Biochemical surface components of Brugia pahangi microfilariae

Ultrastructural analysis of Wuchereria bancrofti (Nematoda: Filarioidea) body wall

Bancroftian filariasis constitutes the principal mosquito-borne nematode infection of humans and the surface of adult of Wuchereria bancrofti seems to be especially important in the intricate interplay between host and parasite. The study of the parasite's surface structure might help to understand the localization and function of various organelles. W. bancrofti adult worms were recovered from untreated patients during hydrocele repair surgery and studied by transmission electron microscopy. The body wall of adult parasite is composed of cuticle, hypodermis and muscular layer. Cuticle is the external layer and shows transverse cuticular striation. It is composed by an epicuticle, cortical layers, median layer, fibrous layers and basal layer. The epicuticle is the most external cuticular layer and appears as a single laminar electron-dense layer. The cortical external region is more electron-dense and granular in appearance than the inner cortical layer. Electron-dense structures, called bosses are randomly distributed filling the cuticular striation. The median layer is formed by an electron-dense and continuous thick line. The fibrous layer is subdivided in inner and external layers connected by projections. The basal layer includes a large quantity of membranous projections directed toward the hypodermis. The hypodermis is a syncytium where some cellular organelles are observed. The somatic musculature is meromyarian. The muscle fibers consist of contractile and non-contractile regions and the contractile region is composed of myofilaments separated by dense body. This is the first study of W. bancrofti adult worms obtained from untreated patients and studied by transmission electron microscopy.

Use of microarray hybridization to identify Brugia genes involved in mosquito infectivity

Brugia malayi and Brugia pahangi microfilariae (mf) require a maturation period of at least 5 days in the mammalian host to successfully infect laboratory mosquitoes. This maturation process coincides with changes in the surface composition of mf that likely are associated with changes in gene expression. To test this hypothesis, we verified the differential infectivity of immature (< or =3 day) and mature (>30 day) Brugia mf for black-eyed Liverpool strain of Aedes aegypti and then assessed transcriptome changes associated with microfilarial maturation by competitively hybridizing microfilarial cDNAs to the B. malayi oligonucleotide microarray. We identified transcripts differentially abundant in immature (94 in B. pahangi and 29 in B. malayi) and mature (64 in B. pahangi and 14 in B. malayi) mf. In each case, >40% of Brugia transcripts shared no similarity to known genes or were similar to genes with unknown function; the remaining transcripts were categorized by putative function based on sequence similarity to known genes/proteins. Microfilarial maturation was not associated with demonstrable changes in the abundance of transmembrane or secreted proteins; however, immature mf expressed more transcripts associated with immune modulation, neurotransmission, transcription, and cellular cytoskeleton elements, while mature mf displayed increased transcripts potentially encoding hypodermal/muscle and surface molecules, e.g., cuticular collagens and sheath components. The results of the homologous B. malayi microarray hybridization were validated by quantitative reverse transcriptase polymerase chain reaction. These findings preliminarily lend support to the underlying hypothesis that changes in microfilarial gene expression drive maturation-associated changes that influence the parasite to develop in compatible vectors.

Ultrastructure of Procamallanus (Spirocamallanus) halitrophus (Nematoda: Camallanidae) parasite of flounder

The ultrastructure of the camallanid nematode Procamallanus (Spirocamallanus) halitrophus, a parasite of flounder, is described for the first time by the use of transmission electron microscopy. The body wall is composed of an outer cuticle, a hypodermis, and a muscular layer. The cuticle comprises the epicuticle, the cortical, median, fibrous, and basal layers. The cortical layer is subdivided into an outer zone and an inner zone; the median layer is subdivided into an outer layer, rich in electrondense fibrils, and an inner layer, which does not contain these fibrils; the fibrous layer is subdivided into three regions delimited by electrondense lines; the basal layer presents electrondense sustaining structures. Underlying the basal layer is the hypodermis where many organelles are observed. The musculature is striated, and each muscle cell consists of individualized contractile and non-contractile regions. Inclusion bodies are present in the muscle fibers, hypodermis, hypodermal chord, and in the intestine.

Cloning and expression analysis of two mucin-like genes encoding microfilarial sheath surface proteins of the parasitic nematodes Brugia and Litomosoides

In several filarial genera the first stage larvae (microfilariae) are enclosed by an eggshell-derived sheath that provides a major interface between the parasite and the host immune system. Analysis of the polypeptide constituents of the microfilarial sheath from the cotton rat filaria Litomosoides sigmodontis identified two abundant surface glycoproteins: Shp3a and Shp3. The corresponding genes and the orthologues of the human parasite Brugia malayi and the rodent filaria Brugia pahangi were cloned and sequenced. They encode secreted, mucin-like proteins with N-terminal Ser/Thr-rich repeats and a C-terminal anchor domain rich in aromatic amino acids. About 75% of the protein molecular masses result from post-translational modifications. The Ser/Thr-rich motifs are supposed to serve as targets for dimethylaminoethanol-phosphate substitutions. These modifications were detected only on the sheaths of the late developmental stage of stretched microfilariae, corresponding with the expression of the proteins in the epithelium of the distal part of the uterus and the specific transcription of shp3 and shp3a in the anterior female worm segment. Genomic analysis of all three species demonstrated a conserved linkage of the two genes. Their transcripts undergo cis- and trans-splicing. The transcription start sites of the primary transcripts were determined for the L. sigmodontis genes. The core promoter regions are remarkably conserved between the paralogue genes Ls-shp3a and Ls-shp3 and their orthologues in Brugia, implicating conserved regulatory elements.

Transglutaminase-catalyzed incorporation of host proteins in Brugia malayi microfilariae

Recently, we have characterized and purified a novel transglutaminase (pTGase) from adults of the filarial worms Brugia malayi. pTGase-catalyzed reactions seem to play an essential role during in utero growth and development of microfilariae. The results presented here demonstrate that exudates from the peritoneal cavity of jirds, the site where adult worms of B. malayi reside and produce microfilariae, contain several host proteins that can serve as substrates in pTGase-catalyzed reactions. The peritoneal exudate proteins are avidly taken up by adult female worms in vitro and incorporated into the developing microfilariae. Among the several host proteins that were crosslinked, a 68-kDa molecular weight protein (p68) was found to be the major protein taken up by the parasites. Following uptake by the parasites, the peritoneal exudate proteins are crosslinked to form high molecular weight aggregates, that are subsequently incorporated into in utero developing embryos and microfilariae. The cross-linking of host proteins was, however, inhibited by monodansylcadaverine (MDC), a competitive inhibitor of pTGase. Antibodies raised against the jird peritoneal exudate proteins strongly immunoreacted with a 68-kDa protein in adult worms and microfilariae extracts but not with infective-stage larvae (L3) of B. malayi. These results suggest that pTGase is involved in covalent incorporation of host proteins (such as p68) into developing embryos and microfilariae of B. malayi.

The conditions required for the maintenance of Onchocerca lienalis microfilariae in vitro

Microfilariae of the bovine parasite Onchocerca lienalis were maintained in vitro using a tick cell line as a feeder layer, and under the conditions provided would develop to the sausage stage. A number of media supported this achievement with CMRL 1066 producing the highest yields, particularly when used in conjunction with either medium 199, HAM's F-12, RPMI 1640 or Mark's M20. The addition of inactivated foetal calf serum (iFCS) suppressed development; on the other hand, the addition of tryptose phosphate broth (TPB) enhanced it. The pH range of the medium preferred by the developing worms was 7.35-7.85, and the most favourable osmolality lay in the range 360 to 390 mosM/kg. Insect-derived hormones did not improve yields of developed larvae nor promote moulting to the second larval stage. The culture conditions described in this work, which favour parasite survival and development, provide further insights into the physiological requirements of filariae as well as guide lines to achieving successful in vitro maintenance of Onchocerca sp. A morphological examination of the developing larvae was carried out at electron microscopical level.

Identification, synthesis and immunogenicity of cuticular collagens from the filarial nematodes Brugia malayi and Brugia pahangi

The major structural proteins of the cuticle of the filarial nematode parasites Brugia malayi and Brugia pahangi were identified by extrinsic iodination and sensitivity to clostridial collagenase. At least 16 acidic components were identified in adult worms by 2-dimensional electrophoresis, with molecular weights ranging from 35,000 to 160,000. These proteins appear to be cross-linked by disulphide bonds, and localised in the basal and inner cortical layers of the cuticle. The outer cortex, containing the epicuticle, is insoluble in 1% sodium dodecyl sulphate and 5% 2-mercaptoethanol, and can be isolated free of cellular material. Despite their inaccessibility to the immune system in intact worms, antibodies to the cuticular collagens are provoked in humans infected with a variety of filarial parasites. Immunological cross-reactivity was demonstrated between a 35 kDa component and human type IV (basement membrane) collagen. Autoantibodies to type IV collagen were detected in a number of individuals with lymphatic filariasis, although no correlation could be drawn with observed pathology. Synthesis of cuticular collagens is discontinuous, occurs at negligible levels in mature adult male worms, and does not appear to involve the production of small molecular weight precursors, in contrast to Caenorhabditis elegans. Hybridisation with a heterologous cDNA probe coding for the alpha 2 chain of chicken type 1 collagen suggests that they are encoded by a multigene family.

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

The objective of this study was to analyze surface properties of larval Dirofilaria immitis with potential relevance to protective immunity. Comparisons were made between third (L3)- and fourth-stage larvae (L4) based on their net surface charge, surface carbohydrate and antigen composition, ability to nonspecifically absorb host proteins, complement activation, and nonspecific cellular adherence. It was determined that L3 had a net negative surface charge, whereas L4 had either a neutral or weakly positive surface charge. The lectin Con A, but not any of the other lectins tested, bound only to the surface of L4, and not to that of L3. Monoclonal antibodies were prepared which reacted with the surface of L3 or with the surface of L4, but never both. L4 were found to nonspecifically adsorb host protein to their surfaces, whereas L3 did not. Both L3 and L4 were found to activate complement through the alternate pathway. Finally, nonspecific cellular adherence was found on L3 both in vitro and in vivo but not on L4. The surfaces of L3 and L4 were thus shown to be significantly different and, potentially, in ways which would have great impact in the generation and effectiveness of a protective immune response.

Immunochemical characterization and biosynthesis of major antigens of iodo-bead surface-labeled Brugia malayi microfilariae

The objectives of the present study were to identify and characterize biochemically the major antigens of Brugia malayi microfilariae, a filarial parasite that infects humans. IgG antibodies in sera of mice which had cleared parasites from the bloodstream reacted with 30, 55, 94 and 150 kDa molecules of living microfilariae radioiodinated by the Iodo-bead method. Sera of humans infected with the related filariae Wuchereria bancrofti, Loa loa or Onchocerca volvulus immunoprecipitated molecules of similar size as well as two additional proteins of 22 and 43 kDa. Sera of uninfected North Americans or mice infected with Trichinella spiralis or Schistosoma mansoni did not recognize these radioiodinated antigens. Experiments to examine the possible surface localization and metabolism of these antigens showed that they were removed from intact parasites exposed to chymotrypsin or trypsin and that immunogenic molecules of 30, 55, and 150 kDa were released into excretory-secretory products by viable microfilariae. [35S]Methionine biosynthetically labeled polypeptide antigens of 22, 30, 35 and 150 kDa were detected by antibody reacted with intact microfilariae and/or their excretion products. Antigens of 30, 55, and 150 kDa appear to be glycoproteins as they bound wheat germ agglutinin and were biosynthetically labeled with [14C]N-acetyl-D-glucosamine. These data suggest that the surface of B. malayi microfilariae is a dynamic structure which synthesizes and sheds antigens.

Formation by the uterus of a peripheral layer of the sheath in microfilariae of Litomosoides carinii and Brugia malayi

The eggshells of young developmental stages in the uterus are rather thin and homogenous. In the brezel stage of Brugia malayi they are 35 nm thick and 20 nm in Litomosoides carinii. In young developmental stages up to brezel stages the eggshells bind the lectins WGA, DBA and PNA labelled with colloidal gold. This shows that GlcNAc, GalNAc and Gal residues are present at the surface of the sheath. In intrauterine microfilariae of B. malayi the original sheath is reduced to a thickness of 7 nm. It is reinforced by secretions from a specialized area of the epithelium of the uterus which do not appear as a homogeneous layer but look like a string of pearls. This layer may be called the "uterine layer". It has a thickness of 40-80 nm. In the microfilaria of L. carinii, the thickness of the original sheath is reduced to 2-3 nm and the uterine layer has a thickness of 7 nm. The uterine layer does not react with any of the lectins, which shows that the surface lacks N-acetylglucosamine, N-acetylgalactosamine and galactose residues. The uterine layer appears to be an ancestral (plesiomorphic) feature which is present in free-living nematodes and the highly specialized bloodforms of filariae. The uterine layer seems to protect and disguise the original sheath against the immune reactions of the host.