An evaluation of the role of carbohydrate epitopes in immunity to Trichinella spiralis

Dual α-1,4- and β-1,4-Glycosidase Activities by the Novel Carbohydrate-Binding Module in α-l-Fucosidase from Vibrio sp. Strain EJY3

Carbohydrates are structurally and functionally diverse materials including polysaccharides, and marine organisms are known to have many enzymes for the breakdown of complex polysaccharides. Here, we identified an α-l-fucosidase enzyme from the marine bacterium Vibrio sp. strain EJY3 (VejFCD) that has dual α-1,4-glucosidic and β-1,4-galactosidic specificities. We determined the crystal structure of VejFCD and provided the structural basis underlying the dual α- and β-glycosidase activities of the enzyme. Unlike other three-domain FCDs, in VejFCD, carbohydrate-binding module-B (CBM-B) with a novel β-sandwich fold tightly contacts with the CatD/CBM-B main body and provides key residues for the β-1,4-glycosidase activity of the enzyme. The phylogenetic tree analysis suggests that only a few FCDs from marine microorganisms have the key structural features for dual α-1,4- and β-1,4-glycosidase activities. This study provides the structural insights into the mechanism underlying the novel glycoside hydrolase activities and could be applied for more efficient utilization in the hydrolysis of complex carbohydrates in biotechnological applications.

Characterization of the carbohydrate components of Taenia solium oncosphere proteins and their role in the antigenicity

This study examines the carbohydrate composition of Taenia solium whole oncosphere antigens (WOAs), in order to improve the understanding of the antigenicity of the T. solium. Better knowledge of oncosphere antigens is crucial to accurately diagnose previous exposure to T. solium eggs and thus predict the development of neurocysticercosis. A set of seven lectins conjugates with wide carbohydrate specificity were used on parasite fixations and somatic extracts. Lectin fluorescence revealed that D-mannose, D-glucose, D-galactose and N-acetyl-D-galactosamine residues were the most abundant constituents of carbohydrate chains on the surface of T. solium oncosphere. Lectin blotting showed that posttranslational modification with N-glycosylation was abundant while little evidence of O-linked carbohydrates was observed. Chemical oxidation and enzymatic deglycosylation in situ were performed to investigate the immunoreactivity of the carbohydrate moieties. Linearizing or removing the carbohydrate moieties from the protein backbones did not diminish the immunoreactivity of these antigens, suggesting that a substantial part of the host immune response against T. solium oncosphere is directed against the peptide epitopes on the parasite antigens. Finally, using carbohydrate probes, we demonstrated for the first time that the presence of several lectins on the surface of the oncosphere was specific to carbohydrates found in intestinal mucus, suggesting a possible role in initial attachment of the parasite to host cells.

Comparison of IgG3 responses to carbohydrates following mouse infection or immunization with six species ofTrichinella

The IgG3 antibody responses to carbohydrate epitopes were compared in BALB/c mice infected or immunized with six species ofTrichinella:T. spiralis(T1),T. nativa(T2),T. britovi(T3), T6,T. nelsoni(T7), and T8. The dynamics of IgG3 responses and antigen recognition following infection or immunization were measured by ELISA and Western blot respectively, using glycosylated and deglycosylated larval crude extracts (LCE) prepared from homologous isolates. A high degree of protein glycosylation was found in all species and with similar profiles. Deglycosylation was completely achieved only in LCE from T1 and T6 isolates. The dynamics of IgG3 responses following infection or immunization significantly differed whereas the antigen recognition profiles appeared similar. Variations in the levels and antigen recognition patterns of IgG3 among the different species were apparent. The highest IgG3 levels were recorded in infections by the T8 isolate and the lowest in infections by the T6 isolate, whereas for immunization the highest IgG3 response was induced by T7 and the lowest by T8. Following antigen deglycosylation, the IgG3 responses were significantly reduced or abrogated and the recognition patterns markedly modified or suppressed in the different species ofTrichinella.

Excreted/secreted glycoproteins of G. intestinalis play an essential role in the antibody response

In the present work, glycoproteins in the excretory/secretory products of G. intestinalis were identified and the reactivity in serum of immunized mice with these molecules was evaluated by western blotting before and after chemical treatment or enzymatic deglycosylation. Glycoproteins of 58 and 63 kDa were revealed in E/S products after periodic acid-Schiff (PAS) stain. Studies of carbohydrate specificity using digoxigenin-labeled lectins, revealed the presence of O-glycans and N-glycans. Chemical treatment of excretory/secretory products with sodium meta-periodate or enzymatic deglycosylation with N-glycosidase F reduced the reactivity in serum for proteins of 36, 58 and 63 kDa, respectively. These results show the presence of glycoproteins in E/S products of G. intestinalis and suggest that the antibody response is directed against glycoepitopes. The expression of carbohydrate moieties in the E/S-G. intestinalis may play an essential role in the antibody response and may be a target for serodiagnosis or immune intervention in human giardiasis.

Impeded establishment of the infective stage of Trichinella in the intestinal mucosa of mice by passive transfer of an IgA monoclonal antibody

Our previous study showed that the IgA monoclonal antibody (mAb) HUSM-Tb1 forms immunoprecipitates on the cuticular surface of infective larvae of Trichinella britovi, and that intraperitoneal injection of this mAb to mice 5 hr before challenge infection confers a high level of protection against intestinal T. britovi. The same treatment produced a similar effect in BALB/c mice inoculated orally with Trichinella pseudospiralis larvae, indicating that the effects may be seen upon most members of the genus Trichinella. Worms recovered from the intestinal mucosa at 1 hr after challenge infection with T. pseudospiralis was few in mice passively immunized with the mAb, whereas a substantial number of worms were recovered from the mucosa of control groups. These results suggest that the IgA mAb impedes establishment of infective Trichinella worms in the intestinal mucosa. Trichinella worms inoculated orally into BALB/c mice vaccinated with ultraviolet-irradiated muscle larvae 3 weeks earlier were expelled between days 4 and 7 after challenge infection. Although the mAb HUSM-Tb1 originated from the mesenteric lymph node cells of mice vaccinated repeatedly with such irradiated larvae, IgA-mediated expulsion does not seem to play an important role in this vaccination model.

Comparison of carbohydrate moieties of sparganum proteins of the snake, mouse and those of adult worm

The carbohydrate moieties of larval sparganum proteins in two different species, the snakes, Elaphe rufodorsata, the Balb/c mouse and those of the adult worm, Spirometra erinacei, were compared using five different lectins including GNA, SNA, MAA, PNA and DSA. The GNA positive 53 kDa molecule, which is excretory-secretory protease in the sparganum from the snake showed a stage specific and developmental regulation. We also suggested that sparganum glycosylation may be involved in immune evasion and differentiation into an adult worm.

Characterization of carbohydrates of adult Echinococcus granulosus by lectin-binding analysis

The identification of lectin-binding structures in adult worms of Echinococcus granulosus was carried out by lectin fluorescence; the distribution of carbohydrates in parasite glycoconjugates was also studied by lectin blotting. The lectins with the most ample recognition pattern were ConA, WGA, and PNA. ConA showed widespread reactivity in tegument and parenchyma components, including the reproductive system, suggesting that mannose is a highly expressed component of the adult glycans. Although reproductive structures appeared to be rich in N-acetyl-D-glucosamine (GlcNAc)-N-acetyl neuraminic acid (NeuAc) and galactose (Gal) as demonstrated by their strong reactivity with WGA and PNA, respectively, some differences were observed in their labeling patterns. This was very clear in the case of the vagina, which only reacted with WGA. Furthermore, WGA and ConA both had reactivity with the excretory canals. RCA, the other Gal binding lectin used, only reacted with the tegument, suggesting that widespread PNA reactivity with the reproductive system is related to the presence of the D-Gal-beta-(1,3)D-GalNAc terminal structure. UEA I failed to bind to any parasite tissues as determined by lectin fluorescence, whereas DBA and SBA showed a very faint staining of the tegument. However, in transferred glycans, N-acetyl-D-galactosamine (GalNAc) and fucose (Fuc) containing glycoproteins were distinctly detected.

Tyvelose and protective responses to the intestinal stages of Trichinella spiralis

The unusual sugar tyvelose is the immunodominant portion of the major larval glycoprotein antigens of Trichinella spiralis, which play an important role in generating immunity against the intestinal stages of infection. The possibility that the tyvelose component itself may have a host- or parasite-protective role in the intestine was tested by following the outcome of challenge infections in mice primed and boosted with tyvelose-BSA, or in mice primed with tyvelose-BSA before boosting with larval antigen. Although antibody responses were raised against tyvelose there was no evidence of protective immunity against the intestinal stages, as assessed by total adult worm recovery or by size and fecundity of female worms in immunized mice. Equally, priming with tyvelose-BSA before boosting with larval antigen had no effect on the expression of immunity against a challenge infection. The predominant antibody isotype recorded in all immunized mice was IgG1, suggesting the induction of type 2 T cell responses, and this was confirmed by cytokine analysis, mesenteric node lymphocytes of all mice showing production of IL-5 but not IFN-gamma. Clearly immunization with tyvelose had no significant effect on T cell polarization. The data show that, with the experimental design employed, there was no evidence for a functional role of tyvelose in either host- or parasite-protection during the intestinal phase of infection.

Human bancroftian filariasis - a role for antibodies to parasite carbohydrates

Studies on immune responses to parasites have been undertaken in filariasis with a view to understand protective immunity, pathogenesis of the disease process and mechanisms of immune deviation. However none of the investigations conducted so far on antibody responses have addressed the issue of immunogenicity of filarial carbohydrate antigens in human lymphatic filariasis. In this communication we report details on relative protein and carbohydrate contents of various developmental stages of filarial parasites and antibody responses to filarial proteins (Fil.Pro) and carbohydrates (Fil.Cho) in different clinical spectrum of human bancroftian filariasis. As expected, antibodies of IgM and IgG2 subclass recognized primarily Fil.Cho while IgG4 filarial antibodies recognized exclusively Fil.Pro. Reactivity of IgG3 to Fil.Cho was similar to that of IgG2 while IgG1 more readily recognized Fil.Pro than Fil.Cho. The IgG2 and IgG3 antibodies to Fil.Cho were found to be significantly more in patients with chronic filarial disease and in endemic normals when compared with microfilariae (mf) carriers while IgG4 antibodies to Fil.Pro were significantly more in mf carriers. The dichotomy in reactivity of filarial IgG2, IgG3 and IgG4 was dependent on active filarial infection as indicated by presence of circulating filarial antigen (CFA). Individuals with CFA were found to possess significantly more IgG4 to Fil.Pro than those without CFA while IgG2 and IgG3 levels to Fil.Cho was significantly more in CFA negative subjects when compared to those with CFA. Although IgG1 reacted more readily with Fil.Pro, unlike IgG4, their levels were significantly more in CFA negative subjects when compared to those with active filarial infection. Absorption of sera with phosphorylcholine (PC) resulted in no significant loss of reactivity to Fil.Cho indicating that most of the anticarbohydrate antibodies were recognizing non-PC determinants in human filariasis. Elevated levels of IgG2 and IgG3 antibodies to Fil.Cho in individuals free of filarial infection indicate a possible role for carbohydrate antigens in induction of protective immunity in human filariasis.

Characterisation of stage-specific proteins of Oesophagostomum dentatum by preparative isoelectric focusing and lectin blotting

The nodular worm of pigs, Oesophagostomum dentatum, has previously been shown to undergo distinct biochemical changes during its life cycle. This phenomenon was studied in more detail for the early parasitic stages. Differences between infective third-stage larvae (L3), parasitic fourth-stage larvae cultivated in vitro (L4c), and pre-adult larvae recovered from the intestinal contents of pigs (L4p) were compared with respect to their protein and glycoprotein patterns by solubility-based protein fractionation and preparative isoelectric focusing followed by SDS-PAGE or by Western blotting with various lectins. While differences between the L4 were only minor (only three bands were specific for either L4c or L4p), L3 displayed distinctly different protein patterns with four L3-specific and nine L4-specific bands. Concanavalin A bound to a variety of glycoproteins, partly in a stage-specific manner, while Ricinus communis Agglutinin 120, Wheat Germ Agglutinin, Peanut Agglutinin and Soybean Agglutinin bound to fewer, partly stage-specific, molecules.

Vaccination of calves with Haemonchus placei intestinal homogenate

The ability of adult Haemonchus placei intestinal homogenate to confer protection against homologous challenge infection was evaluated. Calves were immunized twice with 100 microg H. placei intestinal protein in 5% dextran-sulfate/PBS (vaccinates) or PBS alone (controls) and were challenged with approximately 3300 infective H. placei larvae. There was no significant difference between groups in the total number of nematodes recovered but significantly fewer (p < 0.001) adult females were recovered from vaccinates. The proportion of fourth-stage larvae in vaccinates was significantly greater (p < or = 0.05) than in controls. Lengths of adult male and female nematodes were significantly shorter (p < 0.001) in vaccinated calves, and the numbers of eggs present in the uteri of female nematodes from vaccinates were significantly decreased (p < 0.001). Counts of nematode eggs per gram of feces (EPG) of vaccinates were significantly less than that for controls on Days 29-49 post-challenge (p < or = 0.05). Vaccinates had significant increases in serum IgG1 and IgG2 log(10) titers (p < or = 0.05) but not in serum IgM. EPG, numbers of females, and size of males and females were negatively correlated with increased mean post-challenge IgG1 and IgG2 titers. Reduction in binding of periodate-treated gut homogenate by immune serum indicated a carbohydrate specific component in the immune response.

Changes in antigen and glycoprotein patterns during the development of Oesophagostomum dentatum

During its development from free-living infectious third-stage larvae to the adult worms in the large intestines of pigs, Oesophagostomum dentatum experiences several environmental changes. Differences in protein patterns can reflect such changes. Somatic and ES antigens and glycoproteins of pre-parasitic, histotropic and intestinal stages were compared by single-dimension SDS-PAGE and stage-specific proteins were defined. Furthermore, fourth-stage larvae derived from different sources--in-vitro cultivation and intestinal contents--were compared and also found to be different. It is hypothesised that O. dentatum reacts to environmental stimuli by differential expression of specific proteins as a possible mode of adaptation to the host.

Intestinal nematode parasites, cytokines and effector mechanisms

Laboratory models of intestinal nematode infection have played an important role in developing our understanding of the immune mechanisms that operate against infectious agents. The type of helper T cell response that develops following infection with intestinal nematode parasites is critical to the outcome of infection. The early events that mediate polarisation of the helper T cell subsets towards either Th1 or Th2 during intestinal nematode infection are not well characterised, but it is likely that multiple factors influence the induction of a Th1 or Th2 type response, just as multiple effector mechanisms are involved in worm expulsion. Costimulatory molecules have been shown to be important in driving T helper cell development down a specific pathway as has the immediate cytokine environment during T cell activation. If helper T cells of the Th2 type gain ascendancy then a protective immune response ensues, mediated by Th2 type cytokines and the effector mechanisms they control. In contrast, if an inappropriate Th1 type response predominates the ability to expel infection is compromised. Equally important is the observation that multiple potential effector mechanisms are stimulated by nematode infection, with a unique combination operating against the parasite depending on nematode species and its life cycle stage. Despite the close association between intestinal nematode infection and the generation of eosinophilia, mastocytosis and IgE it has been difficult to consistently demonstrate a role for these effector cells/molecules in resistance to nematode parasites, although mast cells are clearly important in some cases. It therefore seems that, in general, less classical Th2 controlled effector mechanisms, which remain poorly defined, are probably important in resistance to nematode parasites. Thus, our understanding of both the induction and effector phases remains incomplete and will remain an intense area of interest in the coming years.

Trichinella spiralis: ultrastructural localization of a target antigen recognized by a monoclonal antibody

The localization of a 160-kDa molecule recognized by a monoclonal antibody of the IgG1-class (TS32D12) to Trichinella spirilis was demonstrated at the subcellular level. Mature muscle larvae recovered from infected mice were fixed with Zamboni solution, and embedded in LR white resin. Ultrathin sections were incubated with TS32D12 and subsequently stained using a secondary antibody-coated colloidal gold probe. TS32D12 reacted to constituents in the alpha-stichosome cells of the parasite; that is, alpha-granules and rough endoplasmic reticulum. Other structures were not recognized by the immunogold probe, but occasionally weak positive staining was seen on beta-granules, the cuticle, hypodermis and myofibrils.

Carbohydrate epitopes on Haemonchus contortus antigens

Extracts of infective larvae and adults of the trichostrongylid Haemonchus contortus were studied for the presence of carbohydrate moieties. Several different lectin-binding sites were demonstrated in both stages using a panel of nine lectins. The carbohydrate specificity of the lectins used strongly suggests that alpha-D-mannose, alpha-D-glucose, and D-N-acetylglucosamine are the most important carbohydrate epitopes present on H. contortus proteins. Thus, N-linked oligosaccharides form the major part of the carbohydrate moieties on these glycoproteins. Treatment with sodium periodate was performed to investigate the immunoreactivity towards the carbohydrate moieties. This treatment resulted in a reduction in the immunoreactivity of these antigens as demonstrated by enzyme-linked immunosorbent assay (ELISA) and immunoblotting, suggesting that a substantial part of the host immune response against H. contortus is directed against the carbohydrate epitopes on the parasite antigens.

Low molecular weight Cooperia oncophora antigens: characterization and humoral immune responses in calves mono-infected with 100,000 infective larvae

Characteristics of the humoral immune response of Cooperia oncophora-infected calves to low molecular weight antigens of C. oncophora were studied. Immunoblotting with sera obtained from calves 6 weeks after a single oral infection with 100,000 third-stage (L3) C. oncophora larvae revealed several corresponding antigenic fragments between adult worms and the fourth-stage (L4) larvae. No reactivity in the immune sera was found against the L3 stage. A previously defined complex of low molecular weight proteins (12-15 kDa) was found on both L4 and adult Cooperia stages, but not on the L3 stage. C. oncophora adults differed from the L4 larvae at the 31/32 and 37 kDa level. Several adult and L4 proteins were bound by biotinylated Concanavalin A, as was also true for L3 proteins. A 31/32 kDa glycoprotein of adult worms was recognised by a monoclonal antibody with specificity for phosphorylcholine. Using monoclonal antibodies in ELISA and Western blotting, the serum antibody response of C. oncophora-infected calves to adult worm antigen was almost entirely IgG1. Binding of the IgG1 antibodies was restricted to a complex of reduced 12-15 kDa protein(s) and a 27 kDa fragment of adult worms. The data suggest that the systemic humoral immune response of calves during a primary infection with C. oncophora consists mainly of an IgG1 response, and is directed to a non-glycosylated Cooperia protein (molecular weight estimated at 12-15 kDa under reducing conditions and 18 kDa under nonreducing conditions). This protein is probably present in both L4 larvae and adults. Since it was not bound by immune sera from calves mono-infected with several other nematodes, the 12-15 kDa protein complex may represent a Cooperia-specific component that can be used for serodiagnosis.

Immunity to Trichinella spiralis transferred by serum from vaccinated mice not protected by immunization

Serum antibody responses to infection with the intestinal helminth Trichinella spiralis in mice remain at low levels for the first ten to 12 days, slowly increasing to high titres around day 20. It is thought that antibody, therefore, has a limited role in the primary immune response raised against this infection and this is confirmed by the inability of primary infection serum to transfer immunity adoptively. High-responder NIH and low-responder B10 mice were vaccinated with T.spiralis antigen in Freund's complete adjuvant prior to challenge. This procedure conferred significant protection on NIH mice but not B10. Sera from these mice were transferred into recipients before and during challenge infection. Significant levels of protection were obtained in both strains with both homologous and heterologous sera, even though vaccination itself had not resulted in protection of the B10 donor mice. These data indicate that the B10 strain is potentially capable of making a protective immune response against the intestinal phase of T.spiralis.

Characterization of novel fucosyl- and tyvelosyl-containing glycoconjugates from Trichinella spiralis muscle stage larvae

The monosaccharide composition of an affinity-purified family of antigenically-related Trichinella spiralis larval glycoproteins was determined by gas chromatography/mass spectrometry. This group of 6 major glycoproteins, designated TSL-1, originates in the muscle stage (L1) larval stichosome. They are present on the L1 surface and in excretory/secretory products of L1 larvae, are stage-specific, and are highly immunodominant. The glycosyl composition of the TSL-1 antigens was remarkable in 2 respects: (1) fucose accounted for 36 molar percent of the glycosyl residues; and (2) a 3,6-dideoxyhexose was identified, which accounted for at least 24 molar percent of the glycosyl residues. Previously, 3,6-dideoxyhexoses have been found only in certain Gram-negative bacterial lipopolysaccharides and in ascaroside alcohols (ascarylose) of Ascaris eggs. The 3,6-dideoxyhexose found in the TSL-1 antigens also was found in ES. This Trichinella sugar has been chemically identified as a 3,6-dideoxyarabinohexose, the same as found in Ascaris eggs. However, the absolute configuration of the TSL-1 sugar is D-(tyvelose), not L-(ascarylose) as is found in Ascaris eggs. Methylation analysis indicated that the TSL-1 3,6-dideoxy-D-arabinohexose was present entirely as non-reducing terminal residues. Approximately 83% of the fucose was also present as non-reducing terminal residues, with the remaining fucose found as 3,4-linked branched residues.