Detection of Dirofilaria immitis antigen and antibodies against Anaplasma phagocytophilum, Borrelia burgdorferi and Ehrlichia canis in dogs from ten provinces of China

Despite the fact vector-borne diseases (VBDs) have been increasingly reported in dogs worldwide, there are only limited reports on VBDs in dogs in China with most being based on molecular detection of active infections. To provide further data on the exposure of dogs in China to VBD agents, we used commercial immunochromatographic assays to test plasma from 637 apparently healthy indoor and breeding colony dogs from 21 veterinary clinics in 10 provinces in China and a commercial dog breeding facility for circulating antigen of Dirofilaria immitis, and for circulating antibodies against Ehrlichia spp., Anaplasma spp., and Borrelia burgdorferi. Overall, we found only low levels of exposure to Ehrlichia spp. (4.7%; 30/637), Anaplasma spp. (1.4%; 9/637), B. burgdorferi (0.9%; 6/637) and D. immitis (0.2%; 1/637) with most of the positive animals coming from the commercial breeding colony (26/103; 25.2%) where ectoparasites were most commonly noted. At least one vector-borne agent was found in dogs from 6 of the 10 provinces investigated. Our results confirm exposure of dogs from around China to a variety of VBDs, even indoor pets seldom observed to harbor ectoparasites.

Th1 response in BALB/c mice immunized with Dirofilaria immitis soluble antigens: a possible role for Wolbachia?

The immune response to filarial infection has been shown to be of both the Th1 and Th2 types. Studies aimed at developing immunization strategies against Dirofilaria immitis infection in dogs have shown that protection against larval challenge is of the Th2 type and that several proteins are recognized by immunized or infected animals. The bacterial endosymbiont Wolbachia, harbored by many filarial species including D. immitis, has recently been shown to interact with the host immune system. Specific antibodies to the Wolbachia recombinant surface protein (WSPr) have been observed in cats infected with D. immitis. In this work the authors have determined cytokine production and antibody response in BALB/c mice inoculated with soluble antigens from third stage larvae or from adult worms of D. immitis. Inoculated mice first produced IFN-gamma followed by a peak in IL-4. Specific antibodies to the Wolbachia protein WSPr were exclusively IgG2a, while antibodies against peptides derived from antigens of D. immitis were in the IgG1 and IgE subclasses. The cytokine response is thus similar to that reported for other filarial infection, where Th1 response shifts towards Th2. Antibody response indicates that Wolbachia may induce preferentially a Th1 response during filarial infection, while nematode antigens may be involved in Th2 response. There is thus an overall agreement with current opinions on the role of bacterial versus nematode molecules in driving the response towards the different directions.

Immunological responses of dogs experimentally infected with Dirofilaria immitis

Three dogs were experimentally infected with Dirofilaria immitis. All dogs were euthanised at 30, 36 and 37 weeks after inoculation of D. immitis for the recovery of adult worms. Three cases accounted to 42.91 % recovery of inoculated worms. Serum samples from dogs experimentally inoculated with D. immitis were analyzed by ELISA and immunoblotting methods. Antibody titers of dogs detected by ELISA peaked between 7 and 14 weeks then decreased between weeks 15 to 24 followed by another increase during weeks 25 to 30 and persisted throughout the remainder of the experiment period. Analysis of adult D. immitis protein stained with Coomassie brilliant blue R-250 indicated separately more than 10 bands, and the major bands were 22, 40, 46, 56, 70, 72 and 89 kDa. Antigenic identification of extracts antigens of adults D. immitis by immunoblotting analysis revealed several bands from pooled sera of patent infection (30 weeks after inoculation). The detected bands were 24, 70, 80 and 110 kDa, 22, 72 and 84 kDa, and 58 and 72 kDa in dogs 1, 2 and 3, respectively. Results of antibody titers reached high levels on the 4th molting stage after inoculation of infective larva (L3), and reinforced previous findings that high molecular weight regions are detected in young animals.

Element composition and biochemical components of Dirofilaria immitis

Element composition of whole canine heartworms (Dirofilaria immitis) was determined using inductively coupled argon plasma emission spectroscopy. The elements evaluated included Na, K, Ca, Mg, P, Al, B, Ba, Cu, Fe, Mn, Sr, Zn, As, and Pb. The only significant sex difference was calcium concentration which was higher in females. Amino acid analyses of body fluid revealed presence of nine essential and eight non-essential amino acids. Concentrations for male and female heartworms were not significantly different. The spectrum of amino acids was similar to that previously reported for canine plasma. Neurotransmitters or their metabolites detected in whole male and female heartworms using HPLC with electrochemical detector were epinephrine, dihydroxyphenylacetic acid, dopamine, and 5-hydroxyindoleacetic acid. Those not detected were norepinephrine, homovanillic acid, and 5-hydroxytryptamine.

Determination of metabolite and regulatory enzyme levels in Dirofilaria immitis and Ascaris suum: a comparative study

Studies on metabolite levels in Dirofilaria immitis revealed similarities in several metabolites with those of Ascaris suum. The glycogen level in the filariid was however 3-4 times lower than that in A. suum. Levels of three regulatory enzymes were also determined in D. immitis and compared with those in A. suum. The activities of Hexokinase and Phosphofructokinase were similar. However, the levels of Glycogen phosphorylase b appeared to be much lower in the filariid than in A. suum. The subtle but important differences observed may reflect modifications of the parasite enzymes suggesting salient differences in the regulation of energy production from carbohydrates in the worms. The differences may also represent specialization required for the unique life style of the worms in their different locations in their hosts.

Immunofluorescent localization of intermediate filaments (IFs) in helminths using anti-mammalian IFs monoclonal antibody

Intermediate filaments (IFs) make up the cytoskeleton of most eukaryotic cells. In vertebrates, a number of IF proteins have been identified, showing distributions unique to tissue or cell type. Information on helminth IFs is limited to some nematode species. To observe immunofluorescent localization of IFs in helminth tissues, we selected a murine hybridoma clone producing IgM antibody to multiple types of mammalian IF proteins and examined cross-reactivity to helminth proteins. The selected monoclonal antibody (HUSM-9) cross-reacted well with IFs from nematode species such as Toxocara canis, Dirofilaria immitis, Anisakis simplex, and Trichinella britovi; strong immunofluorescence on cryostat sections was detected in the hypodermis, cords, body muscle, smooth muscle of the uterus, and other epithelial structures. In platyhelminths, i.e., adult Schistosoma mansoni, larval Taenia taeniaeformis, adult Taenia crassiceps, and Echinococcus multilocularis protoscolex, the reactivity was weaker than in nematodes, and localized in the body wall muscle and subtegumental tissue. Western blotting of 8 M urea extracts of parasites with the antibody detected a pair of clear bands in nematodes but not in S. mansoni or the cestodes. These results might be explained by sparse distribution of IFs in platyhelminths, or low affinity of the used antibody to platyhelminth IF proteins, or both.

Molecular characterization of a calcium-binding protein from the filarial parasite Dirofilaria immitis

A full length D. immitis cDNA (nDiCal) encoding a protein with significant similarity to the calreticulin protein family was isolated from a 6-day fourth-stage larval cDNA expression library by immunoscreening, using serum from a rabbit immunized by repeated injection of small numbers of third-stage larvae. nDiCal is 1538 bp long and contains the 21 bp nematode splice leader sequence SL1 at the 5' end. nDiCal encodes for a protein (pDiCal) with a predicted molecular mass of 46 kDa. pDiCal sequence analysis revealed similarities with calreticulin, a protein that typically resides in the endoplasmic reticulum. pDiCal possesses three consensus sequences of the calreticulin family of proteins: a neutral N-terminal region with a putative signal sequence; a proline- and tryptophan-rich P region; and a highly acidic C-terminal region. A 45Ca2+-overlay assay showed that recombinant pDiCal (rDiCal) is a Ca2+-binding protein. Antibodies to rDiCal identified a 56 kDa native antigen in all developmental stages including the excretory-secretory products derived from larvae and adult worms. Localization studies demonstrated the ubiquitous presence of pDiCal with intense expression in the hypodermis and syncitial muscle cells in both male and female adult worms. Labeling was also seen in the developing embryos within the uterus of the female worms. Sera from immune as well as chronically-infected microfilaremic dogs contained antibodies that bind rDiCal. In addition, immunoblot analysis showed that serum from a rabbit immunized with L3 cuticles reacted with rDiCal.

Pathologic findings in dogs with shock induced by intravenous administration of heartworm extract

OBJECTIVE

To examine pathologic findings in dogs with shock induced by IV administration of heartworm (HW) extract.

ANIMALS

22 mixed-breed adult dogs.

PROCEDURES

Heartworm extract was administered IV, and pathologic changes in dogs that died or were euthanatized at 24 hours were examined.

RESULTS

The most severe lesions observed during initial collapse were centralobular congestion in the liver, hemorrhage and edema in the gallbladder wall, and congestion and hemorrhage in mucous membranes of the gastrointestinal tract. These findings disappeared with recovery from collapse. Hyalinization of venous walls of the liver and cardiac muscle were observed in dogs that died during initial collapse. Focal coagulation necrosis in hepatic cells was seen in dogs that were euthanatized at 24 hours. One dog with profuse bloody diarrhea that died during secondary collapse had severe hemorrhage in mucous membranes of the large intestine.

CONCLUSION

Heartworm extract appeared to contain some substances constricting hepatosplanchnic vessels and some toxic substances that injured the smooth muscle of venous walls, cardiac muscle, and hepatic cells directly or indirectly.

CLINICAL RELEVANCE

The shock-inducing substances in HW extract may have an important role in the pathophysiologic mechanism of HW disease, and investigation of them may contribute to prevention of the shock reaction attributable to microfilaricide and adulticide use.

The peroxidoxin 2 protein of the human parasite Onchocerca volvulus: recombinant expression, immunolocalization, and demonstration of homologous molecules in other species

The peroxidoxin protein of the filarial parasite Onchocerca volvulus (OvPXN-2) belongs to a group of highly conserved antioxidant molecules. For a more detailed characterization of this protein and for determination of its expression pattern the OvPXN-2 protein was recombinantly expressed as a His-tagged protein. Under reducing conditions the recombinant protein had an apparent molecular mass of 28 kDa. Considering the size of the His-tag and the FLAG epitope introduced to the recombinant protein, this size is in agreement with that of the native protein identified in O. volvulus extract. Antiserum raised against the recombinant protein was used for immunolocalization. In O. volvulus the antigen is predominantly expressed in the hypodermis and particularly the lateral and median chords show high levels of expression. The protein is also expressed strongly in the hypodermis of infective larvae and more weakly in microfilariae. Related cross-reacting proteins were detected in several Onchocerca species and other filariae. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis in combination with Western blotting revealed proteins with almost identical mobility in extracts prepared from O. ochengi, O. gibsoni, and Dirofilaria immitis.

Cloning and characterization of cDNAs encoding beta-tubulin from Dirofilaria immitis and Onchocerca volvulus

Beta-Tubulin is the target for the benzimidazole anthelmintics. Unfortunately, none of these drugs is clinically useful against adult filariae. However, beta-tubulin has been shown to be a target for antibody-based toxicity to Brugia pahangi. We cloned and characterized cDNAs encoding beta-tubulin from 2 filariae, Dirofilaria immitis and Onchocerca volvulus, to explore possible explanations for benzimidazole insensitivity among adult filariae and the likelihood that epitopes of beta-tubulin could be used as antigens for a broad-spectrum filarial vaccine. The proteins predicted by these cDNAs were almost identical to the beta-tubulin previously reported from B. pahangi but were less similar to a beta-tubulin cDNA from Onchocerca gibsoni. We cloned the genomic locus for the O. volvulus beta-tubulin cDNA and compared its organization to the reported genomic loci for beta-tubulin in B. pahangi and O. gibsoni. The comparison reinforces the conclusion that the published O. gibsoni gene is in a different family, possibly the beta2 family previously described in B. pahangi. The substitution of tyr for phe at position 200 of beta-tubulin is associated with benzimidazole resistance. All 4 filarial beta-tubulins are predicted to encode phe at this position, suggesting that filarial beta-tubulin is not inherently insensitive to the benzimidazoles. A monoclonal antibody that recognizes the COOH terminus of B. pahangi beta-tubulin is lethal to this parasite in culture. The COOH terminal region is the most variable among the different isotypes of beta-tubulin and distinguishes mammalian from nematode tubulins. This region is highly conserved in 3 of the filarial beta-tubulins.

Isolation and partial characterization of a fatty-acid-binding protein from Ascaris suum reproductive tissue

A 12-kDa fatty-acid-binding protein was purified to homogeneity from Ascaris suum reproductive tissue as confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. N-terminal amino-acid-sequence analysis of the protein revealed its identity with the ABA-1 allergen protein isolated from A. suum pseudocoelomic fluid. Fatty-acid binding by the protein from A. suum reproductive tissue was investigated using the Lipidex 1000 assay, which revealed the presence of a single class of fatty-acid-binding sites with an apparent dissociation constant for palmitate of about 0.8 microM.

Carboxy-terminal sequence divergence and processing of the polyprotein antigen from Dirofilaria immitis

A polyprotein composed of multiple units arranged in direct tandem arrays has been identified in parasitic and free living nematodes. Analysis of previously cloned units from the Dirofilaria immitis polyprotein antigen (DiPA) indicated the units were nearly identical but here we demonstrate that they segregate into two related families. The consensus repeats, DiPA-CR1 and CR2, derived for each family are 80% identical. However, the repeats at the C-terminus of the polyprotein have diverged from DiPA-CR1 and CR2. This was shown by DNA sequence and Southern blot analysis of a 1.9 kb cDNA clone that encodes 4.4 C-terminal repeats (DiPA-TR1 through TR5). DiPA-TR3 through TR5 show 27-52% amino acid identity with the consensus repeats and 31-35% amino acid identity with one another. Metabolic labeling studies have shown that cleavage of DiPA generates a protein "ladder' from 14 to > 200 kDa. RRKR, a cleavage motif of subtilisin-like proprotein convertases, was identified as the natural cleavage site. In vitro digestion experiments with proteinase K suggest a structural model for DiPA consisting of protease resistant cores joined by protease sensitive linkers containing the RRKR site. This motif is absent between DiPA-TR3 and TR4 and has been altered to KR between DiPA-TR4 and TR5. An immunoblot of D. immitis extract probed with anti-DiPA-TR4/5 serum demonstrates the absence of cleavage at these sites. These divergent repeats provide an opportunity to investigate processing of the D. immitis polyprotein in vivo.

Purification and characterization of three larval excretory-secretory proteins of Dirofilaria immitis

Two proteins were previously described in the excretory-secretory products (ES) collected from Dirofilaria immitis during the molt from the third stage to the fourth stage in vitro. The two proteins were purified using cation exchange and reverse phase HPLC. During the purification of these two proteins, a third protein was identified that co-migrated with one of the others during previous gel analysis. All three had molecular masses of 20-23 kDa as determined by Tris-glycine SDS-PAGE and have been designated 20, 22L and 22U kDa proteins. The three proteins were digested with trypsin. Amino acid sequences were subsequently determined for four peptides and the N-terminus of the 20 kDa protein, five peptides of the 22L kDa protein and three peptides of the 22U kDa protein. The 20 and 22L kDa proteins were quite similar based on sequence and purification characteristics. The 22U kDa protein, but not the 20 and 22L kDa proteins, was also identified in adult worms using tryptic mapping and amino acid sequencing techniques. Immunoblot analysis demonstrated that the 20 and 22L kDa proteins were specifically recognized by sera from dogs immune to infection by D. immitis but not by sera from infected non-immune dogs. The 22U kDa protein was weakly recognized by the same immune sera but not by the infected non-immune dog sera. Since the 20 and 22L kDa proteins appear to be larval specific, associated in time with the molt from L3 to L4 and are specifically recognized by immune dog sera, they are good vaccine candidates.

Characterization of the N-linked oligosaccharides in glycoproteins synthesized by microfilariae of Dirofilaria immitis

In this report, we describe studies on the structures of the N-linked oligosaccharides contained in glycoproteins synthesized by microfilariae of the canine heartworm, Dirofilaria immitis. Microfilariae were incubated in media containing either 2-[3H]mannose, 6-[3H]glucosamine, or 6-[3H]galactose. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorographic analyses indicated that many glycoproteins were radiolabeled by both the mannose and glucosamine, whereas glycoproteins were not radiolabeled by the galactose. Glycopeptides from these total glycoproteins were fractionated and purified by serial lectin affinity chromatography, and the structures of the oligosaccharides in the isolated glycopeptides were analyzed by a variety of techniques. The N-linked oligosaccharides were shown to contain mannose (Man), fucose, N-acetylglucosamine (GlcNAc), and N-acetylgalactosamine (GalNAc). However, they lacked sialic acid and galactose, which are commonly found in mammalian glycoproteins. GalNAc was shown to be in an unusual terminal position and beta-linked in the sequence GalNAc beta GlcNAc beta Man-R, where R is the typical branch of complex-type N-linked oligosaccharides. Similar structures were recently found by us to be synthesized by the helminthic parasite Schistosoma mansoni. These results demonstrate that glycoproteins synthesized by microfilariae of D. immitis have unusual carbohydrate moieties and may lead to a better understanding of the specific roles of glycoprotein oligosaccharides in host-parasite interactions.

Determination of the role of cuticular carbohydrates in the hemocompatibility of Dirofilaria immitis (Nematoda)

We have partially characterized surface glycoproteins of the canine heartworm, Dirofilaria immitis. Histochemical studies indicated the presence of neutral and acidic mucopolysaccharides at the blood-cuticle interface. Fluorescein isothiocyanate-conjugated lectin binding patterns suggested the presence of alpha-D-glucosyl and/or alpha-D-mannosyl, beta-galactosyl, N-acetylneuraminyl and N-acetylated-D-hexosaminyl (sialic and glucuronic acids, respectively) terminal residues among the constituent sugars of the glycocalyx. An additional goal of this study was to assess the significance of each carbohydrate in parasite hemocompatibility by using scanning electron microscopy, internal reflection infrared spectroscopy, and comprehensive contact angle measurements. Each carbohydrate identified in the glycocalyx was selectively cleaved with the appropriate exoglycosidase. Heart-worms bearing native and enzyme-altered surfaces were exposed to platelet-rich canine plasma. Activation and aggregation of platelets were significantly increased on enzyme-treated surfaces as compared with native surfaces. Enzyme-induced cleavage of carbohydrate residues was associated with an increase in critical surface tension or a loss in cuticular structural integrity or both. Hemocompatibility of the heartworm cuticle depends on the retention of a stable saccharide-rich layer that minimizes interaction with plasma proteins and platelets; thus, carbohydrate residues on the glycocalyx may contribute to parasite hemocompatibility. The presence of similar low-critical-surface-tension coatings with high mechanical integrity may impart thromboresistance to other polyphenolic or chitinous substances.

Immunocytochemical localisation of an FMRFamide-like peptide in the filarial nematodesDirofilaria immitis andBrugia pahangi

Immunocytochemical techniques were used to detect FMRFamide-like immunoreactivity in adults of the filarial nematodes Dirofilaria immitis and Brugia pahangi. An FMRFamide-like peptide was also located in third- and fourth-stage larvae of D. immitis. Positive immunoreactivity was observed in all parasites examined, irrespective of developmental stage. The major areas of positive immunoreactivity were located in the anterior nerve ring, lateral/dorso-ventral nerves, cephalic papillary ganglia and lateral ganglia. No staining was seen in the intestine or gonads of any parasite. These results indicate that filarial worms possess a peptidergic component in their nervous system. The possible role of an FMRFamide-like peptide in the control of certain physiological events is discussed.

Metabolic labeling of Dirofilaria immitis third- and fourth-stage larvae and their excretory-secretory products

Infective third-stage larvae of Dirofilaria immitis were collected from Aedes aegypti and cultured in vitro to the fourth stage. Larval proteins were labeled metabolically using [35S]cysteine and methionine in different media and for different lengths of time. Labeled proteins in the excretory-secretory component and the larval homogenates were evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing and nonreducing conditions and by 2-dimensional gel electrophoresis. Numerous proteins ranging from 14 to greater than 200 kDa were identified from both the excretory-secretory components and the larval homogenates. Both fractions demonstrated shared and unique proteins. Using timed labeling, age- and stage-specific proteins were identified; at least 2 proteins of approximately 20.5 and 22 kDa were associated in time with the molt from the third to fourth stage. Two proteins of the same molecular weight were specifically recognized by immune dog sera, but not by sera of their infected nonimmune cohorts.