Brugia pahangi: immunization with early L3 ES alters parasite migration, and reduces microfilaremia and lymphatic lesion formation in gerbils (Meriones unguiculatus)

Previous studies have shown that intradermally (ID) injected Brugia pahangi L3 s migrate through various tissues and into the lymphatics of gerbils in a distinct pattern. Excretory/secretory products (ES) produced at the time of invasion of B. pahangi are likely to be important in this early migration phase of the parasite life cycle in their rodent host. Hence, early L3 ES was collected from 24h in vitro cultures of B. pahangi L3 larvae and used in immunization experiments to investigate the effect of immunity to early L3 ES on worm migration, survival and development of B. pahangi. Immunization of gerbils with ES in RIBI adjuvant produced antibodies to numerous ES proteins eliciting a strong humoral response to ES and indirect fluorescent antibody (IFA) assay using anti-ES serum recognized the ES proteins on the surface of B. pahangi L3 larvae. Following ES immunization, gerbils were challenged either ID or intraperitoneally (IP) with 100 L3 s of B. pahangi and euthanized at 3 or 106 days post inoculation (DPI). Immunization with early ES slowed the migration of ID inoculated L3 at 3 DPI and significantly altered the locations of adult worms at 106 DPI. Immunization did not induce protection in any treatment group. However, immunized animals had significantly fewer microfilariae per female worm suggesting the antigens in ES are important in microfilariae development or survival in the host. The number of lymphatic granulomas was also significantly reduced in ES immunized animals. It is important to note that microfilariae serve as a nidus in these granulomas. Our results shows immunization with early Brugia malayi L3 ES alters the worm migration, affects circulating microfilarial numbers and reduces lymphatic granulomas associated with B. pahangi infection in gerbils.

Inflammatory responses to migrating Brugia pahangi third-stage larvae

Despite being central to parasite establishment and subsequent host pathological and immunologic responses, host-parasite interactions during early third-stage filarial larva (L3) migration are poorly understood. These studies aimed to define early tissue migration of Brugia pahangi L3 in the gerbil (Meriones unguiculatus) and measure host cellular responses during this period. Gerbils were intradermally inoculated in the hind limb with 100 B. pahangi L3, and necropsies were performed at various times. At 3 h, most L3 (96.3%) were recovered from tissues associated with the infection site, with marked L3 migration occurring by 24 h. Larvae were dispersed throughout the lymphatics at 7 days postinfection (dpi), and at 28 dpi, most parasites were recovered from the spermatic cord lymphatics. Parasites were identified histologically at all time points. Inflammatory cells, primarily neutrophils, were frequently observed around larvae in the dermis and muscle near the injection site at 3 h and 24 h. Levels of interleukin-6 (IL-6) and tumor necrosis factor-alpha mRNA peaked at 3 h in all tissues, with IL-6 levels also high in the spleen at 28 dpi. Levels of IL-4 mRNA were elevated in all tissues at 28 dpi. These observations demonstrate that L3 migrate quickly through various tissues and into lymph nodes in a predictable pattern. Migrating L3 induce an early acute inflammatory response that is modulated as parasites establish in the lymphatics. Polarization of the host response towards a dominant Th2-like profile is present at 7 dpi and is well established by 28 dpi in this permissive host.

Critical role for IgM in host protection in experimental filarial infection

We have previously shown that B cells (in particular B1 cells) are important in host protection against brugian infections in a murine i.p. model. In this study, we show that mice deficient in circulating IgM (secIgM-/-), but otherwise normal in their humoral responses, manifest a significant impairment in worm elimination, suggesting that one critical B cell function is the production of Ag-specific IgM. Efficient elimination of larvae is IgM dependent for both primary and challenge infections. The ability to eliminate worms is restored in secIgM-/- mice by administering sera from primed mice. We corroborated these in vivo studies with in vitro observations which show that IgM is the only isotype that reacts strongly with the surface of Brugia L3. Furthermore, activated peritoneal exudate cells adhere to L3 only in the presence of filaria-specific sera or IgM purified from them. This attachment is not reduced by heat inactivation of the serum, suggesting complement independent activity. Peritoneal exudate cells from primed mice, especially activated macrophages, carry high levels of IgM on their surfaces. Our observations suggest that an IgM-mediated reaction initiates the formation of host-protective granulomas.

Mosquito transmission modulates the immune response in mice infected with the L3 of Brugia pahangi

Mice infected by syringe inoculation with the L3 of the filarial nematode Brugia pahangi generate a strong Th2 response. In this study we compared immune responses in mice infected via syringe with those infected by mosquito transmission of L3. Levels of antigen-specific IL-4, IL-5 and IL-10 were significantly reduced in mice infected via mosquito. A possible explanation of these results was that mice infected via mosquito received fewer L3 than those infected via syringe. To investigate this possibility, mice were infected with different numbers of L3 (50, 25 or 10). However there was no difference in responses in these animals, suggesting that the reduced immune reactivity in mice infected by mosquito cannot be solely ascribed to exposure to lower numbers of parasites. These results also demonstrate that the L3 is an extremely potent stimulus for Th2 differentiation, with 10 L3 sufficient to drive a strong Th2 response. The differences in immune reactivity between syringe and mosquito infected mice may relate to the presence of immuno-suppressive factors in mosquito saliva inoculated at the time of transmission or may reflect the interaction of L3 with different populations of antigen presenting cells in the two groups of mice. Further studies will be required to differentiate between these possibilities.

A gene family of cathepsin L-like proteases of filarial nematodes are associated with larval molting and cuticle and eggshell remodeling

Cysteine proteinases are involved in a variety of important biological processes and have been implicated in molting and tissue remodeling in free living and parasitic nematodes. We show that in the lymphatic filarial nematode Brugia pahangi molting of third-stage larvae (L3) to fourth-stage larvae is dependent on the activity of a cathepsin L-like cysteine protease (CPL), which can be detected in the excretory/secretory (ES) products of molting L3. Directed cloning of a cysteine protease gene in B. pahangi and analysis of the expressed sequence tag (EST) and genomic sequences of the closely related human lymphatic filarial nematode Brugia malayi have identified a family of CPLs. One group of these enzymes, Bm-cpl-1, -4, -5 and Bp-cpl-4, is highly expressed in the B. malayi and B. pahangi infective L3 larvae. Immunolocalization indicates that the corresponding enzymes are synthesized and stored in granules of the glandular esophagus of L3 and released during the molting process. Functional analysis of these genes in Brugia and closely related CPL genes identified in the filarial nematode Onchocerca volvulus and the free living model nematode Caenorhabditis elegans indicate that these genes are also involved in cuticle and eggshell remodeling.

Tetracycline treatment and sex-ratio distortion: a role for Wolbachia in the moulting of filarial nematodes?

Filarial nematodes harbour intracellular bacteria of the genus Wolbachia. These bacteria are thought to be beneficial to the host nematode. Indeed, tetracycline treatments reduce the population of Wolbachia in filarial worms and have detrimental effects on the nematode. Even though various antibiotic-curing experiments have been performed on filariae, the actual role of Wolbachia in the biology of these nematodes is not yet clear. To address this issue, we designed a first experiment on a model filaria (Brugia pahangi), maintained in the gerbil (Meriones unguiculatus). In this experiment, timing of tetracycline treatment was set on the basis of the larval stage of the nematode. This first experiment showed that 2 weeks of treatment started after the L(4)-L(5) moult of males, but before the moult of females, led to significant sex-ratio distortion of the nematodes. We thus hypothesised that tetracycline interferes with the moult in B. pahangi. To test this hypothesis, we designed a second experiment in which antibiotic treatments were started (1). before the moult of both sexes, (2). after the moult of males but before the moult of females, or (3). after the moult of both sexes. Treatment 1 determined a reduction of worm recovery with no sex bias. Treatment 2 led to a male-biased sex-ratio. Treatment 3 had no effect on either worm recovery or sex-ratio. These results thus support the hypothesis that tetracycline treatment interferes with the L(4)-L(5) moult of B. pahangi. The nematodes recovered from the treated and control animals were examined for the presence of Wolbachia using both immunohistochemistry and real-time PCR. In general, nematodes from treated animals showed a dramatic reduction in Wolbachia content. In one group, Wolbachia depletion, as observed at the end of the treatment, was followed by a rebound to 'normal' values 160 days later. Prospects for antifilarial therapy using Wolbachia-targeted tetracycline treatments should thus take into account the possibility of Wolbachia rebound.

Effects of Brugia pahangi infection on the cardiovascular system of stroke-prone spontaneously hypertensive rats

To determine if filarial infection causes any effect on the cardiovascular system of the host animal, stroke-prone spontaneously hypertensive rats were infected with Brugia pahangi under the assumption that these rats would reveal pathological changes more clearly and in a shorter period than would ordinary rats. The infection resulted in loss of body weight, increase in heart weight, enlargement of left ventricle, and higher mortality rate.

Expression of the filarial nematode phosphorylcholine-containing glycoprotein, ES62, is stage specific

ES62, an immunomodulatory phosphorylcholine-containing glycoprotein secreted by the rodent filarial nematode Acanthocheilonema viteae, has previously been shown to be produced by L4 larvae and adult worms only. However, homologous sequences to ES62 have recently been found in L1 and L3 cDNA libraries of certain human filarial nematodes. Therefore, the various stages of A. viteae were re-examined and it was again found that only the post-L3 stages secreted ES62. Synthesis but not secretion by earlier stages was ruled out by examination of the protein content of whole worm extracts and by immunoelectron microscopy. However, examination by PCR of the mRNA for ES62 revealed that it was found in the L1 and L3 larvae. This may explain why homologous sequences to ES62 have been found in Brugia malayi and Onchocerca volvulus larval cDNA libraries. It also suggests that filarial nematodes, in general, may secrete ES62. To obtain evidence for this, we investigated production by Brugia pahangi, a close relation of B. malayi. We found that ES62 was indeed secreted but, as with A. viteae, only by the post-L3 stages, although again the mRNA for ES62 could be detected in the earlier stages. Overall our results suggest that production of ES62 is not species specific, that it is indeed stage specific, and that this may be due to post-transcriptional control of expression.

Cloning and characterisation of mmc-1, a microfilarial-specific gene, from Brugia pahangi

Nine differentially expressed genes were cloned from Brugia pahangi in a screen which sought to identify cDNAs that were differentially expressed between the microfilariae from the mammalian host and the mosquito vector. One gene (mmc-1), that was up-regulated in mammalian-derived microfilariae, was characterised in detail. RT-PCR analysis demonstrated that mmc-1 was specific to the microfilarial stage of the life cycle and was not transcribed by developing microfilariae in utero, but only following the release of the microfilariae from the adult female. Analysis of DNA from other filarial worms suggested that mmc-1 may be a Brugia-specific gene. Using serum samples from individuals exposed to Brugia malayi infection, it was shown that MMC-1 was specifically recognised by antibodies of the IgG3 subclass. mmc-1 has no homologues in the data bases and its function in the parasite is unknown.

Infection with Brugia microfilariae induces apoptosis of CD4(+) T lymphocytes: a mechanism of immune unresponsiveness in filariasis

In humans infected with lymphatic filariasis, microfilaraemia [the presence of microfilariae (Mf) in the blood] is generally associated with both poor antigen (Ag)-specific proliferative responses and with protection from severe disease. Clonal deletion has been suggested as one possible mechanism by which parasite-reactive lymphocytes, that may be capable of mediating resistance and/or immunopathology, are silenced in asymptomatic carriers. In this study we demonstrate that splenic lymphocytes from mice infected with microfilariae of Brugia pahangi display an Ag-specific proliferative defect. However, these cells were not completely unresponsive since they produced high levels of Ag-specific IFN-gamma. Using TdT-mediated dUTP-biotin nick end labeling for flow cytometry, CD4(+) lymphocytes from Mf-infected mice cultured with Ag showed high levels of apoptosis when compared to those from L3-infected mice which proliferated well in response to Ag. Treatment of Ag-stimulated cultures with aminoguanidine (AMG), an inhibitor of inducible nitric oxide synthase, rescued the CD4(+) T cells from apoptosis and reversed the proliferative defect. Furthermore, carboxyfluorescein diacetate succinimidyl ester labeling allowed the visualization of dividing CD4(+) T cells in cultures from Mf-infected animals only in the presence of AMG. We hypothesize that CD4(+) T cells indirectly trigger their own apoptosis by secreting significant quantities of IFN-gamma resulting in the induction of high levels of nitric oxide, and the subsequent elimination of effector T cells. Our findings are the first direct evidence that infection with Brugia Mf can selectively induce lymphocyte apoptosis, a phenomenon that could contribute to the proliferative defect and parasite persistence associated with the microfilaraemic state in the infected human.

Temperature is a cue for gene expression in the post-infective L3 of the parasitic nematode Brugia pahangi

The temporal expression pattern of two genes, Bp-cdd and Bp-S3, was studied at defined points throughout the life cycle of Brugia pahangi. Both mRNAs were up-regulated to coincide with the transition of the L3 from the vector to the mammalian host. Bp-cdd was expressed almost exclusively in the post-infective (p.i.) L3 and L4 stages of the life cycle while Bp-S3 was also expressed in adult worms, but at a much lower level than in the larval stages. Immunogold labelling with an antiserum raised to the recombinant Bp-CDD localised the native antigen to the hypodermis in the p.i. L3 and L4. Specific labelling was not detected in the adult worm. The expression of both mRNAs could be triggered by exposure of the vector-derived L3 to a simple mammalian culture system. Analysis of the factors, which induced expression suggested that the temperature shift which accompanies the transition from mosquito to mammal was the most important cue for expression of both genes.

Comparative development of Brugia pahangi and variation in acid hydrolase enzyme titers in

The development of the filarial nematode Brugia pahangi was monitored and compared in susceptible (BLACK EYE) and refractory (ROCK) strains of Aedes aegypti. Simultaneously, the activities of acid phosphatase, beta-glucuronidase, alpha-glucosidase, and N-acetyl-beta-glucosaminidase were measured. Three- to five-day-old females of both strains were fed on infected and uninfected clawed jirds (Meriones unguiculatus) then dissected or homogenized at 2 h, at 24-h intervals for 5 days, and at 8 and 10 days after treatment. Enzyme activities were assayed by a fluorometric procedure. The susceptible strain maintained an 80% infection and 18.6 larvae/mosquito over the 10-day period. In contrast, the refractory strain was initially 33% infected and had a mean of 4.9 larvae/mosquito and this decreased to 20% by 3 days, and to 3% with a mean of 0.33 larvae/mosquito at 10 days. Significantly higher acid phosphatase and beta-glucuronidase activities were observed in the refractory strain at specific time intervals after infection. Alpha-glucosidase and N-acetyl-beta-glucosaminidase were highly variable among strains and according to infection status. Analysis of the results of this study suggests that certain acid hydrolase enzymes could be involved in the elimination of B. pahangi in refractory strains of Ae. aegypti and could be used to monitor biochemical changes in response to filarial nematode infections in certain mosquito populations.

Identification and localization of glutathione S-transferase as a potential target enzyme in Brugia species

Brugia filarial nematodes are pathogenic lymphatic-dwelling parasites that, like other helminths, may modify the host's defense mechanisms by a major detoxification process involving glutathione-binding proteins such as glutathione S-transferases (GSTs). In the present study, soluble extracts of third-stage larvae, adult male and female worms, microfilariae of either B. pahangi or B. malayi or the adult worm excretory-secretory products of B. malayi were used to determine GST activity. These extracts and affinity-purified fractions of B. pahangi adult worms had a specific enzymatic activity when 1-chloro-2,4-dinitrobenzene was used as a substrate. The observance of this enzyme in all life cycle stages of Brugia spp. demonstrates its ubiquitous nature. Lavage of intraperitoneally infected jirds, but not that of uninfected jirds, also showed increased enzymatic activity, suggesting that GST is secreted in vivo. Soluble proteins of both Brugia spp. were strongly recognized by antibodies in sera from rabbits immunized with affinity-purified native GST of Onchocerca volvulus. Immunohistochemical studies localized these proteins in adult worms, demonstrating cross-reactivity between the GST of these two filarial nematodes. The effect of this enzyme on the motility and viability of adult worms, microfilariae, and larvae was tested in vitro using a battery of known GST inhibitors. Of all those tested, ethacrynic acid, N-ethylmalemide, 4-nitropyridine-oxide, or 1-chloro-2,4-dinitrobenzene at micromolar concentrations reduced the viability and motility of microfilariae, third-stage larvae, and adult worms. These results suggest that Brugia GSTs are major metabolic enzymes and may play an important role in the parasite's survival.

Tetracycline inhibits development of the infective-stage larvae of filarial nematodes in vitro

In recent years, studies have linked tetracycline treatment of filaria-infected animals with reduced adult worm burdens and decreased levels of microfilaremia. These observations are believed to be attributable to clearance of Wolbachia, intracellular rickettsial-like organisms found within filarial tissues. Although maximal worm reductions were observed when treatment was initiated early in infection, it is not known whether tetracycline inhibits development of infective-stage larvae. To address this issue, we studied the effect of tetracycline on three different species of filarial nematodes, Brugia malayi, Brugia pahangi, and Dirofilaria immitis, in a serumfree in vitro system supporting molting to the fourth larval stage. Tetracycline was capable of inhibiting L3 to L4 molting within a dosage range similar to that reported for susceptible rickettsial organisms. However, Wolbachia DNA could still be detected in nematodes from tetracycline-treated cultures. In addition, three other antibiotics with anti-rickettsial and anti-chlamydial activity (chloramphenicol, erythromycin, and ciprofloxacin) failed to inhibit L3 to L4 molting. Although tetracycline is capable of completely blocking molting of infective-stage larvae, it remains possible that this effect is due to pharmacological activities unrelated to its anti-rickettsial functions.

Cloning and characterization of two nuclear receptors from the filarial nematode Brugia pahangi

Nuclear receptors (NRs) encompass a superfamily of cytoplasmic/nuclear localized receptors that on ligand binding (or by phosphorylation) directly regulate the transcription of target genes. NRs are involved in many developmental processes, including moulting in insects and dauer larva formation in Caenorhabditis elegans. Here we report the isolation of two genes related to NRs from the filarial nematode Brugia pahangi. Bp-nhr-1 is a member of the NGF1-B subfamily of NRs and is expressed at very low levels in post-infective larval stage 3 (L3) after their transmission to the mammalian host. The second gene, Bp-nhr-2, is related to XR78E/F of Drosophila, a gene involved in the ecdysone response, over the region of its DNA-binding domain. cDNA and genomic clones have been isolated that correspond to Bp-nhr-2. The most striking feature of the encoded protein is that, although there is a DNA-binding domain similar to that of other NRs, the ligand-binding domain is absent. To investigate the pattern of transcription of Bp-nhr-2 in the filarial life cycle, semi-quantitative reverse-transcriptase-mediated PCR was performed; this analysis demonstrated that the gene is expressed in early stages after infection and in the adult and microfilariae, and is up-regulated just before the moult between L3 and L4 but is not expressed during the moult between L4 and adult. Antibodies raised against a peptide corresponding to the transactivation domain of Bp-nhr-2 demonstrate that the protein is expressed in microfilariae and adult samples and that another cross-reactive protein is expressed in these life-cycle stages.

The isolation of differentially expressed cDNA clones from the filarial nematode Brugia pahangi

A cDNA library constructed from 3 day post-infective L3 of the filarial nematode Brugia pahangi was screened by differential hybridization with cDNA probes prepared from different life-cycle stages. Five cDNA clones hybridizing selectively to the mosquito-derived L3 probe were isolated and characterized. Northern blot analysis of 4 of the clones confirmed that each was most highly expressed in the mosquito-derived L3. The expression of each mRNA during parasite development in the mosquito vector was investigated using RT-PCR, and all were shown to be abundant in the immature L3. Four of the 5 cDNAs cloned coded for structural proteins: 2 cuticular collagens, and the muscle proteins tropomyosin and troponin. Further studies on troponin using an antiserum raised to the recombinant protein demonstrated that the protein, unlike the mRNA, was present in all life-cycle stages examined, while immunogold labelling demonstrated that it was localized to the muscle blocks.

cut-1-like genes are present in the filarial nematodes, Brugia pahangi and Brugia malayi, and, as in other nematodes, code for components of the cuticle

A fragment of a cut-1 like gene from the filarial nematode Brugia pahangi (designated Bp-cut-1) was isolated by PCR from genomic DNA. The sequence was used to design primers for use in RT-PCR and resulted in the isolation of a cDNA fragment from larvae in the process of the L3-L4 moult. Screening of a B. malayi genomic library identified a single clone, Bm-cut-1. Using primers designed from the Brugia sequences, semi-quantitative RT-PCR was carried out on 11 different life cycle stages chosen to cover periods around the moult and inter-moult periods. This analysis demonstrated that the cut-1 mRNA was most abundant preceding the moult, consistent with its function as a cuticular protein. Immuno-gold electron microscopy using an affinity purified antiserum raised to the highly conserved region of Ascaris CUT-1 confirmed that the protein was restricted to a tight band in the median layer of the cuticle. Despite the fact that no transcripts could be detected in mature adult worms by RT-PCR, immuno-gold microscopy revealed staining of the microfilarial cuticle within the uterus of the adult female worm, suggesting that other cut-1-like genes are present in Brugia.

Variability among Tunisian populations of Culex pipiens: genetic structure and susceptibility to a filarial parasite, Brugia pahangi

Culex pipiens pipiens is a common mosquito found in North Africa and is the primary vector of Bancroftian filariasis in Egypt. Experimental infections with C. p. pipiens have demonstrated that this species supports Brugia pahangi development (parasitic yield 6.3%). In addition, the genetic variation among C. p. pipiens populations from Ben Arrous (in the suburb of Tunis) estimated from isoenzyme polymorphism of five neutral genes (Pgm, Gpi, Hk1, Got-1, and Got-2) was slight (Fst = +0.083). C. p. pipiens from Tunis seems to consist of a homogeneous population that is susceptible to Brugia infection.

Effect of gamma radiation on Brugia L3 development in vivo and the kinetics of granulomatous inflammation induced by these parasites

Previous studies have shown that the downregulation of parasite-specific cellular immune response in Brugia-infected jirds requires viable worms but is not dependent on microfilariae (MF) for either induction or maintenance of this phenomenon. To clarify further which life cycle stages induce filarial hyporesponsiveness, jirds were infected intraperitoneally with third stage larvae (L3) exposed to 0, 15, 25, 35, 45, or 90 krad of gamma radiation to differentially alter L3 development. Necropsies were performed at 7, 14, 28, and 118 days postinoculation (DPI). The degree of parasite development, intraperitoneal inflammation, and pulmonary granulomatous inflammation (PGRN) to parasite antigen-coated beads embolized in the lungs were monitored at the time of necropsy. Parasite survival and worm lengths were inversely related to the irradiation dose. Gamma radiation at 35, 45, or 90 krad prevented larval molt to the adult stage. Some parasites irradiated with 15 or 25 krad developed beyond fourth stage larvae (L4) to infertile adult females. The PGRN peaked at 14 DPI in all infected groups. Downregulation of the PGRN occurred after 14 DPI in groups that received nonirradiated L3 or L3 irradiated with 15 krad. No significant decrease of the PGRN occurred in groups that received parasites irradiated with more than 15 krad. Significant peritoneal inflammation as indicated by an increase in macrophages occurred only in jirds that received nonirradiated L3. These data demonstrate the importance of the adult stages in inducing downmodulation in the absence of MF and suggest that the L4 may also play a role in the induction of this phenomenon. An alternate conclusion is that parasite burden and not developmental stage is important in the induction of this hyporesponsive state.

A member of the TGF-beta receptor gene family in the parasitic nematode Brugia pahangi

The full length cDNA sequence of a Type I transforming growth factor-beta (TGF-beta) receptor has been isolated from the filarial parasitic nematode Brugia pahangi. This new gene, designated Bp-trk-1, encodes a predicted 645 amino acid sequence with an N-terminal hydrophobic stretch which may act as a signal peptide. The extracellular portion (residues 15-187) is cysteine-rich and has three potential N-glycosylation sites. At positions 250-255 the protein contains the glycine-serine rich motif characteristic of Type I receptors. The closest homologue is a Caenorhabditis elegans gene (Q09488) in cosmid C32D5.2 which shares 67% amino acid identity with Bp-trk-1 in the most conserved kinase domain (aa 259-482). Other type I receptors such as C. elegans daf-1 and Drosophila tkv show 38-53% identity in the same region. Some residues conserved in Drosophila and vertebrates are not present in the B. pahangi sequence. RT-PCR amplification has been used to show that the transcript is expressed in the three main stages of the B. pahangi life cycle: microfilariae, infective larvae and adults. The ligand remains unknown at this time but is likely to be most similar to that for C. elegans Q09488.

A cytidine deaminase expressed in the post-infective L3 stage of the filarial nematode, Brugia pahangi, has a novel RNA-binding activity

A number of genes have been identified that are highly expressed in the post-infective L3 stage of the filarial parasite, Brugia pahangi. Amongst these was a cDNA with homology to the cytidine deaminase (CDD) gene family. Phylogenetic analysis of the various cytosine nucleoside deaminases suggest that Brugia pahangi CDD evolved with significant divergence from the RNA editing family. In order to characterize its function, we have expressed Brugia pahangi CDD in bacteria as a chimera with maltose-binding protein (MBP). Biochemical analysis demonstrates the MBP-CDD fusion protein functions as an authentic cytidine deaminase with an obligate requirement for zinc. In addition to cytidine deaminase activity, however, the fusion protein demonstrates RNA binding activity with specificity for AU-rich sequences and was found to bind an RNA template spanning the edited site of mammalian apolipoprotein B (apoB) mRNA. This RNA binding activity was not found in two different recombinant bacterial CDD proteins. In vitro RNA editing assays revealed that MBP-CDD failed to mediate cytidine deamination of a mammalian apoB RNA template. Furthermore, binding of MBP-CDD to the apoB RNA did not inhibit in vitro editing of this template by apobec-1. The data suggest that the cytosine nucleoside deaminases and RNA editing deaminases have acquired different mechanisms of binding to an AU-rich RNA template, presumably with different functional implications.

Brugia pahangi: characterisation of a small heat shock protein cDNA clone

Microfilariae of Brugia pahangi undergo a transition in their life cycle from the homeothermic mammalian host to the poikilothermic mosquito vector. Coincident with this switch, the developmental cycle of the microfilaria is reinitiated. When cultured at mammalian temperatures (37 degrees C), microfilariae express a complex of small heat shock proteins. In order to further characterise this group of proteins a cDNA library was constructed from heat-shocked microfilariae by reverse-transcriptase PCR and then screened with a heterologous probe. A clone which codes for a small heat shock protein was isolated and characterised in detail. Southern blot analysis identified a putative small heat shock protein multigene family. The expression of the small heat shock protein cDNA appears to be controlled at the level of RNA synthesis and is highly stage specific and temperature dependent.

Cellular immune responses of jirds to extracts of life cycle stages and adult excretory secretory products during the early development of Brugia pahangi

The Brugia-jird model of lymphatic filariasis was used to examine the induction of cellular immune responses during the early premicrofilaremic phases of the infection. The intensity of the pulmonary granulomatous inflammatory response (PGRN) was determined by measuring granuloma areas around Sepharose beads coated with parasite extracts which were embolized in the lungs of jirds prior to necropsy. Necropsies were performed at 7, 14, 28, 56, and 150 days postinfection (DPI). These time points correspond to specific developmental changes in the life cycle. Lymphocyte blastogenesis assays were performed using cells from draining renal lymph nodes and splenocytes at 14 and 150 DPI. Soluble extracts of third stage larvae (L3), fourth stage larvae (L4), adult females, adult males, microfilariae (MF), and excretory secretory products (ES) of males and females were used in both measurements of cellular responsiveness. A marked granulomatous response to parasite extracts peaked at 7 DPI or 14 DPI followed by a gradual decrease to a hyporesponsive state at 120 DPI. The response of renal lymph node cells also was significantly elevated at 14 DPI and significantly decreased at > 150 DPI. The splenocyte responses were erratic and did not follow this pattern. Significant differences in PGRN responses to somatic extract preparations were not seen during the early stages of the infection (7, 14, 28 DPI), but those to MF and L3 were significantly less at 56 and 120 DPI. Although PGRN responses to ES followed a similar pattern, these were less than those to the somatic extract. The data indicated that a rapid, intense cell-mediated inflammatory response is induced early during a primary infection and that this response is rapidly downregulated. This downregulation begins prior to the maturation of adult parasites and microfilarial production. The early phase of the cellular response appears to be compartmentalized in that this response was consistently observed in the renal lymph nodes but not in the spleen. Soluble protein components of the parasites responsible for these responses are likely multiple and shared by all life cycle stages.

Concomitant malaria (Plasmodium gallinaceum) and filaria (Brugia pahangi) infections in Aedes aegypti: effect on parasite development

Mixed infections with malarial (Plasmodium gallinaceum) and filarial (Brugia pahangi) parasites were carried out in 8 trials with filaria susceptible (REFM) and filaria refractory (REP-RR) Aedes aegypti strains. A secondary infection with B. pahangi microfilariae (mff) by intrathoracic inoculation, reduced the development rate of a pre-existing P. gallinaceum infection. The level of reduction ranged from 9.5 to 49% in REFM and from 50 to 90% in REP-RR. An immune response against oocysts was seen as melanization in mosquitoes with a double infection in the strain refractory to B. pahangi (REP-RR) and a reduction in oocyst size in both mosquito strains. Melanization was not observed in mosquitoes infected only with P. gallinaceum. This may indicate that activation of the prophenoloxidase (PPO) cascade in response to mff in the haemolymph can also be addressed against oocysts in the midgut. No significant difference in the number of filarial parasites recovered was observed when comparing groups with a single or double infection. Retardation in development of filaria larvae was observed in mosquitoes with double infection (REFM strain), together with melanization and a higher rate of abnormal development. Nutritional deficiency caused by superinfection might also be responsible for the delay in filarial development and reduced oocyst size.

The fate of Brugia pahangi microfilariae in Armigeres subalbatus during the first 48 hours post ingestion

In Armigeres subalbatus, 60% and 3% of the ingested Brugia pahangi microfilariae (mf) respectively migrated into the haemocoel and the thorax within 5 minutes post ingestion (p.i.). Most of the mf had migrated from the gut into the haemocoel within the first 10 minutes p.i. There was no correlation between the number of mf ingested and the migration rate though those in mosquitoes with a low mf burden tend to migrate earlier. At 24 hours p.i., 5-30% of the mf were still in the gut; 19% of these mf were immobile. At 48 hours p.i. only 2% of the mf were mobile. B. pahangi mf isolated from blood meals at 24 hours p.i., failed to develop when inoculated into Armigeres subalbatus. 54% and 73% of the mf isolated from a 24 hour old clotted blood of a B. pahangi-infected cat and fresh peripheral cat blood respectively developed into stage-1 larva. Probably mf left in the midgut at 24 hours p.i. are the young and immature worms and are physiologically incapable of penetrating the gut.

Filaria vector competence of some Anopheles species

The filaria vector competence of Anopheles stephensi was compared with Brugia-susceptible Aedes aegypti Liverpool strain, An. gambiae Badagry Lagos strain and An. dirus Perlis Malaysia strain. An. stephensi ingested more Brugia pahangi microfilariae, had the highest infectivity rate and yielded more infective mosquitoes than the other two anopheline species. The overall vector competence of An. stephensi was 0.13 times that of Ae. aegypti, 0.62 times that of An. gambiae and 2.17 times that of An. dirus. However, heavy mortality among infected An. stephensi in the present investigation indicates that the filaria vectorial capacity of the mosquito might be limited epidemiologically. The relationship between filaria vector competence and mosquito foregut armature is discussed. It was observed that the relative vector competence of the three anopheline species tested was in the same order as their relative degrees of armature elaboration. The converse would be expected if foregut armatures really give partial protection to the mosquitoes against filarial infection. It is suggested that high host microfilariae density favours larval survival proportional to the degree of armature development in Anopheles (Cellia) species.

The effect of irradiation on the third stage larvae of Brugia pahangi

The effect of irradiation on the third stage larvae of the filarial nematode Brugia pahangi was investigated. Labelling with 35S methionine of control or irradiated L3, post-infective L3 or L4 revealed no consistent alterations in the pattern of proteins synthesized. The only significant difference observed was in 125I labelling, where the specific activity of labelling of soluble cuticular proteins was lower in irradiated than in control parasites. This difference may be related to the reduced size of irradiated parasites rather than to a specific effect of irradiation on the expression of cuticular proteins. Irradiated parasites recovered on day 14 post-infection were significantly shorter than control parasites. Irradiation also appeared to have a lethal effect on male parasites, as no recognizable males were recovered from animals given irradiated L3, nor were microfilariae ever observed in these animals. The mechanisms by which irradiation may enhance the immunogenicity of L3 of filarial nematodes are discussed.

Growth and development of Brugia pahangi larvae under various in vitro conditions

In vitro culture methods were utilized to investigate specific nutritional requirements of Brugia pahangi larvae. Infective third-stage larvae (L3) isolated from Aedes aegypti (Liverpool) mosquitoes were cultured in NCTC 135:IMDM (NI) medium plus various types of serum under 5% CO2/air and 5% CO2/N2 atmospheres. Larvae grew, developed, and molted to the fourth stage (L4); however, further growth and differentiation beyond the mid-L4 were minimal. Serum supplementation was necessary to induce molting of B. pahangi L3s. Iron-supplemented calf serum (FeCS) consistently promoted higher percentages of molting than the other 4 types of serum tested. Specific nutritional requirements for B. pahangi larvae were assessed through testing of supplements known to be important for growth of mammalian cells or other parasites in vitro. Addition of various concentrations and combinations of hemoglobin, insulin, transferrin, selenium, albumin, cholesterol, or a cell feeder layer did not improve larval growth, molting, or survival compared to that obtained with FeCS alone. The L4s derived from in vitro culture, when injected intraperitoneally into jirds, developed to sexually mature, microfilarial-producing adults in a normal in vivo time frame. Developing L4s isolated from jirds molted to young adults in vitro in NI medium plus serum.

IgE responses in cats infected with Brugia pahangi

Passive cutaneous anaphylaxis tests were used to examine the IgE responses of cats repeatedly infected with the filarial nematode Brugia pahangi. Specific IgE was usually detected only in those cats that killed their adult worms and rarely in those cats in which adult worms survived for long periods. We suggest that this specific IgE is actively involved in killing adult worms in the lymphatics.

Brugia pahangi: identification and characterization of an aminopeptidase associated with larval molting

The third-stage larvae (L3) of the filarid parasite Brugia pahangi were surveyed for protease activity beginning with release from the mosquito vector through molting to the fourth-stage larvae (L4). A metalloaminopeptidase with a substrate preference for phenylalanine was released during the molting process. A screen of aminopeptidase inhibitors identified H-boroPhenylalanine-(pinacol) as highly effective, with a Ki of 1.3 x 10(-11) M. This peptidase inhibitor also arrested molting of L3 larvae in vitro at a concentration of 100 microM.

The expression of small heat shock proteins in the microfilaria of Brugia pahangi and their possible role in development

Development of the microfilariae of Brugia pahangi in the mammalian host is blocked until uptake by a mosquito vector when the developmental cycle is re-initiated. Comparison of the profile of polypeptides labelled in microfilariae cultured at mammalian temperature (37 degrees C) or mosquito temperature (28 degrees C) revealed a complex of low-molecular-weight proteins (18 kDa and 22-24 kDa) synthesized only in microfilariae at 37 degrees C. The synthesis of these proteins was also induced by transfer of microfilariae to 41 degrees C (i.e., heat shock conditions), suggesting that these are heat shock proteins. The expression of the small heat shock proteins in the Brugia life cycle is developmentally regulated, as they are not observed in the mature adult female. Their synthesis is strictly temperature dependent and is repressed upon transfer of the microfilariae to 28 degrees C.

Expression of small heat shock proteins by the third-stage larva of Brugia pahangi

Changes in proteins synthesised by the infective third-stage larvae (L3) of the filarial nematode Brugia pahangi were examined with respect to the temperature shift encountered by the parasite as it migrates from insect to mammal, and the presence of serum in the culture medium. While the synthesis of a number of polypeptides is regulated by the temperature shift of the L3 from 28 degrees C to 37 degrees C in vitro, there is no evidence that serum has any significant effect on protein synthesis. Two complexes of small acidic polypeptides (22-24 kDa and 18 kDa) are synthesised for a limited period only by L3 transferred to 37 degrees C. One component of each complex appears to be constitutively expressed at 28 degrees C, but its synthesis is up-regulated at 37 degrees C, while the remaining members of each complex are synthesised only at 37 degrees C. Subjection of L3 and post-infective (p.i.) L3 to heat shock (41 degrees C) also induces synthesis of both complexes, indicating that these heat-inducible polypeptides are related to the family of small heat shock proteins. The possible role of the heat shock-related proteins in this important environmental transition is considered.