized by the antibodies in any of the sera tested. Shedding of surface peptides and reducing surface antigenicity may represent mechanisms by which D. immitis infective-stage larvae evade immune attack.

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.