Nematode Antigens Research Articles

A Structural Analysis of Host-Parasite Interactions in Achatina fulica (Giant African Snail) Infected with Angiostrongylus cantonensis.

Angiostrongylus cantonensis is a nematode parasite that resides in the pulmonary arteries of rodents, serving as its definitive hosts. The life cycle involves several species of non-marine gastropods as intermediate hosts, and the African giant snail Achatina fulica is considered one of the most important around the world. Experimental data concerning A. cantonensis infection in the African giant snail remains notably limited. This helminth causes eosinophilic meningitis or meningoencephalitis in humans, representing an emergent zoonosis in Brazil. Understanding the host-parasite relationship through the application of new tools is crucial, given the complex interaction between zoonosis and the intricate mechanisms involving wild/human hosts, parasite adaptation, and dispersion. The objective of this study was to employ SEM as a novel methodology to understand the structural organization of the host tissue, particularly the granuloma formation. This sheds light on the complex balance between A. fulica and A. cantonensis. Nine three-month-old snails were randomly selected and exposed for 24 h to a concentration of 2000 L1/dose of A. cantonensis. A necropsy was performed 37 days after the infection, and the samples were examined using light and scanning electron microscopy (SEM). The histopathological results revealed third-stage larvae of A. cantonensis associated with granulomas distributed throughout the head-foot mass, mantle, and kidney. Scanning electron microscopy of the histological section surface showed that the granuloma is surrounded by a cluster of spherical particles, which are distributed in the region bordering the larvae. This reveal details of the nematode structure, demonstrating how this methodology can enhance our understanding of the role of granulomas in molluscan tissue. The structural characteristics of granuloma formation in A. fulica suggest it as an excellent invertebrate host for A. cantonensis. This relationship appears to provide protection to the parasite against the host's immune defense system while isolating the snail's tissue from potential exposure to nematode antigens.

Immune and parasitological response in horses infected with gastrointestinal nematodes in the humid tropic of Mexico

The objective of the study was to determine the parasitological and immune response in horses naturally re-infected with gastrointestinal nematodes (GIN) after an- thelmintic treatment in the humid tropic of Mexico. The study was conducted in Tenosique, Tabasco, Mexico. A total of 30 horses were sampled monthly for nine months. Fecal samples were obtained to determine the number of nematode eggs per gram (EPG) of feces. Stool cultures were performed to obtain and identify infective larvae (L3) genera. Blood samples were also obtained to determine the packed cell volume (PCV), the total plasma protein (TPP), and the differential leukocyte count (DLC). Serum enzyme-linked immunosorbent assays (ELISA) were performed to determine IgA levels against adult cyathostomins and Strongylus nematode antigen. The analyses considered the age and gender of the horses, and the season (Cold, rainy and dry). The number of EPG and TPP were higher in females (1224 ± 1269 and 7.6 ± 0.6 gdL−1, respectively) than males (623 ± 671 and 7.4 ± 0.5 gdL−1, respectively), and no differences were observed with animal age (p > 0.05). The number of EPG increased in the rainy season. The main nematodes involved were of the subfamily Cyathostominae (97.4%) and to a lesser degree of species Strongylus equinus, S. edentatus, S. vulgaris, and Oxyuris equii. The season affected the leukocytes, neutrophils, and lymphocytes counts but not eosinophils. Variables such as gender, animal age, and environmental conditions are important elements for a diagnosis of GIN and the application of treatments for its control.

SPECIFIC MAMMALIAN IMMUNE RESPONSE TO NEMATODE INFESTATION

The article analysis the specific mammalian immune response to nematode infestation. The obtained nematode antigens are described. Titers of antibodies in THA and ELISA in the period of infestation and after deworming are given.

Attempts to induce tolerance to Trichostrongylus colubriformis infection in sheep.

The possibility of manipulating the immune response in lambs to the gastrointestinal nematode Trichostrongyluscolubriformis to reduce production losses associated with infection was investigated. In a series of four experiments, attempts to immunize sheep via the mucosal route to modify the immune response and induce mucosal tolerance are outlined. Initially, a proof of concept study was conducted with lambs being injected with multiple doses of a somatic Tcolubriformis antigen without an adjuvant in the rectal submucosa and subsequently challenged with Tcolubriformis L3 larvae. This was followed by a dose-response study comparing different antigen doses to identify the optimum dose of the nematode antigen for successful induction of mucosal tolerance. The final two studies were conducted to determine the larval stage specificity of the parasite antigen and the most suitable site of delivery required to stimulate mucosal tolerance. In the proof of concept study, lambs either received repeated injections in the rectal submucosa at 3×weekly intervals with 15µg of L3, 11µg of L4 and 21µg of immature adult (L5) somatic Tcolubriformis antigens (ANT) or not (INF) prior to infection with Tcolubriformis. In the dose-rate study, antigen dose rates of 100%, 50%, 10%, 1% or 0% of the antigen concentration used in the proof of concept study were compared while the larval stage study compared antigen from either L3, L4, L5 stages or combination of all (COMB) and the route of administration study compared antigen delivery into either the rectal submucosa (RE) or sub-cutaneous injection (SC). During infection, lamb growth was improved by antigen treatment between days 21 and 42 in the proof of concept study (P=.009), for groups 10%, 50% and 100% in the dose-rate study (P<.05 for all) and in RE in the route of administration study with no improvement observed in the larval stage study. No differences in faecal egg counts were observed (P>.05 for all). Parasite-specific IgA and IgE showed a dose-response (the dose-rate study), were not affected by larval stage (the larval stage study) and were greater in RE than SC (the route of administration study). IL-4 production following lymphocyte stimulation was greatest in COMB (the larval stage study) and RE (the route of administration study). Although antigen treatment improved performance, this was inconsistent and appeared to stimulate immunity rather than induce tolerance. Combined larval stages were more efficient than individual stages, and intra-rectal administration was more effective than sub-cutaneous.

Fast One-Step Ultrasensitive Detection of Toxocara canis Antigens by a Nanobody-Based Electrochemical Magnetosensor.

Human toxocariasis (HT) is a cosmopolitan zoonotic disease caused by the migration of the larval stage of the roundworm Toxocara canis. Current HT diagnostic methods do not discriminate between active and past infections. Here, we present a method to quantify Toxocara excretory/secretory antigen, aiming to identify active cases of HT. High specificity is achieved by employing nanobodies (Nbs), single domain antigen binding fragments from camelid heavy chain-only antibodies. High sensitivity is obtained by the design of an electrochemical magnetosensor with an amperometric read-out. Reliable detection of TES antigen at 10 and 30 pg/mL level was demonstrated in phosphate buffered saline and serum, respectively. Moreover, the assay showed no cross-reactivity with other nematode antigens. To our knowledge, this is the most sensitive method to quantify the TES antigen so far. It also has great potential to develop point of care diagnostic systems in other conditions where high sensitivity and specificity are required.

Diagnostic strategies to reveal covert infections with intestinal helminths in dogs

Intestinal helminths are common in dogs in the United States, particularly non-treated dogs in animal shelters, but surveys by fecal flotation may underestimate their prevalence. To determine the prevalence of intestinal helminths and evaluate the ability of fecal flotation and detection of nematode antigen to identify those infections, contents of the entire gastrointestinal tract of 97 adult (>1year) dogs previously identified for humane euthanasia at two animal control shelters in northeastern Oklahoma, USA, were screened. All helminths recovered were washed in saline and fixed prior to enumeration and identification to genus and species. Fecal samples from each dog were examined by passive sodium nitrate (SG 1.33) and centrifugal sugar solution (SG 1.25) flotation. Fecal antigen detection assays were used to confirm the presence of nematode antigen in frozen fecal samples from 92 dogs. Necropsy examination revealed Ancylostoma caninum in 45/97 (46.4%), Toxocara canis in 11/97 (11.3%), Trichuris vulpis in 38/97 (39.2%), Dipylidium caninum in 48/97 (49.5%), and Taenia sp. in 7/97 (7.2%) dogs. Passive fecal flotation identified 38/45 (84.4%) A. caninum, 6/11 (54.5%) T. canis, 26/38 (68.4%) T. vulpis, 2/48 (4.2%) D. caninum, and 1/7 (14.3%) Taenia sp. infections, while centrifugal flotation combined with antigen detection assays identified A. caninum in 97.7% (43/44), T. canis in 77.8% (7/9), and T. vulpis in 83.3% (30/36) of infected dogs based on necropsy recovery of nematodes. Taken together, these data indicate that detection of nematode antigen is a useful adjunct to microscopic examination of fecal samples for parasite eggs, and that this approach can improve diagnostic sensitivity for intestinal nematode infections in dogs.

Epicutaneous sensitization with nematode antigens of fish parasites results in the production of specific IgG and IgE.

Fish consumption plays an important role in the human diet. Hoplias malabaricus, trahira, is a freshwater fish widely appreciated in several Brazilian states and it is frequently infected by Contracaecum multipapillatum third-instar larvae (L3). The aim of the present study was to evaluate the allergenic potential of the C. multipapillatum L3 crude extract (CECM). BALB/c mice were immunized intraperitoneally (ip) with 10 or 50 μg CECM associated with 2 mg of aluminium hydroxide on days 0, 14 and 48. The determination of specific IgG and IgE antibody levels was done after immunization, and the late immunity was evaluated by the intradermal reaction in the ear pavilion. Epicutaneous sensitization was performed in the dorsal region, with antigenic exposure via a Finn-type chamber, containing 100 μg of chicken ovum albumin (OVA) or 100 μg CECM. After the exposures, the specific antibody levels were determined. In the ip immunization, there was a gradual increase in IgG antibody levels, independent of CECM concentration. In relation to IgE production, it was transitory, and immunization with 10 μg was more efficient than that of 50 μg. The same result was observed in the cellular hypersensitivity reaction. In the case of antigen exposure by the epicutaneous route, it was verified that only CECM was able to induce detectable levels of specific IgG and IgE antibodies. In the present study it was demonstrated that both intraperitoneal immunization and epicutaneous contact with C. multipapillatum larval antigens are potentially capable of inducing allergic sensitization in mice.

Colitis Promotes Adaptation of an Intestinal Nematode: A Heligmosomoides Polygyrus Mouse Model System

The precise mechanism of the very effective therapeutic effect of gastrointestinal nematodes on some autoimmune diseases is not clearly understood and is currently being intensively investigated. Treatment with living helminths has been initiated to reverse intestinal immune-mediated diseases in humans. However, little attention has been paid to the phenotype of nematodes in the IBD-affected gut and the consequences of nematode adaptation. In the present study, exposure of Heligmosomoides polygyrus larvae to the changed cytokine milieu of the intestine during colitis reduced inflammation in an experimental model of dextran sulphate sodium (DSS)- induced colitis, but increased nematode establishment in the moderate-responder BALB/c mouse strain. We used mass spectrometry in combination with two-dimensional Western blotting to determine changes in protein expression and changes in nematode antigens recognized by IgG1 in mice with colitis. We show that nematode larvae immunogenicity is changed by colitis as soon as 6 days post-infection; IgG1 did not recognize highly conserved proteins Lev-11 (isoform 1 of tropomyosin α1 chain), actin-4 isoform or FTT-2 isoform a (14-3-3 family) protein. These results indicate that changes in the small intestine provoked by colitis directly influence the nematode proteome. The unrecognized proteins seem to be key antigenic epitopes able to induce protective immune responses. The proteome changes were associated with weak immune recognition and increased larval adaptation and worm growth, altered localization in the intestine and increased survival of males but reduced worm fecundity. In this report, the mechanisms influencing nematode survival and the consequences of changed immunogenicity that reflect the immune response at the site colonized by the parasite in mice with colitis are described. The results are relevant to the use of live parasites to ameliorate IBD.

Serological evidence of Ostertagia ostertagi infection in dairy cows does not impact the efficacy of rabies vaccination during the housing period

Nematode infections modulate the immune reaction of humans and livestock and may impair immune responses to non-parasitic antigens such as those present in vaccines. In this study, the relationship between antibodies directed against Ostertagia ostertagi, the economically most important nematode infection of cattle in temperate regions, and the magnitude and the kinetics of the antibody response to rabies vaccination was investigated in a commercial dairy herd of 46 cows. During the stabling period, all animals received a single intramuscular administration with a commercial inactivated rabies vaccine (Rabisin®, Merial). The serum antibody levels against O. ostertagi on day 0 were compared with anti-rabies IgM, IgA, IgG1, IgG2 and virus-neutralizing antibodies on days 0, 7, 14 and 21 after vaccination. In addition, to explore the potential effect of newly acquired O. ostertagi infections, the kinetics of the O. ostertagi antibody levels during the first 2months after turnout on pasture were compared with concurrent changes in the rabies antibodies. During the stabling period the O. ostertagi antibody level tended to be positively associated with the magnitude, rate of increase and rate of decrease of the rabies antibodies. However, none of these associations were significant (P>0.05). Over the first 2months at pasture, an increase in O. ostertagi antibody level tended to be associated with a decrease in rabies IgG2 and IgM, but again these associations lacked statistical significance (P>0.20). We conclude that the O. ostertagi antibody level in adult cattle over the housing period has no significant association with the antibody response to rabies vaccination. We recommend that future studies aiming to assess the relationship of nematode infections with humoral immune responses to vaccines are conducted on a larger scale and focus on the summer period when cattle are exposed continuously to nematode challenge from the pasture and hence are actively responding immunologically to nematode antigen exposure.

Genetic and phenotypic relationships between carbohydrate larval antigen (CarLA) IgA, parasite resistance and productivity in serial samples taken from lambs after weaning

Genetic selection for enhanced levels of protective antibody to specific nematode antigens may be a more user-friendly means of selecting animals for resistance to gastrointestinal nematodes than obtaining faecal samples and selecting on the basis of faecal egg counts. Saliva IgA antibody levels to the L3-specific surface glycan known as carbohydrate larval antigen were measured on six occasions over a 5month period in approximately 350 lambs. The carbohydrate larval antigen IgA response increased markedly with time as the lambs grazed on pasture naturally contaminated with nematode parasite larvae. The monthly loge transformed carbohydrate larval antigen IgA levels were moderately heritable at all samplings, with a combined value of 0.28±0.10 and a repeatability of 0.35±0.03. The genetic correlations between all samplings were high (0.86), suggesting that testing for a carbohydrate larval antigen IgA response could be carried out at any time in the 5months post-weaning. The transformed carbohydrate larval antigen IgA levels were genetically and phenotypically correlated negatively with loge transformed (faecal egg count+50), averaging −0.57±0.20 and −0.12±0.03 (P<0.05), respectively. The correlations between carbohydrate larval antigen IgA and breech-soiling (dag score) never reached significance. However, genetic correlations between carbohydrate larval antigen IgA and live weight were always positive and significantly so, especially at the beginning and end of the trial, indicating that carbohydrate larval antigen IgA production may be an important genetic determinant of growth rate for lambs experiencing a larval challenge. The data suggest that the ideal time to sample for a carbohydrate larval antigen IgA response and maximise selection for lowered faecal egg count and increased live-weight would be in the first 2months after weaning.

P006 Cytokine and chemokine responses as predictive markers for progressive, stable or cured Echinococcus multilocularis infection in man

Introduction In man the tissue infiltrative growth of Echinococcus multilocularis metacestodes will cause alveolar echinococcosis (AE) with organ malfunction and finally organ failure. In some AE patients, however, metacestode proliferation may regress, but little is known about the mechanism and determinants which may control or even restrain parasite survival and its growth. Methods In this study, chemokine and cytokine responses were investigated in E. multilocularis patients at different states of infection, i.e. with progressive, stable and cured alveolar echinococcosis. We analyzed the serum levels and the ex vivo cytokine and chemokine responsiveness of peripheral blood mononuclear cells (PBMC) from AE patients, reflecting their innate and memory immune responses to E. multilocularis antigens. First, plasma concentrations of pro-inflammatory cytokines and chemokine were investigated, and then the capacity of PBMC from AE patients and infection-free controls was studied in order to distinguish between progressive, stable and cured E. multilocularis infection. Results The plasma levels of the pro-inflammatory cytokines IL-17B and its soluble receptor (sIL-17RB), and MIP-3 α were highly elevated in AE patients as compared to controls while highest concentrations of IL-17F and its common soluble receptor (sIL-17RA), regulatory IL 27, pro-inflammatory IL 31 and IL 33 were detected in controls. Spontaneous release of several cytokines and chemokine was clearly different between AE patients in different stages of infection and controls. Furthermore, a distinct cellular responsiveness was observed in AE patients when their PBMC were activated with antigens from helminthes, bacteria or mitogens. Pro-inflammatory cytokine production of IL17F and IL 17RA, as well as regulatory IL27, was reduced above baseline level in AE patients when their PBMC were co-culture with Em Antigens. Chemokine production of PBMC in AE patients was not inducible by E.multilocularis antigens for pro-inflammatory monocyte inflammatory proteins (MIP-1 α /CCL3//MIP-1 β /CCL4//MIP-3 α /CCL20). Conclusion These observations disclose a distant dynamic of the cytokine and chemokine profile at different stages of AE. Furthermore, cestode and nematode antigens will differ in their capacity to stimulate cellular cytokine and chemokine production, notably for the activation of pro-inflammatory immune mediators. In summary, the analyses of constitutive and inducible chemokine and cytokine profiles may provide a better understanding of their importance during progression, regression and also for the staging of alveolar echinococcosis.

An evolutionary perspective on gastrointestinal nematodes of sheep

The purpose of this paper was to discuss from an evolutionary perspective the interaction between domestic sheep (Ovis aries) and their gastrointestinal nematodes. Although evolution is the central theme of biology, there has been little attempt to consider how evolutionary forces have shaped and continue to shape the relationships between domestic animals and their parasite community. Mathematical modelling of the host-parasite relationship indicated that the system is remarkably robust to perturbations in its parameters. This robustness may be a consequence of the long coevolution of host and parasites. Although nematodes can potentially evolve faster than the host, coevolution is not dominated by the parasite and there are several examples where breeds of cattle or sheep have evolved high levels of resistance to disease. Coevolution is a more equal partnership between host and nematode than is commonly assumed. Coevolution between parasites and the host immune system is often described as an arms race where both host immune response genes and parasite proteins evolve rapidly in response to each other. However, initial results indicate that nematode antigens are not evolving rapidly; the arms race between the immune system and nematodes, if it exists, is happening very slowly. Fisher's fundamental theorem of natural selection states that genes with positive effects on fitness will be fixed by natural selection. Consequently, heritable variation in fitness traits is expected to be low. Contrary to this argument, there is considerable genetic variation in resistance to nematode infection. In particular, the heritabilities of nematode-specific IgA and IgE activity are moderate to high. The reasons for this apparent violation of the fundamental theorem of natural selection are not clear but several possible explanations are explored. Faecal nematode egg counts increase at the beginning of the grazing season - a phenomenon known as the periparturient rise. This increase benefits host and parasite and appears to be a consequence of coevolution. In conclusion, an evolutionary perspective can shed light on many aspects of the host-parasite relationship in domestic animals.

Ascaris lumbricoides: An Overview of Therapeutic Targets

A. lumbricoides is the largest of the common nematode parasites of man and has been associated with intestinal pathology, respiratory symptoms and malnutrition in children from endemic areas. Current anthelmintic treatments have proven to be safe. However, a reduced efficacy of single dose drugs has been reported. In veterinary practice, anthelmintic drug resistance is an irreversible problem. Thus, research and development of sensitive tools for early detection of drug resistance as well as new anthelmintic approaches are urgently needed. In this review, we summarized data providing information about current drug therapy against A. lumbricoides and other intestinal helminths, new drugs in experimental trials, future drugs perspectives and the identification of immunogenic parasite molecules that may be suitable vaccine targets. In addition to the WHO recommended drugs (albendazole, mebendazole, levamisole, and pyrantel pamoate), new anthelmintic alternatives such as tribendimidine and Nitazoxanide have proved to be safe and effective against A. lumbricoides and other soil-transmitted helminthiases in human trials. Also, some new drugs for veterinary use, monepantel and cyclooctadepsipeptides (e.g., PF1022A), will probably expand future drug spectrum for human treatments. The development of genomic technology has provided a great amount of available nematode DNA sequences, coupled with new gene function data that may lead to the identification of new drug targets through efficient mining of nematode genomic databases. On the other hand, the identification of nematode antigens involved in different parasite vital functions as well as immunomodulatory molecules in animals and humans may contribute to future studies of new therapeutic approaches.

Incidental isolation of Setaria equina microfilariae in preparations of equine peripheral blood mononuclear cells

In the course of a vaccine experiment on horses, microfilariae were observed in cultures of peripheral blood mononuclear cells (PBMCs) isolated from eleven of fifteen study horses. The microfilariae were clearly viable as evidenced by their vigorous movements in the cultures, thus indicating that they had survived the Ficoll gradient purification and the cryopreservation method used for retaining the PBMCs. The microfilariae were identified as Setaria equina, which is a vector-borne filarial nematode that causes a relatively benign infection of equids in which the adult worms reside in the peritoneal cavity. Although it is not possible to definitely state where the infections were acquired, the horses originated from Saskatchewan, Canada and spent a relatively short period of time in the United States prior to blood sampling. Therefore, it is likely that the infections occurred in Canada. Interestingly, assays conducted to determine levels of cytokine mRNA transcripts in the isolated PBMCs seemed to be largely unaltered by the presence of the microfilariae in the cell cultures. These findings demonstrate that a standard method used to purify and cryopreserve PBMCs from blood can result in the unintended co-isolation of worms from microfilaremic animals. Furthermore, the presence of the microfilariae did not appear to alter significantly the results of our immunologic assays, suggesting either that the nematode antigens were not recognized or that immunological tolerance may have developed in these horses. Although notable effects on the assays were not observed in this study, it seems possible that microfilarial contamination could represent a confounding variable for experiments examining cellular immunity.

Altered antibody responses in mannose‐binding lectin‐A deficient mice do not affect Trichuris muris or Schistosoma mansoni infections

Parasitic helminths possess surface glycoconjugates that are recognized by the serum collectin molecule, mannose-binding lectin (MBL). Once bound, MBL triggers the lectin pathway of complement. Mice have two MBL, MBL-A and MBL-C. We previously showed that MBL-A deficient (MBL-A(-/-)) mice have enhanced survival of Brugia malayi microfilariae and abrogated microfilariae-specific IgM responses. In this study we show that MBL-A deficiency does not alter immunity to either Trichuris muris or Schistosoma mansoni. However, anti-nematode IgM levels were significantly lower in T. muris infected MBL-A(-/-) than wild-type mice. Interestingly nematode-specific IgG1 and IgG2a levels were higher in MBL-A(-/-) mice. Although, larval schistosomes are surrounded by a complement-sensitive membranous tegument, neither adult worm development, egg output, egg granuloma size nor cellular composition was affected in MBL-A(-/-) mice. In contrast to anti-nematode IgM responses, anti-schistosome IgM (and also IgG1 and IgG2b) responses were unaltered from wild-type mice. Anti-schistosome IgG2a was elevated, while IgG3 was significantly lowered, in MBL-A(-/-) mice. These results suggest that MBL-A is not a necessary component for immunity to either T. muris or S. mansoni helminths, however, MBL-A appears to be necessary for the development of specific IgM responses to nematode antigens.

Failure of ES‐62 to inhibit T‐helper type 1 responses to other filarial nematode antigens

ES-62 is a secreted protein of filarial nematodes that possesses multiple immunomodulatory activities. A full characterization of these activities awaits elucidation but to date it has been shown that ES-62 can inhibit pro-inflammatory/Th1 immune responses and in some studies, it has been found to actively support Th2 development. As an active filarial nematode infection is associated with a Th2-like immunological phenotype, this study investigated whether ES-62 was likely to be responsible for, or at least contribute to, this phenotype. Specifically, we determined ES-62's effect on the immune response to two other filarial nematode antigens, chosen for their ability to promote Th1 responses. The two antigens were recombinant Onchocerca volvulus-Fatty acid And Retinol-binding-1 (rOv-FAR-1) and recombinant Onchocerca volvulus-Activation associated Secreted Protein-1 (Ov-ASP-1). Overall the results show that in spite of its previously characterized immunomodulatory properties, ES-62 was unable to modulate/reverse the Th1 immune responses induced by the two Onchocerca antigens. Therefore, in this study no support is provided for the idea that ES-62 might be a major player in facilitating the overall immunological phenotype in filariasis and reasons for this somewhat surprising outcome are discussed.

Reduced Protective Efficacy of a Blood-Stage Malaria Vaccine by Concurrent Nematode Infection

Helminth infections, which are prevalent in areas where malaria is endemic, have been shown to modulate immune responses to unrelated pathogens and have been implicated in poor efficacy of malaria vaccines in humans. We established a murine coinfection model involving blood-stage Plasmodium chabaudi AS malaria and a gastrointestinal nematode, Heligmosomoides polygyrus, to investigate the impact of nematode infection on the protective efficacy of a malaria vaccine. C57BL/6 mice immunized with crude blood-stage P. chabaudi AS antigen in TiterMax adjuvant developed strong protection against malaria challenge. The same immunization protocol failed to induce strong protection in H. polygyrus-infected mice. Immunized nematode-infected mice produced significantly lower levels of malaria-specific antibody than nematode-free mice produced. In response to nematode and malarial antigens, spleen cells from immunized nematode-infected mice produced significantly lower levels of gamma interferon but more interleukin-4 (IL-4), IL-13, and IL-10 in vitro than spleen cells from immunized nematode-free mice produced. Furthermore, H. polygyrus infection also induced a strong transforming growth factor beta1 response in vivo and in vitro. Deworming treatment of H. polygyrus-infected mice before antimalarial immunization, but not deworming treatment after antimalarial immunization, restored the protective immunity to malaria challenge. These results demonstrate that concurrent nematode infection strongly modulates immune responses induced by an experimental malaria vaccine and consequently suppresses the protective efficacy of the vaccine against malaria challenge.

What causes lymphocyte hyporesponsiveness during filarial nematode infection?

Filarial nematodes persist in the parasitized host by modulating immune responsiveness. A feature of this that has been observed in a multitude of studies dating back several decades is an inability of lymphocytes to respond appropriately to filarial nematode antigens and, in some cases, to other stimuli. The consistency of this observation, allied to the ease of measurement of lymphocyte hyporesponsiveness, has resulted in many attempts to understand its cause.

Increased rat alveolar macrophage expression of functional iNOS induced by a Dirofilaria immitis immunoglobulin superfamily protein

Dirofilaria immitis is a worldwide filarial nematode causing heartworm disease in dogs and cats. Several mosquito species, which are able to feed both on humans and animals, can transmit this parasite. Inflammatory progression of host tissues induced by parasites are mediated by several molecules, including nitric oxide (NO), which usually exerts deleterious effects on parasites and occasionally on the host. We analyze the in vitro effect of total D. immitis adult worm somatic antigens on naïve rat alveolar macrophage NO production and further separation of parasite proteins to define specific D. immitis somatic molecules influencing host cell NO secretion. Additionally, we address the possible influence of Wolbachia spp. on the in vitro production of NO by macrophages. Our results demonstrate that D. immitis adult worm soluble antigens are able to specifically induce NO production from host macrophages. Furthermore, we demonstrated that this effect is due to nematode antigens rather than to defined components (LPS and metabolic molecules) derived from its endosymbiont, Wolbachia spp. In addition, we were able to isolate and identify one of the parasite specific components from the DiSo extract, denominated DiID35.3 and putatively belonging to the Immunoglobulin Superfamily Protein (ISP) group, triggering NO release from macrophages in a dose-dependent and specific manner.

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.